Nickel-induced charge redistribution in Ni-Fe/Fe3C@nitrogen-doped carbon nanocage as a robust Mott-Schottky bi-functional oxygen catalyst for rechargeable Zn-air battery

Designing earth-abundant and advanced bi-functional oxygen electrodes for efficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are extremely urgent but still ambiguous. Thus, metal-semiconductor nanohybrids were developed with functionally integrating ORR-active Ni species, OER-active Fe/Fe3C components, and multifunctional N-doped carbon (NDC) support. Expectantly, the resulted NDC nanocage embedded with Ni-Fe alloy and Fe3C particles, as assembled Mott-Schottky-typed catalyst, delivered a promoted half-wave potential of 0.904 V for ORR and a low overpotential of 315 mV at 10 mA/cm2 for OER both in alkaline media, outperforming those of commercial Pt/C and RuO2 counterparts. Most importantly, the optimized Ni-Fe/Fe3C@NDC sample also afforded a peak power density of 267.5 mW/cm2 with a specific capacity of 773.8 mAh/gZn and excellent durability over 80 h when used as the air electrode in rechargeable Zn-air batteries, superior to the state-of-the-art bi-functional catalysts. Ultraviolet photoelectron spectroscopy revealed that the introduction of Ni into the Fe/Fe3C@NDC component could well manipulate the electronic structure of the designed electrocatalyst, leading to an effective built-in electric field established by the Mott-Schottky heterojunction to expedite the continuous interfacial charge-transfer and thus significantly promote the utilization of electrocatalytic active sites. Therefore, this work provides an avenue for the designing and developing robust and durable Mott-Schottky-typed bi-functional catalysts for promising energy conversion.