Electrocatalytic reduction of nitrite to ammonium ion using Ni(ii) complexes with redox-active di(imino)pyridine ligands†

Human disruption of the nitrogen cycle motivates the exploration into electrocatalytic reduction of nitrite. Homogeneous Ni(ii) complexes with tridentate redox-active bis(imino)pyridine ligands demonstrated high effectiveness and selectivity for electrocatalytic reduction of nitrite to the ammonium ion and hydroxylamine in solutions buffered with 4-morpholinepropanesulfonic acid (MOPS). Controlled potential coulometry at −1.4 V vs. Fc^0/+ predominantly produced the ammonium ion with Faradaic efficiencies of ≥50%. Foot-of-the-wave analysis yielded calculated turn-over frequencies ranging from 790 to 850 s⁻¹. Computational investigations of the catalytic mechanism provided insights into the proposed chemical steps and detailed the energetics of electron and proton transfers.