Current status, key challenges and its solutions in the design and development of graphene based ORR catalysts for the microbial fuel cell applications.

Microbial fuel cells (MFC) are considered as the futuristic energy device that generates electricity from the catalytic degradation of biodegradable organic wastes using microbes, which exist in waste water. In MFCs, oxygen serves as a cathodic electron acceptor and oxygen reduction kinetics played a significant role in the determination of overall efficiency. A wide range of strategies have been developed for the preparation and substantial modification of oxygen reduction reaction (ORR) catalysts to improve the maximum volumetric power density of MFCs, in which the efforts on graphene based ORR catalysts are highly imperative. Although numerous research endeavors have been achieved in relation with the graphene based ORR catalysts applicable for MFCs, still their collective summary has not been developed, which hinders the acquirement of adequate knowledge on tuning the specific properties of said catalysts. The intension of this review is to outline the significant role of ORR catalysts, factors influencing the ORR activity, strategies behind the modifications of ORR catalysts and update the research efforts devoted on graphene based ORR catalysts. This review can be considered as a pertinent guide to understand the design and developmental strategies of competent graphene based ORR catalysts, which are not only applicable for MFCs but also for number of electrochemical applications.