Redox-flow battery design for a methane-producing bioelectrochemical system

Methane production at biocathodes is an innovative approach of storing renewable electrical energy in chemical energy via the biological conversion of carbon dioxide. Methane-producing microorganisms use electricity to catalyze the conversion of carbon dioxide into methane; a form of carbon-neutral natural gas. However, the rates of methane production remain too low for practical application. To improve performance, high area-to-volume ratio with good mass transfer is required. In this study, we used the design of redox flow-batteries with a high area-to-volume ratio of 2.0 cm2/cm3 and an external capillary manifold for flow distribution. Current densities up to 35 A/m2 were applied, resulting in volumetric methane production rates of up to 12.5 L CH4/L/d, three times higher than rates reported so far. The highest energy efficiency of 30% was obtained at 25 A/m2. Even with a low relative abundance of methanogens in the microbial community (20%), dense biofilm growth was observed on the outer surface of the biocathode. Flow-battery cell design shows promising performance for application of methane-producing biocathodes.