Mechanistic Investigation of Biomass Oxidation Using Nickel Oxide Nanoparticles in a CO2‑Saturated Electrolyte for Paired Electrolysis

A highly efficient CO2 electrolysis system could be created by introducing biomass oxidation as an alternative anodic reaction to the sluggish oxygen evolution reaction in a CO2-saturated and near-neutral electrolyte. Here, we successfully demonstrate anodic biomass oxidation by synthesizing 5 nm nickel oxide nanoparticles (NiO NPs). NiO NPs show a unique electrocatalytic activity for 5-hydroxymethylfurfural (HMF) oxidation under near-neutral conditions, exhibiting an anodic current onset (1 mA cm–2) at 1.524 V versus the reversible hydrogen electrode and a total Faradaic efficiency of ≤70%. Electrokinetic and in situ ultraviolet–visible spectroscopic analyses suggest that a redox active nickel hydroxide species is formed on the surface of NiO electrocatalysts during HMF oxidation, and this oxidation of Ni­(II) hydroxide to Ni­(III) oxyhydroxide could be the rate-determining step. This mechanistic study of biomass oxidation in a CO2-saturated electrolyte provides insight into constructing a highly efficient system for the paired electrolysis of CO2 reduction and biomass oxidation.