Plasma-Treated Ultrathin Ternary FePSe₃ Nanosheets as a Bifunctional Electrocatalyst for Efficient Zinc-Air Batteries

Developing novel bifunctional electrocatalysts with advanced oxygen electrocatalytic activity is pivotal for next-generation energy-storage devices. Herein, we present ultrathin oxygen-doped FePSe₃ (FePSe₃-O) nanosheets by Ar/O₂ plasma treatment, with remarkable surface atom reorganization. Such surface atom reorganization generates multiple crystalline-amorphous interfaces that benefit the kinetics of oxygen evolution reaction, achieving a low overpotential of only 261 mV at 10 mA cm^-2 with a small Tafel slope of 41.13 mV dec^-1. Density functional theory calculation indicates that oxygen doping can also modulate the electrical states at the Fermi level with a decreased band gap responsible for the enhanced electrocatalytic performance. Such unique FePSe₃-O nanosheets can be further fabricated as the air cathode in rechargeable liquid zinc-air batteries (ZABs), which deliver a high open circuit potential of 1.47 V, a small charge-discharge voltage gap of 0.80 V, and good cycling stability for more than 800 circles. As a proof of concept, the flexible solid-state ZABs assembled with FePSe₃-O nanosheets as cathode also display a favorable charge-discharge performance, durable stability, and good bendability. This work sheds new insights into the rational design of defect-rich ternary thiophosphate nanosheets by plasma treatment toward enhanced oxygen electrocatalysts in metal-air batteries.