Binary Metal Sulfide Nanoparticles as a Bifunctional Electrocatalyst for Durable Zn-Air Batteries

Transition metal sulfides (TMSs) have gradually become the major catalysts for bifunctional electrocatalytic processes of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) applied in rechargeable Zn-air batteries (ZABs). In this article, by epitaxially growing a Ni complex onto Co-based ZIF-67 as a precursor, an optimal catalyst (abbr. Co 9 S 8 /Ni 3 S 2 @NC-800) incorporating N-doped carbon matrices encapsulated binary Co 9 S 8 and Ni 3 S 2 nanoparticles was constructed by high-temperature pyrolysis, which can efficiently drive bifunctional ORR/OER activity (Δ E = 0.62 V). Notably, the catalyst exhibits remarkable 4e – ORR activity, characterized by a high half-wave potential ( E 1/2 = 0.96 V), exceeding the performance of benchmark Pt/C. It demonstrates commendable OER activity, requiring a modest operating overpotential of only 325 mV ( E J=10 ). Moreover, a ZAB assembled with Co 9 S 8 /Ni 3 S 2 @NC-800 as the air cathode has a substantial power density (213.17 mW·cm –2 ), an elevated specific capacity (771.10 mAh·g Zn –1 ), and exceptional cycle stability (1421 h, 2842 cycles), which is potentially applied in various energy-related devices. The favorable ORR/OER performance may be due to the synergistic interaction of the N-doped carbon matrix and binary Co 9 S 8 and Ni 3 S 2 TMSs in the catalyst.