ZIF-Derived Co9-xNixS8 Nanoparticles Immobilized on N-Doped Carbon as Efficient Catalyst for High-Performance Zinc-air Batteries.

Bimetallic sulfides have been attracting considerable attention because of their high catalytic activities for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER); thus, they are considered efficient catalysts for important energy conversion devices such as fuel cells and metal-air batteries. Here, the catalytic activity of a novel catalyst composed of Co9-xNixS8 nanoparticles immobilized on N-doped carbon (Co9-xNixS8/NC) is reported. The catalyst is synthesized using a Ni-absorbed Co-Zn zeolitic imidazolate framework (ZIF) precursor (NiCoZn-ZIF). Because of the porous structure of ZIF and the high intrinsic activity of the bimetallic sulfide nanoparticles, the Co9-xNixS8/NC catalyst exhibits high half-wave potential 0.86 V vs. RHE for ORR and outstanding bifunctional catalytic performance. When Co9-xNixS8/NC is applied as a cathode catalyst in zinc-air batteries, considerably higher power density about 75 mW cm-2 and discharge voltage are achieved compared to those of batteries with commercial Pt/C and other ZIF-derived catalysts. The zinc-air battery with Co9-xNixS8/NC catalyst showed a high cyclability more than 170 cycles for 60 h with almost negligible decline at 10 mA cm-2. Our work provides a new insight into the design of bimetallic sulfide composites with high catalytic activities.