Chemically controlled in-situ growth of cobalt oxide microspheres on N,S-co-doped reduced graphene oxide as an efficient electrocatalyst for oxygen reduction reaction

Abstract

A chemically controlled facile approach is developed for the in-situ growth of Co3O4 microspheres on N,S-co-doped rGO sheets (Co3O4/N,S-rGO) employing thiamine hydrochloride (THCl) (7.41 mM) as the N and S co-doping agent under mild experimental conditions. The THCl concentration plays a vital role in controlling the growth of cobalt crystals anchored on the surface of N,S-rGO. The change in concentration of THCl from 7.41 to 22.20 mM alters the deposition of cobalt crystal on the N,S-rGO surface from Co3O4 to Co9S8 (Co9S8/N,S-rGO). This change is understood due to the formation of different intermediate complex structure driven by supramolecular interactions. The altered cobalt crystal phase leads to tuned morphologies, surface areas and catalytically active centers which are investigated by various characterization techniques. Co3O4/N,S-rGO exhibits superior electrocatalytic activity for oxygen reduction reaction (ORR) compared to Co9S8/N,S-rGO. Moreover, Co3O4/N,S-rGO shows more positive onset potential (0.90 V vs. RHE), half-wave potential (0.74 V vs. RHE), relatively high limiting current density and smaller Tafel slope (52 mV per decade) compared to its separate components owing to synergistic effects. Co3O4/N,S-rGO hybrid also outperforms the electrocatalytic activity of commercial Pt/C in terms of durability and methanol tolerance under alkaline conditions.