Evaluating the Thermodynamics of Electrocatalytic N2 Reduction in Acetonitrile

Brian M. Lindley; Aaron Appel; Karsten Krogh-Jespersen; James M. Mayer; Alexander J.M. Miller

doi:10.1021/acsenergylett.6b00319

Evaluating the Thermodynamics of Electrocatalytic N₂ Reduction in Acetonitrile

Brian M. Lindley, Aaron Appel, Karsten Krogh-Jespersen, James M. Mayer, Alexander J.M. Miller

Pacific Northwest National Laboratory

Research output: Contribution to journal › Article › peer-review

51 Citations (Scopus)

Abstract

The development of a sustainable ammonia synthesis by proton-coupled electroreduction of dinitrogen (N₂) requires knowledge of the thermodynamics described by standard reduction potentials. The first collection of N₂ reduction standard potentials in an organic solvent are reported here. The potentials for reduction of N₂ to ammonia (NH₃), hydrazine (N₂H₄), and diazene (N₂H₂) in acetonitrile (MeCN) solution are derived using thermochemical cycles. Ammonia is thermodynamically favored, with a 0.43 V difference between NH₃ and N₂H₄ and a 1.26 V difference between NH₃ and N₂H₂. The thermodynamics for reduction of N₂ to the protonated products ammonium (NH₄⁺) and hydrazinium (N₂H₅⁺) under acidic conditions are also presented. Comparison with the H⁺/H₂ potential in MeCN reveals a 63 mV thermodynamic preference for N₂ reduction to NH₃ over H₂ production. Combined with knowledge of the kinetics of electrode-catalyzed H₂ evolution, a wide working region is identified to guide future electrocatalytic studies.

Original language	English
Pages (from-to)	698-704
Number of pages	7
Journal	ACS Energy Letters
Volume	1
Issue number	4
DOIs	https://doi.org/10.1021/acsenergylett.6b00319
Publication status	Published - Oct 14 2016

ASJC Scopus subject areas

Chemistry (miscellaneous)
Renewable Energy, Sustainability and the Environment
Fuel Technology
Energy Engineering and Power Technology
Materials Chemistry

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abstract = "The development of a sustainable ammonia synthesis by proton-coupled electroreduction of dinitrogen (N2) requires knowledge of the thermodynamics described by standard reduction potentials. The first collection of N2 reduction standard potentials in an organic solvent are reported here. The potentials for reduction of N2 to ammonia (NH3), hydrazine (N2H4), and diazene (N2H2) in acetonitrile (MeCN) solution are derived using thermochemical cycles. Ammonia is thermodynamically favored, with a 0.43 V difference between NH3 and N2H4 and a 1.26 V difference between NH3 and N2H2. The thermodynamics for reduction of N2 to the protonated products ammonium (NH4+) and hydrazinium (N2H5+) under acidic conditions are also presented. Comparison with the H+/H2 potential in MeCN reveals a 63 mV thermodynamic preference for N2 reduction to NH3 over H2 production. Combined with knowledge of the kinetics of electrode-catalyzed H2 evolution, a wide working region is identified to guide future electrocatalytic studies.",

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AU - Miller, Alexander J.M.

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N2 - The development of a sustainable ammonia synthesis by proton-coupled electroreduction of dinitrogen (N2) requires knowledge of the thermodynamics described by standard reduction potentials. The first collection of N2 reduction standard potentials in an organic solvent are reported here. The potentials for reduction of N2 to ammonia (NH3), hydrazine (N2H4), and diazene (N2H2) in acetonitrile (MeCN) solution are derived using thermochemical cycles. Ammonia is thermodynamically favored, with a 0.43 V difference between NH3 and N2H4 and a 1.26 V difference between NH3 and N2H2. The thermodynamics for reduction of N2 to the protonated products ammonium (NH4+) and hydrazinium (N2H5+) under acidic conditions are also presented. Comparison with the H+/H2 potential in MeCN reveals a 63 mV thermodynamic preference for N2 reduction to NH3 over H2 production. Combined with knowledge of the kinetics of electrode-catalyzed H2 evolution, a wide working region is identified to guide future electrocatalytic studies.

AB - The development of a sustainable ammonia synthesis by proton-coupled electroreduction of dinitrogen (N2) requires knowledge of the thermodynamics described by standard reduction potentials. The first collection of N2 reduction standard potentials in an organic solvent are reported here. The potentials for reduction of N2 to ammonia (NH3), hydrazine (N2H4), and diazene (N2H2) in acetonitrile (MeCN) solution are derived using thermochemical cycles. Ammonia is thermodynamically favored, with a 0.43 V difference between NH3 and N2H4 and a 1.26 V difference between NH3 and N2H2. The thermodynamics for reduction of N2 to the protonated products ammonium (NH4+) and hydrazinium (N2H5+) under acidic conditions are also presented. Comparison with the H+/H2 potential in MeCN reveals a 63 mV thermodynamic preference for N2 reduction to NH3 over H2 production. Combined with knowledge of the kinetics of electrode-catalyzed H2 evolution, a wide working region is identified to guide future electrocatalytic studies.

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