Combined CO₂-Electroreduction Towards Formate Production and HMF Oxidation

Abstract

Recent advancement on carbon dioxide reduction reaction (CO2RR) has shown promising results on CO2 conversion to value-added carbon products as renewable fuels or valuable chemical feedstocks. Formic acid is one of the products that requires low applied voltage in CO2RR. However, it remains with a low full cell energy efficiency, mainly due to the large full cell applied potential. Traditionally, the anodic reaction is carried out with oxygen evolution reaction (OER), which requires a higher applied potential on the counter electrode. This work reports a viable alternative anodic reaction on electro-oxidative upgrading of biomass-derived 5-hydroxymethylfurfural (HMF) into valorized chemicals such as furandicarboxylic acid (FDCA) using Ni-based catalyst. Experimental results have demonstrated that in the combined electrolyzer, the Faradaic efficiency of formate can increase from 41% to 76%, while keeping the applied potential as low as 2 V for achieving a current density of 10 mA/cm2. In addition, at the anode, the Faradaic efficiency reached 60% towards FDCA using the same combined setup. It is postulated that due to the lower overpotential at anode, the cathodic potential becomes more negative for the same current density, and hence a higher Faradaic efficiency towards formate can be attained. Moreover, compared to conventional systems with OER, the combined system is able to produce a value-added product such as FDCA with a considerable FE, approaching a more economic application.