Facile electrodeposition of Iron-doped NiMo alloys as bifunctional electrocatalysts for alkaline overall water splitting

Nickel-molybdenum (NiMo) alloy has been widely used as electrode materials for alkaline hydrogen evolution reaction (HER). However, pristine NiMo alloy faces problem such as poor oxygen evolution reaction (OER) kinetics, molybdenum dissolution, and unsatisfactory durability. Careful incorporation of the appropriate foreign metallic element into the alloy has been shown to be an effective strategy for improving the electrocatalytic performance. Herein, iron (Fe) was doped into NiMo alloy by a facile electrodeposition process and used as bifunctional electrocatalysts for alkaline water splitting. XRD and TEM techniques confirm the successful doping of Fe. XPS and DFT calculations indicate that the Fe doping effectively modulates the electronic structure of the NiMo alloy, bringing the d-band centre closer to the Fermi energy level, which significantly optimize the adsorption/desorption of the OER/HER intermediates. As a result, the optimized sample, Fe_0.2-NiMo, exhibits outstanding HER and OER performance with overpotentials of 85 mV and 269 mV at ± 10 mA cm⁻², respectively. The two-electrode cell with Fe_0.2-NiMo as both anode and cathode requires only 1.9 V to drive the overall water splitting at 500 mA cm⁻², further demonstrating the huge potential of Fe_0.2-NiMo for alkaline water splitting. Further studies show that the Fe_0.2-NiMo suffers from phase transformation to NiFe(oxy)hydroxide as electrocatalytic active center for HER/OER and that the Fe doping can mitigate the dissolution of Mo to some extent independently of OER and HER.