NiSe₂ Cocatalyst-Modified WO₃ for Efficient Photoelectrochemical Water Splitting

Photoanodes that can absorb sufficient visible light, separate photogenerated charge carriers efficiently, and transport them quickly to the surface remain the primary obstacles to achieving high-efficiency water splitting. Herein, a NiSe₂ nanoparticle-cocatalyst-modified WO₃ is demonstrated as a photoanode with outstanding photoelectrochemical (PEC) water splitting performance, owing to a heterojunction between the WO₃ semiconductor and metallic NiSe₂. With an optimal NiSe₂ loading, the WO₃/NiSe₂ photoanode exhibits a photocurrent density of 1.66 mA cm^-2 at 1.23 V versus RHE under irradiation, surpassing the performance of the pristine WO₃ photoanode by over seven-fold. The superior PEC performance of WO₃/NiSe₂ is ascribed to improved charge-carrier transfer at the electrode/electrolyte interface and enhanced charge-carrier separation and migration resulting from the heterojunction, as corroborated by experimental data and density functional theory (DFT) calculations. The DFT study shows a lower Gibbs free energy change for the potential-determining step (*O → *OOH) on the WO₃/NiSe₂ heterostructure, as compared to WO_3, suggesting efficient oxygen evolution reaction activity and consequently enhanced water splitting performance. Additionally, the hybrid catalyst exhibits an excellent Faradaic efficiency of 94.4% for hydrogen generation and notable structural stability. This work outlines a simple technique for achieving the desired cocatalyst/semiconductor coupling toward highly efficient solar water splitting.