Trends and perspectives of microbial electrolysis cell technology for ultimate green hydrogen production

Currently, gray hydrogen and blue hydrogen are widely recognized as renewable energy, but in reality, they are made from fossil fuels. The most important task to achieve the hydrogen-based society is the development of economic green hydrogen production technology. Microbial electrolysis cell (MEC) is a next-generation energy-producing wastewater treatment technology that treats renewable organic wastewater and simultaneously produces the ultimate green hydrogen. For hydrogen production in MFC, it is necessary to input electrical energy into MEC. However, that energy is all covered by the energy produced by the MEC. Therefore, hydrogen production in MEC can be defined as the ultimate green hydrogen. This review contains an in-depth summary and analysis of the principles and feasibility of MEC technology, the composition and shape of MEC, electrode materials, and practical application cases in various types of wastewaters. Furthermore, compatibility and scalability with other environmental systems were reviewed at the pilot scale. Based on this, the technical limitations of MEC were diagnosed and future research directions for the practical application of MEC technology were suggested.