This review comprehensively summarizes ORR catalysts used in MFCs with a focus on their synthesis/modification procedure, durability, economics, performance and stability.

Graphene is an emerging material with superior physical and chemical properties, which can benefit the development of microbial fuel cells (MFC) in several aspects. Graphene-based anodes can enhance MFC performance with increased electron transfer efficiency, higher specific surface area and more active microbe-electrode-electrolyte interaction. For cathodic processes, oxygen reduction reaction is effectively catalyzed by graphene-based materials because of a favorable pathway and an increase in active sites and conductivity. Despite challenges, such as complexity in synthesis and property degeneration, graphene-based electrodes will be promising for developing MFCs and other bioelectrochemical systems to achieve sustainable water/wastewater treatment and bioenergy production.

Microbial electrolysis cells (MECs) can produce hydrogen gas from organic compounds in an energy‐efficient way by taking advantage of the potential generated by microorganisms. However, hydrogen evolution reaction (HER) in MECs is slow and thus requires catalysts. A challenge for MEC development therefore lies in the development of cost‐effective HER catalysts. In this study, a nanocomposite with molybdenum disulfide (MoS2) coated on highly conductive carbon nanotubes (CNTs) was synthesized as an alternative HER catalyst, and examined in an MEC for hydrogen production. Linear sweep voltammogram experiments demonstrated enhanced HER activity with increasing CNT content. The results suggest that conductivity may be the main limiting factor for overall HER catalysis by MoS2. MEC tests showed that MoS2/CNT‐90 achieved hydrogen production that was comparable to the Pt‐based catalyst. The low cost of the MoS2 composites will make it competitive as an effective HER catalyst for future MEC applications.

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Bioelectrochemical systems (BES) represent an energy-efficient approach for wastewater treatment, but the effluent still requires further treatment for direct discharge or reuse. Integrating membrane filtration in BES can achieve high-quality effluents with additional benefits. Three types of filtration membranes, dynamic membrane, ultrafiltration membrane and forward osmosis membrane that are grouped based on pore size, have been studied for integration in BES. The integration can be accomplished either in an internal or an external configuration. In an internal configuration, membranes can act as a separator between the electrodes, or be immersed in the anode/cathode chamber as a filtration component. The external configuration allows BES and membrane module to be operated independently. Given much progress and interest in the integration of membrane filtration into BES, this paper has reviewed the past studies, described various integration methods, discussed the advantages and limitations of each integration, and presented challenges for future development.