Round-the-Clock Photocatalysts in the Post-Irradiation Dark Period: From Light Charging to “Memory” Dark Discharging Toward Hydrogen Production

Abstract

The intermittent nature of solar irradiance is a critical constraint for the realization of continuous photocatalytic hydrogen evolution, thus urging the development of more powerful systems persistently active after illumination. This limitation is bypassed in round-the-clock photocatalytic architectures, which incorporate advanced charge storage to de-correlate photon absorption and catalytic turnover time scales. The strategies involve defect-mediated trap states, multi-electron redox processes, radical-dependent stabilization, and an interfacial charge pool in Faradaic junctions to work together, leading to extended hydrogen evolution reaction (HER) in the dark. Long afterglow phosphorescent materials (e.g., Sr2MgSi2O7:Eu2+, Dy3+) incorporated in heterojunction architectures with type II or Z-scheme band alignments can also promote fast charge separation for energy storage and subsequently enable controlled release after light quenching by the phosphorescent emission. Advances in band-structure engineering, plasmonic coupling, and redox-active interfacial design result in systems with extraordinary stability and catalytic activity under natural day–night cycles. These stable photocatalytic systems offer a fundamentally new strategy for efficient and environmentally benign sunlight-driven fuel production, meeting both performance and sustainability challenges to renewable energy technologies.