The Role of the Copper Oxidation State in the Electrocatalytic Reduction of CO2 into Valuable Hydrocarbons
Juan-Jesús Velasco-Vélez1,2, Travis Jones2, Dunfeng Gao3,4, Emilia Carbonio2,10, Rosa Arrigo5,6, Cheng-Jhih Hsu7, Yu-Cheng Huang7,8, Chung-Li Dong7, Jin-Ming Chen8, Jyh-Fu Lee8, Peter Strasser9, Beatriz Roldan Cuenya3,4, Robert Schlögl1,2, Axel Knop-Gericke1,2, Cheng-Hao Chuang7*
1Department of Heterogeneous Reactions, Max Planck Institute for Chemical Energy Conversion, Mülheim an der Ruhr, Germany
2Department of Inorganic Chemistry, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany
3Department of Physics, Ruhr-University Bochum, Bochum, Germany
4Department of Interface Science, Fritz-Haber-Institute of the Max-Planck Society, Berlin, Germany
5Diamond Light Source Ltd., Harwell Science & Innovation Campus, Oxfordshire, UK
6School of Environment and Life Sciences, University of Salford, Manchester, UK
7Department of Physics, Tamkang University, New Taipei City, Taiwan
8National Synchrotron Radiation Research Center, Hsinchu, Taiwan
9Department of Chemistry, Technical University Berlin, Berlin, Germany
10Helmholtz-Center Berlin for Materials and Energy, BESSY II, Berlin, Germany
* Presenter:Cheng-Hao Chuang,
Redox-active copper catalysts with accurately prepared oxidation states (Cu0, Cu+, and Cu2+) and high selectivity to C2 hydrocarbon formation, from electrocatalytic cathodic reduction of CO2, were fabricated and characterized. The electrochemically prepared copper-redox electro-cathodes yield higher activity for the production of hydrocarbons at lower oxidation state. By combining advanced X-ray spectroscopy and in situ micro-reactors, it was possible to unambiguously reveal the variation in the complex electronic structure that the catalysts undergo at different stages (i.e., during fabrication and electrocatalytic reactions). It was found that the surface, subsurface, and bulk properties of the electrochemically prepared catalysts are dominated by the formation of copper carbonates on the surface of cupric-like oxides, which prompts catalyst deactivation by restraining effective charge transport. Furthermore, the formation of reduced or partially reduced copper catalysts yields the key dissociative proton-consuming reactive adsorption of CO2 to produce CO, allowing the subsequent hydrogenation into C2 and C1 products by dimerization and protonation. These results yield valuable information on the variations in the electronic structure that redox-active copper catalysts undergo in the course of the electrochemical reaction, which, under extreme conditions, are mediated by thermodynamics, but critically, kinetics dominate near the oxide/metal phase transitions.

Keywords: CO2RR, In situ X-ray spectroscopy, Copper carbonate passivation layer, Electrocatalytically active reduced copper oxides