Chalcopyrites are promising photocathodes for the hydrogen evolution reaction (HER). Using a combination of spectrochemical and computational tools, we show for the model composition CuIn_0.3Ga_0.7S₂ that surface In, Ga and S rather than Cu atoms act as active sites and that surface Ga and In vacancies act as traps, leading to voltage losses and limiting the catalytic performance. These insights enable tuning the surface composition for optimal catalytic performance.

This work was carried out in collaboration between the groups of Ulrich Aschauer and Néstor Guijarro (EPFL, LIMNO).

References:

• Y. Liu, M. Bouri, L. Yao, M. Xia, M. Mensi, M. Grätzel, K. Sivula, U. Aschauer, N. Guijarro;
  "Identifying Reactive Sites and Surface Traps in Chalcopyrite Photocathodes"
  Angew. Chem. Int. Ed., 2021, 60(44), 23651-23655; doi:10.1002/anie.202108994.