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.

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Author notes

    • Min-Kyu Son

    Present address: International Institute for Carbon-Neutral Energy Research (I2CNER), Kyushu University, Fukuoka, Japan


  1. Laboratory of Photomolecular Science, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland

    • Linfeng Pan
    •  & Anders Hagfeldt
  2. Laboratory of Photonics and Interfaces, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland

    • Linfeng Pan
    • , Matthew T. Mayer
    • , Min-Kyu Son
    • , Amita Ummadisingu
    • , Jingshan Luo
    •  & Michael Grätzel
  3. School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology, Ulsan, South Korea

    • Jin Hyun Kim
    •  & Jae Sung Lee
  4. Institute of Photoelectronic Thin Film Devices and Technology, College of Electronic Information and Optical Engineering, Nankai University, Tianjin, China

    • Jingshan Luo


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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.

Competing interests

The authors declare no competing interests.

Corresponding authors

Correspondence to Jingshan Luo or Michael Grätzel.

Supplementary information

  1. Supplementary Information

    Supplementary Figures 1–20, Supplementary Table1, Supplementary References

  2. Supplementary Video 1

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

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