Yosuke Watanabe

Methanogens are used as catalysts for cathodes in microbial fuel cells, to reduce CO 2 to CH 4 . However, the attachment of microbes to the electrodes via culturing is time‐consuming, and inadequate biofilm formation can lead to lesser surface area coverage, resulting in reduced methane formation. This study aims to improve the production efficiency and performance of methanogen cathodes developed using 3D printing of bioink containing live methanogens. A progressive cavity pump is used for the 3D gel‐printing of methanogens and micro‐sized white charcoal particles into the desired structure. Despite the absence of anaerobic conditions during printing, the 3D‐printed cathodes with higher concentrations of microbial inoculum in the bioink produce more methane gas. Even with an unconcentrated inoculum, the methanogens multiply 800‐fold during incubation, resulting in increased methane gas production. The predominant methanogens in the electrodes included the hydrogenotrophic Methanobacterium spp. Therefore, the technique used in this study can be used to successfully develop 3D‐printed biocathodes catalyzed by methanogenic microbes with verifiable practical applicability. This study is the first to report the growth of methanogens and their methanogenic activity in 3D‐printed cathodes.