Hydrothermal Synthesis of CaMn 2 O 4 · xH 2 O Nanorods as Co‐Catalysts on GaN Nanowire Photoanode

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. CaMn 2 O 4 ·xH 2 O has been extensively studied for the purpose of decreasing the overpotential in the oxygen evolution reaction. In this study, CaMn 2 O 4 ·xH 2 O was synthesized via a hydrothermal method, and loaded onto a GaN nanowire (NW) photoanode. Optimized CaMn 2 O 4 ·xH 2 O layers were decorated on GaN NWs to create CaMn 2 O 4 @GaN, which delivered a maximum photocurrent of 0.4 mA/cm 2 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/cm 2 ) of bare GaN NWs. Thus, highly efficient and stable PEC water splitting was achieved on the GaN NW photoanode.