Small sized Fe–Co sulfide nanoclusters anchored on carbon for oxygen evolution

Abstract

The activity of oxygen evolution reaction (OER) catalysts is strongly dependent on the activity of each catalytic site, which can be improved through interactions among the species present, and the number of accessible catalytic sites, which can be increased by downsizing the electrocatalysts. In this study, small sized Fe–Co sulfide nanoclusters (2–3 nm) in situ anchored on carbon were designed and prepared as an OER catalyst. Due to the smaller size, a large number of catalytic sites are exposed. The optimized Fe–Co bimetal sulfide nanoclusters/carbon composite exhibits an overpotential of only 247 mV to deliver a current density of 10 mA cm⁻² and a low Tafel slope of 35 mV dec⁻¹. In addition, the formed nanocluster catalyst also showed superior stability without activity decay and metal component dissolution during the OER process. Experimental and theoretical calculations indicate that on the Fe–Co sulfide nanoclusters, Fe sites are preferred to enrich the sulfide surface; surface oxidation will occur during the OER process in alkaline electrolyte forming Fe–Co–S–O species. The electron transfer interactions from Fe to S sites induce stronger acidity on Fe sites, which would facilitate OH⁻ and water adsorption, thus inducing the enhancement of electrocatalytic performance.