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Development of a photoelectrochemically self-improving Si/GaN photocathode for efficient and durable H2 production


Development of an efficient yet durable photoelectrode is of paramount importance for deployment of solar-fuel production. Here, we report the photoelectrochemically self-improving behaviour of a silicon/gallium nitride photocathode active for hydrogen production with a Faradaic efficiency approaching ~100%. By using a correlative approach based on different spectroscopic and microscopic techniques, as well as density functional theory calculations, we provide a mechanistic understanding of the chemical transformation that is the origin of the self-improving behaviour. A thin layer of gallium oxynitride forms on the side walls of the gallium nitride grains, via a partial oxygen substitution at nitrogen sites, and displays a higher density of catalytic sites for the hydrogen-evolving reaction. This work demonstrates that the chemical transformation of gallium nitride into gallium oxynitride leads to sustained operation and enhanced catalytic activity, thus showing promise for oxynitride layers as protective catalytic coatings for hydrogen evolution.

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Fig. 1: Self-improving behaviour of Si/GaN photocathodes.
Fig. 2: Photoconductive AFM characterization on CA-0 h and CA-10 h samples.
Fig. 3: Chemical analysis of Si/GaN photocathode surface.
Fig. 4: DFT calculation on N-polar c plane and non-polar m plane.

Data availability

The data that support the findings of this study are available at HydroGEN Data Hub ( Additional data reported in the Supplementary Information are available from the corresponding authors upon request. Source data for Figs. 1–4 are available at


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We gratefully acknowledge research support from the HydroGEN Advanced Water Splitting Materials Consortium, established as part of the Energy Materials Network under the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office, under contract no. DE-AC02-05CH11231 for Lawrence Berkeley National Laboratory, under contract no. DE-EE0008086 for the University of Michigan. Part of the work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under contract no. DE-AC52-07NA27344. 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. We thank N. Danilovic, A. K. Buckley, J. L. Young, H. Li, D. Wang, R. Chen and Y. He for insightful discussions. We would also like to acknowledge the HydroGEN EMN data team, led by the National Renewable Energy Laboratory (NREL), for their assistance in reviewing the uploaded data and metadata to the Data Hub repository, making it public and obtaining the DOIs for the data. The HydroGEN Data Hub ( combines experimental and computational data into a searchable water splitting materials data infrastructure and distributes data to the scientific community and the public.

Author information




F.M.T., Z.M. and T.O. conceived the idea. F.M.T. supervised the work. G.Z. conducted the PEC testing, pc-AFM and XPS measurements. G.Z. and F.M.T. analysed and interpreted the results. J.K.C. helped with XPS experiment design and data interpretation. S.V. synthesized the material and conducted intensified stability tests. T.A.P. and T.O. performed the DFT calculations. G.L. and C.S. conducted the STEM–EELS experiments. G.Z., T.A.P. and F.M.T. wrote the manuscript. All of the authors contributed to the final version of the manuscript.

Corresponding authors

Correspondence to Zetian Mi or Tadashi Ogitsu or Francesca M. Toma.

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Competing interests

Some intellectual property related to the synthesis of GaN nanowires was licensed to NS Nanotech Inc., which was co-founded by Z.M.

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Peer review information Nature Materials thanks Nathan Neale, Yuan Ping and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary Figs. 1–10, Tables 1–3 and refs. 1–10.

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Zeng, G., Pham, T.A., Vanka, S. et al. Development of a photoelectrochemically self-improving Si/GaN photocathode for efficient and durable H2 production. Nat. Mater. (2021).

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