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 −FeN 4 /C) is composed of nickel/iron-based heterostructures sparsely grown on carbon black (CB) with single FeN 4 sites. The NiFe-LDH/F x − FeN 4 /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, (NH 4 ) 3 FeF 6 , and NiF 2 . 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 − FeN 4 /C facilitate the exposure of active sites and enhance mass transfer. These features contribute to the outstanding bifunctional activity of NiFe-LDH/F x − FeN 4 /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 − FeN 4 /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.
Modulating the microenvironment of single-metal active sites holds excellent promises for developing highly efficiently oxygen electrocatalysts. Herein, by combining theoretical predictions and experiments, we reported a general strategy to engineer the electronic properties of iron-nitrogen-carbon (FeN 4 /C) catalysts via the incorporation of the boron (B) atom for achieving improved catalytic activity in oxygen electrocatalysis. Our theoretical results revealed that B modulation effectively tunes the d-band center of the iron (Fe) active site to optimize its adsorption strength with oxygenated species, greatly enhancing oxygen reduction reaction (ORR) and oxygen evolution reactions (OER) activity. Our experimental measurements then confirmed the above theoretical predictions: the as-synthesized B-doped FeN 4 /C (Fe-N 4 -B) material can perform as an eligible bifunctional catalyst for ORR and OER in alkaline media, and its catalytic activity even outperforms the commercial noble metal benchmarks. The present findings provide a promising strategy to further design the advanced catalysts for a wide range of electrochemical applications.
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