Ultrasmall FeNi3N particles with an exposed active (110) surface anchored on nitrogen-doped graphene for multifunctional electrocatalysts

High-performance multifunctional catalysts are very important to various energy conversion and storage devices. FeNi bimetal electrocatalysts have been reported to have good activities toward the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), but negligible oxygen reduction reaction (ORR) activity. Herein, we report an advanced multifunctional electrocatalyst based on 7.6 nm FeNi3N nanoparticles anchored on N-doped graphene (FeNi3N/NG). The as-prepared FeNi3N/NG exhibits not only excellent OER and HER activities, but also unprecedented ORR activity in alkaline media. The density functional theory (DFT) calculations demonstrate that FeNi3N with an active (110) surface has stronger capability for O-2 adsorption and cleavage of the O-O bond than Ni4N, leading to significantly enhanced ORR activity of the FeNi3N nanoparticles. As a result, the specific capacity of the primary FeNi3N/NG-based Zn-air battery is as high as 785.2 mA h g(-1) at 10 mA cm(-2), higher than that assembled with a benchmarked Pt/C + IrO2 catalyst. Besides, the overall water splitting device with the FeNi3N/NG electrode material delivers 20 mA cm(-2) at 1.585 V, outperforming electrolyzers assembled with the state-of-the-art bifunctional catalysts. Our results highlight the importance of the fabrication of ultrasmall-sized electrocatalysts with an exposed active surface to the development of renewable energy conversion and storage devices.