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-N-4 and Cu-N-4 catalysts for highly efficient nitrite electroreduction to NH2OH by adopting density functional theory (DFT) calculations. DFT calculations reveal that the high selectivity of Ni-N-4 and Cu-N-4 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-N-4 and Cu-N-4 with fully occupied d(xz), d(yz), and d(z2) 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.