Electrocatalytic Oxidative Dehydrogenation of Furfural in Alkaline Electrolyte

Conventional water electrolysis to generate green hydrogen gas produces H2 at the cathode of an electrochemical cell and O2 at the anode. This process is still not economically competitive with fossil-derived hydrogen due to a high thermodynamic cell potential and a high overpotential to overcome slow anodic oxygen evolution reaction (OER) kinetics. Replacing OER with electrocatalytic oxidative dehydrogenation (EOD) reactions such as the conversion of furfural (FF) to furoic acid (FA) may lower the cost of renewably-produced H2 by simultaneously generating valuable organic products in addition to anode-derived H2.

Copper has been shown to have good catalytic activity for the EOD of FF to FA due in part to affinity for C-H bond cleavage and affinity for recombination of adsorbed hydrogen (H*) rather than for proton discharge. This study hypothesizes that the conversion and selectivity of EOD can be improved upon by strategically creating Cu-alloy catalysts, such as CuNi, as the addition of Ni would slightly compress the lattice of Cu, weakening H* interactions and promoting recombination to H2.

Herein we have examined how best to increase the conversion and selectivity of EOD electrolysis of FF to FA. We examined different electrolysis conditions, namely electrolyte pH, oxidation potential, and the type of membrane used. To enhance the catalytic activity of the pure Cu catalyst, we increased the surface area of the copper foam working electrode via electrochemical surface roughening and by electrodepositing varying amounts of additional Cu onto the Cu foam. Additionally, we investigated the effect of CuNi alloys deposited onto the Cu foam by different electrodeposition methods in varying Cu:Ni ratios.

We found that among the tested conditions, a Nafion membrane, 0.25 V vs RHE electrolysis potential, and pH 13 electrolyte were the best reaction conditions in terms of limiting side reactions. We further found that increasing the surface area of Cu-foam by both methods increased conversion of FF. Adding Ni to Cu also increased conversion of FF in some ratios of Cu:Ni deposited.