Synergistic Dual-Channel Charge Separation in Cr-TiO_2-x for Solar H₂O₂ Synthesis

Solar-driven hydrogen peroxide (H₂O₂) synthesis offers a sustainable alternative to the energy-intensive anthraquinone process, yet its efficiency is fundamentally constrained by the inability to simultaneously harness photogenerated electrons and holes in a balanced, synergistic manner. Here we report a spatially separated yet electronically coupled dual-active-site photocatalyst, comprising atomic chromium (Cr) and oxygen vacancies (O_Vs) anchored on ultrathin TiO₂ nanosheets (Cr-TiO_2-x), that enables the cooperative coupling of two-electron water oxidation (2e^- WOR) and oxygen reduction (2e^- ORR) in a single photocatalytic framework. In situ x-ray absorption/emission spectroscopy and excited-state density functional theory calculations reveal that Cr single atoms selectively accumulate photogenerated holes to drive 2e^- WOR, while O_V sites trap electrons to activate O₂ for 2e^- ORR. This self-sustaining proton-coupled electron transfer (PCET) loop not only suppresses charge recombination but also achieves a record H₂O₂ production rate of 764.9 µmol g^-1 h^-1 in pure water without sacrificial agents, with a solar-to-chemical conversion efficiency of 1.23% and an apparent quantum yield of 11.5% at 420 nm. This work establishes a blueprint for the atomic-level design of dual-redox photocatalysts and provides direct spectroscopic evidence of excited-state charge partitioning, opening new avenues for efficient solar-fuel synthesis.