Biocompatible Cu/NiMo Composite Electrocatalyst for Hydrogen Evolution Reaction in Microbial Electrosynthesis; Unveiling the Self-Detoxification Effect of Cu

Abstract

H2-driven microbial electrosynthesis (MES) is an emerging bioelectrochemical technology that enables the production of complex compounds from CO2. Although the performance of microbial fermentation in the MES system is closely related to the H2 production rate, high-performing metallic H2-evolving catalysts (HEC) generate cytotoxic H2O2 and metal cations from undesirable side reactions, severely damaging microorganisms. Herein, a novel design for self-detoxifying metallic HEC, resulting in biologically benign H2 production, is reported. Cu/NiMo composite HEC suppresses H2O2 evolution by altering the O2 reduction kinetics to a four-electron pathway and subsequently decomposes the inevitably generated H2O2 in sequential catalytic and electrochemical pathways. Furthermore, in situ generated Cu-rich layer at the surface prevents NiMo from corroding and releasing cytotoxic Ni cations. Consequently, the Cu/NiMo composite HEC in the MES system registers a 50% increase in the performance of lithoautotrophic bacterium Cupriavidus necator H16, for the conversion of CO2 to a biopolymer, poly(3-hydroxybutyrate). This work successfully demonstrates the concept of self-detoxification in designing biocompatible materials for bioelectrochemical applications as well as MES systems.