Lattice Contraction of MxOy-Decorated ZnS Nanoparticles (M = Fe, Co) Boosting Oxygen Reduction for Zinc–Air Batteries

The limited application of rechargeable zinc–air batteries (ZAB) is mainly attributed to the sluggish kinetics of the oxygen reduction reaction (ORR) in an air cathode. Therefore, designing catalysts to improve the ORR kinetics is significantly important. Herein, we synthesize metal oxide-decorated ZnS nanoparticles (NPs) supported on nitrogen-doped porous carbon (denoted as M_xO_y-ZnS-N-C; M = Fe, Co) by a two-step pyrolysis strategy. The lattice contraction of ZnS NPs induced by the introduction of the M_xO_y moiety is confirmed by systematic characterizations, including XRD, TEM, and XANES. The Fe_xO_y-ZnS-NC/Co_xO_y-ZnS-NC catalysts exhibit an apparently improved ORR activity with E_1/2 of 0.895/0.86 V, respectively, compared to the pure ZnS-N-C reference sample (0.75 V). Importantly, the Fe_xO_y-ZnS-NC ORR catalyst-based ZAB also delivered a high power density of 243 mW cm^–2 and a long durability over 400 h. These excellent properties of M_xO_y-ZnS-NC catalysts were attributed to the fact that introduction of M_xO_y leads to the lattice contraction of ZnS NPs, which efficiently optimizes the electronic structure of the as-prepared samples and therefore improves the ORR performance. This paper provides a useful strategy of using lattice strain to regulate the electronic structure of catalysts for boosting their electrochemical properties.