Photoelectrochemical comproportionation of pre-treated PET plastics and CO₂ to formate

Pairing plastic waste reforming and carbon dioxide (CO₂) utilisation to produce chemical energy carriers provides an attractive means to mitigate waste and create value, but challenges persist in achieving selective product formation, separation and overall device integration. Herein, we present an organic-inorganic photoelectrochemical (PEC) tandem device that enables the solar-powered comproportionation of plastic waste and CO₂ into a single product, formate. The hematite photoanode achieves continuous and selective oxidation of alkaline pre-treated polyethylene terephthalate (PET) plastics to formate, while an organic semiconductor photocathode coupled to a biocatalyst achieves selective CO₂ photoreduction to formate under neutral pH conditions. The integrated PEC device operates without external voltage input to achieve simultaneous plastic oxidation and CO₂ reduction, leading to a near-200% formate Faradaic efficiency and an average formate production rate of 11 μmol cm^-2 h^-1 for 10 h under simulated AM1.5G irradiation at room temperature. This work introduces a strategy for the visible-light promoted processing of two distinct waste streams into a single product, thereby enhancing product formation rates, reducing limitations arising from product separation and advancing efforts toward a sustainable circular industry.