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

H-driven microbial electrosynthesis (MES) is an emerging bioelectrochemical technology that enables the production of complex compounds from CO. Although the performance of microbial fermentation in the MES system is closely related to the H production rate, high-performing metallic H-evolving catalysts (HEC) generate cytotoxic HO and metal cations from undesirable side reactions, severely damaging microorganisms. Herein, a novel design for self-detoxifying metallic HEC, resulting in biologically benign H production, is reported. Cu/NiMo composite HEC suppresses HO evolution by altering the O reduction kinetics to a four-electron pathway and subsequently decomposes the inevitably generated HO 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 CO 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.