Leaf-like\nMultiphase Metal Phosphides as Bifunctional\nOxygen Electrocatalysts toward Rechargeable Zinc-Air Batteries

Developing a bifunctional oxygen electrocatalyst is crucial\nto\nimprove the reversibility and cycle life of a rechargeable zinc-air\nbattery (RZAB). Here, transition metal phosphides (TMPs) with a leaf-like\nhierarchical structure and multiphase composition can be synthesized\nby the “alloying–dealloying–phosphating”\nstrategy. The as-prepared P-NiCo(1:1) electrode takes advantage of\nits internal dense nanoholes and synergistic effects induced by NiCoP-containing\npolyphase to reveal multifunctional catalysis, such as OER and ORR.\nIn combination of these advantages, P-NiCo(1:1) exhibits an extremely\nlow OER overpotential of 220 mV at 10 mA cm<sup>–2</sup>, a\nhigher half-wave potential of 0.79 V for ORR, and a smaller potential\ndifference (Δ<i>E</i>) of 0.66 V. The liquid RZAB\nwith P-NiCo(1:1) as a cathodic bifunctional catalyst delivers a higher\nopen-circuit voltage (OCV), a larger power density of 175 mW cm<sup>–2</sup>, and longer cycling life for more than 180 h. Even\nwhen applied in solid-state flexible RZABs, the lightweight module\ncould start high-power devices. With theoretical confirmation, the\nmajor phase NiCoP of P-NiCo(1:1) is helpful to increase the density\nof states, regulate the d-band center, and decrease the energy barrier\nto 2.13 eV, which are significantly superior to those of Co<sub>2</sub>P and Ni<sub>2</sub>P. It is believable that the synthetic strategy\nand activity-promoting mechanism acquired from this research can offer\na guide to designing a promising rechargeable zinc-air battery system.