Paired Electrocatalytic Valorization of CO2 and Hydroxymethylfurfural in a Noble Metal-free Bipolar Membrane Electrolyzer

Direct electrocatalytic valorization of CO2 in low-temperature electrolyzers is emerging as a new nonfossil, one-step process toward e-fuels and e-chemicals, such as CO. However, Faradaic and energy efficiencies have remained low due to the sluggish 4-electron oxidation of water [oxygen evolution reaction (OER)] at the anode. Replacement of the OER with a thermodynamically and kinetically less-demanding reaction would increase efficiency and overall valorization. This article demonstrates the first full paired implementation of a noble metal-free CO2 and hydroxymethylfurfural (HMF) valorization in a single cell at industrially relevant current densities. We stepwise design, assemble, test, and analyze the first complete paired low-temperature bipolar membrane (BPM)-based hydroxymethylfurfural oxidation and CO2 electroreduction electrolyzer cell. The electrolyzer couples a CO2-to-CO electrolyzer half-cell to an aqueous HMF-to-2.5-furandicarboxylic acid half-cell via a water dissociation membrane operating in reverse bias. We investigate and compare the bipolar membrane voltage penalties with the single-pass reactant conversion advantages and estimate cell performance benefits due to the more favorable thermodynamic and kinetic processes at the anode. We report successfully suppressing undesired CO2 loss due to acid-base neutralization with generated alkalinity.