Additively Manufactured High Surface Area 3D Cathodes for Efficient and Productive Electro-Bio-Methanation

CO2 conversion to methane in an electrified bioreactor presents a promising “power-to-gas” technology. Achieving higher productivity at higher energy efficiency, while maintaining biocompatibility, is a major challenge for the commercial deployment of this technology. This work introduces additively manufactured cathodes designed for bubble column type reactors to improve the performance in electro-bio-methanation. The additively manufactured electrodes in this study offered higher volumetric surface area and higher multi-scale porosity over conventional planar electrodes and have the additional benefit of being suitable for rapid prototyping. Additively manufactured electrodes with micro- to nanosized surface features show surface-area-to-volume ratios >2, enabling high rates of in-situ hydrogen evolution while maintaining biocompatible conditions near the cathode surface and in the bulk electrolyte. We show that these novel cathodes facilitate methane production at an exceptionally high rate: 3.4 ± 0.1 L/Lcatholyte/day (or 12.8 ± 0.4 L/Lcathodevolume/day) with a methanogenic mixed culture. These 3D electrodes demonstrate stable performance for more than 2 months with 99 ± 1% Coulombic efficiency, 97 ± 2% peak single-pass conversion efficiency of CO2, and 42 ± 1% energy efficiency at 1.0 ± 0.1 L/Lcatholyte/day (or 4.0 ± 0.4 L/Lcathodevolume/day) volumetric productivity of methane with a pure Methanococcus maripaludis culture. This study exhibits the best reported combinations of volumetric productivities and efficiencies for electro-bio-methanation and highlights the opportunities of additively manufactured or injection molded electrodes for advancing the performance of electrified bioreactors.