Cu and Fe Co-Doped 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 co-doped with Cu and Fe prepared by thermal reduction of pre-synthesized Cu, Fe co-doped Ni(OH)2 nanowires is reported. The sample consists of nanoparticles of ~80 nm, which form highly porous network clusters of ~1 µm with a pore size of 10 nm - 100 nm. Among the various doped compositions, the NiCu0.05Fe0.025 porous network exhibits the best catalytic activity with a low overpotential of 60 mV for hydrogen evolution reaction (HER) in 1 M KOH solution and 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 co-doping 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 (∆GH = -0.131 eV), which is close to ∆GH for Pt (-0.09 eV). When NiCu0.05Fe0.025(OH)¬2 nanowires is used as an oxygen evolution reaction (OER) catalyst and is coupled with NiCu0.05Fe0.025 porous networks for overall water splitting, the NiCu0.05Fe0.025 || NiCu0.05Fe0.025(OH)¬2 catalyst couple achieves a current density of 10 mA cm-2 at 1.491 V similar to that of Pt/C || RuO2 couple and offers a negligible loss in the performance when operated at 20 mA cm-2 for 30 hours.