Coupling dark fermentation and microbial electrolysis cells for higher hydrogen yield: Technological competitiveness and challenges

Hydrogen (H2) is considered as a renewable energy source which has the potential to replace the fossil fuel-based economy. When it comes to achieve H2 production in a sustainable manner, biological methods are preferred among all other technologies. Out of the biological processes, microbial electrolysis cell (MEC) and dark fermentation (DF) have attracted significant attention for H2 production because the energy requirement is significantly reduced and a wide range of organic matter can be used as substrate. However, the underlying biochemical reactions and generated energy molecule(s)/products associated with DF or MEC, can benefit in achieving higher H2 production when coupled together. The DF can provide better substrate with high conductivity to overcome charge transfer challenges associated with MEC, and thereby it can further help to improve energy recovery. Thus, this review provides insights into the technological, microbiological, and economic competitiveness of coupling DF-MEC while it also identifies limitations and po-tential solutions. (c) 2023 The Authors. Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).