Simultaneous CO₂ Reduction and 5-Hydroxymethylfurfural Oxidation to Value-Added Products by Electrocatalysis

Abstract

A typical CO2 reduction reaction (CO2RR) electrolyzer is often carried out with sluggish kinetics of the oxygen evolution reaction (OER) as the accompanying anodic reaction, leading to a low value product in the anode and an undesired operation cost. To optimize the economic viability of the electrolyzer, it is important that both electrochemical half reactions produce value-added chemicals. However, the achievement of high efficiency at both half-cells simultaneously is very difficult, because in addition to the design of suitable catalyst and electrolyte, the potentials at each electrode should meet the optimized condition. Herein, for the first time, we report a cathodic CO2RR integrated with an anodic 5-hydroxymethylfurfural (HMF) oxidation reaction (HMFOR) to form a brand-new paired electrolysis system. Using PdOx/ZIF-8 (a Zn-based metal organic framework) as cathode and PdO as anode, the established electrolyzer only required a 1.06 V onset cell voltage for the efficient conversion of both CO2 and HMF, in contrast to the 1.77 V for a conventional CO2RR–OER system. The CO Faradaic efficiency (FE) achieved 97.0% with a high current density of 103.5 mA·cm–2 for CO2RR, and the organic acid yield reached 84.3% for HMFOR including 20.0% of maleic acid (MA) and 64.3% of formic acid (FA). This paired electrolysis system was outstanding in terms of FE and current density. This work opens new avenues for the efficient conversion of CO2 and biomass simultaneously.