Nickel-Based Photocatalyst: From Structure to Application.

Nickel, an earth-abundant metal, significantly contributes to industrial advancement due to its unique electronic configuration, small atomic radius, low electronegativity, and notable redox potential, which collectively render it highly promising for photocatalytic applications. Recent research extensively explores diverse nickel-based materials in fields such as CO2 conversion, water splitting, and organic transformations. Although prior reviews have addressed materials synthesis, performance, and various applications, a comprehensive mechanistic understanding of nickel's role in photocatalytic processes remains underexplored. Herein, we systematically consolidate various forms of nickel-based photocatalysts, including single atoms, nanoparticles, alloys, metal-organic frameworks (MOFs), covalent organic frameworks (COFs), and coordination complexes, across different oxidation states, structural motifs, and dimensions. We elucidate how their distinct architectures leverage nickel's electronic and geometric attributes to facilitate light absorption, charge separation, and surface reactivity. We further review recent advances in nickel-based cocatalysts for hydrogen evolution, CO2 reduction, and nitrogen conversion, critically assessing proposed mechanisms, active sites, and prevailing challenges. Finally, we propose future research directions─such as in situ spectroscopic monitoring, theoretical modeling of charge-transfer events, and the design of hybrid architectures─to guide deeper applications in energy conversion, environmental remediation, and advanced materials development.