FIGURE 4 (A) Schematic illustration of the CuS/GaN/Si photocathode synthesis and PEC experiments. (B) FEHCOOH and (C) jCOOH of the CuS/GaN/Si photocathode. Reproduced with permission.[54] Copyright 2021, American Chemical Society. (D) FECO and (E) STC efficiency of the Cu2O and Cu3(BTC)2/Cu2O/ITO photocathode. Reproduced with permission.[57]Copyright 2019, American Chemical Society. The calculated energy barrier for forming (F) EtOH and (G) acetate for the CuO and CuNx/CuO photocathode. Reproduced with permission.[58] Copyright 2022, Elsevier.