Technische Chemie / ECEMS-Gruppe

Publications 2022-2023

Jason S. Bates, Jesse J. Martinez, Melissa N. Hall, Abdulhadi A. Al-Omari, Eamonn Murphy, Yachao Zeng, Fang Luo, Mathias Primbs, Davide Menga, Nicolas Bibent, Moulay Tahar Sougrati, Friedrich E. Wagner, Plamen Atanassov, Gang Wu, Peter Strasser, Tim-Patrick Fellinger, Frédéric Jaouen, Thatcher W. Root and Shannon S. Stahl

Chemical Kinetic Method for Active-Site Quantification in Fe-N-C Catalysts and Correlation with Molecular Probe and Spectroscopic Site-Counting Methods.

Journal of the American Chemical Society 2023

DOI: 10.1021/jacs.3c08790

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Mononuclear Fe ions ligated by nitrogen (FeNx) dispersed on nitrogen-doped carbon (Fe-N-C) serve as active centers for electrocatalytic O2 reduction and thermocatalytic aerobic oxidations. Despite their promise as replacements for precious metals in a variety of practical applications, such as fuel cells, the discovery of new Fe-N-C catalysts has relied primarily on empirical approaches. In this context, the development of quantitative structure–reactivity relationships and benchmarking of catalysts prepared by different synthetic routes and by different laboratories would be facilitated by the broader adoption of methods to quantify atomically dispersed FeNx active centers. In this study, we develop a kinetic probe reaction method that uses the aerobic oxidation of a model hydroquinone substrate to quantify the density of FeNx centers in Fe-N-C catalysts. The kinetic method is compared with low-temperature Mössbauer spectroscopy, CO pulse chemisorption, and electrochemical reductive stripping of NO derived from NO2 on a suite of Fe-N-C catalysts prepared by diverse routes and featuring either the exclusive presence of Fe as FeNx sites or the coexistence of aggregated Fe species in addition to FeNx. The FeNx site densities derived from the kinetic method correlate well with those obtained from CO pulse chemisorption and Mössbauer spectroscopy. The broad survey of Fe-N-C materials also reveals the presence of outliers and challenges associated with each site quantification approach. The kinetic method developed here does not require pretreatments that may alter active-site distributions or specialized equipment beyond reaction vessels and standard analytical instrumentation.

 

Lujin Pan, Alice Parnière, Olivia Dunseath, Dash Fongalland, Guillermo Nicolau, C. Cesar Weber, Jiasheng Lu, Malte Klingenhof, Aleks Arinchtein, Hyung-Suk Oh, Pierre-Yves Blanchard, Sara Cavaliere, Marc Heggen, Rafal E. Dunin-Borkowski, Alex Martinez Bonastre, Fabio Dionigi, Jonathan Sharman, Deborah Jones and Peter Strasser

Enhancing the Performance of Shape-Controlled Octahedral Rhodium-Doped PtNi Nanoalloys inside Hydrogen–Air Fuel Cell Cathodes Using a Rational Design of Catalysts, Supports, and Layering.

ACS Catalysis 2023

DOI: 10.1021/acscatal.3c02619

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Octahedral PtNi alloy nanoparticles show a very high catalytic activity for the oxygen reduction reaction. However, their integration into membrane electrode assemblies (MEAs) is challenging, resulting in low fuel cell performance. We report the application of three strategies that are promising to improve the MEA-based fuel cell performance of octahedral PtNi alloy nanoparticles: (1) Rh surface doping to stabilize the morphology, (2) high Pt weight percentage loading on carbon to decrease the catalyst layer thickness (at parity of geometric-area-normalized Pt loading), and (3) N-functionalized carbon supports to more homogeneously distribute the ionomer. The surface chemistry of the Rh dopants is analyzed by in situ X-ray absorption spectroscopy (XAS) under applied potentials in a liquid half-cell. The Rh dopants are present at the catalyst surface with a local coordination to oxygen atoms as in Rh oxide and show potential dependent changes in the oxidation states. A rotating disk electrode (RDE) screening showed advantages in using Ketjen Black EC300J instead of carbon Vulcan XC72R to accommodate high Pt weight percentage loading (∼30 Pt wt %). Finally, a Rh-doped PtNi nanoparticle catalyst was grown on 3% nitrogen-doped Ketjen Black and tested in a MEA-based single cell after being annealed and acid washed. The results showed modest mass activity (MA), 0.35 A mgPt–1 at 0.9 V, but significantly high performance at high current density for octahedral PtNi nanoparticles, 1500 mA cm–2 at 0.6 V, to our knowledge the highest to date for this class of catalysts. Despite this achievement, the full potential of N doping could not be utilized, with samples showing negligible differences with respect to undoped carbon in both high- and low-humidity MEA testing. Even though no enhancement of mass transport at high current density by better distribution of the ionomer on the N-doped carbon was seen in MEA, this could be due to the diffusion of Ni cations, affecting ionomer interaction and overwhelming the effect of nitrogen species on the support.

 

Marvin L. Frisch, Longfei Wu, Clément Atlan, Zhe Ren, Madeleine Han, Rémi Tucoulou, Liang Liang, Jiasheng Lu, An Guo, Hong Nhan Nong, Aleks Arinchtein, Michael Sprung, Julie Villanova, Marie-Ingrid Richard and Peter Strasser

Unraveling the synergistic effects of Cu-Ag tandem catalysts during electrochemical CO(2) reduction using nanofocused X-ray probes.

Nature Communications 2023

DOI: 10.1038/s41467-023-43693-2

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Controlling the selectivity of the electrocatalytic reduction of carbon dioxide into value-added chemicals continues to be a major challenge. Bulk and surface lattice strain in nanostructured electrocatalysts affect catalytic activity and selectivity. Here, we unravel the complex dynamics of synergistic lattice strain and stability effects of Cu-Ag tandem catalysts through a previously unexplored combination of in situ nanofocused X-ray absorption spectroscopy and Bragg coherent diffraction imaging. Three-dimensional strain maps reveal the lattice dynamics inside individual nanoparticles as a function of applied potential and product yields. Dynamic relations between strain, redox state, catalytic activity and selectivity are derived. Moderate Ag contents effectively reduce the competing evolution of H2 and, concomitantly, lead to an enhanced corrosion stability. Findings from this study evidence the power of advanced nanofocused spectroscopy techniques to provide new insights into the chemistry and structure of nanostructured catalysts.

 

Matej Zlatar, Daniel Escalera-López, Miquel Gamón Rodríguez, Tomáš Hrbek, Carina Götz, Rani Mary Joy, Alan Savan, Hoang Phi Tran, Hong Nhan Nong, Paulius Pobedinskas, Valentín Briega-Martos, Andreas Hutzler, Thomas Böhm, Ken Haenen, Alfred Ludwig, Ivan Khalakhan, Peter Strasser and Serhiy Cherevko

Standardizing OER Electrocatalyst Benchmarking in Aqueous Electrolytes: Comprehensive Guidelines for Accelerated Stress Tests and Backing Electrodes.

ACS Catalysis 2023

DOI: 10.1021/acscatal.3c03880

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The scarcity of iridium, needed to catalyze the sluggish oxygen evolution reaction (OER), hinders large-scale hydrogen production with proton exchange membrane water electrolyzers (PEMWEs). Crucial steps require reducing its loading while improving its overall activity and stability. Despite knowledge transfer challenges, cost and time constraints still favor aqueous model systems (AMSs) over real devices for the OER electrocatalyst testing. During AMS testing, benchmarking strategies such as accelerated stress tests (ASTs) aim at improving catalyst lifetime estimation compared to constant current loads. This study systematically evaluates a commercial Ir catalyst by modifying both AST parameters and the employed backing electrodes to examine their impact on activity−stability relationships. A comprehensive set of spectroscopy and microscopy techniques, including in situ inductively coupled plasma mass spectrometry, is employed to monitor Ir and backing electrode modifications. Our findings demonstrate that the choice of both lower potential limit (LPL) in ASTs and backing electrode significantly influences the estimation of Ir-based electrocatalysts’ activity and stability. Unique degradation mechanisms, such as passivation, redeposition on active sites, and contribution to the OER, were observed for different backing electrodes at varying LPLs. These results emphasize the importance of optimizing parameters and electrode selection in ASTs to accurately assess the electrocatalyst performance. Furthermore, they establish the foundation for developing relevant standardized test protocols, enabling the cost-effective development of high-performance catalysts for PEMWE applications.

 

Cheoulwoo Oh, Man Ho Han, Young‐Jin Ko, Jun Sik Cho, Min Wook Pin, Peter Strasser, Jae‐Young Choi, Hansung Kim, Chang Hyuck Choi, Woong Hee Lee and Hyung‐Suk Oh

Activity Restoration of Pt–Ni Octahedron via Phase Recovery for Anion Exchange Membrane‐Unitized Regenerative Fuel Cells.

Advanced Energy Materials 2023

DOI: 10.1002/aenm.202302971

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Unitized regenerative fuel cells (URFCs) offer a cost-effective solution for energy conversion by functioning as both fuel cells and electrolyzers. Anion-exchange membrane-based URFCs (AEM-URFCs) require bifunctional electrocatalysts, such as Pt–Ir alloys, for the oxygen evolution reaction (water electrolysis mode) and oxygen reduction reaction (fuel cell mode). However, the low stability of Pt in alkaline media and the high cost of Ir remain challenges for the widespread application of these URFCs. In this study, a Pt–Ni octahedral alloy is synthesized to replace Ir with Ni as the oxygen evolution reaction catalyst. The alloying effect of Pt–Ni inhibits the dissolution of Pt and transforms PtOx to metallic Pt via a recovery process, thereby providing a new operational strategy for improving the durability of AEM-URFCs. Remarkably, the performance of the AEM-URFC single cell is maintained over ten cycles after the recovery process, demonstrating the viability of this approach for long-term operations. These findings pave the way for broader applications and advancements of AEM-URFCs.

 

Y. Yang, W. H. Lie, R. R. Unocic, J. A. Yuwono, M. Klingenhof, T. Merzdorf, P. W. Buchheister, M. Kroschel, A. Walker, L. C. Gallington, L. Thomsen, P. V. Kumar, P. Strasser, J. A. Scott and N. M. Bedford

Defect-Promoted Ni-Based Layer Double Hydroxides with Enhanced Deprotonation Capability for Efficient Biomass Electrooxidation.

Advanced Materials 2023

DOI: 10.1002/adma.202305573

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Ni-based hydroxides are promising electrocatalysts for biomass oxidation reactions, supplanting the oxygen evolution reaction (OER) due to lower overpotentials while producing value-added chemicals. The identification and subsequent engineering of their catalytically active sites are essential to facilitate these anodic reactions. Herein, the proportional relationship between catalysts’ deprotonation propensity and Faradic efficiency of 5-hydroxymethylfurfural (5-HMF)-to-2,5 furandicarboxylic acid (FDCA, FEFDCA) is revealed by thorough density functional theory (DFT) simulations and atomic-scale characterizations, including in situ synchrotron diffraction and spectroscopy methods. The deprotonation capability of ultrathin layer-double hydroxides (UT-LDHs) is regulated by tuning the covalency of metal (M)-oxygen (O) motifs through defect site engineering and selection of M3+ co-chemistry. NiMn UT-LDHs show an ultrahigh FEFDCA of 99% at 1.37 V versus reversible hydrogen electrode (RHE) and retain a high FEFDCA of 92.7% in the OER-operating window at 1.52 V, about 2× that of NiFe UT-LDHs (49.5%) at 1.52 V. Ni–O and Mn–O motifs function as dual active sites for HMF electrooxidation, where the continuous deprotonation of Mn–OH sites plays a dominant role in achieving high selectivity while suppressing OER at high potentials. The results showcase a universal concept of modulating competing anodic reactions in aqueous biomass electrolysis by electronically engineering the deprotonation behavior of metal hydroxides, anticipated to be translatable across various biomass substrates.

 

Honglei Wang, Yifan Bo, Malte Klingenhof, Jiali Peng, Dong Wang, Bing Wu, Jörg Pezoldt, Pengfei Cheng, Andrea Knauer, Weibo Hua, Hongguang Wang, Peter A. van Aken, Zdenek Sofer, Peter Strasser, Dirk M. Guldi and Peter Schaaf

A Universal Design Strategy Based on NiPS3 Nanosheets towards Efficient Photothermal Conversion and Solar Desalination.

Advanced Functional Materials 2023.

DOI: 10.1002/adfm.202310942

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2D nanomaterials are proposed as promising photothermal materials for interfacial photothermal water evaporation. However, low evaporation efficiency, the use of hazardous hydrofluoric solution, and poor stability severely limit their practical applications. Here, a mixed solvent exfoliation surface deposition (MSESD) strategy for the preparation of NiPS3 nanosheets and NiPS3/polyvinyl alcohol (PVA) converter is successfully developed. The converter is obtained by drop-casting the NiPS3/PVA nanosheets onto a sponge. The PVA is mainly deposited on the edge of NiPS3 nanosheets, which not only improves the stability of NiPS3 nanosheets, but also adheres to the sponge to prepare a 3D photothermal converter, which shows an evaporation rate of 1.48 kg m−2 h−1 and the average photothermal conversion efficiency (PTCE) of 93.5% under a light intensity of 1 kW m−2. The photothermal conversion mechanism reveals that the energy of absorbed photons in NiPS3 nanosheets can be effectively converted into heat through non-radiative photon transitions as well as multiple optical interactions. To the best of the knowledge, this is the first report on the application of 2D metal-phosphorus-chalcogen (MPChx) for solar desalination, which provides new insights and guidance for the development of high-performance 2D photothermal materials.

 

Michael Filippi, Tim Möller, Liang Liang and Peter Strasser

Understanding the impact of catholyte flow compartment design on the efficiency of CO2 electrolyzers.

Energy & Environmental Science 2023.

DOI: 10.1039/d3ee02243a

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This work explores and provides new understanding how catholyte flow compartment design and catholyte bubble flow characteristics of a gas diffusion electrode inside a CO2 flow cell electrolyzer affect its electrocatalytic reactivity and product selectivity. Focusing on Cu-based GDEs for CO2 electroreduction to hydrocarbons at high current densities (50–700 mA cm-2), four basic compartment designs were selected, 3D printed and investigated. Experiments were coupled to computational fluid dynamics simulation of catholyte flow and bubble dynamics. The findings from this work suggest a homogenous fluid velocity distribution combined with fluid velocity in the range between 0.1–0.01 m s-1 to be optimal for high yields in C2+ products at high current densities. Special focus was placed on the role and relation between gas bubble dynamics and local pH, both strongly affected by the design architecture. From our experimental observations and simulations, we propose a hydrodynamic ‘‘volcano’’ model addressing the competition between bubble release rate and local pH, both controlled by catholyte flow velocity. The balance between fast bubble release and high enough local pH across the electrode surface puts the electrolyzer operation at the top of the performance volcano.

 

Xuecheng Cao, Meng Tian, Zhihui Sun, Xiangjun Zheng, Kai Zeng, Peter Strasser and Ruizhi Yang

Three-Dimensional WCoFe Ternary Metal Oxide Nanowire Network as a Carbon-Free Cathode Catalyst for High-Performance Li–O2 Batteries.

ACS Sustainable Chemistry & Engineering 2023

DOI: 10.1021/acssuschemeng.3c00964

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Rechargeable aprotic Li–O2 batteries own great potential in large-scale energy storage and electric vehicles due to high theoretical energy density. However, batteries utilizing the carbon-based cathodes are unstable because the parasitic reaction with discharge products usually leads to the decomposition of carbon and formation of insulating byproducts, thus greatly decreasing the efficiency and cycling stability of batteries. Herein, we report a class of WCoFe@Ni cathodes based on Magnéli phase sub-stoichiometric W18O49 and amorphous cobalt/ferric oxide as carbon-free catalyst for high-performance Li–O2 batteries. The prepared cathode delivers a high discharge capacity of 5800 mAh g–1 and enhanced cycling stability (more than 400 cycles). X-ray photoelectron spectroscopy and synchrotron-based X-ray absorption spectroscopy reveal that the local coordination environments and Co/Fe electronic structures are modulated after the addition of the W element in catalysts. Furthermore, the theoretical calculation results testify that the high-valence state Fe in catalysts stabilizes the Co element at the low-valence state, which boosts the formation of Co(II)O species that is favorable for the Li2O2 decomposition. The synergistic effect among W, Co, and Fe plays a very essential role in improving the performance of Li–O2 batteries.

 

Fang Luo, Aaron Roy, Moulay Tahar Sougrati, Anastassiya Khan, David A. Cullen, Xingli Wang, Mathias Primbs, Andrea Zitolo, Frédéric Jaouen and Peter Strasser

Structural and Reactivity Effects of Secondary Metal Doping into Iron-Nitrogen-Carbon Catalysts for Oxygen Electroreduction.

Journal of the American Chemical Society 2023

DOI: 10.1021/jacs.3c03033

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While improved activity was recently reported for bimetallic iron-metal-nitrogen-carbon (FeMNC) catalysts for the oxygen reduction reaction (ORR) in acid medium, the nature of active sites and interactions between the two metals are poorly understood. Here, FeSnNC and FeCoNC catalysts were structurally and catalytically compared to their parent FeNC and SnNC catalysts. While CO cryo-chemisorption revealed a twice lower site density of M-Nx sites for FeSnNC and FeCoNC relative to FeNC and SnNC, the mass activity of both bimetallic catalysts is 50–100% higher than that of FeNC due to a larger turnover frequency in the bimetallic catalysts. Electron microscopy and X-ray absorption spectroscopy identified the coexistence of Fe-Nx and Sn-Nx or Co-Nx sites, while no evidence was found for binuclear Fe-M-Nx sites. 57Fe Mössbauer spectroscopy revealed that the bimetallic catalysts feature a higher D1/D2 ratio of the spectral signatures assigned to two distinct Fe-Nx sites, relative to the FeNC parent catalyst. Thus, the addition of the secondary metal favored the formation of D1 sites, associated with the higher turnover frequency.

 

Wen Ju, Alexander Bagger, Nastaran Ranjbar Saharie, Sebastian Mohle, Jingyi Wang, Frederic Jaouen, Jan Rossmeisl and Peter Strasser

Electrochemical carbonyl reduction on single-site M-N-C catalysts.

Communications Chemistry 2023

DOI: 10.1038/s42004-023-01008-y

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Electrochemical conversion of organic compounds holds promise for advancing sustainable synthesis and catalysis. This study explored electrochemical carbonyl hydrogenation on single-site M–N–C (Metal Nitrogen-doped Carbon) catalysts using formaldehyde, acetaldehyde, and acetone as model reactants. We strive to correlate and understand the selectivity dependence on the nature of the metal centers. Density Functional Theory calculations revealed similar binding energetics for carbonyl groups through oxygen-down or carbon-down adsorption due to oxygen and carbon scaling. Fe–N–C exhibited specific oxyphilicity and could selectively reduce aldehydes to hydrocarbons. By contrast, the carbophilic Co–N–C selectively converted acetaldehyde and acetone to ethanol and 2-propanol, respectively. We claim that the oxyphilicity of the active sites and consequent adsorption geometry (oxygen-down vs. carbon-down) are crucial in controlling product selectivity. These findings offer mechanistic insights into electrochemical carbonyl hydrogenation and can guide the development of efficient and sustainable electrocatalytic valorization of biomass-derived compounds.

 

Philipp Hauke, Sven Brückner and Peter Strasser

Paired Electrocatalytic Valorization of CO2 and Hydroxymethylfurfural in a Noble Metal-free Bipolar Membrane Electrolyzer.

Acs Sustain Chem Eng 2023

DOI: 10.1021/acssuschemeng.3c03144

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Direct electrocatalytic valorization of CO2 in low-temperature electrolyzers is emerging as a new nonfossil, one-step process toward e-fuels and e-chemicals, such as CO. However, Faradaic and energy efficiencies have remained low due to the sluggish 4-electron oxidation of water [oxygen evolution reaction (OER)] at the anode. Replacement of the OER with a thermodynamically and kinetically less-demanding reaction would increase efficiency and overall valorization. This article demonstrates the first full paired implementation of a noble metal-free CO2 and hydroxymethylfurfural (HMF) valorization in a single cell at industrially relevant current densities. We stepwise design, assemble, test, and analyze the first complete paired low-temperature bipolar membrane (BPM)-based hydroxymethylfurfural oxidation and CO2 electroreduction electrolyzer cell. The electrolyzer couples a CO2-to-CO electrolyzer half-cell to an aqueous HMF-to-2.5-furandicarboxylic acid half-cell via a water dissociation membrane operating in reverse bias. We investigate and compare the bipolar membrane voltage penalties with the single-pass reactant conversion advantages and estimate cell performance benefits due to the more favorable thermodynamic and kinetic processes at the anode. We report successfully suppressing undesired CO2 loss due to acid–base neutralization with generated alkalinity.

 

Tim Moller, Michael Filippi, Sven Bruckner, Wen Ju and Peter Strasser

A CO(2) electrolyzer tandem cell system for CO(2)-CO co-feed valorization in a Ni-N-C/Cu-catalyzed reaction cascade.

Nature Communications 2023

DOI: 10.1038/s41467-023-41278-7

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Coupled tandem electrolyzer concepts have been predicted to offer kinetic benefits to sluggish catalytic reactions thanks to their flexibility of reaction environments in each cell. Here we design, assemble, test, and analyze the first complete low-temperature, neutral-pH, cathode precious metal-free tandem CO2 electrolyzer cell chain. The tandemsystemcouples an Ag-freeCO2-toCO2/CO electrolyzer (cell-1) to a CO2/CO-to-C2+ product electrolyzer (cell-2). Cell-1 and cell-2 incorporate selective Ni-N-C-based and Cu-based Gas Diffusion Cathodes, respectively, and operate at sustainable neutral pH conditions. Using our tandem cell system, we report strongly enhanced rates for the production of ethylene (by 50%) and alcohols (by 100%) and a sharply increased C2+ energy efficiency (by 100%) at current densities of up to 700mAcm−2
compared to the single CO2-to-C2+ electrolyzer cell system
approach. This study demonstrates that coupled tandem electrolyzer cell systems can offer kinetic and practical energetic benefits over single-cell designs for the production of value-added C2+ chemicals and fuels directly from CO2 feeds without intermediate separation or purification.

 

Michal Ronovsky, Lujin Pan, Malte Klingenhof, Isaac Martens, Lukas Fusek, Peter Kus, Raphael Chattot, Marta Mirolo, Fabio Dionigi, Harriet Burdett, Jonathan Sharman, Peter Strasser, Alex Martinez Bonastre and Jakub Drnec

Assessing Utilization Boundaries for Pt-Based Catalysts in an Operating Proton-Exchange Membrane Fuel Cell.

ACS Applied Energy Materials 2023

DOI: 10.1021/acsaem.3c01243

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Octahedra (oh) PtNiX/C catalysts are notable cathode catalysts for proton-exchange membrane fuel cells due to their exceptional oxygen reduction reaction activity. Here, we investigate the degradation of oh-PtNiIr catalysts under fuel-cell conditions using operando X-ray diffraction (XRD). Employing two accelerated stress tests with different lower potential limits and XRD-coupled cyclic voltammetry on benchmark Pt and oh-PtNiIr catalysts, we find that dissolution and degradation are proportional to the extent of reduction, independent of the catalyst’s nature. Our method identifies the optimal potential range for Pt-based catalysts to minimize degradation without lengthy stress tests.

 

Philipp Hauke, Thomas Merzdorf, Malte Klingenhof and Peter Strasser

Hydrogenation versus hydrogenolysis during alkaline electrochemical valorization of 5-hydroxymethylfurfural over oxide-derived Cu-bimetallics.

Nature Communications 2023

DOI: 10.1038/s41467-023-40463-y

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The electrochemical conversion of 5-Hydroxymethylfurfural, especially its reduction, is an attractive green production pathway for carbonaceous e-chemicals. We demonstrate the reduction of 5-Hydroxymethylfurfural to 5-Methylfurfurylalcohol under strongly alkaline reaction environments over oxide-derived Cu bimetallic electrocatalysts. We investigate whether and how the surface catalysis of the MOx phases tune the catalytic selectivity of oxide-derived Cu with respect to the 2-electron hydrogenation to 2.5-Bishydroxymethylfuran and the (2 + 2)-electron hydrogenation/hydrogenolysis to 5-Methylfurfurylalcohol. We provide evidence for a kinetic competition between the evolution of H2 and the 2-electron hydrogenolysis of 2.5-Bishydroxymethylfuran to 5-Methylfurfurylalcohol and discuss its mechanistic implications. Finally, we demonstrate that the ability to conduct 5-Hydroxymethylfurfural reduction to 5-Methylfurfurylalcohol in alkaline conditions over oxide-derived Cu/MOx Cu foam electrodes enable an efficiently operating alkaline exchange membranes electrolyzer, in which the cathodic 5-Hydroxymethylfurfural valorization is coupled to either alkaline oxygen evolution anode or to oxidative 5-Hydroxymethylfurfural valorization.

 

Robert Marić, Christian Gebauer, Florian Eweiner and Peter Strasser,

A Comparative Study on the Activity and Stability of Iridium-Based Co-Catalysts for Cell Reversal Tolerant PEMFC Anodes.

Journal of the Electrochemical Society 2023

DOI: 10.1149/1945-7111/aceb8d

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In fuel cell applications with long lifetime requirements, the management of stressing operating conditions—such as hydrogen starvation events—plays a pivotal role. Among other remedies, the incorporation of an OER-enhancing co-catalyst, is widely employed to improve the intrinsic stability of Pt/C-based anode catalyst layers in PEM fuel cells. The present study investigates several supported and unsupported Ir-based co-catalysts comprising different oxidation states of iridium: from metallic to oxidic character, both anhydrous rutile-type IrO2 and hydrated amorphous form. Utilizing a single-cell setup, cell reversal experiments were conducted initially after break-in of the MEA and after seven days of continuous operation under reductive H2 atmosphere at application-relevant conditions. The initial cell reversal tolerance was found to increase in the order metallic Ir < crystalline Ir oxide < amorphous Ir oxyhydroxide. By contrast, after continuous operation under H2 the order changes drastically to amorphous Ir oxyhydroxide ∼ metallic Ir < crystalline Ir oxide. This led us to conclude that the amorphous Ir oxyhydroxide is likely reduced to metallic Ir during continuous H2 operation, while IrO2 provides a reasonable trade-off between initial OER activity, high structural and chemical stability at high anode potentials during H2 starvation and low reducibility under prolonged H2 operation.

 

Jingyi Wang, Terrence R. Willson, Sven Brückner, Daniel K. Whelligan, Chunning Sun, Liang Liang, Xingli Wang, Peter Strasser, John Varcoe and Wen Ju

Design of NiNC single atom catalyst layers and AEM electrolyzers for stable and efficient CO2-to-CO electrolysis: Correlating ionomer and cell performance

Electrochimica Acta, 2023

DOI: 10.1016/j.electacta.2023.142613

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Deploying single-site NiNC catalysts in cathode catalyst layers of bipolar electrolyzer cells enables catalytic CO2 valorization to e-CO at industrially relevant yields and efficiencies. The performance of the cathode layers is controlled by the turnover frequency of the active sites as well as mass transfer to and from the active sites. While the atomic scale structure-reactivity relations of single-site NiNC catalysts have been extensively studied, the mass transfer characteristics of single atom catalyst layers were poorly discussed. In this work, we design, build, and test NiNC catalyst layers using a novel set of distinct ion exchange ionomer materials and correlate the performance of cathode catalyst layers with their reactivity and stability in full single MEA electrolyzer cells. The Sustainion anion exchange ionomer delivered optimal performance, yielding about 90% CO faradaic efficiency up to 300 mA cm−2 and 15 h stable performance at 200 mA cm−2. Our analysis attributes its favorable electrolyzer performance to its balanced conductivity and hydrophobicity, which mitigates electrode flooding while ensuring excellent ion and CO2 transfer rates even at high current densities.

 

Katherine E. MacArthur, Shlomi Polani, Malte Klingenhof, Nina Gumbiowski, Tim Möller, Paul  Paciok, Jiaqi  Kang, Matthias  Epple, Shibabrata  Basak, Rüdiger A.  Eichel, Peter  Strasser, Rafal E.  Dunin-Borkowski and Marc  Heggen

Post-Synthesis Heat Treatment of Doped PtNi-Alloy Fuel-Cell Catalyst Nanoparticles Studied by In-Situ Electron Microscopy

ACS Applied Energy Materials; 2023

DOI: 10.1021/acsaem.3c00405

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Octahedral-shaped PtNi-alloy nanoparticles are highly active oxygen reduction reaction catalysts for the cathode in proton exchange membrane fuel cells. However, one major drawback in their application is their limited long-term morphological and compositional stability. Here, we present a detailed in situ electron microscopy characterization of thermal annealing on octahedral-shaped PtNi catalysts as well as on doped octahedral PtNi(Mo) and PtNi(MoRh) catalysts. The evolution of their morphology and composition was quantified during both ex situ and in situ experiments using energy dispersive X-ray spectroscopy in a scanning transmission electron microscope under a hydrogen atmosphere and in vacuum. Morphological changes upon heating, i.e., a gradual loss of the octahedral shape and a continuous rounding of the particles, were observed, as well as evidence for increased alloying. Furthermore, the evolution of the shape of the PtNi(Mo) nanoparticles was quantified using in situ experiments under hydrogen atmosphere in a transmission electron microscope. The shape change of the particles was quantified using segmentation maps created by a neural network. It has been demonstrated that morphological changes crucially depend on the composition and surface doping: doping with Mo or Mo/Rh significantly stabilizes the structure, allowing for persistence of a truncated octahedral shape during heat treatments.

 

Michael Schwarze, Steffen Borchardt, Marvin L. Frisch, Jason Collis, Carsten Walter, Prashanth W. Menezes, Peter Strasser, Matthias Driess and Minoo Tasbihi

Degradation of Phenol via an Advanced Oxidation Process (AOP) with Immobilized Commercial Titanium Dioxide (TiO(2)) Photocatalysts.

Nanomaterials (Basel), 2023

DOI: 10.3390/nano13071249

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Four commercial titanium dioxide (TiO2) photocatalysts, namely P25, P90, PC105, and PC500, were immobilized onto steel plates using a sol-gel binder and investigated for phenol degradation under 365 nm UV-LED irradiation. High-performance liquid chromatography (HPLC) and total organic carbon (TOC) analyses were performed to study the impact of three types of oxygen sources (air, dispersed synthetic air, and hydrogen peroxide) on the photocatalytic performance. The photocatalyst films were stable and there were significant differences in their performance. The best result was obtained with the P90/UV/H2O2 system with 100% degradation and about 70% mineralization within 3 h of irradiation. The operating conditions varied, showing that water quality is crucial for the performance. A wastewater treatment plant was developed based on the lab-scale results and water treatment costs were estimated for two cases of irradiation: UV-LED (about 600 EUR/m3) and sunlight (about 60 EUR/m3). The data show the high potential of immobilized photocatalysts for pollutant degradation under advanced oxidation process (AOP) conditions, but there is still a need for optimization to further reduce treatment costs.

 

Christopher Gort, Paul W. Buchheister, Malte Klingenhof, Stephen D. Paul, Fabio Dionigi, Roel van de Krol, Ulrike I. Kramm, Wolfram Jaegermann, Jan P. Hofmann, Peter Strasser and Bernhard Kaiser

Effect of Metal Layer Support Structures on the Catalytic Activity of NiFe(oxy)hydroxide (LDH) for the OER in Alkaline Media

ChemCatChem, 2023

DOI: 10.1002/cctc.202201670

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Photoelectrochemical (PEC) cells promise to combine the benefits of photovoltaics and electrolysis in one device. They consist of a photoabsorber functionalized with an electrocatalyst to harvest faradaic currents under reduced overpotentials. To protect the absorber from the harsh reaction conditions, a protective buffer layer (e. g. TiO2) is added between absorber and catalyst. In this work, we investigate the influence of the catalyst support systems Ti/TiOx and Ti/TiOx/M (M=Au, Ni, Fe) on the overall activity and stability of nickel and iron mixed layered double hydroxides for the alkaline oxygen evolution reaction (OER). The catalyst performance on the bare Ti/TiOx substrate is very poor, but the incorporation of a metallic interlayer leads to two orders of magnitude higher OER current densities. While a similar effect has been observed for M=gold supported systems, we show that the same effect can be achieved with M=nickel/iron, already contained in the catalyst. This proprietary metal interlayer promises a cheap OER performance increase for PEC cells protected with titania buffer layers. Detailed XPS show an improved transformation of the starting catalyst material into the highly active (oxy)hydroxide phase, when using metallic interlayers. From these experiments a pure conductivity enhancement was excluded as possible explanation, but instead an additional change in the local atomic and electronic structure at the metal-support and metal-catalyst interfaces is proposed.

 

Marvin L. Frisch, Trung Ngo Thanh, Aleks Arinchtein, Linus Hager, Johannes Schmidt, Sven Brückner, Jochen Kerres, and Peter Strasser

Seawater Electrolysis using All-PGM-Free Catalysts and Cell Components in an Asymmetric Feed

ACS Energy Lett., 2023

DOI:10.1021/acsenergylett.3c00492

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In arid coastal zones, direct seawater electrolysis appears particularly intriguing for green hydrogen production. State of-the-art direct seawater electrolyzers, however, show unsatisfactory performance and rely on large amounts of platinum-group metals (PGMs) in the electrodes or hidden as transport layer coatings. Herein, we report an asymmetric-feed electrolyzer design, in which all cell components consist of PGM-free materials. Cobalt- and nickel based phosphides/chalcogenides not only serve as active and robust electrocatalysts but also are put forth as porous transport layer (PTL) surface coatings enhancing selective seawater splitting performance. In a systematic design study at the single-cell level, we report the integration of our catalysts and PTLs into a membrane−electrode assembly (MEA) using a customized, terphenyl-based anion-exchange membrane (AEM). The presented entirely PGM-free electrolyzer achieves industrially relevant current densities of up to 1.0 A cm−2 below 2.0 Vcell in standardized alkaline seawater and dry cathode operation.

 

Young-Jin Ko, Hyunchul Kim, Woong Hee Lee, Man Ho Han, Cheoulwoo Oh, Chang Hyuck Choi, cd Woong Kim, Jeong Min Baik, Jae-Young Choi, Peter Strasser and Hyung-Suk Oh

Electrochemically robust oxide-supported dendritic Pt and Ir nanoparticles for highly effective polymer electrolyte membrane-unitized regenerative fuel cells

Journal of Materials Chemistry A, 2023

DOI:10.1039/d2ta08322a

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Polymer electrolyte membrane-unitized regenerative fuel cells (PEM-URFCs) are promising energy storage and conversion systems. However, the dissolution of metal species due to frequent phase transformation and support corrosion at high voltages must be addressed. Herein, we design dendritic Pt (PtND) and Ir (IrND) combined with a robust oxide support (antimony doped tin oxide, ATO) for the oxygen electrode. Under ORR and OER potentials, a PtND–IrND/ATO catalyst produced lower average oxidation states of Pt and Ir than a Pt–Ir/C catalyst. Consequently, the Pt and Ir dissolution of PtND–IrND/ATO derived from the phase transition was significantly less than that of Pt–Ir/C. By investigating the operation factors of the URFC, PtND–IrND/ATO was found to exhibit a high round trip efficiency of 50% at 0.4 A cm−2 with enhanced long-term stability. Our study not only reveals the fundamental reversible catalytic properties of dendritic catalysts, but also offers insights into the catalyst design concept for the oxygen electrode of URFCs.


Liang Liang, Quanchen Feng, Xingli Wang, Jessica Hübner, Ulrich Gernert, Marc Heggen, Longfei Wu, Tim Hellmann, Jan P. Hofmann, and Peter Strasser

Electroreduction of CO(2) on Au(310)@Cu High-index Facets

Angew. Chem. Int. Ed., 2023

DOI:10.1002/anie.202218039

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The chemical selectivity and faradaic efficiency of high-index Cu facets for the CO2 reduction reaction (CO2RR) is investigated. More specifically, shape-controlled nanoparticles enclosed by Cu {hk0} facets are fabricated using Cu multilayer deposition at three distinct layer thicknesses on the surface facets of Au truncated ditetragonal nanoprisms (Au DTPs). Au DTPs are shapes enclosed by 12 high-index {310} facets. Facet angle analysis confirms DTP geometry. Elemental mapping analysis shows Cu surface layers are uniformly distributed on the Au {310} facets of the DTPs. The 7 nm Au@Cu DTPs high-index {hk0} facets exhibit a CH4 :CO product ratio of almost 10 : 1 compared to a
1 : 1 ratio for the reference 7 nm Au@Cu nanoparticles (NPs). Operando Fourier transform infrared spectroscopy spectra disclose reactive adsorbed *CO as the main intermediate, whereas CO stripping experiments reveal the high-index facets enhance the *CO formation followed by rapid desorption or hydrogenation


Hao Wan, Xingli Wang, Lei Tan, Michael Filippi, Peter Strasser, Jan Rossmeisl, and Alexander Bagger

Electrochemical Synthesis of Urea: Co-reduction of Nitric Oxide and Carbon Monoxide

ACS Catalysis, 2023

DOI:10.1021/acscatal.2c05315

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Electrocatalytic conversion is a promising technology for storing renewable electricity in the chemical form. Substantial efforts have been made on the multicarbon feedstock production, while little is known about producing nitrogencontaining chemicals like urea via C−N coupling. Here, we elucidate the possible urea production on metals through coreduction of nitric oxide (NO) and carbon oxide (CO). Based on adsorption energies calculated by density functional theory (DFT), we find that Cu is able to bind both *NO and *CO while not binding *H. During NO + CO coreduction, we identify two kinetically and thermodynamically possible C−N couplings via *CO + *N and *CONH + *N, and further hydrogenation leads to urea formation. A 2-D activity heatmap has been constructed for describing nitrogen conversion to urea. This work provides a clear example of using computational simulations to predict selective and active materials for urea production.

 

Muhammad Zubair, Priyank Kumar, Malte Klingenhof, Bijil Subhash, Jodie A. Yuwono, Soshan Cheong, Yin Yao, Lars Thomsen, Peter Strasser, Richard D. Tilley, and Nicholas M. Bedford

Vacancy Promotion in Layered Double Hydroxide Electrocatalysts for Improved Oxygen Evolution Reaction Performance

ACS Catalysis, 2023

DOI:10.1021/acscatal.2c05863

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Layered double hydroxides (LDHs) are promising catalysts for the oxygen evolution reaction (OER) given their modular chemistry and ease of synthesis. Herein, we report a facile strategy for inclusion of oxygen vacancies (VO) using Ce as a promoter in Co−Ni LDHs that significantly enhances the activity for OER. In situ X-ray absorption spectroscopy (XAS) uncovers an increase in octahedral Co sites and VO upon addition of Ce that promotes the transformation of the LDH into an oxyhydroxide-reactive phase more readily. The presence of an OER-active oxyhydroxide phase along with the generation of VO facilitated by the partial reduction of Ce4+ to Ce3+ under oxidizing conditions results in a better electrochemical activity of Ce-doped electrocatalysts. Density functional theory calculations further corroborate the in situ XAS experimental findings by showcasing that the presence of both Ce and VO reduces the free-energy barrier of the ratelimiting OH* deprotonation step during OER. This work showcases how an enhanced understanding of the role of VO promoters in LDH electrocatalysts can provide insights for future catalyst design in anodic reactions.

 

Sun Seo Jeon, Phil Woong Kang, Malte Klingenhof, Hyunjoo Lee, Fabio Dionigi, and Peter Strasser

Active Surface Area and Intrinsic Catalytic Oxygen Evolution Reactivity of NiFe LDH at Reactive Electrode Potentials Using Capacitances

ACS Catalysis, 2023

DOI:10.1021/acscatal.2c04452

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Determination of the electrochemically active surface area (ECSA) is essential in electrocatalysis to provide surface normalized intrinsic catalytic activity. Conventionally, ECSAs of metal oxides and hydroxides are estimated using double layer capacitance (Cdl) measured at nonfaradaic potential windows. However, in the case of Ni-based hydroxide catalysts for the oxygen evolution reaction (OER), the nonfaradaic potential region before the Ni(II) oxidation peak is nonconductive, which hinders accurate electrochemical measurements. To overcome this problem, in this work, we have investigated the use of electrochemical impedance spectroscopy (EIS) at reactive OER potentials to extract the capacitance that is hypothesized to arise due to reactive OER intermediates (O*, OH*, OOH*) adsorbed on the catalyst surface. This allowed the estimation of ECSA and intrinsic activity of NiFe layered double hydroxide (NiFe LDH), the most active, state-of-the-art OER electrocatalyst in alkaline media. We analyzed the OER adsorbates capacitance (Ca) on NiFe LDH and Ni(OH)2 at different electrode potentials and identified a suitable potential range for accurate ECSA evaluation. Finally, we validated our method and the choice of potential range through rigorous catalyst loading and support studies.

 

Kai Zeng, Ming Chao, Meng Tian, Jin Yan, Mark H. Rummeli, Peter Strasser and Ruizhi Yang

Atomically Dispersed Cerium Sites Immobilized on Vanadium Vacancies of Monolayer Nickel‐Vanadium Layered Double Hydroxide: Accelerating Water Splitting Kinetics.

Advanced Functional Materials 2023

DOI: 10.1002/adfm.202308533

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Rational design of efficient single-atom catalysts is a potential avenue to mitigate the sluggish oxygen evolution reaction (OER) kinetics. Adopting appropriate matrixes to stabilize the single-atom active centers with the optimized geometric and electronic structure plays an essential role in enhancing catalytic activities. Herein, massive isolated Ce atoms are successfully anchored on monolayer nickel-vanadium layered double hydroxide support (Ce SAs/m-NiV LDH) via the vanadium defects trapping strategy, resulting in stabilized Ce single-atom with the maximum loading of 8.07 wt.%. Benefitting from the strong synergetic electronic interaction between Ce single atoms and monolayer NiV LDH matrix, thus-prepared catalyst possesses favorable OER (209 mV @ 10 mA cm−2) and water electrolysis performance (1.47 V @ 10 mA cm−2), surpassing other catalysts and even the commercial RuO2 catalyst. Density functional theory (DFT) calculations in combination with in situ electrochemical impedance spectroscopy analysis reveal that the immobilization of monatomic Ce can effectively narrow the band gap and strengthen the density states near the Fermi level as well as more easily adsorb the surficial OH, leading to a lower charge transfer barrier and faster water splitting kinetics.

 

Kai Zeng, Yibing Li, Meng Tian, Chaohui Wei, Jin Yan, Mark H. Rummeli, Peter Strasser and Ruizhi Yang

Molybdenum-leaching induced rapid surface reconstruction of amorphous/crystalline heterostructured trimetal oxides pre-catalyst for efficient water splitting and Zn-air batteries.

Energy Storage Materials 2023

DOI: https://doi.org/10.1016/j.ensm.2023.102806

Crystalline and amorphous structure can entitle a catalyst with high stability and activity, respectively. Oxygen evolution reaction (OER) catalysts, which widely used in water electrolysis and rechargeable Zn-air batteries, often undergo a surface phase reconstruction process and generate amorphous active phases under applied anodic potential. Although widely known, few studies and strategies have been reported to rationally tune OER pre-catalysts for enhanced reaction kinetics. Herein, we report a trimetallic oxides (a/c-NiFeMoOx) OER per-catalyst with rationally tunable amorphous/crystalline heterostructure degrees by a precise-tuning component strategy. The best a/c-NiFeMoOx electrode exhibits an OER overpotential merely of 256 mV and a small cell-voltage of 1.52 V to reach 10 mA cm–2 for water electrolysis, respectively. It is find that Mo leaching with tailored amorphous/crystalline heterostructure via the rational tuned degree of amorphousness promotes a rapid surface reconstruction of the a/c-NiFeMoOx pre-catalyst to form (oxy)hydroxide active species, whilst operando Raman, ex-situ X-ray photoelectron spectroscopy and density functional theory (DFT) analysis show the ample oxygen vacancies generated by phase transition significantly accelerates the deprotonation of OH* and lower the O* ➝ OOH* free energy for a fast oxygen evolution kinetics. Additionally, the practical application of a/c-NiFeMoOx cathode in rechargeable Zn-air battery delivers a robust long-term cycling (over 840 cycles).

 

Kai Zeng, Meng Tian, Xin Chen, Jinlei Zhang, Mark H. Rummeli, Peter Strasser, Jingyu Sun and Ruizhi Yang

Strong electronic coupling between single Ru atoms and cobalt-vanadium layered double hydroxide harness efficient water splitting.

Chemical Engineering Journal 2023

DOI: https://doi.org/10.1016/j.cej.2022.139151

Atomic coordination modulation and electronic structure engineering are appealing routes to develop versatile electrocatalysts targeting high-performance water electrolysis. Herein, atomically dispersed Ru sites are successfully anchored on the surface of CoV layered double hydroxide (LDH), affording a vertically aligned and interconnected nanosheet array architecture. Benefitting from the strong electronic coupling, fast charge transfer capability and well-defined morphology of as-prepared catalyst, ultralow overpotentials for hydrogen evolution reaction (HER, η10 = 28 mV) and oxygen evolution reaction (OER, η25 = 263 mV) are required. The two-electrode configuration cell only requires a cell voltage of 1.52 V to reach 10 mA cm−2, which is lower than that of commercialized Pt/C||RuO2 couple. Synchrotron X-ray absorption spectroscopy studies in combination with density functional theory calculations reveal that the strong electronic coupling between monatomic Ru with CoV LDH induces spatial charge redistribution and a distorted coordination environment around V atoms, thereby accelerating the hydrogen release for HER and reducing the rate-determining step (O* → OOH*) free energy for OER.

 

Yiming Zhu, Jiaao Wang, Toshinari Koketsu, Matthias Kroschel, Jin-Ming Chen, Su-Yang Hsu, Graeme Henkelman, Zhiwei Hu, Peter Strasser, Jiwei Ma

Iridium single atoms incorporated in Co3O4 efficiently catalyze the oxygen evolution in acidic conditions

Nature Communications, 2022

DOI: 10.1038/s41467-022-35426-8

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Designing active and stable electrocatalysts with economic efficiency for acidic oxygen evolution reaction is essential for developing proton exchange membrane water electrolyzers. Herein, we report on a cobalt oxide incorporated with iridium single atoms (Ir-Co3O4), prepared by a mechanochemical approach. Operando X-ray absorption spectroscopy reveals that Ir atoms are partially oxidized to active Ir>4+ during the reaction, meanwhile Ir and Co atoms with their bridged electrophilic O ligands acting as active sites, are jointly responsible for the enhanced performance. Theoretical calculations further disclose the isolated Ir atoms can effectively boost the electronic conductivity and optimize the energy barrier. As a result, Ir-Co3O4 exhibits significantly higher mass activity and turnover frequency than those of benchmark IrO2 in acidic conditions. Moreover, the catalyst preparation can be easily scaled up to gram-level per batch. The present approach highlights the concept of constructing single noble metal atoms incorporated cost-effective metal oxides catalysts for practical applications.

 

Malte Klingenhof, Philipp Hauke, Matthias Kroschel, Xingli Wang, Thomas Merzdorf, Christoff Binninger, Trung Ngo Thanh, Benjamin Paul, Detre Teschner, Robert Schlögl, Robert Schlögl and Peter Strasser

Anion-Tuned Layered Double Hydroxide Anodes for Anion Exchange Membrane Water Electrolyzers: From Catalyst Screening to Single-Cell Performance

ACS Energy Letter, 2022

DOI: 10.1021/acsenergylett.2c01820

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Anion exchange membrane water electrolysis (AEMWE) is an attractive emerging green hydrogen technology. However, the scaling of trends in activity of anode catalysts for the oxygen evolution reaction (OER) from a liquid-electrolyte, three-electrode environment to the two-electrode single-cell format has remained poorly considered. Herein, we critically investigate the scaling of kinetic and catalytic properties of a family of highly active Ni foam (NF) supported, anion (A–)-tuned NiFe(-A–)-OER catalysts. Trends in catalytic activity suggest impressive improvements of up to 91-fold in three-electrode setups (3LC) compared to uncoated NF. While we demonstrate the successful qualitative structure–performance tunability in a 5 cm2 AEMWE single cell, we also find serious limitations in the quantitative predictability of three-electrode setups for single-cell performance trends. Cell environments appear to equalize the cell performances of designer catalysts, which has important ramifications for electrode development. We succeed in analyzing and discussing some of these translation limitations in terms of previously overlooked effects summarized in the activity improvement factor f.

 

Hoang Phi Tran, Hong Nhan Nong, Hyung-Suk Oh, Malte Klingenhof, Matthias Kroschel, Benjamin Paul, Jessica Hübner, Detre Teschner, and Peter Strasser

Catalyst−Support Surface Charge Effects on Structure and Activity of IrNi-Based Oxygen Evolution Reaction Catalysts Deposited on Tin-Oxide Supports

Chemistry of Materials, 2022

DOI: 10.1021/acs.chemmater.2c01098

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Ir-based nanoparticles supported on conductive oxide supports show high water oxidation (oxygen evolution reaction, OER) activity and represent a promising alternative to state-of-art anode catalysts in water electrolyzers. Physicochemical interactions between the Ir-based catalytic nanoparticles and the oxide supports can critically affect the weight loading, surface area, activity, and stability of the Ir-based catalysts under electrochemical OER conditions. However, systematic insight on the influences of surface charge on deposition yield and dispersion of the nanoparticles on oxide supports and the influence of this interaction on the catalytic performance of supported Ir-based alloys is missing. In this work, the impact of electrostatic interactions between catalyst–support surface charges during catalyst synthesis on the structure and performance of Ir-based OER electrocatalysts is studied. Supported IrNi NPs were synthesized comparing a direct and a stepwise deposition technique onto selected doped tin oxide supports including antimony tin oxide (ATO), In-rich indium tin oxide (ITO), and fluorine tin oxide (FTO), with commercial ATO and unsupported particles as references. Data suggest that electrostatic attractions between particles and supports majorly impact the deposition yield of IrNi NPs. Photoemission spectra, XPS, of supports and supported catalysts show declines in the doping elements concomitant to the variation of the oxide oxidation state. We demonstrate how controlled pretreatments and alterations of repulsive forces between supports and nanoparticles resulted in great improvements in nanoparticle deposition and thus enhanced OER activity. Our findings can be transferred to other nanoparticles/support couples to help improve the distribution and adhesion of the nanoparticles and therefore improve their catalytic performances.

 

Young-Jin Ko, Man Ho Han, Haesol Kim, ..., Chang Hyuck Choi, Peter Strasser, Hyung-Suk Oh

Unraveling Ni-Fe 2d Nanostructure with Enhanced Oxygen Evolution Via In-Situ/Operando Spectroscopies

Chem Catalysis, 2022

DOI:10.2139/ssrn.4067931

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Ni-Fe-based materials are well known as one of the most active  electrocatalysts for the oxygen evolution reaction (OER) in alkaline environments. In this study, we propose a facile and scaling up synthesis route using a surfactant for Ni-Fe 2D nanostructured electrocatalysts. Furthermore, we uncovered the hidden phase transformation mechanism of 2D Ni-Fe layered double hydroxide (LDH) electrocatalysts by combining various in situ and operando analyses. The Ni-Fe LDH underwent a chemically induced phase transformation in an alkaline environment without applied potential. The resulting phase transformation product persisted throughout the entire OER mechanism cycle, such that it played a dominant role in the process. The presence of high-valent Ni and Fe was observed on the surface; hence, the OER selectivity and catalytic turnover frequency were enhanced in the low-overpotential domain. Our study not only uncovers the fundamentals of Ni-Fe LDH but also expands the potential for practical alkaline water splitting.

 

Xuecheng Cao, Chaohui Wei, Xiangjun Zheng, Kai Zeng, Xin Chen, Mark H. Rummeli, Peter Strasser, Ruizhi Yang

Ru clusters anchored on Magnéli phase Ti4O7 nanofibers enables flexible and highly efficient Li–O2 batteries

Energy Storage Materials, 2022

DOI:10.1016/j.ensm.2022.05.028

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Lithium–oxygen (Li–O2) batteries have attracted tremendous attention due to their high specific energy density. However, their sluggish conversion kinetics and detrimental parasitic reactions would deteriorate the lifespan of batteries. Herein, a combined density functional theory (DFT) calculation and experimental approach is carried out to design an efficient cathode electrocatalyst for Li–O2 batteries. A self-supporting film of Ru clusters anchored on Magnéli phase Ti4O7 enriched with oxygen vacancy (Ru/Ti4O7) is fabricated upon electrospinning and carbothermal reduction. In such a synergistic configuration of Ru/Ti4O7 hybrid film, the strong metal-support interaction (SMSI) between Ru and Ti4O7 can improve the charge transfer at the interface and enhance the adsorption energy of intermediates, accelerating the reaction kinetics of the formation/decomposition of Li2O2. Benefitting from this SMSI, the electrochemical stability of Ru/Ti4O7 over cycling is also enhanced. As a result, as-prepared Ru/Ti4O7 cathodes could realize excellent electrochemical performance, including high specific capacity (11000 mAh g–1), low discharge/charge polarization (0.36 V), long lifespan (> 100 cycles) and superior rate capability. Furthermore, a flexible Li–O2 pouch cell, constructed with as-fabricated Ru/Ti4O7 film cathode, lithium foil anode and GPE, can exert an impressive areal capacity of 5 mAh cm–2 with a low voltage gap of 0.82 V in ambient air. This work suggests that the activity of catalysts can be significantly enhanced with interfacial modification, offering an efficient approach for rational designing of electrocatalysts for use in Li–air batteries and beyond.

 

Sebastian Ott, Fengmin Du, Mauricio Lopez Luna, Tuan Anh Dao, Beatriz Roldan Cuenya, Alin Orfanidi and Peter Strasser

Understanding the Performance Increase of Catalysts Supported on N-Functionalized Carbon in PEMFC Catalyst Layers

Journal of the Electrochemical Society, 2022

DOI:10.1149/1945-7111/ac6e4d

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Applying nitrogen-modified carbon support in PEMFCs has been attracting arising interest due to the resulting performance enhancement. In the present study, we attempt to uncover the origin and gain a deeper understanding of the different Nmodification processes, whose influences are responsible for the performance improvement. By utilizing chemically modified Ketjenblack supports comprising altered fraction of N-functionalities, we investigate the underlying mechanism of the drastically reduced voltage losses under fuel cell operation conditions. In all, we demonstrate the key role of support modification induced by
ammonia in strengthened support/ionomer interactions and alter physico-chemical properties of the carbon support contributing towards enhanced MEA performance. With the use of X-ray photoelectron spectroscopy (XPS), we show unambiguous evidences that not all N modified surfaces yield the desired performance increase. Rather, the latter depends on a complex interplay between different electrochemical parameter and catalyst properties. We want to emphasize the ionomer/support interaction as one important factor for enhanced ionomer distribution and present a prove of a direct interaction between the ionomers´ sidechains and N-functional groups of the support.

 

Feitao Li, Dong Wang, Malte Klingenhof, Dominik Flock, Honglei Wang, Peter Strasser, and Peter Schaaf

Controllable Si oxidation mediated by annealing temperature and atmosphere

Journal of Materials Science, 2022

DOI:10.1007/s10853-022-07354-x

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The morphology evolution by thermal annealing induced dewetting of gold (Au) thin films on silicon (Si) substrates with a native oxide layer and its dependences on annealing temperature and atmosphere are investigated. Both dewetting degree of thin film and Au/Si interdiffusion extent are enhanced with the annealing temperature. Au/Si interdiffusion can be observed beyond 800 °C and Au–Si droplets form in both argon and oxygen (Ar + O2) and argon and hydrogen (Ar + H2) environments. In Ar + O2 case, the passive oxidation (Si + O2 → SiO2) of diffused Si happens and thick silicon oxide (SiOx) covering layers are formed. A high temperature of 1050 °C can even activate the outward growth of free-standing SiOx nanowires from droplets. Similarly, annealing at 800 °C under Ar + H2 situation also enables the slight Si passive oxidation, resulting in the formation of stripe-like SiOx areas. However, higher temperatures of 950–1050 °C in Ar + H2 environment initiate both the SiOx decomposition and the Si active oxidation (2Si + O2 → 2SiO(g)), and the formation of solid SiOx is absent, leading to the only formation of isolated Au–Si droplets at elevated temperatures and droplets evolve to particles presenting two contrasts due to the Au/Si phase separation upon cooling.

 

Elisabeth Hornberger, Malte Klingenhof, Shlomi Polani, Paul Paciok, Attila Kormanyos, Raphael Chattot, Katherine E. MacArthur, Xingli Wang, Lujin Pan, Jakub Drnec, Serhiy Cherevko, Marc Heggen, Rafal E. DuninBorkowski  and Peter Strasser

On the electrocatalytical oxygen reduction reaction activity and stability of quaternary RhMo-doped PtNi/C octahedral nanocrystals

Chemical Science, 2022

DOI:10.1039/d2sc01585d

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Recently proposed bimetallic octahedral Pt–Ni electrocatalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cell (PEMFC) cathodes suffer from particle instabilities in the form of Ni corrosion and shape degradation. Advanced trimetallic Pt-based electrocatalysts have contributed to their catalytic performance and stability. In this work, we propose and analyse a novel quaternary octahedral (oh-)Pt nanoalloy concept with two distinct metals serving as stabilizing surface dopants. An efficient solvothermal one-pot strategy was developed for the preparation of shape-controlled oh-PtNi catalysts doped with Rh and Mo in its surface. The as-prepared quaternary octahedral PtNi(RhMo) catalysts showed exceptionally high ORR performance accompanied by improved activity and shape
integrity after stability tests compared to previously reported bi- and tri-metallic systems. Synthesis, performance characteristics and degradation behaviour are investigated targeting deeper understanding for catalyst system improvement strategies. A number of different operando and on-line analysis techniques were employed to monitor the structural and elemental evolution, including identical location scanning transmission electron microscopy and energy dispersive X-ray analysis (IL-STEM-EDX), operando wide angle X-ray spectroscopy (WAXS), and on-line scanning flow cell inductively coupled plasma mass spectrometry (SFC-ICP-MS). Our studies show that doping PtNi octahedral catalysts with small amounts of Rh and Mo suppresses detrimental Pt diffusion and thus offers an attractive new family
of shaped Pt alloy catalysts for deployment in PEMFC cathode layers.

 

Pengfei Cheng, Yuanwu Liu, Mario Ziegler, Malte Klingenhof, Dong Wang, Zhang Zhang, Peter Strasser, and Peter Schaaf

Improving Silicon Photocathode Performance for Water Reduction through Dual Interface Engineering and Integrating ReS2 Photocatalyst

ACS Appl. Energy Mater., 2022

DOI: 10.1021/acsaem.2c00761

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Photoelectrochemical (PEC) water splitting for H2 production is a possible alternative for fossil energy in the future. However, there exists three problems in PEC water splitting with the silicon (Si) photocathode: poor light absorption of the untreated Si substrate, bad stability in strong acid solution, and poor photocatalytic activity of Si. Here, a strategy of dual interface engineering and photocatalyst deposition is proposed to improve the PEC performance, which consists of fabricating black Si (b-Si) by reactive ion etching, depositing of TiO2 on the b-Si by atomic layer deposition, and growing ReS2 on top of the TiO2 by chemical vapor deposition. Owing to the suitable band alignment of b-Si, TiO2, and ReS2, the ReS2/TiO2/b-Si shows obviously enhanced PEC performance compared to b-Si, TiO2/b-Si, and ReS2/b-Si photocathodes. Results of electrochemical impedance spectroscopy and Mott–Schottky plot analysis demonstrate that the TiO2 layer plays an important role and the charge-transfer kinetics of the system is clearly improved. Transient photocurrent measurements indicate that the ReS2/TiO2/b-Si photocathode has the most remarkable photocurrent response. In addition, the ReS2/TiO2/b-Si photocathode also shows excellent stability after being operated for 25 h.

 

Quanchen Feng; Xingli Wang; Malte Klingenhof; Marc Heggen and Peter Strasser

Low-Pt NiNC-Supported PtNi Nanoalloy Oxygen Reduction Reaction Electrocatalysts-in situ Tracking of the Atomic Alloying Process

Angew Chem Int Ed Engl, 2022

DOI: 10.1002/anie.202203728

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Carbon-supported platinum-nickel (Pt-Ni) alloy nanoparticles (NPs) emerge as the electrocatalysts of choice for deployment in polymer electrolyte membrane fuel cell (PEMFC) cathodes. To date, viable PtNi nanoalloy catalysts are characterized by large Pt weight loading of up to 50 wt%. To a large extent, their preparation processes often involve the use of expensive or even hazardous organometallic metal precursors, solvents and capping agents, substantially limiting their synthetic scalability and sustainability. Here, we report a novel synthetic strategy toward highly active low-Pt loaded PtNi nanoalloy Oxygen Reduction Reaction (ORR) catalysts. The synthesis involves the Pyrolysis and Leaching of Ni-organic polymers, subsequent Pt nanoparticle Deposition followed by thermal Alloying (referred to as PLDA) to prepare single Ni atom site (NiNC)-supported bimetallic PtNi nanoalloy electrocatalysts with very low Pt weight contents of 3–5 wt% Pt loading. We demonstrate that despite this low Pt weight loading, the catalysts exhibit more favorable Pt-mass activities compared to conventional, carbon-supported 20–30 wt%Pt Pt-loaded benchmark PtNi alloy catalysts. Using in situ transmission electron microscopy, cyclic voltammetry, and surface CO stripping techniques, we track and unravel the key stages of the formation process of the PtNi nanoparticle catalysts directly at the atomic scale. By carefully chosen reference experiments, we find that carbon-encapsulated Ni NPs, rather than NiNx single sites, serve exclusively as the Ni atom source for PtNi alloy formation during thermal treatments. Our materials concepts offer a pathway to further decrease the overall Pt content of PEM fuel cell devices.

 

Fang Luo, Stephan Wagner, Wen Ju, Mathias Primbs, Shuang Li, Huan Wang, Ulrike I. Kramm and Peter Strasser

Kinetic Diagnostics and Synthetic Design of Platinum Group Metal Free Electrocatalysts for the Oxygen Reduction Reaction Using Reactivity Maps and Site Utilization Descriptors

Journal of the American Chemical Society, 2022

DOI: doi.org/10.1021/jacs.2c01594

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The experimental development of catalytically evermore active platinum group metal (PGM)-free materials for the oxygen reduction reaction (ORR) at fuel cell cathodes has been until recently to a large extent a rather empirical iteration of synthesis and testing. Here, we present how kinetic reactivity maps established based on kinetic descriptors of PGM-free single-metal- site ORR electrocatalysts can help better understand the origin of catalytic reactivity and help derive rational synthetic guidelines toward improved catalysts. Key in our analysis are the catalytic surface site density (SD) and the catalytic turnover frequency (TOF) in their role as controlling kinetic parameters for the ORR reactivity of PGM-free nitrogen-coordinated single-metal M-site carbon (MNC) catalysts. SD−TOF plots establish two-dimensional reactivity maps. We also consider the ratio between SD and the total number of single-metal sites in the bulk, referred to as the site utilization factor, which we propose as another guiding parameter for optimizing the synthesis of MNC catalysts. Exemplified by two sets of FeNC, CoNC, and SnNC catalysts prepared using two distinctly different N- and C-precursor material classes (Zn-based zeolitic imidazolate frameworks and covalent polyaniline), we comparatively diagnose the intrinsic kinetic ORR parameters as well as structural, morphological, and chemical properties. From there, we derive and discuss possible synthetic guidelines for further improvements. Our approach can be extended to other families of catalysts and may involve kinetic performance data of idealized liquid-electrolyte cells as well as gas diffusion layer-type flow cells.

 

Ifan E. L. Stephens, Karen Chan, Alexander Bagger, Shannon W. Boettcher, Julien Bonin, Etienne Boutin, Aya Buckley, Raffaella Buonsanti, Etosha Cave, Xiaoxia Chang, See Wee Chee, Alisson H. M. da Silva, Phil De Luna, Oliver Einsle, Balázs Endrődi, María Escudero Escribano, Jorge V. Ferreira de Araujo, Marta C. Figueiredo, Christopher Hahn18, Kentaro U. Hansen, Sophia Haussener, Sara Hunegnaw, Ziyang Huo, Yun Jeong Hwang, Csaba Janáky, Buddhinie S. Jayathilake21, Feng Jiao, Zarko P. Jovanov, Parisa Karimi, Marc T. M. Koper, Kendra Kuh, Woong Hee Lee, Zhiqin Liang, Xuan Liu, Sichao Ma, Ming Ma, Hyung-Suk Oh, Marc Robert, Beatriz Roldan Cuenya, Jan Rossmeis, Claudie Roy, Mary P Ryan, Edward H Sargent, Paula Sebastián-Pascua, Brian Seger, Ludmilla Steier, Peter Strasser, Ana Sofia Varela, Rafaël E Vos, Xue Wang, Bingjun Xu, Hossein Yadegari and Yuxiang Zhou

2022 Roadmap on Low Temperature Electrochemical CO2 Reduction

Journal of Physics: Energy, 2022

DOI: 10.1088/2515-7655/ac7823

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Electrochemical CO2 reduction is an attractive option for storing renewable electricity and for the sustainable production of valuable chemicals and fuels. In this roadmap, we review recent progress in fundamental understanding, catalyst development, and in engineering and scale-up. We discuss the outstanding challenges towards commercialization of electrochemical CO2 reduction technology: energy efficiencies, selectivities, low current densities, and stability. We highlight the opportunities in establishing rigorous standards for benchmarking performance, advances in in operando characterization, the discovery of new materials towards high value products, the investigation of phenomena across multiple-length scales and the application of data science towards doing so. We hope that this collective perspective sparks new research activities that ultimately bring us a step closer towards establishing a low- or zero-emission carbon cycle.

 

Shlomi Polani, Katherine E. MacArthur, Jiaqi Kang, Malte Klingenhof, Xingli Wang, Tim Möller, Raffaele Amitrano, Raphaël Chattot, Marc Heggen, Rafal E. Dunin-Borkowski and Peter Strasser

Highly Active and Stable Large Mo-Doped Pt-Ni Octahedral Catalysts for ORR: Synthesis, Post-treatments, and Electrochemical Performance and Stability

ACS Appl Mater Interfaces, 2022

DOI: 10.1021/acsami.2c02397

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Over the past decade, advances in the colloidal syntheses of octahedral-shaped Pt–Ni alloy nanocatalysts for use in fuel cell cathodes have raised our atomic-scale control of particle morphology and surface composition, which, in turn, helped raise their catalytic activity far above that of benchmark Pt catalysts. Future fuel cell deployment in heavy-duty vehicles caused the scientific priorities to shift from alloy particle activity to stability. Larger particles generally offer enhanced thermodynamic stability, yet synthetic approaches toward larger octahedral Pt–Ni alloy nanoparticles have remained elusive. In this study, we show how a simple manipulation of solvothermal synthesis reaction kinetics involving depressurization of the gas phase at different stages of the reaction allows tuning the size of the resulting octahedral nanocatalysts to previously unachieved scales. We then link the underlying mechanism of our approach to the classical “LaMer” model of nucleation and growth. We focus on large, annealed Mo-doped Pt–Ni octahedra and investigate their synthesis, post-synthesis treatments, and elemental distribution using advanced electron microscopy. We evaluate the electrocatalytic ORR performance and stability and succeed to obtain a deeper understanding of the enhanced stability of a new class of relatively large, active, and long-lived Mo-doped Pt–Ni octahedral catalysts for the cathode of PEMFCs.

 

Elisabeth Hornberger, Thomas Merzdorf, Henrike Schmies, Jessica Hübner, Malte Klingenhof, Ulrich Gernert, Matthias Kroschel, Björn Anke, Martin Lerch, Johannes Schmidt, Arne Thomas, Raphaël Chattot, Isaac Martens, Jakub Drnec, and Peter Strasser

Impact of Carbon N-Doping and Pyridinic-N Content on the Fuel Cell Performance and Durability of Carbon-Supported Pt Nanoparticle Catalysts

ACS Appl. Mater. Interfaces, 2022

DOI: doi.org/10.1021/acsami.2c00762

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Cathode catalyst layers of proton exchange membrane fuel cells (PEMFCs) typically consist of carbon-supported platinum catalysts with varying weight ratios of proton-conducting ionomers. N-Doping of carbon support materials is proposed to enhance the performance and durability of the cathode layer under operating conditions in a PEMFC. However, a detailed understanding of the contributing N-moieties is missing. Here, we report the successful synthesis and fuel cell implementation of Pt electrocatalysts supported on N-doped carbons, with a focus on the analysis of the N-induced effect on catalyst performance and durability. A customized fluidized bed reduction reactor was used to synthesize highly monodisperse Pt nanoparticles deposited on N-doped carbons (N–C), the catalytic oxygen reduction reaction activity and stability of which matched those of state-of-the-art PEMFC catalysts. Operando high-energy X-ray diffraction experiments were conducted using a fourth generation storage ring; the light of extreme brilliance and coherence allows investigating the impact of N-doping on the degradation behavior of the Pt/N–C catalysts. Tests in liquid electrolytes were compared with tests in membrane electrode assemblies in single-cell PEMFCs. Our analysis refines earlier views on the subject of N-doped carbon catalyst supports: it provides evidence that heteroatom doping and thus the incorporation of defects into the carbon backbone do not mitigate the carbon corrosion during high-potential cycling (1–1.5 V) and, however, can promote the cell performance under usual PEMFC operating conditions (0.6–0.9 V).

 

Asad Mehmood, Mengjun Gong, Frédéric Jaouen, Aaron Roy, Andrea Zitolo, Anastassiya Khan, Moulay-Tahar Sougrati, Mathias Primbs, Alex Martinez Bonastre, Dash Fongalland, Goran Drazic, Peter Strasser & Anthony Kucernak

High loading of single atomic iron sites in Fe–NC oxygen reduction catalysts for proton exchange membrane fuel cells

Nature Catalysis, 2022

DOI:doi.org/10.1038/s41929-022-00772-9

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Non-precious iron-based catalysts (Fe–NCs) require high active site density to meet the performance targets as cathode catalysts in proton exchange membrane fuel cells. Site density is generally limited to that achieved at a 1–3 wt%(Fe) loading due to the undesired formation of iron-containing nanoparticles at higher loadings. Here we show that by preforming a carbon–nitrogen matrix using a sacrificial metal (Zn) in the initial synthesis step and then exchanging iron into this preformed matrix we achieve 7 wt% iron coordinated solely as single-atom Fe–N4 sites, as identified by 57Fe cryogenic Mössbauer spectroscopy and X-ray absorption spectroscopy. Site density values measured by in situ nitrite stripping and ex situ CO chemisorption methods are 4.7 × 1019 and 7.8 × 1019 sites g−1, with a turnover frequency of 5.4 electrons sites−1 s−1 at 0.80 V in a 0.5 M H2SO4 electrolyte. The catalyst delivers an excellent proton exchange membrane fuel cell performance with current densities of 41.3 mA cm−2 at 0.90 ViR-free using H2–O2 and 145 mA cm−2 at 0.80 V (199 mA cm−2 at 0.80 ViR-free) using H2–air.

 

Changxia Li, Wen Ju, Sudarshan Vijay, Janis Timoshenko, Kaiwen Mou, David A. Cullen, Jin Yang, Xingli Wang, Pradip Pachfule, Sven Brückner, Hyo Sang Jeon, Felix T. Haase, Sze-Chun Tsang, Clara Rettenmaier, Karen Chan, Beatriz Roldan Cuenya, Arne Thomas, and Peter Strasser

Covalent Organic Framework (COF) Derived Ni-N-C Catalysts for Electrochemical CO2 Reduction: Unraveling Fundamental Kinetic and Structural Parameters of the Active Sites

Angewandte Chemie, 2022

DOI:doi.org/10.1002/anie.202114707

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Electrochemical CO2 reduction is a potential approach to convert CO2 into valuable chemicals using electricity as feedstock. Abundant and affordable catalyst materials are needed to upscale this process in a sustainable manner. Nickel-nitrogen-doped carbon (Ni-N-C) is an efficient catalyst for CO2 reduction to CO, and the single-site Ni Nx motif is believed to be the active site. However, critical metrics for its catalytic activity, such as active site density and intrinsic turnover frequency, so far lack systematic discussion. In this work, we prepared a set of covalent organic framework (COF)-derived Ni-N-C catalysts, for which the Ni Nx content could be adjusted by the pyrolysis temperature. The combination of high-angle annular dark-field scanning transmission electron microscopy and extended X-ray absorption fine structure evidenced the presence of Ni single-sites, and quantitative X-ray photoemission addressed the relation between active site density and turnover frequency

 

Chengyi Lu, Meng Tian, Xiangjun Zheng, Chaohui Wei, Mark H. Rummeli, Peter Strasser, Ruizhi Yang

Cotton pad derived 3D lithiophilic carbon host for robust Li metal anode: In-situ generated ionic conductive Li3N protective decoration

Chemical Engineering Journal, 2022

DOI:10.1016/j.cej.2021.132722

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Lithium metal anode is considered as one of the most promising candidates for the next-generation batteries with high specific energy density. However, several thorny problems encompassing uncontrollable Li dendritic growth and wild volume variation during cycling, accompanied by the short lifespan and alarming safety concerns, have hindered the commercial viability of Li metal-based batteries. In this contribution, we designed a Li composite anode fabricated via Li infusion into N, O co-doped and Ag coated 3D carbon host from simple treatments of commercial cotton pads, referred as Ag-NOCP@Li. The incorporation of multi lithiophilic atoms can significantly improve the affinity of 3D carbon host towards Li. More importantly, during molten Li infiltration, the composite anode can in-situ generate Li3N decoration, an excellent Li+ conductor and electron insulator. The first-principles calculations further revealed that the active sites for the Li3N generation most likely are pyrrolic nitrogen sites. The Li3N with favorable mechanical strength and ultra-fast Li+ diffusion rate can effectively boost the kinetics of Li transport and redox, as well as inhibit the dendritic generation. Besides, the Ag-NOCP with hierarchical pores and multi-microchannel within the nanofibers, allows the rapid Li+ diffusion and buffers the volume change over long cycling. Therefore, such Ag-NOCP@Li electrode could maintain a stable cycling for 1400 h at 1.0 mA cm− 2/1.0 mAh cm− 2. The full cells using Ag-NOCP@Li anode paired with LiFePO4 and LiNi0.5Co0.2Mn0.3O2 cathodes, displayed impressive long-term cyclic stability up to 400cycles at 0.5 and 1.0C, respectively. This work paves new way for rational design of 3D lithiophilic host towards durable Li anode.

 

Sebastian Ott, Fengmin Du, Mauricio Lopez Luna, Tuan Anh Dao, Sören Selve, Beatriz Roldan Cuenya, Alin Orfanidi, Peter Strasser

Property-Reactivity Relations of N-doped PEM Fuel Cell Cathode Catalyst Supports

Applied Catalysis B: Environmental, 2022

DOI: 10.1016/j.apcatb.2022.121118

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This study clarifies the effect of the nature of solid N-precursor molecules on the N-modification, more specifically unravels how the N-precursors affect the physiochemical and catalytic properties of the resulting carbon supports and final catalysts. Therefore, cyanamide and melamine were used as N-source. Utilizing such modified high surface area carbons, in situ measurements as humidity dependent performance, electrochemical surface area, proton resistivity and limiting current measurements were conducted to access the role and degree of ionomer coverage and transport resistances. Additional X-ray photoelectron spectroscopy (XPS) proves molecular interaction between acidic side chains and basic N-groups. Overall, we show the importance of the N-precursor and synthetic route determining which physiochemical parameter will be influenced in the resulting catalytic layer. Based on this, the pure presence of some N-moieties does not guarantee an improved ionomer distribution, but the modification process enables a tailoring effect of the carbon specie itself affecting transport phenomena.