Flower-shaped disorderly nickel-iron nitride nanosheets as a robust bifunctional electrocatalyst for overall water splitting

Developing highly efficient bifunctional transition metal-based electrocatalysts is important for reducing the practical costs of water splitting. Herein, we present a flower-shaped disorderly nickel-iron nitride nanosheets bifunctional electrocatalysts (NiFeNx/NF), which was prepared in situ on a nickel foam substrate using a hydrothermal and thermal ammonia-reduction method. The unique structure of the flower-shaped disorderly nanosheets increases the amount of electrocatalytic active sites and promotes efficiency of both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) by facilitating charge and mass transfer. The bifunctional catalyst demonstrated exceptional performance with overpotentials of only 78 mV for HER and 280 mV for OER at current densities of 10 mA cm−2 and 100 mA cm−2, respectively. Additionally, the NiFeNx/NF exhibited outstanding stability, achieving a cell voltage of only 1.53 V for overall water splitting at 10 mA cm−2 in 1.0 M KOH, and continuously operated for 90 h at 20 mA cm−2 without significant voltage increase. These findings contribute to the development of high-performance, cost-effective, and environmentally friendly bifunctional catalysts based on transition metals for water splitting.