Boosting the performance of Cu2O photocathodes for unassisted solar water splitting devices

Abstract

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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Fig. 1: SEM imaging and photoluminescence of Cu2O electrodes.
Fig. 2: Band energy diagrams derived from absorption and XPS measurements.
Fig. 3: PEC performance of Cu2O nanowire photocathodes.
Fig. 4: Electron microscopy of NiMo-modified Cu2O photocathodes.
Fig. 5: PEC measurements on NiMo-modified Cu2O photocathodes.
Fig. 6: Unassisted all-oxide solar water splitting.

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Acknowledgements

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.

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L.P., J.L. and M.T.M. conceived and designed the experiment. L.P. and J.H.K carried out device fabrication, characterization and testing. M.T.M. conducted the Ga2O3 ALD deposition. M.-K.S. conducted the IPCE measurements. A.U. conducted the confocal laser scanning microscopy measurements. J.L. conducted the XRD, transmission electron microscopy and UV-vis characterizations. L.P. and J.L. wrote the first draft. J.L. and M.G. directed the work. J.S.L. and A.H. provided constructive advice. All authors discussed the results and contributed to the manuscript.

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Correspondence to Jingshan Luo or Michael Grätzel.

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Supplementary Information

Supplementary Figures 1–20, Supplementary Table1, Supplementary References

Supplementary Video 1

Unassisted solar water splitting using a Cu2O photocathode and a BiVO4 photoanode

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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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