Theoretical Insights into the Selectivity of Nitrite Reduction to NH₂OH on Single-Atom Catalysts

Electroreduction of nitrate/nitrite to high-value-added products, including NH₂OH, is an important way to achieve sustainable production of green energy. However, this electrosynthesis of NH₂OH still suffers from poor selectivity due to the various competing reactions. Here, we screen out Ni-N₄ and Cu-N₄ catalysts for highly efficient nitrite electroreduction to NH₂OH by adopting density functional theory (DFT) calculations. DFT calculations reveal that the high selectivity of Ni-N₄ and Cu-N₄ is ascribed to their weak adsorption of *NH₂OH and *NH intermediates, thereby preventing the further reduction of NH₂OH. Moreover, using *NO as a model intermediate, we studied the relationship between the 3d orbital occupancy and adsorption strength of the intermediate. It is found that Ni-N₄ and Cu-N₄ with fully occupied d, d, and d orbitals have poor adsorption of *NO intermediate. This work provides a new route for NH₂OH synthesis and offers perspectives on the crucial factors in determining the catalytic selectivity.