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

Electroreduction of nitrate/nitrite to high-value-added products, including NH 2 OH, is an important way to achieve sustainable production of green energy. However, this electrosynthesis of NH 2 OH 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 NH 2 OH 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 *NH 2 OH and *NH intermediates, thereby preventing the further reduction of NH 2 OH. 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 NH 2 OH synthesis and offers perspectives on the crucial factors in determining the catalytic selectivity.