Photon-coupled-proton buffers: reshaping solar-driven hydrogen and formic acid production with biomass

Solar-driven selective biomass conversion presents a promising pathway for green hydrogen production. However, conventional approaches are hindered by solar intermittency and the challenge of balancing conversion efficiency with over-oxidation. Here, we design photon-coupled-proton buffers (PCPBs) based on heteropolyacids, integrating photosensitivity, proton storage, and redox modulation. Under illumination, the PCPB material H₅SiVMo₂W₉O₄₀·10H₂O catalyzes glucose oxidation to formic acid while capturing protons via self-reduction to heteropolyblue. This proton-rich species can be electrolyzed at ultralow potentials (0.58/0.62 V vs. RHE at 50/100 mA cm⁻²) for on-site H₂ production alongside PCPB self-regeneration. The system achieves 56.05% formic acid conversion from 0.1 M glucose and sustains H₂ evolution (≥91 mL H₂ per mmol glucose) over 14 cycles. Notably, the PCPB prototype delivers 82.44 g H₂ per kg of glucose in aqueous solution—23.78% higher than the theoretical H₂ output from aerobic glucose-to-formic acid conversion—surpassing conventional biomass photo-reforming. Furthermore, the PCPB is also effective for fructose, maltose, starch, and cellulose. Time-resolved spectroscopy and density functional theory (DFT) calculations reveal that Mo–O_b–W sites enable photon-coupled-proton transfer under illumination, suppressing over-oxidation through dynamic proton buffering. By reshaping the photocatalytic biomass valorization pathway, this approach provides a proof-of-concept for stable, transportable, and energy-efficient solar-H₂ production.