Synergistic Dual-Channel Charge Separation in Cr-TiO2-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 (OVs) anchored on ultrathin TiO2 nanosheets (Cr-TiO2-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 OV 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.