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 cm(2)/cm(3) and an external capillary manifold for flow distribution. Current densities up to 35 A/m(2) 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/m(2). 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. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.