In-situ growth of NiFe-LDH/fluoride heterostructures on FeN4/C for bifunctional oxygen electrocatalysis

Abstract

The design of low-cost and highly efficient bifunctional electrocatalyst towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is challengeable, which limits the commercial application of rechargeable zinc-air battery. Herein, an efficient ORR and OER bifunctional electrocatalyst (NiFe-LDH/F_x−FeN₄/C) is composed of nickel/iron-based heterostructures sparsely grown on carbon black (CB) with single FeN₄ sites. The NiFe-LDH/F_x−FeN₄/C electrocatalysts are prepared through the pyrolysis of hemin chloride adsorbed on CB, followed by in-situ hydrothermal growth of NiFe-LDH/F_x heterostructures. The NiFe-LDH/F_x heterostructures are composed of NiFe-LDH, (NH₄)₃FeF₆, and NiF₂. The elevated valence states of Fe and Ni in heterostructures significantly increase the OER activity. The mesopores and large pores of the NiFe-LDH/F_x−FeN₄/C facilitate the exposure of active sites and enhance mass transfer. These features contribute to the outstanding bifunctional activity of NiFe-LDH/F_x−FeN₄/C, achieving a half-wave potential of 0.906 V for the ORR, an OER overpotential of 246 mV at 10 mA cm⁻², and an extremely small voltage gap of 0.57 V. Additionally, the NiFe-LDH/F_x−FeN₄/C-based RZAB also exhibits a peak power density of 209 mW cm⁻² and charging/discharging cycling stability for 445 h. This work establishes a novel strategy for the preparation of highly efficient bifunctional electrocatalysts through in-situ growth and heterostructure engineering.