Co9S8-porous carbon spheres as bifunctional electrocatalysts with high activity and stability for oxygen reduction and evolution reactions

Abstract

The oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) of multi-electron transfer are footstone and crucial reactions for energy conversion and storage technologies. The catalysts play the important roles in both ORR and OER. It is particularly desirable but difficult to use cheap raw materials and facile way to prepare non-noble metal bifunctional electrocatalysts with high activity and stability for both ORR and OER. Here, a simple and effective method is reported for synthesizing cobalt sulfide (Co9S8)-porous carbon spheres composite catalyst (Co9S8/CS) with thiourea, glucose and cobalt nitrate. The material structures of N, S co-doped carbon combined with Co9S8 have been evidenced by high-resolution transmission electron microscopy, X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy. Under the thermal treatment temperature of 800 °C, the prepared catalyst exhibits an analogous oxygen reduction dynamics behavior to the commercial platinum catalyst with a four-electron pathway, and a superior oxygen evolution performance with the small reversible potential gap of 0.78 V (ΔE = Ej=10 – E1/2) to most of the bifunctional electrocatalysts reported to date, such as metal-free carbon hybrids and transition metal doped carbon materials. Due to the interaction between Co9S8 and N, S co-doping carbon, Co9S8/CS-800 exhibits exceptionally good durability and excellent activity compared with the commercial Pt/C for ORR and OER, predicting a promising application in metal-air batteries and fuel cells.