Hydrothermal Synthesis of Fe-Doped Nickel Cobalt Phosphate Nanofibers for High-Stability Electrochemical Overall Water Splitting

In this study, we synthesized new iron-doped nickel cobalt phosphate nanofibers, deposited them on nickel foam (NF), and deployed them as active catalysts for oxygen evolution reactions (OERs), hydrogen evolution reactions (HERs), and overall water splitting. Our catalyst, the Fe-doped nickel cobalt phosphate nanofiber at 1.05 Fe atom% (Fe-1.05), exhibited a Brunauer–Emmett–Teller surface area (BET SA) of 57.0 m² g⁻¹ and a Barrett−Joyner−Halenda (BJH) mesopore of 3.7 nm. Because of its large surface area and mesopore architecture, which facilitate ionic diffusion, NF-deposited Fe-1.05 (Fe-1.05@NF) exhibited exceptional OER (η = 234 mV @ 10 mA cm⁻²) and HER (η = 104 mV @ 10 mA cm⁻²) performance. Overall water splitting analysis showed the lowest potentials of 1.59, 1.76, and 1.86 V at 10, 50, and 100 mA cm⁻², respectively. These results show the superior OER and HER performance of Fe-1.05@NF over that of the best-performing nickel cobalt phosphates and their Fe-dopped analogs in the literature. A stability test for overall water splitting for 100 h in a 1-M KOH electrolyte at a current density of 100 mA cm⁻² demonstrated remarkable durability. The enhanced electrochemical activity of Fe-1.05@NF can be attributed to the synergistic effect between the metal atoms and phosphate ligands, which facilitates favorable conditions for the adsorption and oxidation of electrolyte ions, enhanced electrical conductivity, and active site availability due to Fe (dopant) metal atoms, providing a nanostructured (nanofiber) morphology with high porosity.