Cu- and Fe-Codoped Ni Porous Networks as an Active Electrocatalyst for Hydrogen Evolution in Alkaline Medium

Highly active catalysts from the earth-abundant metals are essential to materialize the low-cost production of hydrogen through water splitting. Herein, nickel porous networks codoped with Cu and Fe prepared by thermal reduction of presynthesized Cu, Fe-codoped Ni(OH)₂ nanowires are reported. The sample consists of nanoparticles of ∼80 nm, which form highly porous network clusters of ∼1 μm with a pore size of 10-100 nm. Among the various doped compositions, the NiCu_0.05Fe_0.025 porous network exhibits the best catalytic activity with a low overpotential of 60 mV for a hydrogen evolution reaction (HER) in 1 M KOH solution and a specific activity of 0.1 mA cm^-2 at 117 mV overpotential calculated based on the electrochemical active surface area (ECSA). The density functional theory calculations reveal that codoping of Fe and Cu into the Ni lattice results in a shift of d-bands of nickel to lower energy levels and thus in the reduced hydrogen adsorption energy (ΔG_H = -0.131 eV), which is close to ΔG_H for Pt (-0.09 eV). When NiCu_0.05Fe_0.025(OH)₂ nanowires is used as an oxygen evolution reaction (OER) catalyst and is coupled with NiCu_0.05Fe_0.025 porous networks for overall water splitting, the NiCu_0.05Fe_0.025∥NiCu_0.05Fe_0.025(OH)₂ catalyst couple achieves a current density of 10 mA cm^-2 at 1.491 V, similar to that of the Pt/C∥RuO₂ couple and offers a negligible loss in the performance when operated at 20 mA cm^-2 for 30 h.