NiCoS/carbon black based bifunctional air electrode for Zn-air secondary batteries

Nickel cobalt sulfide bifunctional catalysts were synthesized on a carbon black (CB) catalyst support through hydrothermal and solvothermal methods for the oxygen reduction (ORR) and evolution reactions (OER) in secondary rechargeable Zn-air batteries. It was found that NiCo2S4/CB was more suitable to be synthesized using ethylene glycol as the dispersing agent than water, and had better ORR/OER catalytic activities than the NiCoS composites with other Ni/Co ratios. In particular, NiCo2S4 showed significantly enhanced electrocatalytic activities when incorporated with CB to form NiCo2S4/CB, with superior ORR/OER electrocatalytic activities compared to NiCo2O4/CB. Even though, the ORR electrocatalytic activity was lower compared to Pt/C, NiCo2S4/CB showed a significantly superior OER activity (~ 0.75 V @ 10 mA cm−2), demonstrating better overall bifunctional characteristics towards the ORR and OER. The NiCo2S4/CB based bifunctional air electrode in a Zn-air single cell exhibited a higher stability (≤1.0 V charge/discharge plateau separation for 400 cycles) and longer cycle life (>500 cycles) than Pt/C (~ 250 cycles), and so has potential commercial viability.