Journal
CATALYSIS SCIENCE & TECHNOLOGY
Volume 12, Issue 9, Pages 3028-3043Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/d2cy00227b
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Funding
- Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) [406944504 - SPP 2080, EXC 2008 - 390540038 - UniSysCat]
- European Research Council [ERC-725915]
- IMPRS Elementary Processes in Physical Chemistry
- Max Planck Society
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Copper-based catalysts are widely used for the electrocatalytic CO2 reduction reaction (CO2RR) to convert CO2 into valuable industrial chemicals. Bimetallic materials, such as ZnO/Cu2O nanocubes, show promising catalytic performance for CO2RR. In this study, operando spectroscopy and data analysis were used to investigate the chemical and structural changes of the catalysts under CO2RR conditions. It was found that the addition of Zn affects the kinetics of subsurface processes, while the Cu surface layer remains unchanged. The presence of Zn stabilizes cationic Cu(i) species and increases the selectivity towards C2+ products, while Zn-rich alloy phases promote the formation of CO and the parasitic hydrogen evolution reaction.
Copper-based catalysts are established catalytic systems for the electrocatalytic CO2 reduction reaction (CO2RR), where the greenhouse gas CO2 is converted into valuable industrial chemicals, such as energy-dense C2+ products, using energy from renewable sources. However, better control over the catalyst selectivity, especially at industrially relevant high current density conditions, is needed to expedite the economic viability of the CO2RR. For this purpose, bimetallic materials, where copper is combined with a secondary metal, comprise a promising and a highly tunable catalyst for the CO2RR. Nevertheless, the synergy between copper and the selected secondary metal species, the evolution of the bimetallic structural motifs under working conditions and the effect of the secondary metal on the kinetics of the Cu redox behavior require careful investigation. Here, we employ operando quick X-ray absorption fine structure (QXAFS) spectroscopy coupled with machine-learning based data analysis and surface-enhanced Raman spectroscopy (SERS) to investigate the time-dependent chemical and structural changes in catalysts derived from shape-selected ZnO/Cu2O nanocubes under CO2RR conditions at current densities up to -500 mA cm(-2). We furthermore relate the catalyst transformations observed under working conditions to the catalytic activity and selectivity and correlate potential-dependent surface and subsurface processes. We report that the addition of Zn to a Cu-based catalyst has a crucial impact on the kinetics of subsurface processes, while redox processes of the Cu surface layer remain largely unaffected. Interestingly, the presence of Zn was found to contribute to the stabilization of cationic Cu(i) species, which is of catalytic relevance since Cu(0)/Cu(i) interfaces have been reported to be beneficial for efficient electrocatalytic CO2 conversion to complex multicarbon products. At the same time, we attribute the increase of the C2+ product selectivity to the formation of Cu-rich CuZn alloys in samples with low Zn content, while Zn-rich alloy phases result in an increased formation of CO paralleled by an increase of the parasitic hydrogen evolution reaction.
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