Iron-doped nickel phosphide hollow nanospheres synthesized by solvothermal phosphidization of layered double hydroxides for electrocatalytic oxygen evolution

Abstract

Active and stable electrocatalysts for the oxygen evolution reaction (OER) are the key to producing hydrogen from alkaline water electrolysis. Here, iron-doped nickel phosphide grown on nickel foam ((Ni_0.83Fe_0.17)₂P/NF) is synthesized by solvothermal phosphidization of NiFe-layered double hydroxides (LDHs) on NF with white phosphorus. (Ni_0.83Fe_0.17)₂P consists of hollow nanospheres with diameters around 50 nm. For the OER in 1 M KOH, (Ni_0.83Fe_0.17)₂P/NF requires low overpotentials of only 215 mV and 247 mV to reach current densities of 10 mA cm⁻² and 50 mA cm⁻², respectively, which are significantly lower than Ni₂P/NF and most of the reported metal phosphide materials to date. The high OER activity of (Ni_0.83Fe_0.17)₂P/NF is attributed to the improved intrinsic activity caused by electron interactions between Fe, Ni, and P, which tunes the adsorption energy of the hydroxyl groups, ultimately leading to more facile OER kinetics. The reduced charge transfer resistance, Tafel slope value, and apparent activation energy corroborate the facile kinetics in (Ni_0.83Fe_0.17)₂P/NF. Both (Ni_0.83Fe_0.17)₂P/NF and Ni₂P/NF involve decoupled electron and proton transfer processes. (Ni_0.83Fe_0.17)₂P/NF also displays good long-term durability, with the conversion of surface metal phosphides to oxides and (oxy)hydroxides observed after prolonged galvanostatic OER tests.