Inept N2 Activation of Tri-Nuclear Nickel Complex with Labile Sulfur Ligands Facilitates Selective N2H4 Formation in Electrocatalytic Conversion of N2.

Abstract

Conversion of N2 to the energy vector N2H4 under benign conditions is highly desirable. However, such N2 fixation processes are extremely rare. It has been recently reported that N2 to N2H4 conversion can be achieved electrochemically by using a trinuclear [Ni3(S2C3H6)4]2- complex (named as [Ni3S8]2-). There are hardly any precedents of Nitrogen Reduction Reaction (NRR) by molecular catalysts having Ni and the highly unusual selectivity for N2H4 over NH3 makes this electrochemical reduction unique. A systematic theoretical study employing calibrated Density Functional Techniques to unearth the mechanisms of NRR (4e-/4H+) and HER (2e-/2H+) was conducted for the aforementioned trinuclear Ni complex. Our findings unravel a curious case of ligand lability working in tandem with metal centers in facilitating this unprecedented electrocatalytic activity. Furthermore, it is shown that the poor N-N bond activation property of Ni is responsible for this unusual selectivity. Additionally, the HER mechanistic pathways have also been delineated in this report. The mechanistic intricacies thus unearthed in this study may assist in developing more efficient electrocatalysts for N2H4 production through NRR.