Laccase-Mediated Oxygen Reduction in Liquid Flow Fuel Cells for Efficient Oxidation of Biomass-Derived Aldehydes with Co-Generation of Electricity

Laccase was produced by heterologous expression of gene lacc6 from Pleurotus otreatus HAUCC 162 and then employed as an efficient catalyst to increase the kinetics of the oxygen reduction reaction in a liquid flow fuel cell (LFFC). An electron transport chain (ETC) was constructed in the LFFC with Ag₂O as an anode electrocatalyst and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and laccase as the cathode electron mediators. The LFFC could well convert furfural to furoic acid with co-generation of electricity. Under the optimized cathodic conditions of 40 °C, pH 4.0, 50 mM ABTS, and laccase loading of 300 U/mmol ABTS, a P_max of 70.8 mW/cm² could be obtained. For furoic acid production, a 91% yield could be obtained under the anodic condition of 100 mM furfural and 1.5 M KOH. The electrons released from the oxidation of furfural on the Ag₂O catalyst could be well transferred to that external circuit with a Faraday efficiency of 96.2%. This work thus can provide a novel route for clean production of biomass-based chemicals and electricity by a combination of chemical, electrochemical, and biological processes.