Although large research efforts have been devoted to photoelectrochemical (PEC) water splitting in the past several decades, the lack of efficient, stable and Earth-abundant photoelectrodes remains a bottleneck for practical application. Here, we report a photocathode with a coaxial nanowire structure implementing a Cu2O/Ga2O3-buried p–n junction that achieves efficient light harvesting across the whole visible region to over 600 nm, reaching an external quantum yield for hydrogen generation close to 80%. With a photocurrent onset over +1 V against the reversible hydrogen electrode and a photocurrent density of ~10 mA cm−2 at 0 V versus the reversible hydrogen electrode, our electrode constitutes the best oxide photocathode for catalytic generation of hydrogen from sunlight known today. Conformal coating via atomic-layer deposition of a TiO2 protection layer enables stable operation exceeding 100 h. Using NiMo as the hydrogen evolution catalyst, an all Earth-abundant Cu2O photocathode was achieved with stable operation in a weak alkaline electrolyte. To show the practical impact of this photocathode, we constructed an all-oxide unassisted solar water splitting tandem device using state-of-the-art BiVO4 as the photoanode, achieving ~3% solar-to-hydrogen conversion efficiency.
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The authors thank P. Mettraux for XPS measurements, and L. Yao, X. Yu and K. Sivula for Raman and steady-state photoluminescence measurements. This work was supported by the following projects: National Research Programme 'Energy Turnaround' (NRP 70) of the Swiss National Science Foundation; PECHouse3, funded by the Swiss Federal Office of Energy under contract SI/500090-03; PECDEMO, co-funded by Europe's Fuel Cell and Hydrogen Joint Undertaking (621252); the Marie Skłodowska-Curie Fellowship (awarded to J.L.) from the European Union's Seventh Framework Programme for research, technological development and demonstration under grant agreement 291771; the Thousand Talents Plan for young professionals (awarded to J.L.); and the European Union's Horizon 2020 programme, through an FET-Open research and innovation action under grant agreement 687008.
The authors declare no competing interests.
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Pan, L., Kim, J.H., Mayer, M.T. et al. Boosting the performance of Cu2O photocathodes for unassisted solar water splitting devices. Nat Catal 1, 412–420 (2018). https://doi.org/10.1038/s41929-018-0077-6
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