Spatial Programming of Redox Pathways for Z-Scheme Photocatalytic Water Splitting

Abstract Particulate Z-scheme overall water splitting holds considerable promise for solar hydrogen production, yet its potential is persistently constrained by mediator-involved reverse reactions and related interfacial charge loss. Here we show that water-splitting reactions and parasitic mediator redox can be spatially decoupled across microscale surface domains, thereby suppressing reverse chemistry at its origin. Using facet-engineered Y2Ti2O5S2 and BiVO4 microcrystals as H2-evolving and O2-evolving photocatalysts, respectively, anisotropic charge separation together with facet-selective mediator adsorption directs mediator redox to specific facets, while H2 and O2 evolution proceed on the lateral facets of both photocatalysts. This spatially organized interfacial architecture separates forward and parasitic pathways within individual particles, suppressing mediator self-cycling and H2/O2 recombination without hindering productive interparticle charge transfer. Consequently, visible-light-driven overall water splitting activity is enhanced by over 60-fold relative to the nonfaceted counterpart, delivering an apparent quantum yield of 17.1% at 420 nm, a solar-to-hydrogen efficiency exceeding 1.0%, and sustained activity near atmospheric pressure. These findings establish spatial decoupling of interfacial redox sites as a general design principle for mitigating reverse reactions in Z-scheme artificial photosynthesis for solar hydrogen production.