Sustainable Hydrogen Production in Microbial Electrolysis Cells through Activity Control of Electrochemically Active Bacteria

Abstract

A microbial electrolysis cell (MEC) is an environmentally sustainable energy production platform where electrochemically active bacteria (EAB) convert the organic substances in wastewater into hydrogen. MEC is driven by the two major processes: 1) degradation of organic matters into protons (H+), electrons (e-) and carbon dioxide (CO2) in the anode, and followed by 2) reduction of H+ and e- that produces hydrogen gas (H2) in the cathode. Therefore, the sufficient provision of H+ and e- is crucial for fluent H2 production via increasing both the electrobiochemical activity of the anode and the reduction efficiency of the cathode. In this study, the problems of core technology in MEC was identified and solved to increase the efficiency of bioelectrochemical hydrogen production. First, the inefficient use of space in carbon materials based anode, where EABs grow. Carbon-based materials are mainly used in oxidation electrodes due to their high electrical conductivity and porosity, but the hydrophobic nature of carbon-based anodes suppresses the release of the produced gas and water penetration, significantly reducing the possibility of microbial attachment. Therefore, we tried to utilize all areas smoothly through surface improvement. The next problem is the interspecies substrate competition of microorganisms. The anaerobic sludge used for microbial species contains a large amount of methane bacteria as well as EABs, and the electron generated by methane is a loss in terms of hydrogen production. In order to fully use this electrons for hydrogen production, methanogenesis were controlled to reduce methane production and increase hydrogen production. Finally, the reduction of hydrogen ion transfer efficiency due to biofilm formation on the surface of the proton exchange membrane (PEM). When MEC is operated for a long time, microorganisms formated bio-films on the surface of the PEM, a channel where protons are transferred, and these bio-films reduce the efficiency of proton transfer, reducing hydrogen production. Therefore, a synergistic anti-biofouling technology was developed and applied to increase durability of PEM. The development of such core technologies for MEC has enabled economic and efficient hydrogen production, which will contribute to the establishment of a diverse types of larger bioelectrochemical hydrogen production platform in the future.