Proving the existence of Mn porphyrin-like complexes hosted in reduced graphene oxide with outstanding performance as oxygen reduction reaction catalysts

Abstract

The lack of low-cost, durable and highly efficient electrocatalysts to perform oxygen reduction reaction (ORR) still represents a significant challenge for the development of fuel cells cathodes. Recently, Pt-free metalloporphyrins supported on N-doped reduced graphene oxide (N-rGO) have been proposed as innovative ORR catalysts characterized by notable stability and superior performance. In this paper, we propose a fast and green microwave-assisted method to synthetize manganese-nitrogen co-doped rGO, characterized by catalytic activity comparable to Pt-containing materials and improved long-term stability. Theoretical calculations and experimental results showed that our synthetic method produces N-rGO matrices which coordinate Mn2+ ions in porphyrin-like structures. These Mn/N-rGO complexes are responsible for the outstanding performance of the proposed catalyst, being able to weaken O–O molecular bond, thus effectively reducing the activation energy towards oxygen catalytic reaction. Our findings open the path to a green co-doping process of graphene for the production of low-cost and efficient alternatives to noble metals-based ORR catalysts.