A Fe-Ni-Zn triple single-atom catalyst for efficient oxygen reduction and oxygen evolution reaction in rechargeable Zn-air batteries

The rechargeable Zn-air battery (ZAB) is a promising device for energy storage. A good bifunctional catalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) plays a decisive role in the ZAB. Here, we prepare a Fe-Ni-Zn triple single-atom catalyst (SAC) anchored in the nitrogen-doped porous carbon framework (NC) denoted as SAC(Fe, Ni, Zn)/NC or A-SAC(Fe, Ni, Zn)/NC (ammonia-treated) for the ZAB study. We found that not only Fe-Nx, Ni-Nx, and Zn-Nx act as excellent catalytic sites for ORR and OER, but the synergetic effect by the three adjacent SAC(Fe, Ni, Zn) in the NC enhances the catalytic performance. As a result, the voltage dif-ference (Delta E) of 0.75 V is achieved (half-wave potential of ORR: 0.88 V and the potential of OER at 10 mA cm-2: 1.63 V). In the rechargeable ZAB study, the battery with the A-SAC(Fe, Ni, Zn)/NC has a good specific capacity of 809 mAh/g @ 50 mA cm-2, the excellent power density of 300 mW cm-2 @ 406 mA cm-2 and superior cycle stability (2150 cycles, 358.3 h @ 10 mA cm-2) while the all-soild-state ZAB showed promising power density of 64.5 mW cm-2 and acceptable cycling durability over 25 h@1 mA cm-2. Triple SAC(Fe, Ni, Zn) in the hierar-chical porous NC possesses the bifunctional catalytic capability, high ionic diffusivity, and electron conductivity.