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

An iron doping strategy was applied to construct a Fe-doped NiMo alloy for HER/OER in alkaline media, which was found to effective modulate the electronic structure and promote the phase transformation, thus enhancing the HER and OER performance in alkaline media. [Display omitted] •Fe doping strategy is applied to improve the alkaline HER/OER kinetics of NiMo alloy.•Fe-doped NiMo exhibits enhanced HER and OER with 87 mV and 269 mV at ± 10 mA cm−2.•Two-electrode cell with Fe-doped NiMo as anode/cathode shows exceptional performance.•Role of doping Fe in electronic structure is studied by post XPS and DFT calculations.•Dissolution of Mo and phase transformation during HER/OER are studied and explained. 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, Fe0.2-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 Fe0.2-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 Fe0.2-NiMo for alkaline water splitting. Further studies show that the Fe0.2-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.