Recent Developments in Z-Scheme Systems for Overall Water Splitting: A Focus on (Oxy)Nitride Photocatalysts

Visible-light-driven photocatalytic water splitting (OWS) has emerged as a promising approach for solar hydrogen production. However, conventional one-step photoexcitation systems impose stringent thermodynamic constraints on the band structure of photocatalysts, severely limiting the number of materials that can simultaneously exhibit visible-light absorption and high catalytic efficiency. In contrast, the Z-scheme overall water splitting substantially mitigates these thermodynamic demands, thereby enabling the utilization of a wider spectrum of visible-light-responsive semiconductors. Among the semiconductor materials investigated, (oxy)nitrides have attracted significant attention as ideal candidates for Z-scheme systems, owing to their tunable electronic structures, strong visible-light absorption, and favorable band edge positions. Nevertheless, issues such as photocorrosion, high defect densities, and sluggish surface reaction kinetics continue to hinder their catalytic performance. This review comprehensively summarizes recent advances in three types of Z-scheme overall water splitting systems based on (oxy)nitride photocatalysts: redox couple-based ionic Z-schemes, solid-mediator Z-schemes, and direct Z-schemes. It focuses on the material design strategies and the structure-performance relationships of (oxy)nitrides within these distinct Z-scheme systems. Finally, the challenges and future prospects of (oxy)nitride-based Z-scheme overall water splitting systems are discussed, offering insights into the optimization of material synthesis, surface modification, and mechanistic understanding.