Electrocatalytic hydrogenation of furfural paired with photoelectrochemical oxidation of water and furfural in batch and flow cells

The valorization of biomass-derived furfural (FF) provides platform chemicals such as furfuryl alcohol (FA) and furoic acid (FU) for the polymer, pharmaceutical, and bio-fuel industries. The valorization based upon electrocatalytic reactions is a green and economical approach; however, utilization of solar energy can further reduce the overall cost and electrical energy requirement. Herein, we analyzed the generation of FA from electrocatalytic hydrogenation (ECH) of FF in an electrochemical cell (EC) using the Cu–Ni/NF cathode/Pt anode and in a photoelectrochemical cell (PEC) using the Cu–Ni/NF cathode/TiO2 nanotube photoanode. The PEC saved 50% of electrical energy as compared to the EC due to the use of solar energy. We demonstrated the feasibility of the PEC for paired ECH and TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) mediated photoelectrochemical oxidation of FF to generate FA at the cathode and FU at the photoanode. The formation rate of FA and FU was obtained as 9.1 ± 0.3 μmol h−1 and 0.65 ± 0.03 μmol h−1, respectively, at an applied bias of 1 V for 4 h in a 21 mL batch PEC. A flow PEC was employed to increase the cell capacity and to tackle the mass transfer limitations, demonstrating the sustainable industrial-scale generation of platform chemicals. For the flow PEC at a flow rate of 1.5 mL min−1 at 1 V for 1.1 h, the single-pass conversion of FF in the cathode and anode compartments was 14.5% and 11.6%, respectively. The FA and FU formation rates were obtained as 6.4 ± 0.5 μmol h−1 and 5.4 ± 0.2 μmol h−1, respectively, indicating the better performance of the flow PEC as compared to the batch PEC.