Towards efficient oxygen reduction reaction electrocatalysts through graphene doping

The incessant and drastic growth of global energy demand make it imperative to develop new affordable high-quality materials at a large scale to act as powerful electrocatalysts (ECs) on the relevant energy reactions. Here, we report the synthesis and characterization (FTIR, Raman, XPS, XRD, TEM and SEM) of new engineered electrocatalysts based on situ co-precipitation of Co3O4 or Mn3O4 nanoparticles in the presence of N, S-doped graphene (Co/N3S3-GF and Mn/N3S3-GF). The nitrogen, sulphur dual-doped graphene was achieved by a scalable dry ball-milling procedure followed by thermal treatment using graphene flakes as carbon source and trithiocyanuric acid as the precursor. The three materials prepared were applied as electrocatalysts for the oxygen reduction reaction (ORR) and demonstrated excellent electrocatalytic performance in alkaline medium with Co/N3S3-GF and Mn/N3S3-GF presenting onset potentials of 0.87 V vs. RHE. These were comparable to Pt/C onset potential (0.91 V). All materials showed good diffusion-limiting current densities (-3.49 to -4.17 mA cm-2) and selectivity for the 4-electron O-2 reduction to H2O. Furthermore, the Co/N3S3-GF and Mn/N3S3-GF electrocatalysts presented good tolerance to methanol poisoning and good stability with current retentions (76-81%). The approach followed in this work showed that affordable, simple and scalable procedures can be applied to develop ORR electrocatalysts with enhanced performances. (C) 2019 Elsevier Ltd. All rights reserved.