Interface Engineering of a Hierarchical P‑Modified Co/Ni₃P Heterostructure for Highly Efficient Water Electrolysis Coupled with Hydrazine Degradation

Energy-saving water electrolysis is an ideal strategy to realize the grid-scale generation of hydrogen fuel, especially by coupling with an alternating hydrazine oxidation reaction (HzOR). However, the lack of self-supporting electrodes with excellent bifunctional performance is the key to the problem of high operating voltages. Herein, a unique alternating electrodeposition strategy is first developed to design a (P–Co/Ni₃P)_A3/NF (NF = nickel foam) electrode, which has a hierarchical heterostructure for more active sites and robust interface interactions, resulting in excellent bifunctional activity. The (P–Co/Ni₃P)_A3/NF electrode exhibits small potentials of −10 and −79 mV at 10 mA cm^–2 as well as low Tafel slopes of 45 and 1.8 mV dec^–1 for the hydrogen evolution reaction (HER) and HzOR, respectively. Inspiringly, an extremely small-cell voltage of 50 mV is required to realize a high current density of 300 mA cm^–2 in the two-electrode device, which is 1.77 V lower than that in the overall water splitting (1.82 V) system. Density functional theory calculations confirm that the construction of the P–Co/Ni₃P heterostructure achieves the improvement of the calculated adsorption energy of the H₂O molecule (ΔG_H2O), ΔG_H*, as well as the dehydrogenation kinetics of reaction intermediates, thereby accelerating the overall electrocatalytic activity of HER/HzOR. Our strategy suggests a possibility for the development of other material synthesis and performance optimization for hydrogen production.