Evaluating the Thermodynamics of Electrocatalytic N2 Reduction in Acetonitrile

The development of a sustainable ammonia synthesis by proton-coupled electroreduction of dinitrogen (N 2 ) requires knowledge of the thermodynamics described by standard reduction potentials. The first collection of N 2 reduction standard potentials in an organic solvent are reported here. The potentials for reduction of N 2 to ammonia (NH 3 ), hydrazine (N 2 H 4 ), and diazene (N 2 H 2 ) in acetonitrile ( MeCN ) solution are derived using thermochemical cycles. Ammonia is thermodynamically favored, with a 0.43 V difference between NH 3 and N 2 H 4 and a 1.26 V difference between NH 3 and N 2 H 2 . The thermodynamics for reduction of N 2 to the protonated products ammonium (NH 4 + ) and hydrazinium (N 2 H 5 + ) under acidic conditions are also presented. Comparison with the H + /H 2 potential in MeCN reveals a 63 mV thermodynamic preference for N 2 reduction to NH 3 over H 2 production. Combined with knowledge of the kinetics of electrode-catalyzed H 2 evolution, a wide working region is identified to guide future electrocatalytic studies.