Electron Density Modulation of Metallic MoO₂ by Ni Doping to Produce Excellent Hydrogen Evolution and Oxidation Activities in Acid

Development of non-noble metal electrocatalysts for hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) in acid is a great challenge for the development of polymer electrolyte membrane water electrolysis (PEMWE) and polymer electrolyte membrane fuel cells (PEMFC). Here, we report an efficient strategy for modulating the electron density of MoO2 by Ni doping to accelerate HER and HOR in acid. This is particularly important for PEMWE, PEMFC, and regenerative fuel cells. X-ray absorption spectroscopy demonstrates that Ni is doped by replacing Mo atoms in MoO2. Then Ni doping can lead to electron deficiency on neighboring O sites, which are induced to adsorb hydrogen and then increase the surface hydrogen coverage. Therefore, the doping of Ni can modulate the electron density of MoO2 for accelerating HER and HOR. Our results indicate that the incorporation of a high-electronegativity transition metal into MoO2 provides a new strategy for replacing Pt as an electrocatalyst for HER and HOR in acid.