Technische Chemie / ECEMS-Gruppe

Publications 2024

Sven Brückner, Quanchen Feng, Wen Ju, Daniela Galliani, Anna Testolin, Malte Klingenhof, Sebastian Ott and Peter Strasser

Design and diagnosis of high-performance CO2-to-CO electrolyzer cells.

Nature Chemical Engineering 2024

DOI: 10.1038/s44286-024-00035-3

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This work reports the design and diagnostic analysis of a pH-neutral CO2-to-CO zero-gap electrolyzer cell incorporating a nickel–nitrogen-doped carbon catalyst. The cell yields ~100% CO faradaic efficiency at applied current densities of up to 250 mA cm−2 at low cell voltage and 40% total energy efficiency. It features a low stoichiometric CO2 excess, λstoich, of 1.2 that yields a molar CO concentration of ~70%vol in the electrolyzer exit stream at 40% single-pass CO2 conversion, with over 100 h stability. Here we introduce the experimental carbon crossover coefficient (CCC) as a tool for electrolyzer cell diagnostics. The CCC describes the ratio between noncatalytic acid–base CO2 consumption and catalytically generated alkalinity, thereby offering insight into the nature of the prevalent ionic transport and transport mechanisms of undesired CO2 losses. We demonstrate the diagnostic value of the CCC in transport-based cell failure during oscillatory cell flooding between salt precipitation and salt redissolution. The present dynamic cell diagnostics provide practical guidelines toward improved CO2 electrolyzer designs.

 

Michael Filippi, Tim Möller, Remigiusz Pastusiak, Erhard Magori, Benjamin Paul and Peter Strasser

Scale-Up of PTFE-Based Gas Diffusion Electrodes Using an Electrolyte-Integrated Polymer-Coated Current Collector Approach.

Acs Energy Letters 2024

DOI: 10.1021/acsenergylett.4c00114

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Nonconductive porous polymer substrates, such as PTFE, have been pivotal in the fabrication of stable and high-performing gas diffusion electrodes (GDEs) for the reduction of CO2/CO in small scale electrolyzers; however, the scale-up of polymer-based GDEs without performance penalties to technologically more relevant electrode sizes has remained elusive. This work reports on a new current collector concept that enables the scale-up of PTFE-based GDEs from 5 to 100 cm2 and beyond. The present approach builds on a multifunctional current collector concept that enables multipoint front-contacting of thin catalyst coatings, which mitigates performance losses even for high resistivity cathodes. Our improved current collector design concomitantly incorporates a flow-field functionality in a monopolar plate configuration, keeping electrolyte gaps small for increased performance. Experiments with 100 cm2 cathodes were conducted in a one-gap alkaline AEM and acid CEM system. Our design represents an important step forward in the development of larger-size CO2 electrolyzers.

 

J. L. Hübner, L. E. B. Lucchetti, H. N. Nong, D. I. Sharapa, B. Paul, M. Kroschel, J. Kang, D. Teschner, S. Behrens, F. Studt, A. Knop-Gericke, S. Siahrostami and P. Strasser

Cation Effects on the Acidic Oxygen Reduction Reaction at Carbon Surfaces.

Acs Energy Letters 2024

DOI: 10.1021/acsenergylett.3c02743

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Hydrogen peroxide (H2O2) is a widely used green oxidant. Until now, research has focused on the development of efficient catalysts for the two-electron oxygen reduction reaction (2e ORR). However, electrolyte effects on the 2e ORR have remained little understood. We report a significant effect of alkali metal cations (AMCs) on carbons in acidic environments. The presence of AMCs at a glassy carbon electrode shifts the half wave potential from −0.48 to −0.22 VRHE. This cation-induced enhancement effect exhibits a uniquely sensitive on/off switching behavior depending on the voltammetric protocol. Voltammetric and in situ X-ray photoemission spectroscopic evidence is presented, supporting a controlling role of the potential of zero charge of the catalytic enhancement. Density functional theory calculations associate the enhancement with stabilization of the *OOH key intermediate as a result of locally induced field effects from the AMCs. Finally, we developed a refined reaction mechanism for the H2O2 production in the presence of AMCs.

 

Y. Zhu, M. Klingenhof, C. Gao, T. Koketsu, G. Weiser, Y. Pi, S. Liu, L. Sui, J. Hou, J. Li, H. Jiang, L. Xu, W. H. Huang, C. W. Pao, M. Yang, Z. Hu, P. Strasser and J. Ma

Facilitating alkaline hydrogen evolution reaction on the hetero-interfaced Ru/RuO(2) through Pt single atoms doping.

Nature Communications 2024

DOI: 10.1038/s41467-024-45654-9

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Exploring an active and cost-effective electrocatalyst alternative to carbon-supported platinum nanoparticles for alkaline hydrogen evolution reaction (HER) have remained elusive to date. Here, we report a catalyst based on platinum single atoms (SAs) doped into the hetero-interfaced Ru/RuO2 support (referred to as Pt-Ru/RuO2), which features a low HER overpotential, an excellent stability and a distinctly enhanced cost-based activity compared to commercial Pt/C and Ru/C in 1 M KOH. Advanced physico-chemical characterizations disclose that the sluggish water dissociation is accelerated by RuO2 while Pt SAs and the metallic Ru facilitate the subsequent H* combination. Theoretical calculations correlate with the experimental findings. Furthermore, Pt-Ru/RuO2 only requires 1.90 V to reach 1 A cm−2 and delivers a high price activity in the anion exchange membrane water electrolyzer, outperforming the benchmark Pt/C. This research offers a feasible guidance for developing the noble metal-based catalysts with high performance and low cost toward practical H2 production.

 

Liang Liang, Li Yang, Thomas Heine, Aleks Arinchtein, Xingli Wang, Jessica Hübner, Johannes Schmidt, Arne Thomas and Peter Strasser

Asymmetric Copper‐Sulphur Sites Promote C–C Coupling for Selective CO2 Electroreduction to C2 Products.

Advanced Energy Materials 2024

DOI: 10.1002/aenm.202304224

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Sustainable multicarbon e-chemicals are of particular interest due to their potential future, high market values, and demand. In the direct electrocatalytic formation of multicarbon e-chemicals from CO2, the elementary C–C coupling by CO dimerization is considered the rate-limiting step. Here, a generalized surface structural design principle of asymmetric metal pair sites is proposed, explored, and experimentally tested in order to promote CO dimerization on surfaces. First a computational model of N-doped Cu2S layers featuring adjacent, electronically asymmetric Cuδ1+-Cuδ2+ (0 < δ1+ < δ2+ < 1) metal atomic pairs evidenced by their non-uniform charge distribution is considered. The electronic asymmetry resulted in distinct CO adsorption energies and the associated self-adjusting structures, which lowered C–C coupling energy barriers significantly. The computational hypotheses are experimentally tested using X-ray photoelectron spectroscopy of Cu-N moieties within N-doped Cu2S layers. In-situ Fourier-transform infrared spectroscopy confirms linear *CO and *CO-CO adsorption configuration by the peaks of ≈2080 and 1920 cm−1, respectively. After N-doping, the catalytically C2 faradaic efficiency can significantly be elevated to 14.72% due to the promotion of C–C coupling.