An Effective Approach to Enhance Hydrogen Evolution Reaction and Hydrogen Oxidation Reaction by Ni Doping to MoO 3 .

The development of bifunctional catalysts that facilitate both the hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) in alkaline environment is crucial for realizing unitized regenerative anion-exchange membrane fuel cells. In this study, a novel strategy to modulate the electron density of MoO 3 through Ni doping (sample named Ni x Mo 1- x O 3 ) is reported. Ni is incorporated to replace Mo atoms in MoO 3 . Specifically, Ni x Mo 1- x O 3 is combined with optimal adsorption energy, along with MoO 2 /Mo 2 N hybrid with high conductivity. The resulting Ni x Mo 1- x O 3 supported on MoO 2 /Mo 2 N hybrid (sample named as Ni x Mo 1- x O 3 -H) exhibits excellent alkaline HER activity, with an overpotential of only 16 mV at 10 mA cm -2 and a Tafel slope of 54 mV dec -1 . In addition, the Ni x Mo 1- x O 3 -H demonstrates an ultrahigh HOR performance with a high exchange current density (3.852 mA cm -2 ). The catalyst's breakdown potential of 0.23 V indicates its ability to withstand higher voltages without breaking down. As evidenced by the results, this characteristic leads to improved stability. These results are higher than those of the other catalysts reported, which indicates that the electron density of MoO 3 can be effectively modulated through Ni doping, leading to excellent HER and HOR performance.