The chemical transformations that occur in metal oxides under operating conditions limit their applications for artificial photosynthesis. Understanding these chemical changes is a prerequisite to achieve sustainable production of solar fuels and chemicals. Herein, we use a correlative approach to unravel how cuprous oxide (Cu2O) photoelectrodes change under reaction conditions and, consequently, provide a protection scheme to mitigate degradation. In agreement with theoretical predictions, we find that under illumination the Cu2O concurrently undergoes reduction by photoelectrons and oxidation by holes in the material at electrolyte-dependent degradation rates. These mechanistic insights led us to design a protection scheme that uses a silver catalyst to accelerate transfer of photogenerated electrons and a Z-scheme heterojunction to extract holes. The resulting photocathode exhibits a stable photocurrent for CO2 reduction with ~60% Faradaic efficiency for ethylene with a balance of hydrogen for hours, whereas bare Cu2O degrades within minutes.
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This study is based on work performed at the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the US Department of Energy under award no. DE-SC0004993. Some data collection and some X-ray photoelectron spectroscopy measurements were performed by the Liquid Sunlight Alliance, which is supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Fuels from Sunlight Hub under award no. DE-SC0021266. The computational resources were provided by National Energy Research Scientific Computing center (NERSC) located in Lawrence Berkeley National Laboratory and Oak Ridge Leadership Computing Facility at the Oak Ridge National Laboratory under the Innovative and Novel Computational Impact on Theory and Experiment project. Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under contract no. DE-AC02-05CH11231. This research used Beamline 9.3.1 of the Advanced Light Source, which is a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231. The authors also thank J. Cooper for help with the design of the photoelectrochemical cell, as well as G. Panzeri at Politecnico di Milano and K. A. Persson from the University of California at Berkeley/Lawrence Berkeley National Laboratory for insightful discussions.
The authors declare no competing interests.
Peer review information Nature Energy thanks Martina Lessio and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Liu, G., Zheng, F., Li, J. et al. Investigation and mitigation of degradation mechanisms in Cu2O photoelectrodes for CO2 reduction to ethylene. Nat Energy 6, 1124–1132 (2021). https://doi.org/10.1038/s41560-021-00927-1
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