Electrocatalytic, Homogeneous Ammonia Oxidation in Water to Nitrate and Nitrite with a Copper Complex

Liu, Han-Yu; Lant, Hannah M. C.; Troiano, Jennifer L.; Hu, Gongfang; Mercado, Brandon Q.; Crabtree, Robert H.; Brudvig, Gary W.

doi:10.1021/jacs.2c01788

Cited by 60 publications

(54 citation statements)

References 24 publications

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“…While most of the complexes discussed here operate in nonaqueous solvents to suppress possible competitive WO, the inability of 9 to oxidize water favors its high chemoselectivity toward AO in aqueous media. 42 Warren and co-workers recently described a low-coordinate Cu(I) complex 10 that oxidizes NH 3 in MeCN. 43 Unless otherwise specified, potentials measured in water are versus NHE; in organic solvents, potentials are versus Fc +/0 .…”

Section: ■ Biological Ammonia Oxidationmentioning

confidence: 99%

“…In 2022, our group reported the first Cu(II) molecular AO catalyst 9 that performs a 6e – or 8e – oxidation to generate NO 2 – and NO 3 – . While most of the complexes discussed here operate in nonaqueous solvents to suppress possible competitive WO, the inability of 9 to oxidize water favors its high chemoselectivity toward AO in aqueous media . Warren and co-workers recently described a low-coordinate Cu(I) complex 10 that oxidizes NH 3 in MeCN …”

Section: Artificial Ammonia Oxidationmentioning

confidence: 99%

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Electrochemical Ammonia Oxidation with Molecular Catalysts

et al. 2023

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Electrocatalytic ammonia oxidation (AO) provides an attractive route to a carbonneutral fuel economy and the energy-efficient production of value-added feedstocks. The design and study of molecular catalysts can give a deeper mechanistic understanding of AO, which will aid in optimizing catalysts for overpotential, efficiency, and chemoselectivity. This Perspective introduces the topic with biological AO chemistry and then surveys the recent developments of molecular AO electrocatalysts, followed by a discussion of design strategies for new catalysts.

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Section: ■ Biological Ammonia Oxidationmentioning

confidence: 99%

Section: Artificial Ammonia Oxidationmentioning

confidence: 99%

Electrochemical Ammonia Oxidation with Molecular Catalysts

et al. 2023

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“…Nishibayashi and co-workers reported chemical and electrochemical NH 3 oxidation using a Mn salen-based catalyst with an overpotential above 1.5 V . Producing oxygenated products, Brudvig and colleagues recently described a copper electrocatalyst for ammonia oxidation to nitrate and nitrite in water …”

Section: Introductionmentioning

confidence: 99%

“…15 Nishibayashi and co-workers reported chemical and electrochemical NH 3 oxidation using a Mn salen-based catalyst with an overpotential above 1.5 V. 25 Producing oxygenated products, Brudvig and colleagues recently described a copper electrocatalyst for ammonia oxidation to nitrate and nitrite in water. 26 N−N bond formation represents a key step in ammonia oxidation en route to N 2 formation. Mechanistic data on current homogeneous systems for ammonia oxidation suggest that N−N bond formation may occur after 3-, 2-, or 1-electron oxidation of a metal−ammine complex [M n ]-NH 3 (Scheme 1).…”

Section: ■ Introductionmentioning

confidence: 99%

Electrocatalytic Ammonia Oxidation by a Low-Coordinate Copper Complex

et al. 2022

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Molecular catalysts for ammonia oxidation to dinitrogen represent enabling components to utilize ammonia as a fuel and/or source of hydrogen. Ammonia oxidation requires not only the breaking of multiple strong N–H bonds but also controlled N–N bond formation. We report a novel β-diketiminato copper complex [ i Pr2NNF6]CuI-NH3 ([CuI]-NH3 (2)) as a robust electrocatalyst for NH3 oxidation in acetonitrile under homogeneous conditions. Complex 2 operates at a moderate overpotential (η = 700 mV) with a TOFmax = 940 h–1 as determined from CV data in 1.3 M NH3–MeCN solvent. Prolonged (>5 h) controlled potential electrolysis (CPE) reveals the stability and robustness of the catalyst under electrocatalytic conditions. Detailed mechanistic investigations indicate that electrochemical oxidation of [CuI]-NH3 forms {[CuII]-NH3}+ (4), which undergoes deprotonation by excess NH3 to form reactive copper(II)–amide ([CuII]-NH2, 6) unstable toward N–N bond formation to give the dinuclear hydrazine complex [CuI]2(μ-N2H4). Electrochemical studies reveal that the diammine complex [CuI](NH3)2 (7) forms at high ammonia concentration as part of the {[CuII](NH3)2}+/[CuI](NH3)2 redox couple that is electrocatalytically inactive. DFT analysis reveals a much higher thermodynamic barrier for deprotonation of the four-coordinate {[CuII](NH3)2}+ (8) by NH3 to give the copper(II) amide [CuII](NH2)(NH3) (9) (ΔG = 31.7 kcal/mol) as compared to deprotonation of the three-coordinate {[CuII]-NH3}+ by NH3 to provide the reactive three-coordinate parent amide [CuII]-NH2 (ΔG = 18.1 kcal/mol) susceptible to N–N coupling to form [CuI]2(μ-N2H4) (ΔG = −11.8 kcal/mol).

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“…The field has been appreciably enriched with the recent contributions reporting two Fe complexes based on the N4 polypyridyl type of ligands [Fe(TPA)(NH 3 ) 2 ] 2+ and [(bpyPy 2 Me)Fe(MeCN) 2 ] , (Table , entries 6–7) reaching TONs of ≈150, with relatively high E app , in the range of 0.85 to 1.10 V vs Fc +/0 , which implies an overpotential of ≈1.6 to 1.9 V for AO ( E o = −0.81 V vs Fc +/0 ). Cu complexes with β-diketiminato and 2-[(2,2′-bipyridin)-6-yl]propan-2-ol ligands have also been reported to be active for AO. The former has been shown to oxidize NH 3 to N 2 in acetonitrile at an E app = 0.0 V vs Fc +/0 with a TON of 18.2 over 26.5 h (Table , entry 9) …”

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Heterogeneous Electrochemical Ammonia Oxidation with a Ru-bda Oligomer Anchored on Graphitic Electrodes via CH−π Interactions

et al. 2022

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Molecular catalysts can promote ammonia oxidation, providing mechanistic insights into the electrochemical N 2 cycle for a carbon-free fuel economy. We report the ammonia oxidation activity of carbon anodes functionalized with the oligomer {[Ru II (bda-κ-N 2 O 2 )(4,4′bpy)] 10 (4,4′-bpy)}, Rubda-10, where bda is [2,2′-bipyridine]-6,6′dicarboxylate and 4,4′-bpy is 4,4′-bipyridine. Electrocatalytic studies in propylene carbonate demonstrate that the Ru-based hybrid anode used in a 3-electrode configuration transforms NH 3 to N 2 and H 2 in a 1:3 ratio with near-unity faradaic efficiency at an applied potential of 0.1 V vs Fc +/0 , reaching turnover numbers of 7500. X-ray absorption spectroscopic analysis after bulk electrolysis confirms the molecular integrity of the catalyst. Based on computational studies together with electrochemical evidence, ammonia nucleophilic attack is proposed as the primary pathway that leads to critical N−N bond formation.

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Electrocatalytic, Homogeneous Ammonia Oxidation in Water to Nitrate and Nitrite with a Copper Complex

Cited by 60 publications

References 24 publications

Electrochemical Ammonia Oxidation with Molecular Catalysts

Electrochemical Ammonia Oxidation with Molecular Catalysts

Electrocatalytic Ammonia Oxidation by a Low-Coordinate Copper Complex

Heterogeneous Electrochemical Ammonia Oxidation with a Ru-bda Oligomer Anchored on Graphitic Electrodes via CH−π Interactions

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