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 PO43– 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.