Rosa M. Arán-Ais, Fabio Dionigi, Thomas Merzdorf, Martin Gocyla, Marc Heggen, Rafal E. Dunin-Borkowski, Manuel Gliech, José Solla-Gullón, Enrique Herrero, Juan M. Feliu, and Peter Strasser
Elemental Anisotropic Growth and Atomic-Scale Structure of Shape-Controlled Octahedral Pt−Ni−Co Alloy Nanocatalysts
Nano Lett. 15, 7473−7480
Multimetallic shape-controlled nanoparticles offer great opportunities to tune the activity, selectivity, and stability of electrocatalytic surface reactions. However, in many
cases, our synthetic control over particle size, composition, and shape is limited requiring trial and error. Deeper atomic-scale insight in the particle formation process would enable more rational syntheses. Here we exemplify this using a family of trimetallic PtNiCo nanooctahedra obtained via a low-temperature, surfactant-free solvothermal synthesis. We analyze the competition between Ni and Co precursors under coreduction “one-step” conditions when the Ni reduction rates prevailed. To tune the Co reduction rate and final content, we develop a “two-step” route and track the evolution of the composition and morphology of the particles at the atomic scale. To achieve this,
scanning transmission electron microscopy and energy dispersive X-ray elemental mapping techniques are used. We provide evidence of a heterogeneous element distribution caused by element-specific anisotropic growth and create octahedral nanoparticles with tailored atomic composition like Pt1.5M, PtM, and PtM1.5 (M = Ni + Co). These trimetallic electrocatalysts have been tested toward the oxygen reduction reaction (ORR), showing a greatly enhanced mass activity related to commercial Pt/C and less activity loss than binary PtNi and PtCo after 4000 potential cycles.
Tran Ngo Huan, Eugen. S. Andreiadis, Jonathan Heidkamp, Philippe Simon, Etienne Derat, Saioa Cobo, Guy Royal, Arno Bergmann, Peter Strasser, Holger Dau, Vincent Artero and Marc Fontecave
From molecular copper complexes to composite electrocatalytic materials for selective reduction of CO2 to formic acid
J. Mater. Chem. A 3, 3901–3907
The development of new energy storage technologies is central to solving the challenges facing the widespread use of renewable energies. An option is the reduction of carbon dioxide (CO2) into carbon-based products which can be achieved within an electrochemical cell. Future developments of such processes depend on the availability of cheap and selective catalysts at the electrode. Here we show that a unique well-characterized active electrode material can be simply prepared via electrodeposition from a molecular copper complex precursor. The best performances, namely activity (150 mV onset overpotential and 1 mA cm-2 current density at 540 mV overpotential), selectivity (90% faradaic yield) and stability for electrocatalytic reduction of CO2 into formic acid in DMF/H2O (97:3 v/v) have been obtained with the [Cu(cyclam)](ClO4)2 complex (cyclam = 1,4,8,11-tetraazacyclotetradecane) as the precursor. Remarkably the organic ligand of the Cu precursor remains part of the composite material and the electrocatalytic activity is greatly dependent on the nature of that organic component.
Erik Ortel, Jörg Polte, Denis Bernsmeier, Björn Eckhardt, Benjamin Paul, Arno Bergmann, Peter Strasser, Franziska Emmerling, Ralph Kraehnert
Pd/TiO2 coatings with template-controlled mesopore structure as highly active hydrogenation catalyst
Applied Catalysis A: General 493, 25–32
Micro-structured reactors offer excellent mass and heat transport capabilities and can therefore sustain very high reaction rates and space–time-yields also for highly exothermic catalytic reactions. However, such high rates cannot be reached when the reactors are coated or filled with conventional catalysts powders. We present a strategy for the direct synthesis of highly active wall-coated supported catalysts via co-deposition of a pore template (here micelles formed from PEO-b-PPO-b-PEO) and a precursors for the metal oxide (TiCl4) along with a compatible precursor for the active metal (PdCl2). The obtained catalytic coatings possess a template-controlled open pore structure and excellent mechanical stability. Moreover, the active metal is highly dispersed and well-distributed across the coating also at high Pd loadings. The corresponding high activity along with rapid mass transfer enabled by the open pore system results in the best space–time-yields in the gas-phase hydrogenation of butadiene reported so far in literature for a supported catalyst.
Guang-Ping Hao, Nastaran Ranjbar Sahraie, Qiang Zhang, Simon Krause, Martin Oschatz, Alicja Bachmatiuk, Peter Strasser and Stefan Kaskel
Hydrophilic non-precious metal nitrogen-doped carbon electrocatalysts for enhanced efficiency in oxygen reduction reaction
Chem. Commun. 51, 17285-17288
Exploring the role of surface hydrophilicity of non-precious metal N-doped carbon electrocatalysts in electrocatalysis is challenging. Herein we discover an ultra-hydrophilic non-precious carbon electrocatalyst, showing enhanced catalysis efficiency on both gravimetric and areal basis for oxygen reduction reaction due to a high dispersion of active centres.
Xin Gong, Shanshan Liu, Chuying Ouyang, Peter Strasser, and Ruizhi Yang
Nitrogen- and Phosphorus-Doped Biocarbon with Enhanced Electrocatalytic Activity for Oxygen Reduction
ACS Catal. 5(2), 920–927
The oxygen reduction reaction (ORR) at the cathode of fuel cells and metal–air batteries requires efficient electrocatalysts to accelerate its reaction rate due to its sluggish kinetics. Nitrogen- and phosphorus-doped biocarbon has been fabricated via a simple and low-cost biosynthesis method using yeast cells as a precursor. The as-prepared biocarbon exhibits excellent electrocatalytic activity for the ORR. An onset potential of −0.076 V (vs Ag/AgCl) and a negative shift of only about 29 mV in the half-wave potential of the biocarbon as compared to commercial Pt/C (20 wt % Pt on Vulcan XC-72, Johnson Matthey) is achieved. The biocarbon possesses enhanced electron poverty in carbon atoms and a decreasing amount of less electroactive nitrogen and phosphorus dopants due to the biomineralization during the synthesis. The surface gap layer along with the mesopores in the biocarbon increases accessible active sites and facilitates the mass transfer during the ORR. These factors correlate with the high ORR activity of the biocarbon. The results demonstrate that biomineralization plays a critical role in tailoring the structure and the electrocatalytic activity of the biocarbon for ORR.
Xuecheng Cao, Jiao Wu, Chao Jin, Jinghua Tian, Peter Strasser, and Ruizhi Yang
MnCo2O4 Anchored on P‑Doped Hierarchical Porous Carbon as an Electrocatalyst for High-Performance Rechargeable Li−O2 Batteries
ACS Catal. 5 (8), 4890–4896
The design and synthesis of MnCo2O4 anchored on P-doped hierarchical porous carbon (MCO/P-HPC) is reported. Without harsh oxidative treatment, creating anchoring sites for MnCo2O4 on the surface of carbon is realized by P-doping in carbon. The chemical coupling between P-HPC and MCO induced by P-doping provides pathways for fast charge transport. This hybrid with a hierarchical porous structure favors efficient electrolyte penetration, oxygen transport, and effective accommodation of insoluble discharge product Li2O2. When employed as an electrocatalyst in rechargeable Li–O2 batteries, the MCO/P-HPC hybrid delivers a high discharge capacity (13 150 mAh g–1 at 200 mA g–1), excellent rate capability (7028 mAh g–1 at 1000 mA g–1), and long cycle stability (200 cycles at a capacity of 1000 mAh g–1 under 200 mA g–1).
Arno Bergmann, Elias Martinez-Moreno, Detre Teschner, Petko Chernev, Manuel Gliech, Jorge Ferreira de Araújo, Tobias Reier, Holger Dau, and Peter Strasser
Reversible amorphization and the catalytically active state of crystalline Co3O4 during oxygen evolution
Nature Communications 6 (8625), 1-9
Water splitting catalysed by earth-abundant materials is pivotal for global-scale production of non-fossil fuels, yet our understanding of the active catalyst structure and reactivity is still insufficient. Here we report on the structurally reversible evolution of crystalline Co3O4 electrocatalysts during oxygen evolution reaction identified using advanced in situ X-ray techniques. At electrode potentials facilitating oxygen evolution, a sub-nanometre shell of the Co3O4 is transformed into an X-ray amorphous CoOx(OH)y which comprises di-μ-oxo-bridged Co3+/4+ ions. Unlike irreversible amorphizations, here, the formation of the catalytically-active layer is reversed by re-crystallization upon return to non-catalytic electrode conditions. The Co3O4 material thus combines the stability advantages of a controlled, stable crystalline material with high catalytic activity, thanks to the structural flexibility of its active amorphous oxides.We propose that crystalline oxides may be tailored for generating reactive amorphous surface layers at catalytic potentials, just to return to their stable crystalline state under rest conditions.
Nastaran Ranjbar Sahraie, Ulrike I. Kramm, Julian Steinberg, Yuanjian Zhang, Arne Thomas, Tobias Reier, Jens-Peter Paraknowitsch, and Peter Strasser
Quantifying the density and utilization of active sites in non-precious metal oxygen electroreduction catalysts
Nature Communications 6 (8618), 1-9
Carbon materials doped with transition metal and nitrogen are highly active, non-precious metal catalysts for the electrochemical conversion of molecular oxygen in fuel cells, metal air batteries, and electrolytic processes. However, accurate measurement of their intrinsic turn-over frequency and active-site density based on metal centres in bulk and surface has remained difficult to date, which has hampered a more rational catalyst design. Here we report a successful quantification of bulk and surface-based active-site density and associated turn-over frequency values of mono- and bimetallic Fe/N-doped carbons using a combination of chemisorption, desorption and 57Fe Mossbauer spectroscopy techniques. Our general approach yields an experimental descriptor for the intrinsic activity and the active-site utilization, aiding in the catalyst development process and enabling a previously unachieved level of understanding of reactivity trends owing to a deconvolution of site density and intrinsic activity.
Rosa M. Arán-Ais, Fabio Dionigi, Thomas Merzdorf, Martin Gocyla, Marc Heggen, Rafal E. Dunin-Borkowski, Manuel Gliech, José Solla-Gullón, Enrique Herrero, Juan M. Feliu, and Peter Strasser
Elemental Anisotropic Growth and Atomic-Scale Structure of Shape-Controlled Octahedral Pt–Ni–Co Alloy Nanocatalysts
Nano Lett. 15 (11), 7473–7480
Multimetallic shape-controlled nanoparticles offer great opportunities to tune the activity, selectivity, and stability of electrocatalytic surface reactions. However, in many cases, our synthetic control over particle size, composition, and shape is limited requiring trial and error. Deeper atomic-scale insight in the particle formation process would enable more rational syntheses. Here we exemplify this using a family of trimetallic PtNiCo nanooctahedra obtained via a low-temperature, surfactant-free solvothermal synthesis. We analyze the competition between Ni and Co precursors under coreduction “one-step” conditions when the Ni reduction rates prevailed. To tune the Co reduction rate and final content, we develop a “two-step” route and track the evolution of the composition and morphology of the particles at the atomic scale. To achieve this, scanning transmission electron microscopy and energy dispersive X-ray elemental mapping techniques are used. We provide evidence of a heterogeneous element distribution caused by element-specific anisotropic growth and create octahedral nanoparticles with tailored atomic composition like Pt1.5M, PtM, and PtM1.5 (M = Ni + Co). These trimetallic electrocatalysts have been tested toward the oxygen reduction reaction (ORR), showing a greatly enhanced mass activity related to commercial Pt/C and less activity loss than binary PtNi and PtCo after 4000 potential cycles.
Mahdi Ahmadi, Chunhua Cui, Hemma Mistry, Peter Strasser, and Beatriz Roldan Cuenya
Carbon Monoxide-Induced Stability and Atomic Segregation Phenomena in Shape-Selected Octahedral PtNi Nanoparticles
ACS Nano 9 (11), 10686–10694
The chemical and morphological stability of size- and shape-selected octahedral PtNi nanoparticles (NP) were investigated after different annealing treatments up to a maximum temperature of 700°C in vacuum and under 1 bar of CO. Atomic force microscopy (AFM) was used to examine the mobility of the NPs and their stability against coarsening, and X-ray photoelectron spectroscopy (XPS) to study the surface composition, chemical state of Pt and Ni in the NPs and thermally and CO-induced atomic segregation trends. Exposing the samples to 1 bar of CO at room temperature before annealing in vacuum was found to be effective at enhancing the stability of the NPs against coarsening. In contrast, significant coarsening was observed when the sample was annealed in 1 bar of CO, most likely as a result of Ni(CO)4 formation and their enhanced mobility on the support surface. Sample exposure to CO at room temperature prior to annealing lead to the segregation of Pt to the NP surface. Nevertheless, oxidic PtOx and NiOx species still remained at the NP surface, and, irrespective of the initial sample pretreatment, Ni surface segregation was observed upon annealing in vacuum at moderate temperature (T<300°C). Interestingly, a distinct atomic segregation trend was detected between 300°C-500°C for the sample pre-exposed to CO, namely, Ni surface segregation was partially hindered. This might be attributed to the higher bonding energy of CO to Pt as compared to Ni. Annealing in the presence of 1-bar CO also resulted in the initial surface segregation of Ni (T<400°C) as long as PtOx and NiOx species were
available on the surface as a result of the higher affinity of Ni for oxygen. Above 500°C, and regardless of the sample pretreatment, the diffusion of Pt atoms to the NP surface and the formation of a Ni-Pt alloy is observed.
Tobias Reier, Zarina Pawolek, Serhiy Cherevko, Michael Bruns, Travis Jones, Detre Teschner, Sören Selve, Arno Bergmann, Hong Nhan Nong, Robert Schlögl, Karl J. J. Mayrhofer, and Peter Strasser
Molecular Insight in Structure and Activity of Highly Efficient, Low-Ir
Ir−Ni Oxide Catalysts for Electrochemical Water Splitting (OER)
J. Am. Chem. Soc. 137 (40), 13031-13040
Mixed bimetallic oxides offer great opportunities for a systematic tuning of electrocatalytic activity and stability. Here, we demonstrate the power of this strategy using well-defined thermally prepared Ir–Ni mixed oxide thin film catalysts for the electrochemical oxygen evolution reaction (OER) under highly corrosive conditions such as in acidic proton exchange membrane (PEM) electrolyzers and photoelectrochemical cells (PEC). Variation of the Ir to Ni ratio resulted in a volcano type OER activity curve with an unprecedented 20-fold improvement in Ir mass-based activity over pure Ir oxide. In situ spectroscopic probing of metal dissolution indicated that, against common views, activity and stability are not directly anticorrelated. To uncover activity and stability controlling parameters, the Ir–Ni mixed thin oxide film catalysts were characterized by a wide array of spectroscopic, microscopic, scattering, and electrochemical techniques in conjunction with DFT theoretical computations. By means of an intuitive model for the formation of the catalytically active state of the bimetallic Ir–Ni oxide surface, we identify the coverage of reactive surface hydroxyl groups as a suitable descriptor for the OER activity and relate it to controllable synthetic parameters. Overall, our study highlights a novel, highly active oxygen evolution catalyst; moreover, it provides novel important insights into the structure and performance of bimetallic oxide OER electrocatalysts in corrosive acidic environments.
Amandine Guiet, Caren Göbel, Katharina Klingan, Michael Lublow, Tobias Reier, Ulla Vainio, Ralph Krähnert, Helmut Schlaad, Peter Strasser, Ivelina Zaharieva, Holger Dau, Matthias Driess, Jörg Polte, and Anna Fischer
Hydrophobic Nanoreactor Soft-Templating: A Supramolecular Approach to Yolk@Shell Materials
Adv. Func. Mater. 25, 6228–6240
Due to their unique morphology-related properties, yolk@shell materials are promising materials for catalysis, drug delivery, energy conversion, and storage. Despite their proven potential, large-scale applications are however limited due to demanding synthesis protocols. Overcoming these limitations, a simple soft-templated approach for the one-pot synthesis of yolk@shell nanocomposites and in particular of multicore metal nanoparticle (NP)@metal oxide nanostructures (MNP@MOx) is introduced. The approach here, as demonstrated for AuNP@ITOTR (ITOTR standing for tin-rich ITO), relies on polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) inverse micelles as two compartment nanoreactor templates. While the hydrophilic P4VP core incorporates the hydrophilic metal precursor, the hydrophobic PS corona takes up the hydrophobic metal oxide precursor. As a result, interfacial reactions between the precursors can take placebetween the compartments, leading to the formation of yolk@shell structures in solution, which once calcined yield AuNP@ITOTR nanostructures, composed of multiple 6 nm sized Au NPs strongly anchored onto the inner surface of porous 35 nm ITOTR hollow spheres. Although of multicore nature, only limited sintering of the metal nanoparticles is observed at high temperatures (700
C). In addition, the as-synthesized yolk@shell structures exhibit high and stable activity toward CO electrooxidation, thus proving the functionality of this approach for the design of yolk@shell nanocatalysts.
Ana Sofia Varela, Nastaran Ranjbar Sahraie, Julian Steinberg, Wen Ju, Hyung-Suk Oh, and Peter Strasser
Metal-Doped Nitrogenated Carbon as Efficient Catalyst for Direct CO2 Electroreduction to CO and Hydrocarbons
Angew. Chem. Int. Ed. 54 (37), 10758-10762
This study explores the kinetics, mechanism, and active sites of the CO2 electroreduction reaction (CO2RR) to syngas and hydrocarbons on a class of functionalized solid carbon-based catalysts. Commercial carbon blacks were functionalized with nitrogen and Fe and/or Mn ions using pyrolysis and acid leaching. The resulting solid powder catalysts were found to be active and highly CO selective electrocatalysts in the electroreduction of CO2 to CO/H2 mixtures outperforming a low-area polycrystalline gold benchmark. Unspecific with respect to the nature of the metal, CO production is believed to occur on nitrogen functionalities in competition with hydrogen evolution. Evidence is provided that sufficiently strong interaction between CO and the metal enables the protonation of CO and the formation of hydrocarbons. Our results highlight a promising new class of low-cost, abundant electrocatalysts for synthetic fuel production from CO2.
Claudio Baldizzone, Lin Gan, Nejc Hodnik, Gareth Keeley, Aleksander Kostka, Marc Heggen, 3 Peter Strasser and Karl J. J. Mayrhofer
Stability of Dealloyed Porous Pt/Ni Nanoparticles
ACS Catal. 5, 5000-5007
We provide a comprehensive durability assessment dedicated to a promising class of electrocatalysts for the oxygen reduction reaction (i.e., porous platinum nanoparticles). The stability of these nanoengineered open structures is tested under two accelerated degradation test conditions (ADT), particularly selected to mimic the potential regimes experienced by the catalyst during the operative life of a fuel cell (i.e., load cycles (up to 1.0 VRHE) and start-up cycles (up to 1.4 VRHE)). To understand the evolution of the electrochemical performance, the catalyst properties are investigated by means of fundamental rotating disc electrode studies, identical location transmission electron microscopy (IL-TEM) coupled with electron energy loss spectroscopy chemical mapping (IL-EELS), and post-use chemical analysis and online highly sensitive potential resolved dissolution concentration monitoring by scanning flow cell inductively coupled plasma-mass spectrometry (SFC-ICP-MS). The experimental results on the nanoporous Pt revealed distinctive degradation mechanisms that could potentially affect a wide range of other nanoengineered open structures. The study concludes that, although providing promising activity performance, under the relevant operational conditions of fuel cells, the nanoporosity is only metastable and subjected to a progressive reorganization toward the minimization of the nanoscale curvature. The rate and pathways of this specific degradation mechanism together with other well-known degradation mechanisms like carbon corrosion and platinum dissolution are strongly dependent on the selected upper limit potential, leading to distinctly different durability performance.
Catalysts by Platonic design
Science 349, 379
Sophisticated shape-controlled design is yielding ever more active nanocatalysts
Nina Erini, Paul Krause, Manuel Gliech, Ruizhi Yang, Yunhui Huang, Peter Strasser
Comparitive assessment of synthetic strategies toward active platinum-rhodium-tin electrocatalysts for efficient ethanol electro-oxidation
Journal of Power Sources 294, 299-304
The present work explores the effect of autoclave-based autogenous-pressure vs. ambient pressure conditions on the synthesis and properties of carbon-supported Pt–Rh–Sn nanoparticle electrocatalysts. The Pt–Rh–Sn nanoparticles were characterized by X-ray spectroscopy, electron microscopy and mass spectroscopy and deployed as catalysts for the electrocatalytic ethanol oxidation reaction. Pt–Rh–Sn catalysts precipitated with carbon already present showed narrow particle size distribution around 7 nm, while catalysts supported on carbon after particle formation showed broader size distribution ranging from 8 to 16 nm, similar metal loadings between 40 and 48 wt.% and similar atomic ratios of Pt:Rh:Sn of 30:10:60. The highest ethanol oxidation activity at low overpotentials associated with exceptionally early ethanol oxidation onset potential was observed for ambient-pressure catalysts with the active ternary alloy phase formed in presence of the carbon supports. In contrast, catalysts prepared under ambient pressure in a two-step approach, involving alloy particle formation followed by particle separation and subsequent deposition on the carbon support, yielded the highest overall mass activities. Based on the observed synthesis–activity correlations, a comparative assessment is provided of the synthetic techniques at high vs. low pressures, and in presence and absence of carbon support. Plausible hypotheses in terms of particle dispersion and interparticle distance accounting for these observed differences are discussed.
Michael Bernicke, Erik Ortel, Tobias Reier, Arno Bergmann, Jorge Ferreira de Araujo, Peter Strasser and Ralph Kraehnert
Iridium Oxide Coatings with Templated Porosity as Highly Active Oxygen Evolution Catalysts: Structure-Activity Relationships
ChemSusChem 8 (11), 1908-1915
Iridium oxide is the catalytic material with the highest stability in the oxygen evolution reaction (OER) performed under acidic conditions. However, its high cost and limited availability demand that IrO2 is utilized as efficiently as possible. We report the synthesis and OER performance of highly active mesoporous IrO2 catalysts with optimized surface area, intrinsic activity, and pore accessibility. Catalytic layers with controlled pore size were obtained by soft-templating with micelles formed from amphiphilic block copolymers poly(ethylene oxide)-b-poly(butadiene)-b-poly(ethylene oxide). A systematic study on the influence of the calcination temperature and film thickness on the morphology, phase composition, accessible surface area, and OER activity reveals that the catalytic performance is controlled by at least two independent factors, that is, accessible surface area and intrinsic activity per accessible site. Catalysts with lower crystallinity show higher intrinsic activity. The catalyst surface area increases linearly with film thickness. As a result of the templated mesopores, the pore surface remains fully active and accessible even for thick IrO2 films. Even the most active multilayer catalyst does not show signs of transport limitations at current densities as high as 75 mA cm−2.
Lei Wang, Fabio Dionigi, Nhat Truong Nguyen, Robin Kirchgeorg, Manuel Gliech, Sabina Grigorescu, Peter Strasser and Patrik Schmuki
Tantalum Nitride Nanorod Arrays: Introducing Ni–Fe Layered Double Hydroxides as a Cocatalyst Strongly Stabilizing Photoanodes in Water Splitting
Chem. Mater. 27 (7), 2360-2366
Ta3N5 nanostructures are widely explored as anodes for photoelectrochemical (PEC) water splitting. Although the material shows excellent semiconductive properties for this purpose, the key challenge is its severe photocorrosion when used in typical aqueous environments. In the present work we introduce a NiFe layered double hydroxide (LDH) cocatalyst that dramatically reduces photocorrosion effects. To fabricate the Ta3N5 electrode, we use through-template anodization of Ta and obtain oxide nanorod arrays that then are converted to Ta3N5 by high temperature nitridation. After modification with our cocatalyst system, we obtained solar photocurrents of 6.3 mA cm–2 at 1.23 VRHE in 1 M KOH, and an electrode maintains about 80% of the initial activity for extended irradiation times.
Hyung-Suk Oh, Hong Nhan Nong, Tobias Reier, Manuel Gliech and Peter Strasser
Oxide-supported Ir nanodendrites with high activity and durability for the oxygen evolution reaction in acid PEM water electrolyzers
Chem. Sci. 6, 3321-3328
Reducing the noble-metal catalyst content of acid Polymer Electrolyte Membrane (PEM) water electrolyzers without compromising catalytic activity and stability is a goal of fundamental scientific interest and substantial technical importance for cost-effective hydrogen-based energy storage. This study presents nanostructured iridium nanodendrites (Ir-ND) supported on antimony doped tin oxide (ATO) as efficient and stable water splitting catalysts for PEM electrolyzers. The active Ir-ND structures exhibited superior structural and morphological properties, such as particle size and surface area compared to commercial state-of-art Ir catalysts. Supported on tailored corrosion-stable conductive oxides, the Ir-ND catalysts exhibited a more than 2-fold larger kinetic water splitting activity compared with supported Ir nanoparticles, and a more than 8-fold larger catalytic activity than commercial Ir blacks. In single-cell PEM electrolyzer tests, the Ir-ND/ATO outperformed commercial Ir catalysts more than 2-fold at technological current densities of 1.5 A cm−2 at a mere 1.80 V cell voltage, while showing excellent durability under constant current conditions. We conclude that Ir-ND/ATO catalysts have the potential to substantially reduce the required noble metal loading, while maintaining their catalytic performance, both in idealized three-electrode set ups and in the real electrolyzer device environments
Hyung-Suk Oh, Hong Nhan Nong and Peter Strasser
Preparation of Mesoporous Sb-, F-, and In-Doped SnO2 Bulk Powder with High Surface Area for Use as Catalyst Supports in Electrolytic Cells
Adv. Func. Mater. 25, 1074-1081
The M-doped tin oxides (M = Sb, F, and In) to be used as catalyst support are synthesized by using templating process with tetradecylamine (TDA) as the template, combined with a hydrothermal (HT) method to improve its thermal stability. The obtained materials are characterized by XRD, SAXS, TEM, EDX, SEM, and BET to study microstructure and physical properties, which have a mesoporous structure, small particle size, and high surface area (125–263 m2 g–1). The materials show an overall conductivity of 0.102–0.295 S cm–1. Repetitive potential cycling is employed to characterize the electrochemical properties and stability. The M-doped tin oxides are highly electrochemical stable compared to carbon black. From the observed results, it can be concluded that the combination of TDA and HT treatment are an effective synthetic method for designing mesoporous M-doped tin oxide as catalyst supports.
Hong Nhan Nong, Hyung-Suk Oh, Tobias Reier, Elena Willinger, Marc-Georg Willinger, Valeri Petkov, Detre Teschner and Peter Strasser
Oxide-Supported IrNiOx Core–Shell Particles as Efficient, Cost-Effective, and Stable Catalysts for Electrochemical Water Splitting
Angew. Chem. 127, 3018-3022
Active and highly stable oxide-supported IrNiOx core–shell catalysts for electrochemical water splitting are presented. IrNix@IrOx nanoparticles supported on high-surface-area mesoporous antimony-doped tin oxide (IrNiOx / Meso-ATO) were synthesized from bimetallic IrNix precursor alloys (PA-IrNix/Meso-ATO) using electrochemical Ni leaching and concomitant Ir oxidation. Special emphasis was placed on Ni/NiO surface segregation under thermal treatment of the PA-IrNix/Meso-ATO as well as on the surface chemical state of the particle/oxide support interface. Combining a wide array of characterization methods, we uncovered the detrimental effect of segregated NiO phases on the water splitting activity of core–shell particles. The core–shell IrNiOx/Meso-ATO catalyst displayed high water-splitting activity and unprecedented stability in acidic electrolyte providing substantial progress in the development of PEM electrolyzer anode catalysts with drastically reduced Ir loading and significantly enhanced durability.
Prashanth W. Menezes, Arindam Indra, Diego González‑Flores, Nastaran Ranjbar Sahraie, Ivelina Zaharieva, Michael Schwarze, Peter Strasser, Holger Dau and Matthias Driess
High-Performance Oxygen Redox Catalysis with Multifunctional 2 Cobalt Oxide Nanochains: Morphology-Dependent Activity
ACS Catal. 5, 2017-2027
Future advances in renewable and sustainable energy require advanced materials based on earth-abundant elements with multifunctional properties. The design and the development of cost-effective, robust, and high-performance catalysts that can convert oxygen to water, and vice versa, is a major challenge in energy conversion and storage technology. Here we report cobalt oxide nanochains as multifunctional catalysts for the electrochemical oxygen evolution reaction (OER) at both alkaline and neutral pH, oxidant-driven, photochemical water oxidation in various pH, and the electrochemical oxygen reduction reaction (ORR) in alkaline medium. The cobalt oxide nanochains are easily accessible on a multigram scale by low-temperature degradation of a cobalt oxalate precursor. What sets this study apart from earlier ones is its synoptical perspective of reversible oxygen redox catalysis in different chemical and electrochemical environments.
Nina Erini, Stefan Rudi, Vera Beermann, Paul Krause, Ruizhi Yang, Yunhui Huang and Peter Strasser
Exceptional Activity of a Pt–Rh–Ni Ternary Nanostructured Catalyst for the Electrochemical Oxidation of Ethanol
ChemElectroChem 2 (6), 903-908
Alloying Pt with highly oxophilic transition metals such as Rh, Ni, or Sn has been a promising strategy to modify the electrocatalytic surface properties of Pt in order to supply active
oxygen-containing species for ethanol electrooxidation. A new, highly active, ternary single-phased cubic PtRhNi/C nanoparticle electrocatalyst for the electrocatalytic oxidation of ethanol (EOR) is reported and its morphology (XRD and TEM), composition (inductively coupled plasma optical emission spectroscopy), and electrochemical activity are discussed in comparison with the state-of-art PtRhSn/C electrocatalyst. The EOR activity of the PtRhNi/C material outperformed the benchmark PtRhSn/ C material in acidic and alkaline media, showing high stability, especially in alkaline media. The higher intrinsic EOR activity of the Ni-containing electrocatalyst lends support to the notion that surface NiOx is an excellent oxygenate-supplying catalyst component for the oxidation of ethanol.
Prashanth W. Menezes, Arindam Indra, Nastaran Ranjbar Sahraie, Arno Bergmann, Peter Strasserand Matthias Driess
Cobalt–Manganese-Based Spinels as Multifunctional Materials that Unify Catalytic Water Oxidation and Oxygen Reduction Reactions
ChemSusChem 8 (1), 164-171
Recently, there has been much interest in the design and development of affordable and highly efficient oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) catalysts that can resolve the pivotal issues that concern solar fuels, fuel cells, and rechargeable metal-air batteries. Here we present the synthesis and application of porous CoMn2O4 and MnCo2O4 spinel microspheres as highly efficient multifunctional catalysts that unify the electrochemical OER with oxidant-driven and photocatalytic water oxidation as well as the ORR. The porous materials were prepared by the thermal degradation of the respective carbonate precursors at 400 °C. The as-prepared spinels display excellent performances in electrochemical OER for the cubic MnCo2O4 phase in comparison to the tetragonal CoMn2O4 material in an alkaline medium. Moreover, the oxidant-driven and photocatalytic water oxidations were performed and they exhibited a similar trend in activity to that of the electrochemical OER. Remarkably, the situation is reversed in ORR catalysis, that is, the oxygen reduction activity and stability of the tetragonal CoMn2O4 catalyst outperformed that of cubic MnCo2O4 and rivals that of benchmark Pt catalysts. The superior catalytic performance and the remarkable stability of the unifying materials are attributed to their unique porous and robust microspherical morphology and the intrinsic structural features of the spinels. Moreover, the facile access to these high-performance materials enables a reliable and cost-effective production on a large scale for industrial applications.
Binghong Han, Christopher E. Carlton, Anusorn Kongkanand, Ratandeep S. Kukreja, Brian R. Theobald, Lin Gan, Rachel O’Malley, Peter Strasser, Frederick T. Wagner, Yang Shao-Horn
Record Activity and Stability of Dealloyed Bimetallic Catalysts for Proton Exchange Membrane Fuel Cells
Energy & Environmental Science 8, 258-266
We demonstrate unprecedented Proton exchange membrane fuel cell (PEMFC) performance durability of a family of dealloyed Pt-Ni nanoparticle catalysts for oxygen reduction reaction (ORR), exceeding scientific and technological state-of-art activity and stability targets. We provide atomic-scale insight in key factors controlling the stability of the cathode catalyst by studying the influence of particle size, dealloyingprotocol and post-acid-treatment annealing on nanoporosity and passivation of the alloy nanoparticles. Scanning transmission electron microscopy coupled to energy dispersive spectroscopy data revealed the compositional variations of Ni in the particle surface and core, which were combined with an analysis of the particle morphology evolution during PEMFC voltage cycling; together, this enabled the elucidation of alloy structure and compositions conducive to long-term PEMFC device stability. We found that smaller size, less-oxidative acid treatment and annealing significantly reduced Ni leaching and nanoporosity formation while encouraged surface passivation, all resulting in improved stability and higher catalytic ORR activity. This study demonstrates a successful example of how a translation of basic catalysis research into a reallife device technology may be done.
Stefan Rudi, Lin Gan, Chunhua Cui, Manuel Gliech and Peter Strasser
Electrochemical Dealloying of Bimetallic ORR Nanoparticle Catalysts at Constant Electrode Potentials
J. Electrochem. Soc. 162 (4), F403-F409
Dealloyed, that is, selectively leached Pt-based oxygen reduction reaction (ORR) nanoparticle catalysts have demonstrated previously unachieved initial reactivity and performance durability in single cell of PEM fuel cells. Dealloying is typically achieved using free corrosion in acid or electrochemical cycling. Here, we explore dealloying at constant electrode potentials of PtNi3 bimetallic alloy nanoparticles at 5–7 nm and >20 nm size ranges. We investigate how Ni dissolution at four distinct electrode potentials affects the composition, morphology, and surface roughness of the resulting dealloyed catalysts. The electrode potentials cover the hydrogenadsorption, the double layer region, and the oxygenate adsorption region to examine whether adlayers affect the characteristics of the dealloyed catalysts. We show that large alloy nanoparticles invariably dealloy into porous nanoparticles with a relatively low Ni molar ratio of 0.4, while the smaller size particles show non-porous solid core-shell structures with a monotonic dependence between Ni at% and potential.We provide evidence that the dealloyed catalyst surface is strongly influenced by the presence/absence of adsorbed adlayers of hydrogen or oxygenates. In particular, data suggest that adsorbate adlayers modify the balance between Ni dissolution and Pt surface diffusion during the dealloying process resulting in rougher catalyst surfaces with enhanced surface area values.
Lin Gan, Chunhua Cui, Marc Heggen, Fabio Dionigi, Stefan Rudi and Peter Strasser
Element-specific anisotropic growth of shaped platinum alloy nanocrystals
Science 346, 1502-1506
Morphological shape in chemistry and biology owes its existence to anisotropic growth and is closely coupled to distinct functionality. Although much is known about the principal growth mechanisms of monometallic shaped nanocrystals, the anisotropic growth of shaped alloy nanocrystals is still poorly understood. Using aberration-corrected scanning transmission electron microscopy, we reveal an element-specific anisotropic growth mechanism of platinum (Pt) bimetallic nano-octahedra where compositional anisotropy couples to geometric anisotropy. A Pt-rich phase evolves into precursor nanohexapods, followed by a slower step-induced deposition of an M-rich (M = Ni, Co, etc.) phase at the concave hexapod surface forming the octahedral facets. Our finding explains earlier reports on unusual compositional segregations and chemical degradation pathways of bimetallic polyhedral catalysts and may aid rational synthesis of shaped alloy catalysts with desired compositional patterns and properties.
Arindam Indra, Prashanth W. Menezes, Nastaran Ranjbar Sahraie, Arno Bergmann, Chittaranjan Das, Massimo Tallarida, Dieter Schmeißer, Peter Strasser and Matthias Driess
Unification of Catalytic Water Oxidation and Oxygen Reduction Reactions: Amorphous Beat Crystalline Cobalt Iron Oxides
J. Am. Chem. Soc. 136 (50), 17530 – 17536
Catalytic water splitting to hydrogen and oxygen is considered as one of the convenient routes for the sustainable energy conversion. Bifunctional catalysts for the electrocatalytic oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are pivotal for the energy conversion and storage, and alternatively, the photochemical water oxidation in biomimetic fashion is also considered as the most useful way to convert solar energy into chemical energy. Here we present a facile solvothermal route to control the synthesis of amorphous and crystalline cobalt iron oxides by controlling the crystallinity of the materials with changing solvent and reaction time and further utilize these materials as multifunctional catalysts for the unification of photochemical and electrochemical water oxidation as well as for the oxygen reduction reaction. Notably, the amorphous cobalt iron oxide produces superior catalytic activity over the crystalline one under photochemical and electrochemical water oxidation and oxygen reduction conditions.
Serhiy Cherevko, Tobias Reier, Aleksandar R. Zeradjanin, Zarina Pawolek, Peter Strasser and Karl J. J. Mayrhofer
Stability of nanostructured iridium oxide electrocatalysts during oxygen evolution reaction in acidic environment
Electrochemistry Communications 48, 81 - 85
The electrochemical stability of thermally prepared Ir oxide films is investigated using a scanning flow cell (SFC)–inductively coupled plasma mass-spectrometer (ICP-MS) setup under transient and stationary potential and/or current conditions. Time-resolved dissolution rates provide important insights into critical conditions for material breakdown and a fully quantitative in-situ assessment of the electrochemical stability during oxygen evolution reaction (OER) conditions. In particular, the results demonstrate that stability and OER activity of the IrOx catalysts strongly depend on the chemical and structural nature of Ir oxide species and their synthesis conditions.
Nastaran Ranjbar Sahraie, Jens Peter Paraknowitsch, Caren Göbel, Arne Thomas, Peter Strasser
Noble-Metal-Free Electrocatalysts with Enhanced ORR Performance by Task-Specific Functionalization of Carbon using Ionic Liquid Precursor Systems
J. Am. Chem. Soc. 136 (41), 14486 - 14497
The synthesis and characterization of functionalized carbon using variable doping profiles are presented. The hybrids were obtained from nitrile-functionalized ionic precursors and a ferric chloride mediator. This way, novel nitrogen doped and nitrogen‑sulfur, nitrogen‑phosphorus, and nitrogen‑boron codoped carbon hybrids with a morphology containing microporous nanometer-sized particles were obtained. As-prepared heteroatom doped carbons exhibited superior electrocatalytic activity toward the oxygen reduction reaction (ORR) in alkaline and acid electrolytes. In particular, both the heteroatom type and iron were found to play crucial roles in improving the catalytic activity of functionalized carbon. It is worth noting that sulfur−nitrogen codoped functionalized materials synthesized in the presence of ferric chloride showed higher activity and stability in comparison to those of the commercial state-of-the-art Pt catalyst in alkaline electrolyte. Moreover, in acid electrolyte, sulfur‑nitrogen codoped catalyst rivaled the activity of Pt with a stability outperforming that of Pt. Our X-ray photoelectron spectroscopy (XPS) investigation revealed a distinctive atomic structure in nitrogen−sulfur codoped material in comparison to other codoped catalysts, most likely explaining its superior electrocatalytic activity. This work presents a novel toolbox for designing advanced carbon hybrids with variable heteroatom doping profiles which presents tunable and enhanced ORR performance.
Jiao Wu, Zhenrong Yang, Qijun Sun, Xiaowei Li, Peter Strasser, Ruizhi Yang
Synthesis and electrocatalytic activity of phosphorus-doped carbon xerogel for oxygen reduction
Electrochimica Acta 127, 53 – 60
The electrocatalyst for oxygen reduction reaction (ORR) plays an important role in determining the per-formance, cost and durability of fuel cells and metal–air batteries. In this study, low-cost and highly active phosphorus (P)-doped carbon xerogel electrocatalyst for the ORR was facilely synthesized. The catalytic activity of P-doped carbon xerogel for the ORR in 0.1 M KOH solution has been studied by using a rotating ring-disk electrode (RRDE) technique. The RRDE results show that P-doped carbon xerogel exhibits excellent catalytic activity for the ORR and long-term stability in basic media. The ORR on P-doped carbon xerogel with optimized amount of P mainly favors a direct four electron pathway. The high electrocatalytic activity and durability of P-doped carbon xerogel are primarily attributed to the P-doping in the carbon lattice. Furthermore, the amount of P incorporated into carbon instead of the specific surface area of the P-doped carbon xerogel is found to play a critical role in the ORR activity enhancement and the ORR pathway modification.
Rameshwori Loukrakpam, Qiuyi Yuan, Valeri Petkov, Lin Gan, Stefan Rudi, Ruizhi Yang, Yunhui Huang, Stanko R. Brankovic and Peter Strasser
Efficient C–C bond splitting on Pt monolayer and sub-monolayer catalysts during ethanol electrooxidation: Pt layer strain and morphology effects
Phys. Chem. Chem. Phys. 16, 18866 - 18876
Efficient catalytic C–C bond splitting coupled with complete 12-electron oxidation of the ethanol molecule to CO2 is reported on nanoscale electrocatalysts comprised of a Pt monolayer (ML) and sub-monolayer (sML) deposited on Au nanoparticles (Au@Pt ML/sML). The Au@Pt electrocatalysts were synthesized using surface limited redox replacement (SLRR) of an underpotentially deposited (UPD) Cu monolayer in an electrochemical cell reactor. Au@Pt ML showed improved catalytic activity for ethanol oxidation reaction (EOR) and, unlike their Pt bulk and Pt sML counterparts, was able to generate CO2 at very low electrode potentials owing to efficient C–C bond splitting. To explain this, we explore the hypothesis that competing strain effects due to the Pt layer coverage/morphology (compressive) and the Pt–Au lattice mismatch (tensile) control surface chemisorption and overall activity. Control experiments on well-defined model Pt monolayer systems are carried out involving a wide array of methods such as high-energy X-ray diffraction, pair-distribution function (PDF) analysis, in situ electrochemical FTIR spectroscopy, and in situ scanning tunneling microscopy. The vibrational fingerprints of adsorbed CO provide compelling evidence on the relation between surface bond strength, layer strain and morphology, and catalytic activity.
Hemma Mistry, Rulle Reske, Zhenhua Zeng, Zhi-Jian Zhao, Jeffrey Greeley, Peter Strasser and Beatriz Roldan Cuenya
Exceptional Size-Dependent Activity Enhancement in the Electroreduction of CO2 over Au Nanoparticles
J. Am. Chem. Soc. 136 (47), 16473 – 16476
The electrocatalytic reduction of CO2 to industrial chemicals and fuels is a promising pathway to sustainable electrical energy storage and to an artificial carbon cycle, but it is currently hindered by the low energy efficiency and low activity displayed by traditional electrode materials. We report here the size-dependent catalytic activity of micelle-synthesized Au nanoparticles (NPs) in the size range of ~ 1−8 nm for the electroreduction of CO2 to CO in 0.1 M KHCO3. A drastic increase in current density was observed with decreasing NP size, along with a decrease in Faradaic selectivity toward CO. Density functional theory calculations showed that these trends are related to the increase in the number of low-coordinated sites on small NPs, which favor the evolution of H2 over CO2 reduction to CO. We show here that the H2/CO product ratio can be specifically tailored for different industrial processes by tuning the size of the catalyst particles.
Zhen Li,Yan Jiang,Lixia Yuan,Ziqi Yi,Chao Wu,Yang Liu,Peter Strasser, and Yunhui Huang
A Highly Ordered Meso@Microporous Carbon-Supported Sulfur@Smaller Sulfur Core-Shell Structured Cathode for Li-S Batteries
ACS Nano 8 (9), 9295 – 9303
For lithiumsulfur batteries, commercial application is hindered by the insulating nature of sulfur and the dissolution of the reaction intermediates of polysulfides. Here, we present an ordered meso-microporous coreshell carbon (MMCS) as a sulfur container, which combines the advantages of both mesoporous and microporous carbon. With large pore volume and highly ordered porous structure, the“core”promises a sufficient sulfur loading and a high utilization of the active material, while the“shell”containing microporous carbon and smaller sulfur acts as a physical barrier and stabilizes the cycle capability of the entire S/C composite. Such a S/MMCS composite exhibits a capacity as high as 837 mAh g 1 at 0.5 C after 200 cycles witha capacity retention of 80% vs the second cycle (a decay of only 0.1% per cycle), demonstrating that the diffusion of the polysulfides into the bulk electrolyte can be greatly reduced. We believe that the tailored highly ordered meso-microporous coreshell structured carbon can also be applicable for designing some other electrode materials for energy storage.
Stefan Rudi,Chunhua Cui, Lin Gan and Peter Strasser
Comparative Study of the Electrocatalytically Active Surface Areas (ECSAs) of Pt Alloy Nanoparticles Evaluated by Hupd and CO-stripping voltammetry
Electrocatalysis 5, 408 - 418
This study intends to provide some insight in the up-to-date elusive assessment of a correct choice of method for estimating the active surface area of Pt alloy nanoparticle catalysts. Taking PtNi3nanoparticles as an example, we have compared three types of electrochemically active surface area (ECSA) data, CO-ECSA, Hupd-ECSA, and Hupd/CO-ECSA, which were evaluated from CO stripping and underpotentially deposited hydrogen stripping steps applied at different times along a reference catalyst activity test protocol. Considering a total of six different detailed voltammetric test protocols, we address Pt alloy particle size effects, analyze the effect of the time of application of CO and hydrogen stripping, and study their effect on the Pt mass and Pt surface-specific activities for the oxygen reduction reaction (ORR). In a discussion of theratio of CO charge to hydrogen charge, it is shown that this quantity is more complex than previously thought and not associated with a specific surface structure. The Hupd/COECSA data are found to be a reasonable balance for the estimate of surface area normalized, so-called specific catalytic ORR activities.
T. Reier, D. Teschner, T. Lunkenbein, A. Bergmann,S. Selve,R. Kraehnert,R. Schlögl and P. Strasser
Electrocatalytic Oxygen Evolution on Iridium Oxide: Uncovering Catalyst-Substrate Interactions and Active Iridium Oxide Species
J. Electrochem. Soc. 161 (9), 876 - 882
The morphology, crystallinity, and chemical state of well-defined Ir oxide nanoscale thin-film catalysts prepared on Ti substrates at various calcination temperatures were investigated. Special emphasis was placed on the calcination temperature-dependent interaction between Ir oxide film and Ti substrate and its impact on the electrocatalytic oxygen evolution reaction (OER) activity. The Ir oxide films were characterized by scanning electron microscopy, transmission electron microscopy, scanning transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and cyclic voltammetry. Furthermore, temperature programmed reduction was applied to study the Ir oxide species formed as a function of calcination temperature and its interaction with the Ti substrate. A previously unachieved correlation between the electrocatalytic OER activity and the nature and structural properties of the Ir oxide film was established. We find that the crystalline high temperature Ir oxide species is detrimental, whereas low temperature amorphous Ir oxy-hydroxides are highly active and efficient catalysts for the OER. Moreover, at the highest applied calcination temperature (550°C), Ti oxides, originating from the substrate, strongly affect chemical state and electrocatalytic OER activity of the Ir oxide film.
Hong Nhan Nong, Lin Gan, Elena Willinger, Detre Teschner and Peter Strasser
IrOx core–shell nanocatalysts for cost- and energy-efficient electrochemical water splitting
Chem. Sci. 5, 2955 - 2963
A family of dealloyed metal–oxide hybrid (M1M2@M1Ox) core@shell nanoparticle catalysts is demonstrated to provide substantial advances toward more efficient and less expensive electrolytic water splitting. IrNi@IrOx nanoparticles were synthesized from IrNi precursor alloys through selective surface Ni dealloying and controlled surface oxidation of Ir. Detailed depth-resolved insight into chemical structure,composition, morphology, oxidation state was obtained using spectroscopic, diffraction, and scanning microscopic techniques (XANES, XRD, STEM-EDX, XPS), which confirmed our structural hypotheses at the outset. A 3-fold catalytic activity enhancement for the electrochemical oxygen evolution reaction (OER) over IrO2 and RuO2 benchmark catalysts was observed for the core–shell catalysts on a noble metal mass basis. Also, the active site-based intrinsic turnover frequency (TOF) was greatly enhanced for the most active IrNi@IrOx catalyst. This study documents the successful use of synthetic dealloying for the preparation of metal–oxide hybrid core–shell catalysts. The concept is quite general, can be applied to other noble metal nanoparticles, and points out a path forward to nanostructured proton exchange-electrolyzer electrodes with dramatically reduced noble metal content.
Rulle Reske, Hemma Mistry, Farzad Behafarid, Beatriz Roldan Cuenya and Peter Strasser
Particle Size Effects in the Catalytic Electroreduction of CO2 on Cu Nanoparticles
J. Am. Chem. Soc. 136, 6978 − 6986
A study of particle size effects during the catalytic CO2 electroreduction on size-controlled Cu nanoparticles (NPs) is presented. Cu NP catalysts in the 2−15 nm mean size range were prepared, and their catalytic activity and selectivity during CO2 electroreduction were analyzed and compared to a bulk Cu electrode. A dramatic increase in the catalytic activity and selectivity for H2 and CO was observed with decreasing Cu particle size, in particular, for NPs below 5 nm. Hydrocarbon (methane and ethylene) selectivity was increasingly suppressed for nanoscale Cu surfaces. The size dependence of the surface atomic coordination of model spherical Cu particles was used to rationalize the experimental results. Changes in the population of low-coordinated surface sites and their stronger chemisorption were linked to surging H2 and CO selectivities, higher catalytic activity, and smaller hydrocarbon selectivity. The presented activity−selectivity− size relations provide novel insights in the CO2 electroreduction reaction on nanoscale surfaces. Our smallest nanoparticles (∼2 nm) enter the ab initio computationally accessible size regime, and therefore, the results obtained lend themselves well to density functional theory (DFT) evaluation and reaction mechanism verification.
Aleksandar R. Zeradjanin, Nadine Menzel, Wolfgang Schuhmann and Peter Strasser
On the faradaic selectivity and the role of surface inhomogeneity during the chlorine evolution reaction on ternary Ti–Ru–Ir mixed metal oxide electrocatalysts
Phys. Chem. Chem. Phys 16 (27), 13741 - 13747
The faradaic selectivity of the chlorine evolution reaction (CER) and oxygen evolution reaction (OER) on the industrially important Ti–Ru–Ir mixed metal oxide is discussed. Absolute evolution rates as well as volume fractions of Cl2 and O2 were quantified using differential electrochemical mass spectrometry (DEMS), while the catalyst surface redox behavior was analyzed using cyclic voltammetry. The spatial inhomogeneity of the surface catalytic reaction rate was probed using Scanning Electrochemical Microscopy (SECM). Although the nature of the competition between electrochemical discharging of chloride ions and water molecules remains elusive on a molecular scale, new insights into the spatial reactivity
distribution of the CER and OER were obtained. Oxidation of water is the initial step in corrosion and concomitant deactivation of the oxide electrodes; however, at the same time the nature of interaction between the oxide surface and water is used as a rational indicator of selectivity and catalytic activity. An experimental procedure was established that would allow the study of selectivity of a variety of differentcatalyst materials using polycrystalline electrode surfaces.
Nina Erini, Rameshwori Loukrakpam, Valeri Petkov, Elena A. Baranova, Ruizhi Yang, Detre Teschner, Yunhui Huang, Stanko R. Brankovic and Peter Strasser
Ethanol Electro-Oxidation on Ternary Platinum−Rhodium−Tin Nanocatalysts: Insights in the Atomic 3D Structure of the Active Catalytic Phase
ACS Catal. 4 (6), 1859 − 1867
Novel insights in the synthesis−structure−catalytic activity relationships of nanostructured trimetallic Pt−Rh−Sn electrocatalysts for the electrocatalytic oxidation of ethanol are reported. In particular, we identify a novel single-phase Rh-doped Pt−Sn Niggliite mineral phase as the source of catalytically active sites for ethanol oxidation; we discuss its morphology, composition, chemical surface state, and the detailed 3D atomic arrangement using high-energy (HE-XRD), atomic pair distribution function (PDF) analysis, and X-ray photoelectron spectroscopy (XPS). The intrinsic ethanol oxidation activity of the active Niggliite phase exceeded those of earlier reports, lending support to the notion that the atomic-scale neighborhood of Pt, Rh, and Sn is conducive to the emergence of active surface catalytic sites under reaction conditions. In situ mechanistic Fourier transform infrared (in situ FTIR) analysis confirms an active 12 electron oxidation reaction channel to CO2 at electrode potentials as low as 450 mV/RHE, demonstrating the favorable efficiency of the PtRhSn Niggliite phase for C−C bond splitting.
Chunhua Cui, Lin Gan, Maximilian Neumann, Marc Heggen, Beatriz Roldan Cuenya and Peter Strasser
Carbon Monoxide-Assisted Size Confinement of Bimetallic Alloy Nanoparticles
J. Am. Chem. Soc. 136 (13), 4813 − 4816
Colloid-based chemical synthesis methods of bimetallic alloy nanoparticles (NPs) provide good monodispersity, yet generally show a strong variation of the resulting mean particle size with alloy composition. This severely compromises accurate correlation between composition of alloy particles and their size-dependent properties. To address this issue, a general CO adsorption-assisted capping ligand-free solvothermal synthesis method is reported which provides homogeneous bimetallic NPs with almost perfectly constant particle size over an unusually wide compositional range. Using Pt-Ni alloy NPs as an example, we show that variation of the reaction temperature between 160 and 240 degrees C allows for precise control of the resulting alloy particle bulk composition between 15 and 70 atomic % Ni, coupled with a constant mean particle size of similar to 4 nm. The size-confining and Ni content-controlling role of CO during the nucleation and growth processes are investigated and discussed. Data suggest that size-dependent CO surface chemisorption and reversible Ni-carbonyl formation are key factors for the achievement of a constant particle size and temperature-controlled Ni content. To demonstrate the usefulness of the independent control of size and composition, size-deconvoluted relations between composition and electrocatalytic properties are established. Refining earlier reports, we uncover intrinsic monotonic relations between catalytic activity and initial Ni content, as expected from theoretical considerations.
Panagiotis Trogadas, Thomas F. Fuller and Peter Strasser
Carbon as Catalyst and Support for Electrochemical Energy Conversion
Carbon75, 5 - 42
Carbon has unique characteristics that make it an ideal material for use in a wide variety of electrochemical applications ranging from metal refining to electrocatalysis and fuel cells. In polymer electrolyte fuel cells (PEFCs), carbon is used as a gas diffusion layer, electrocatalyst support and oxygen reduction reaction (ORR) electrocatalyst. When used as electrocatalyst support, amorphous carbonaceous materials suffer from enhanced oxidation rates at high potentials over time. This drawback has prompted an extensive effort to improve the properties of amorphous carbon and to identify alternate carbon-based materials to replace carbon blacks. Alternate support materials are classified in carbon nanotubes and fibers, mesoporous carbon, multi-layer graphene (undoped and doped with metal nanoparticles) and reduced graphene oxide. A comparative review of all these supports is provided. Work on catalytically active carbon hybrids is focused on the development of non-precious metal electrocatalysts that will significantly reduce the cost without sacrificing catalytic activity. Of the newer electrocatalysts, nitrogen/metal-functionalized carbons and composites are emerging as possible contenders for commercial PEFCs. Nitrogen-doped carbon hybrids with transition metals and their polymer composites exhibit high ORR activity and selectivity and these catalytic properties are presented in detail in this review.
Tomokazu Sakamoto, Koichiro Asazawa, Jean Sanabria-Chinchilla, Ulises Martinez, Barr Halevi, Plamen Atanassov, Peter Strasser and Hirohisa Tanaka
Combinatorial discovery of Ni-based binary and ternary catalysts for hydrazine electrooxidation for use in anion exchange membrane fuel cells
Journal of Power Sources 247, 605 - 611
Ni-based catalysts, binary Ni-M (with M = Mn, Fe, Zn, La) and ternary Ni-Mn-Fe and Ni-Zn-La were investigated for hydrazine oxidation in direct hydrazine hydrate fuel cell anodes by a temperature controlled 16-channel electrochemical combinatorial array. The binary Ni0.8Zn0.2 and Ni0.9La0.1 catalysts are significantly more active than the Ni reference catalyst for hydrazine oxidation. While the best Ni0.8Zn0.1La0.1 ternary catalyst is close to the high active binary catalysts in composition. Additionally, Ni0.6Fe0.2Mn0.2 catalysts also showed high catalytic activity for hydrazine oxidation in alkaline media over standard Ni catalyst. The X-ray diffraction (XRD) analysis indicated that the alloying effect between Ni and added elements improves the catalytic activity for hydrazine oxidation. As a result of the screening tests and our previous research, unsupported binary Ni0.87Zn0.13 and Ni0.9La0.1 catalysts were synthesized by spray pyrolysis and tested in a direct hydrazine hydrate fuel cell MEA (DHFC) producing 486 mW cm-2 and 459 mW cm-2, respectively.
Lin Gan, Stefan Rudi and Peter Strasser
Core-Shell and Nanoporous Particle Architectures and Their Effect on the Activity and Stability of Pt ORR Electrocatalysts
Topics in Catalysis 57 (1-4), 236 - 244
We review our recent progress in the development of Pt-Ni bimetallic electrocatalysts with both high sustained activity and sustained stability for oxygen reduction reaction (ORR). This was achieved by an atomic understanding and rational control of the core-shell compositional patterns and size-related nanoporosity within the bimetallic nanoparticles formed during chemical and electrochemical pretreatment and electrocatalysis. In particular, we reveal how the size of the nanoparticle directly influences the nanoporosity formation and thereby the near surface composition, catalytic activity and stability. Our atomic insights provide a clearer picture on how bimetallic nanoparticles should be tailored for optimal ORR performance.
Weiyong Bian, Zhenrong Yang, Peter Strasser, Ruizhi Yang
A CoFe2O4/graphene nanohybrid as an efficient bi-functional electrocatalyst for oxygen reduction and oxygen evolution
Journal of Power Sources 250, 196 - 203
Development of efficient electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) remain key issues for the commercialization of fuel cells and metal-air batteries. In this study, A CoFe2O4/graphene nanohybrid is facilely synthesized via a two-step process and applied as an electrocatalyst for the ORR and the OER. The as-prepared CoFe2O4/graphene nanohybrid demonstrates excellent catalytic activity for the ORR. At the same mass loading, the Tafel slope of CoFe2O4/graphene electrocatalyst for the ORR is comparable to that of the commercial Pt/C (20 wt% Pt on Vulcan XC-72, Johnson Matthey). The ORR on CoFe2O4/graphene mainly favours a direct 4e- reaction pathway. The CoFe2O4/graphene nanohybrid also affords high catalytic activity for the OER. The chronoamperometric tests show that CoFe2O4/graphene catalyst exhibits excellent stability for both the ORR and the OER, outperforming the commercial Pt/C. The high electrocatalytic activity and durability of CoFe2O4/graphene nanohybrid are attributed to the strong coupling between CoFe2O4 nanoparticles and graphene.