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

H 2 -driven microbial electrosynthesis (MES) is an emerging bioelectrochemical technology that enables the production of complex compounds from CO 2 . Although the performance of microbial fermentation in the MES system is closely related to the H 2 production rate, high-performing metallic H 2 -evolving catalysts (HEC) generate cytotoxic H 2 O 2 and metal cations from undesirable side reactions, severely damaging microorganisms. Herein, a novel design for self-detoxifying metallic HEC, resulting in biologically benign H 2 production, is reported. Cu/NiMo composite HEC suppresses H 2 O 2 evolution by altering the O 2 reduction kinetics to a four-electron pathway and subsequently decomposes the inevitably generated H 2 O 2 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 2 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.