Charge redistribution caused by sulfur doping of bimetal FeCo phosphides supported on heteroatoms-doped graphene for Zn-air batteries with stable cycling

Exploring feasible synthesis approaches to highly efficient and robust bifunctional electrocatalysts toward both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is triggering researcher’s even-increasing interest in rechargeable Zn-air batteries. Herein, sulfur-doped bimetal FeCo phosphide nanoparticles dispersed on N,P,S-tri-doped graphene (donated as S-FeCo3P/NPSG) are rationally prepared through a controllable one-step carbothermal-phosphorization strategy. The modified charge distribution and electron-donor properties of S-FeCo3P/NPSG caused by S decoration render a significantly beneficial effect on the electrocatalytic activities. Consequently, the S-FeCo3P/NPSG electrode exhibits extraordinary bifunctional activities toward oxygen electrochemistry of the OER overpotential of 290 mV at 10 mA cm−2 and the ORR half-wave potential of 0.83 V, approaching to that of noble-metal IrO2 (289 mV) and Pt/C (0.84 V), respectively, but with more stronger operation stability in alkaline media. When S-FeCo3P/NPSG serves as the air cathode for liquid-state Zn-air battery, the large peak power density and energy density, as well as superb discharge-charge durability (cycling life > 600 h) of this device are obtained. Furthermore, all-solid-state Zn-air battery with S-FeCo3P/NPSG as air electrode also displays excellent mechanical flexibility, high power density and stable cycling stability. The self-reconstruction behavior of the S-FeCo3P/NPSG cathode catalysts is also investigated during the electrocatalytic Zn-air battery operation. This work would provide some novel inspiration from aspects of bonding and charge distribution for the rational construction of active and cost-efficient bifucntional oxygen electrocatalysts for energy storage and conversion devices.