A mediator-free enzyme carbonaceous cathode for bioelectrocatalytic reduction of furfural to furfuryl alcohol†

Abstract

The valorisation of biomass derivatives into fine chemicals through the combination of electro-enzymatic catalysis under green chemistry principles holds promising potential. However, bottlenecks, including poor electron transfer efficiency between the electrode surface and electron mediators, inefficient cofactor regeneration, and the high cost of enzymes and electron mediators, continue to hinder practical applications. Herein, to address the abovementioned technical barriers, we proposed an electron mediator-free bioelectrocatalytic system that integrated electrochemical NADH regeneration and enzymatic reactions. The proposed system was based on a novel, orderly assembled composite bioelectrode composed of a conjugated structure of covalent organic frameworks (COFs, namely, TpBD), which encapsulated cofactor-dependent oxidoreductases. The as-prepared composite bioelectrode was further applied to the highly selective hydrogenation of furfural to furfuryl alcohol. Results indicated that the electron pathway involved in the TpBD conjugated structure guaranteed effective cofactor regeneration on the composite bioelectrode without the assistance of costly electron mediators, thereby promoting the enzymatic reduction of furfural. A high furfural conversion of 98.94% was realized, accompanied by remarkable furfuryl alcohol selectivity of 90.13% at −1.4 V (vs. Ag/AgCl). The novel composite bioelectrode also showed good stability and reusability. Up to 88.1% of the original furfuryl alcohol selectivity was preserved after 10 cycles of recycling. This work presents a promising green alternative route for the valorisation of furfural, with great potential for extending to the valorization of other renewable biomass derivatives.