In-situ building of multiscale porous NiFeZn/NiZn-Ni heterojunction for superior overall water splitting

The development of efficient nonprecious bifunctional electrocatalysts for water electrolysis is crucial to enhance the sluggish kinetics of the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). A self-supporting, multiscale porous NiFeZn/NiZn-Ni catalyst with a triple interface heterojunction on nickel foam (NF) (NiFeZn/NiZn-Ni/NF) was in-situ fabricated using an electroplating−annealing−etching strategy. The unique multi- interface engineering and three-dimensional porous scaffold significantly modify the mass transport and electron interaction, resulting in superior bifunctional electrocatalytic performance for water splitting. The NiFeZn/NiZn-Ni/NF catalyst demonstrates low overpotentials of 187 mV for HER and 320 mV for OER at a current density of 600 mA/cm², along with high durability over 150 h in alkaline solution. Furthermore, an electrolytic cell assembled with NiFeZn/NiZn-Ni/NF as both the cathode and anode achieves the current densities of 600 and 1000 mA/cm 2 at cell voltages of 1.796 and 1.901 V, respectively, maintaining the high stability at 50 mA/cm 2 for over 100 h. These findings highlight the potential of NiFeZn/NiZn-Ni/NF as a cost-effective and highly efficient bifunctional electrocatalyst for overall water splitting.