Integrated Electrochemical Conversion of Plastic Waste and CO₂ to Formate Using Non-Noble-Metal Catalysts: In Situ Raman Study

Poly(ethylene terephthalate) (PET), a common single-use plastic, significantly contributes to CO2 emissions when discarded or incinerated. In this study, we have employed an innovative approach by combining electrochemical PET hydrolysate oxidation and CO2 reduction reaction (CO2RR) to simultaneously produce formate in a single electrochemical cell. Utilizing simple electrochemical methods, a porous 3D carbon felt (CF) electrode was anodically oxidized to produce activated carbon felt (aCF). The latter was used as a support for the electrochemical deposition of bismuth oxide carbonate (Bi2O2CO3) and nickel cobalt phosphate (NiCoPOx) for CO2RR and anodic PET hydrolysate oxidation, respectively. In situ Raman analysis indicated that MOOH (M = Ni, Co) intermediates acted as active sites for PET hydrolysate oxidation, with the ability to regenerate into lower-valence nickel species post-reaction. Both electrodes exhibited Faradaic efficiencies (FEs) exceeding 90% in their respective half-cell reactions. When implemented in a two-electrolyzer setup, a combined FE of up to 158% for both reactions was recorded at a remarkably low cell voltage of 1.8 V. This research highlights the use of non-noble metals to transform PET plastic waste and CO2 into valuable fuels.