Robust Oxygen Evolution on Ni-Doped MoO: Overcoming Activity-Stability Trade-Off in Alkaline Water Splitting.

Electrochemical water splitting using earth-abundant materials is crucial for enabling green hydrogen production and energy storage. In recent years, molybdenum trioxide (MoO), a semiconducting material, has been proposed as a candidate catalyst for the oxygen evolution reaction (OER). Here, we advance nickel (Ni) doping of MoO as a strategy to increase the activity and stability of the material during alkaline electrochemical water splitting, thereby overcoming the typical activity-stability trade-off encountered with OER catalysts. The instability of MoO in alkaline media can be mitigated by doping with Ni, whose oxide is stable under such conditions. Using density functional theory (DFT) with Hubbard corrections, we show that Ni doping reduces the thermodynamic OER overpotential on the MoO basal plane to 0.64 V. Experiments demonstrate that Ni-doped MoO requires an overpotential of 0.34 V for an OER current density of 10 mA/cm (and 0.56 V at 100 mA/cm), as opposed to a value of 0.40 V for pure MoO. Further, Ni-doped MoO exhibits a lower Tafel slope of 74.8 mV/dec, compared to 98.3 mV/dec for the pristine material under alkaline conditions. While Mo leaches in alkaline conditions, X-ray photoelectron spectroscopy reveals enhanced stability with Ni doping. Overall, our work advances Ni-doped MoO as a promising water-splitting electrocatalyst and provides new insights into its OER mechanism and stability in alkaline media. More generally, the work sheds light on choosing a dopant to increase a material's activity and stability, which will also find applications in other catalytic materials.