Using copper-based biocathodes to improve carbon dioxide conversion efficiency into methane in microbial methanogenesis cells

Copper can be used as a metal catalyst for abiotic CO₂ conversion into methane and organic chemicals, but it has not been examined as a catalyst for enhancing biotic methane generation in microbial methanogenesis cells (MMCs). In this study, copper-based electrodes prepared using several different techniques were compared to the performance of MMCs containing graphite block cathodes. Gas production was examined under both abiotic and biotic conditions at a fixed cathode potential of –0.9 V vs. Ag/AgCl in two-chamber electrochemical cells. All copper-based cathodes showed better methane production than plain graphite blocks except for the cathode made from copper foil which lacked a biocompatible surface. The cathode prepared by an electroless Cu deposition (electroless-Cu) method had the highest current density production of 0.6 A/m² and methane production rate of 201 nmol/cm³/d, and its performance was stable over time. Both the electroless-Cu and electro-deposited Cu electrodes produced more current than that obtained with copper powders with a Nafion binder (Nafion-Cu), likely due to different surface characteristics such as hydrophobicity and uniformity of the copper layer. The results of this study showed that copper-based biocathodes improved methane production relative to plain graphite materials and techniques for preparing copper electrodes impact bioelectrochemical performance with the highest performance in the electroless-Cu reactors.