Cathode materials are critical for microbial electrolysis cell (MEC) development and its contribution to achieving a circular hydrogen economy. There are numerous reports on the progress in MEC cathode development during the past decade, but a comprehensive review on the quantitative comparisons and critical assessments of these works is lacking. This Review summarizes and analyzes the published literature on MEC cathode and catalyst development in the past decade, providing an overview of new materials examined during this time period and quantitative analyses on system performance and trends in materials development. Collected data indicate that hybrid materials have become the most popular catalyst candidate while nickel materials also attract increasing interest and exploration. However, the dilemma between higher H 2 production rate and larger MEC volume remains and still requires more investigation of novel MEC cathode catalysts and configurations to offer a solution.

Microbial electrolysis cells (MECs) represent a renewable hydrogen production technology that offers the possibility of converting wastewater to hydrogen through a bioelectrochemical process. Particularly, the MEC substrate has a significant effect on the performance of MECs, and in this review, the performances of over 30 substrates examined since 2015 are summarized and compared. It was evident that popular MEC substrates include dark fermentation effluents, pyrolysis products, and raw wastewaters. Additionally, the different MEC substrates investigated yielded different MEC performances, indicating that further studies are required before MECs can become a mature technology for up-scale applications.