Secondary Heteroatoms (S, P) Optimize the Local Coordination Environment of NiFe Sites as a Trifunctional Electrocatalyst for Overall Water Splitting and Zn-Air Batteries

Developing multifunctional, low-cost electrocatalysts with high activity and stability for energy storage and conversion is important, but still a significant challenge. Here, a trifunctional electrocatalyst derived from nickel foam (NiFePS/CNT@NF) is synthesized by a combined chemical vapor deposition and solvothermal strategy that exhibits superior catalytic activity and stability for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). Benefiting from the secondary heteroatoms (P, S) that optimize the local microenvironment of the NiFe active center, NiFePS/CNT@NF demonstrates higher half-wave potential toward the ORR (E_1/2@0.88 V vs RHE) as well as lower overpotentials for the OER (232 mV) and HER (183 mV) at 10 mA cm^-2. When equipped in liquid- or flexible solid-state rechargeable zinc (Zn)-air batteries, NiFePS/CNT@NF shows high power and energy density, as well as excellent long-term cycling stability. Moreover, an assembled device for overall water splitting operates at a current density of 20 mA cm^-2 with no less than 20 h. It suggests great potential for applications in rechargeable Zn-air batteries (ZABs) and overall water splitting devices.