Evaluating the Thermodynamics of Electrocatalytic N₂ Reduction in Acetonitrile

Abstract

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.

Achieving a Record‐High Yield Rate of 120.9 for N2 Electrochemical Reduction over Ru Single‐Atom Catalysts

“…Recently, a variety of sustainable routes for fixing N 2 to NH 3 have been developed by using biological nitrogenase, photocatalysis, and electrocatalysis . As a strategy of NH 3 synthesis under the ambient reaction condition, electrochemical reduction of N 2 into NH 3 has attracted particular attention, because this process utilizes H 2 O as hydrogen source and can be facilely controlled by altering the applied electrode potential.…”

The Potential Economic Feasibility of Direct Electrochemical Nitrogen Reduction as a Route to Ammonia

“…The electrochemical potentials at standard state (1 M solutes, 1 atm gases, 298 K) for these half-reactions, and the potential for the overall reaction, are given in equations 7-9. [75][76] All potentials are presented versus the standard hydrogen electrode, SHE.…”

Selectivity of tungsten mediated dinitrogen splitting vs. proton reduction

“…3,4 Lindley et al estimated a suitable overpotential window of 1-1.5 V for selective NR (in MeCN) prior to competing hydrogen reduction (HR) at a glassy carbon cathode. 5 However, besides the thermochemical framework, mechanistic models that account for NR vs. HR selectivities of molecular catalysts are generally poorly developed.…”