Microbial electrolysis cell (MEC): Reactor configurations, recent advances and strategies in biohydrogen production

Hydrogen gas has a lot of potential as an ecologically friendly and efficient vehicle fuel. Nearly all hydrogen gas is generated using non-renewable fossil fuels such as coal, oil, and natural gas. As a result of climate change and declining oil supplies linked to fossil fuel use, hydrogen production from renewable energy sources is becoming a viable option. Biohydrogen is produced from various biomasses and wastes through several methods. Hydrogen can be produced through multiple technologies, such as electrochemical, biochemical, photochemical, and thermochemical processes. Among these techniques, Microbial electrolysis cells (MECs) are plausible bioelectrochemical systems to produce hydrogen; wherein organic compounds are oxidized with the chemical evolution of hydrogen in the cathode chamber. MECs combine microbial and electrochemical processes and are progressively contemplated as a better option for biohydrogen production. Therefore, elaborated data on the MECs-based hydrogen production is signposted in this review. The reactor design is one of the most important variables affecting hydrogen and current production rates in MECs. Upscaling is also influenced by the reactor design. Initially, the mechanism, microbiology, and thermodynamics of MEC for hydrogen production are explained to comprehend the technology. The different types of MECs are articulated in this review using sundry literature. Further, the prerequisite factors for improving MECs efficacy, such as biological factors, cathodes, catalysts, anode materials, and substrates, are discussed.