Interfacial heterophase BaTa2O6:N with spatial CoOx/Pt cocatalysts for stable water oxidation in pH-unadjusted Fe3+ redox media toward solar energy storage

Abstract

Developing acid-tolerant photocatalysts for efficient water oxidation in unmodified Fe³⁺ redox media is pivotal for realizing solar energy storage via the “hydrogen farm” strategy, yet remains challenging due to intrinsic charge recombination and corrosion issues. Here, we introduce a nitrogen-doped hexagonal/tetragonal BaTa₂O₆ heterophase photocatalyst decorated with spatially separated Pt and CoO_x cocatalysts for stable oxygen evolution in acidic Fe(NO₃)₃ solutions (pH 1.8). The heterophase junction, corroborated by high-resolution transmission electron microscopy (HRTEM), creates a directional built-in electric field (evidenced by surface photovoltage spectroscopy) that minimizes interfacial energy loss (<0.2 eV, confirmed by density functional theory calculations). Selective photodeposition of Pt at particle termini and CoO_x on lateral surfaces spatially decouples Fe³⁺ reduction and water oxidation half-reactions, effectively suppressing charge recombination. Enabled by nitrogen doping-induced bandgap narrowing (light absorption up to 630 nm), the optimized catalyst achieves an unprecedented O₂ evolution rate of 124 μmol h⁻¹ under visible light, with apparent quantum efficiencies of 10.5% at 420 nm and 0.3% at 600 nm. The system maintains over 93% activity for 12 h and demonstrates robust compatibility with Fe²⁺/Fe³⁺ redox cycling, confirmed by the stoichiometric production of H₂/O₂ (2 : 1) in a Z-scheme overall water splitting configuration. This work establishes a novel heterophase engineering approach for designing acid-stable photocatalysts, offering a promising pathway toward practical solar-to-chemical energy conversion.