ZIF-Derived Co<sub>9–<i>x</i></sub>Ni<sub><i>x</i></sub>S<sub>8</sub> Nanoparticles Immobilized on N-Doped Carbons as Efficient Catalysts for High-Performance Zinc–Air Batteries
Zuocheng Cai, Ikuya Yamada, Shunsuke Yagi
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 Co9–xNixS8 nanoparticles immobilized on N-doped carbons (Co9–xNixS8/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 Co9–xNixS8/NC catalyst exhibits high half-wave potential 0.86 V versus reversible hydrogen electrode 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 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 Co9–xNixS8/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.