Hierarchical Highly Wrinkled Trimetallic NiFeCu Phosphide Nanosheets on Nanodendrite Ni₃S₂/Ni Foam as an Efficient Electrocatalyst for the Oxygen Evolution Reaction

The sluggish oxygen evolution reaction (OER) and costly noble-metal oxide catalysts hinder the vast usage of environmentally friendly water splitting for hydrogen production. Elemental doping by partial replacing of parent metal elements with elements of higher electronegativity is considered to be one of the most efficient strategies to promote the electrocatalytic OER performance. In this work, we synthesize an efficient hierarchical highly wrinkled NiFeCu phosphide nanosheet on nanodendrite Ni₃S₂/NiF substrates through partial replacement of Cu instead of Ni and Fe in NiFeP@Ni₃S₂/NiF by using a facile electrodeposition method. The NiFeCuP@Ni₃S₂/NiF electrocatalyst needs only 230, 282, and 351 mV to reach 10, 50, and 100 mA × cm^–2, respectively. Notably, this electrocatalyst shows one of the lowest OER overpotentials at 10 mA/cm^–2 for metal phosphides and endured the OER at 20 mA × cm^–2 for 18 h with negligible voltage elevation. The X-ray photoelectron spectroscopy (XPS), double-layer capacitance (C_dl) plots, and electrochemical impedance spectroscopy show that the partial Cu doping in NiFeP@Ni₃S₂/NiF not only can change the electron density around Ni and Fe but also can increase the electrochemically active surface area and conductivity of electrocatalysts.