Direct pyrolysis and ultrasound assisted preparation of N, S co-doped graphene/Fe₃C nanocomposite as an efficient...

Bifunctional electrocatalysts to enable efficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are essential for fabricating high performance metal-air batteries and fuel cells. Here, a defect rich nitrogen and sulfur co-doped graphene/iron carbide (NS-GR/Fe₃C) nanocomposite as an electrocatalyst for ORR and OER is demonstrated. An ink of NS-GR/Fe₃C is developed by homogeneously dispersing the catalyst in a Nafion containing solvent mixture using an ultrasonication bath (Model-DC150H; power - 150 W; frequency - 40 kHz). The ultrasonically prepared ink is used for preparing the electrode for electrochemical studies. In the case of ORR, the positive half-wave potential displayed by NS-GR/Fe₃C is 0.859 V (vs. RHE) and for the OER, onset potential is 1.489 V (vs. RHE) with enhanced current density. The optimized NS-GR/Fe₃C electrode exhibited excellent ORR/OER bifunctional activities, high methanol tolerance and excellent long-term cycling stability in an alkaline medium. The observed onset potential for NS-GR/Fe₃C electrocatalyst is comparable with the commercial noble metal catalyst, thereby revealing one of the best low-cost alternative air-cathode catalysts for the energy conversion and storage application.