Chloride ion-assisted high-efficiency natural seawater splitting enabled by noble-metal-free MnOx(OH)y/GaN nanowires.

Solar-driven natural seawater overall splitting presents a paradigm-shifting solution for hydrogen production to achieve global decarbonization. Herein, we present a noble-metal-free MnOx(OH)y/GaN nanowire photocatalyst grown on silicon that enables unbiased seawater overall splitting without sacrificial agents. Density functional theory calculations and in-situ spectroscopic characterizations reveal that MnOx(OH)y/GaN lowers the Coulomb attraction energy between photogenerated holes and electrons, thereby accelerating charge-transfer kinetics. Meanwhile, the decorated MnOx(OH)y facilitates the in-situ *OH and *OOH formation during water oxidation by photogenerated holes. More importantly, with the assistance of chloride species, the reaction energy barrier of water oxidation is significantly reduced. Additionally, a hydroxyl exchange mechanism between H2O and MnOx(OH)y further enhances the reaction kinetics. Collectively, the MnOx(OH)y/GaN hybrid photocatalyst achieves a high light-to-hydrogen efficiency of 6.15% and maintains stability over 360 min in natural seawater, delivering a distinct hydrogen evolution rate of 15.2 mol gMnOx(OH)y/GaN-1 h-1 (3.3 W cm-2). This work provides a promising strategy for efficient solar-driven seawater splitting by integrating earth-abundant materials, sunlight, and marine resources.