Upcycling CO<sub>2</sub> and PET Waste: Ampere-Level Formate Electrosynthesis in an Integrated Electrolyzer.

Abstract

The rising accumulation of poly(ethylene terephthalate) (PET) waste and atmospheric CO₂ presents serious environmental and health challenges. Herein, we introduce a novel strategy for the simultaneous electrochemical upcycling of PET and CO₂ in a single integrated electrolyzer, enabling ampere-level coproduction of formate. Leveraging careful electrode design of three-dimensional Ni foam at the anode for ethylene glycol (EG, derived from PET hydrolysis) electrolysis, formate formation at 1.2 A cm^-2 was achieved─outperforming all reported performances for non-noble metal catalysts. A Bi₂O₂CO₃-based gas diffusion electrode (GDE) enabled the selective reduction of CO₂ (CO₂RR) to formate at the cathode. By prioritizing enhanced reactant transport and electrode architecture beyond catalyst discovery, this integrated system achieved 100 h of stable operation at 0.50 A cm^-2 with Faradaic efficiencies of 93.7% (anode) and 86.0% (cathode). Superior energy efficiency was achieved in the proposed membrane-free electrolyzer, with a cell voltage of 2.91 V at 1.0 A cm^-2, reducing the input energy by 65% to ca. 0.1 kWh mol^-1. This study highlights the critical role of anodic reaction choices and electrode engineering strategies in developing integrated electrolyzers with superior performance metrics.