Confinement Catalyst of Co9S8@N-Doped Carbon Derived from Intercalated Co(OH)2 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 Co9S8@NC with a flower-like morphology was derived from metanilic intercalated Co(OH)2 through interlayer-confined carbonation accompanied with host-layer sulfidation. The surface of the Co9S8 particles is covered with a few layers of nitrogen-doped graphene, which can prevent the Co9S8 particles from agglomeration and also produce catalytic activity affected by internal Co9S8. Thus, the Co9S8@NC material achieves excellent ORR performance with a half-wave potential of 0.861 VRHE. In addition, an oxide layer on the surface of Co9S8@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 Co9S8@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.