Enhancing CO2-reduction methanogenesis in microbial electrosynthesis: Role of oxygen-containing groups on carbon-based cathodes.

Microbial electrosynthesis is a promising technology that recovers energy from wastewater while converting CO₂ into CH₄. Constructing a biocathode with both strong H₂-mediated and direct electron transfer capacities is crucial for efficient startup and long-term stable CH₄ production. This study found that introducing carboxyl groups onto the cathode effectively enhanced both electron transfer pathways, improving the reduction rate and coulombic efficiency of CH₄ production and increasing the CH₄ yield by 2-3 times. Carboxyl groups decreased the overpotential for H₂ evolution and increased current density, thereby enhancing H₂-mediated electron transfer. Additionally, carboxyl groups increased the relative abundance of Methanosaeta by 3%-10%, doubled the protein content in extracellular polymeric substances, and boosted the expression of cytochrome c-related genes, thereby enhancing direct electron transfer capacity. These findings present a novel and efficient approach for constructing a stable, high-performance biocathode, contributing to energy recovery and CO₂ fixation.