Optimizing Electrolyte Design for Bioelectrochemical Methanation.

Bioelectrochemical methanation (BEM) can contribute to the energy transition by converting renewable electrical energy to synthetic methane, which can be transported and stored for prolonged periods of time in the natural gas grid. The BEM technology combines hydrogen production through water electrolysis and biomethanation in the same space. A major hurdle to commercializing the technology is its low productivity, which is largely caused by the low conductivity of the electrolytes. Increasing the conductivity of the catholyte by increasing the salt concentration is challenging because the biocatalyst, which facilitates the methanation, performs best within a certain salinity range. This work demonstrates that it is possible to utilize a highly productive biocatalyst outside of its optimum, at a higher salinity, and thus increase the performance of the bioelectrochemical system. The electrolyte design is further enhanced by switching the anion in the catholyte from chloride to sulfate. With the improved electrolyte design, a bioelectrochemical methanation system runs stably for multiple hundred hours and with a threefold increase in current density, showing a huge increase in performance. Furthermore, the formation of oxidative chlorine species is prevented, and thus, the fast degradation of materials is avoided. This brings the technology one step closer to commercialization.