Synthesis of Ultrasmall, Homogeneously Distributed Ni₃Fe Alloy Nanoparticles on N-Doped Porous Graphene as a Bifunctional Electrocatalyst for Rechargeable Flexible Solid Zinc-Air Batteries

Rechargeable solid-state Zn-air batteries (ZABs) have drawn attractive prospects for flexible wearable electronic devices; however, their practical application is severely hindered due to the sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in air cathode. Herein, the N-doped porous graphene is coupled with Ni3Fe alloys (Ni3Fe/NPG) by the phase transformation method. By optimizing the Ni3Fe alloy content and nanoparticle size, the bifunctional Ni3Fe/NPG-1 electrocatalyst with a super-high specific surface area (1081.8 m2 g–1), ultralow alloy loading content (2.4 wt %), and the best electrocatalytic activity and stability is obtained, which exhibits a low overpotential of 329 mV to achieve a 10 mA cm–2 current density for the OER, and positive onset and half-wave potentials of 0.874 and 0.83 V for the ORR, superior to the state-of-the-art Pt/C and RuO2 and most highly active bifunctional catalysts reported to date. Furthermore, density functional theory calculation results prove that the synergetic effect is beneficial to favorable conjugated electronic environments and increasing OER/ORR catalytic activities. Impressively, the liquid ZAB with the optimized bifunctional catalyst shows a high voltage of 1.50 V, maximum power density of 143 mW cm–2, outstanding cycling and mechanical stability, and superior charging-discharging performance. More importantly, the Ni3Fe/NPG-1 based all-solid-state ZAB also presents a superb open-circuit voltage of 1.45 V, high peak power density of 50.0 mW cm–2, and cyclic durability for 150 cycles. The designed air-cathode and competitive catalytic performance contribute significant enlightenment toward the next-generation electrochemical devices.