Bias-free photoelectrochemical co-production of formate from CO₂ and biomass-derived plastic precursors

Coupling CO₂ reduction with selective oxidation of biomass-derived molecules enables simultaneous carbon utilisation and value-added chemical synthesis, offering a sustainable pathway when driven by solar energy. Here, we report a bias-free photoelectrochemical platform that co-produces formate from CO₂ and 5-formyl-2-furoic acid, a key precursor to bio-based plastics. The system integrates a Co₃O₄/WO₃/g-C₃N₄ heterojunction photoanode on carbon paper, which selectively oxidises 5-hydroxymethyl-2-furoic acid to 5-formyl-2-furoic acid with a Faradaic efficiency of 95%, and a tin nanoparticle-decorated carbon paper cathode, which reduces CO₂ to formate with a Faradaic efficiency of 93% under solar irradiation and without external bias. The WO₃/g-C₃N₄ heterojunction promotes efficient Z-scheme charge transfer, enabling spatially separated oxidation and reduction reactions using earth-abundant materials and scalable electrode architectures. Life cycle assessment demonstrates low greenhouse gas emissions and low water consumption potential of the CO₂-to-formate pathway, highlighting the environmental sustainability of the process. By directly coupling CO₂ reduction with the upgrading of biomass-derived furanics into polymer-relevant intermediates, this work establishes a practically meaningful and scalable co-production strategy for solar-driven carbon utilisation and sustainable plastic precursor synthesis.