Elucidating the Impact of Doping and Strain on the\nElectrochemical Oxidation of Ammonia over <i>β-</i>M@NiOOH(0001) (M = Fe, Co, and Cu): A Comprehensive Theoretical Investigation

Designing\neffective Pt-free catalysts and understanding their mechanism\nof the electrochemical ammonia oxidation reaction (AOR) are critical\nfor hydrogen production. In this study, we theoretically investigated\nthe AOR mechanism underlying N<sub>2</sub> formation over the β-NiOOH(0001)\nand β-M@NiOOH(0001) (M = Fe, Co, and Cu) surfaces to explore\nthe roles of doping and strain on the AOR. The enhancement in the\nβ-NiOOH(0001) catalyst activity observed with the doping effect\nwas essentially attributed to the upshifted ε<sub>d</sub>, which\nstrengthened the key intermediate <i>E</i><sub>ads</sub>(NH<sub>2</sub>). The strain effect enabled high activity in catalysts\nby enhancing <i>E</i><sub>ads</sub>(NH<sub>2</sub>) through\nincreased amounts of electron transfer from the strain-applied surface\nto adsorbed NH<sub>2</sub>, and all potential-determining steps were\nNH<sub>3</sub>* deprotonation on the catalysts. In addition, an analysis\nof nitrogen-containing products indicated that compressive strain-applied <i>β-</i>NiOOH(0001) surfaces with high catalytic activity\nand N<sub>2</sub> selectivity can be superior to those of Pt-free\nAOR catalysts. The relation between the limiting potential and <i>E</i><sub>ads</sub>(NH<sub>2</sub>) exhibited a volcano curve.