Step Towards Enzymatic Bioelectrorefinery: Design of a Ligninolytic Hybrid Air-Breathing Biocathode

Abstract

Lignins, abundant aromatic biopolymers and one of the major components of lignocellulosic biomass, remain the most underutilized renewable bioresources of aromatics and hydrocarbons on the Earth. Numerous physical and chemical processes have been developed for lignin valorization; however, they generally suffer from environmentally unfriendly, harsh conditions and lack reaction specificity. On the other hand, milder methods involving biocatalysts exist but are impeded by many limitations, such as cofactor regeneration, deleterious enzyme–lignin interactions, and low stability. In this work, we attempt to eliminate the constrains encountered in enzyme-based lignin valorization processes through the development of a novel electrochemically assisted bioprocess. This “all-in-one” biocathode incorporates a hybrid electrocatalytic interface combining a hydrogen peroxide-generating passive air-breathing gas diffusion electrode with an immobilized hydrogen peroxide-consuming lignin peroxidase on a single surface and catalyzing the depolymerization of lignins. The ligninolytic potential of this bioelectrochemical device is demonstrated using both lignin models (veratryl alcohol and veratrylglycerol β-guaiacyl ether) and a technical lignin at room temperature in aqueous media with the reaction efficiency of 14.9% per hour.