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Fouling of Cu Catalysts during Electrochemical Hydrogenation and Hydrogenolysis of Furfural in Acidic Media

Electrochemical processes offer sustainable means of production when coupled with renewable energy. While thermocatalytic processes require external hydrogen gas for reduction reactions, which generates copious amounts of CO2 in the generation of the hydrogen gas, electrochemical processes have the ability to use protons from the electrolyte in lieu of external hydrogen gas as a reactant. In addition to eliminating the hydrogen gas reactant, electrochemical processes can operate at room temperature and pressure. The development of electrochemical reactors for transformation of biomass derived species is of growing interest for the sustainable production routes it enables of various fine chemicals and fuels. Furfural (FF), one such biomass derived species can be electrochemically reduced to furfuryl alcohol (FA), a resin, and 2-methylfuran (MF), a potential fuel. To produce both FA and MF, acidic electrolytes and Cu catalysts can be used. While Cu electrodes allow for high selectivity to furfuryl alcohol or 2-methylfuran, the Cu electrodes suffer from stability issues caused by things such as fouling over longer durations of electrolysis.
 In this work, we intentionally operated FF ECH under conditions to promote fouling so that the impact of fouling could be investigated. This consisted of 200mM FF in the catholyte with pH 0 electrolyte in 20:80 acetonitrile:water. We used a Cu flag working electrode of 6cm2. We then recycled the Cu electrode for 3 runs of ECH at 3 hours, refreshing the catholyte after each run. A polymeric substance was observed on the Cu electrode surface after multiple uses which had identical IR spectroscopic features to poly(furfuryl alcohol). The impact of the polymeric coating was investigated further using electrochemical impedance spectroscopy, the chemical characterization was determined using x-ray photoelectron spectroscopy, and morphology was imaged using scanning electron microscopy.