ZIF-Derived Co_9–<i>x</i>Ni_<i>x</i>S₈ Nanoparticles Immobilized on N-Doped Carbons as Efficient Catalysts for High-Performance Zinc–Air Batteries

Abstract

Bimetallic sulfides have been attracting considerable attention because of their high catalytic activities for oxygen reduction reaction (ORR) and oxygen evolution reaction; 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 Co_9-<i>x</i>Ni_<i>x</i>S₈ nanoparticles immobilized on N-doped carbons (Co_9-<i>x</i>Ni_<i>x</i>S₈/NC) is reported. The catalyst is synthesized using a Ni-adsorbed 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 Co_9-<i>x</i>Ni_<i>x</i>S₈/NC catalyst exhibits high half-wave potential 0.86 V versus reversible hydrogen electrode for ORR and outstanding bifunctional catalytic performance. When Co_9-<i>x</i>Ni_<i>x</i>S₈/NC is applied as a cathode catalyst in zinc-air batteries, considerably higher power density of 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 the Co_9-<i>x</i>Ni_<i>x</i>S₈/NC catalyst shows 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.