Defective TiO _<i>x</i> Sublayers Break the Activity–Stability Trade-Off for Green Flexible Water Photoelectrolysis

Catalyst deactivation, especially under the uneven supply of renewable energy, presents a fundamental challenge to advancing net-zero energy technologies, often beyond the reach of conventional modifications. Here, taking TiO₂ as a benchmark photoanode, we harness oxygen vacancies just beneath the surface to break the activity-stability trade-off in renewable-energy-driven water photoelectrolysis. These spatially controlled sublayer defects serve as stable electron reservoirs, buffering nonoriented electron migration under power fluctuation while minimizing direct involvement in surface reactions. The proposed architecture enhances structural robustness for over 119 operational cycles and sustains high performance across diverse dynamic environments, including alkaline solutions and natural seawater. By coupling the electron-regulating properties of the defective subsurface with cobalt-phosphate hole extractors, we achieve a photocurrent of 2.67 mA cm^-2 at 1.23 V_RHE and an applied bias photon-to-current efficiency of 1.45% under natural sunlight, outperforming most of the TiO₂-based photoelectrocatalytic systems. Theoretical modeling suggests that unsaturated Ti³⁺ sites on subsurface (001) facets confine electrons, stabilizing vacancies, and suppressing charge recombination, collectively enhancing reactivity. This work provides principles for designing industrially relevant catalysts, enabling flexible operation in renewably powered systems.