Ni–Fe Phosphate/Ni Foam Electrode: Facile Hydrothermal Synthesis and Ultralong Oxygen Evolution Reaction Durability

Nickel–iron phosphate film with a porous surface formed by ultrathin nanotubes was successfully grown on Ni foam (NF) through a simple hydrothermal route at 150 °C for 90 min in the presence of HCl and urea with proper amounts, employing Fe­(NO₃)₃·9H₂O as the iron source, Na₂HPO₄ as the PO₄^3– source, and NF as the nickel source and the substrate. The as-obtained product (labeled as NiFe-Pi/NF) was characterized by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), X-ray energy dispersive spectroscopy (EDS), EDS mapping, X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) spectroscopy, and nitrogen adsorption–desorption isotherms. Experiments showed that the as-obtained NiFe-Pi/NF presented excellent OER catalytic activity in a 1 M KOH solution. To deliver a current density of 10 mA cm^–2, the present catalyst only required the overpotential of 206 mV with the Tafel slope of 31 mV dec^–1. More importantly, the catalytic activity of the as-obtained NiFe-Pi/NF catalyst hardly decreased after continuously catalyzing 300 h at the current density of 20 mA cm^–2, displaying excellent long-term stability. Compared with commercial RuO₂, the present NiFe-Pi/NF catalyst possessed better catalytic activity, indicating that the as-obtained NiFe-Pi/NF catalyst can be used as a potential OER catalyst in practical application.