Confinement Catalyst of CoS@N-Doped Carbon Derived from Intercalated Co(OH) Precursor and Enhanced Electrocatalytic Oxygen Reduction Performance.

Oxygen reduction reaction (ORR) is an important cathode reaction in fuel cells and metal-air batteries. Composites of transition-metal sulfides (TMSs) and nitrogen-doped carbon (NC) are promising alternative ORR catalysts because of their high catalytic activity. However, the agglomeration of TMS particles limits practical applications. Here, a confinement catalyst composed of CoS@NC with a flower-like morphology was derived from metanilic intercalated Co(OH) through interlayer-confined carbonation accompanied with host-layer sulfidation. The surface of the CoS particles is covered with a few layers of nitrogen-doped graphene, which can prevent the CoS particles from agglomeration and also produce catalytic activity affected by internal CoS. Thus, the CoS@NC material achieves excellent ORR performance with a half-wave potential of 0.861 V. In addition, an oxide layer on the surface of CoS@NC is fabricated shortly after the ORR starts. Further tests and density functional theory calculations indicated that this cobalt oxide layer can increase the electrochemically active area of CoS@NC as well as reduce the ORR energy barrier, thereby providing more catalytic active sites and enhancing the intrinsic catalytic activity, thus achieving a self-activation effect during the electrochemical reaction process.