Selective electrochemical oxidation of biomass and waste plastic at higher current densities for simultaneous hydrogen generation through hybrid water electrolysis

Abstract

The electrochemical oxidation of lignocellulose and plastic waste has been considered a clean and reliable strategy to produce feedstocks for various chemicals and fuels. In this study, we tackle the challenging selective oxidation of various lignocellulose and mixed biodegradable and bio-nondegradable plastics by targeting the oxidative cleavage of the specific C(OH)–C moiety. A monometallic Ni(O)O–H electrocatalyst was used for valorization of cellulose-based biomass, a series of lignin-based model complexes, lignin-derived secondary alcohols (KA oil), and mixed plastic waste based on the catalyst's O–H bond dissociation free energy. The catalyst performs remarkably well to selectively oxidize cellulose and lignin-based model complexes like HMF and PED with excellent yield at a higher current density of 100 mA cm−2. Mechanical insights into this reaction were obtained by in situ transmitted light spectroscopy and Raman measurements. The catalyst was also able to oxidize KA oil to adipic acid with 54% yield at a constant current electrolysis of 20 mA cm−2. Furthermore, plastic waste precursors having a C(OH)–C bond were selectively oxidized using this catalyst, which was further expanded to mixed plastic waste upgradation resulting in the generation of formate and acetate with faradaic efficiencies of 66% and 74%, respectively, and 100% yield in terephthalic acid accompanied by the co-production of hydrogen.