Co-catalysts play a crucial role in photoelectrochemical (PEC) water splitting reactions by improving slow kinetics and reducing surface recombination, thereby enhancing PEC performance. However, achieving a well-defined interface between low-dimensional semiconductors and co-catalysts is challenging due to difficulties in depositing a uniform co-catalyst layer and attaining mixed and disordered states. CaMn2O4·xH2O has been extensively studied for the purpose of decreasing the overpotential in the oxygen evolution reaction. In this study, CaMn2O4·xH2O was synthesized via a hydrothermal method, and loaded onto a GaN nanowire (NW) photoanode. Optimized CaMn2O4·xH2O layers were decorated on GaN NWs to create CaMn2O4@GaN, which delivered a maximum photocurrent of 0.4 mA/cm2 at 0 V vs. the Ag/AgCl reference electrode under an AM 1.5 G solar simulator, 1.6-fold higher than that (0.25 mA/cm2) of bare GaN NWs. Thus, highly efficient and stable PEC water splitting was achieved on the GaN NW photoanode.
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