Kinetic and deuterium isotope analyses of ammonia electrochemical synthesis

Li, Chien-I; Matsuo, Hiroki; Otomo, Junichiro

doi:10.1039/d1ra00190f

Cited by 4 publications

(3 citation statements)

References 40 publications

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“…However, much of the mechanism remains unclear, especially in the specific scope of ammonia synthesis. Based on results from an isotopic analysis, our group proposed that protons conducted via the electrolyte aid N2 dissociation, but that the subsequent nitrogen hydrogenation steps occur using gaseous H2 fed into the cathode side (7)(8).…”

Section: Introductionmentioning

confidence: 99%

Iron-Based Electrode Structures for Ammonia Electrosynthesis Cells with Proton-Conducting Ceramic Electrolytes

Okazaki¹,

Otomo²

2022

ECS Trans.

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Ammonia electrosynthesis was conducted using proton-conducting ceramic electrolysis cells in a single chamber supplied with mixed N2 and H2, to determine the active electrode regions for the electrochemical promotion of catalysis (EPOC). Cells with Fe-based cathodes of either a metal, cermet, or mixed ionic-electronic conductor (MIEC) structure were compared, to assess whether the triple-phase boundaries (TPBs) or the Fe catalyst surfaces are more effective for ammonia synthesis. Upon cathodic polarization at 600˚C, high ammonia formation rates on the order of 10−8 mol s−1 cm−2 were obtained with both Fe metal and Fe-BaZr0.8Y0.2O3 (Fe-BZY) cermet cathodes. Comparisons of the three electrode structures suggest that when H2 is also supplied to the cathode, ammonia formation occurring on bulk Fe surfaces leads to a greater promotional effect than that at TPBs. There also remains a possibility that the interfacial layer formed at the cathode-electrolyte interface due to cation interdiffusion aids ammonia formation.

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Section: Introductionmentioning

confidence: 99%

Iron-Based Electrode Structures for Ammonia Electrosynthesis Cells with Proton-Conducting Ceramic Electrolytes

Okazaki¹,

Otomo²

2022

ECS Trans.

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“…Here, as the proton flux through the electrolyte does not appear to be the rate-limiting factor for ammonia formation, we assume that the reaction is closer to a catalytic reaction and consider the dissociative mechanism hereon. Indeed, our group previously showed using deuterium isotopic analysis that most of the hydrogen atoms that constitute the produced ammonia are from the cathode gas feed . In the dissociative mechanism, the dissociation of the N 2 triple bond (step 2) has been shown to be the rate-limiting step .…”

Section: Results and Discussionmentioning

confidence: 99%

“…Indeed, our group previously showed using deuterium isotopic analysis that most of the hydrogen atoms that constitute the produced ammonia are from the cathode gas feed. 33 In the dissociative mechanism, the dissociation of the N 2 triple bond (step 2) has been shown to be the rate-limiting step. 31 Adequately high temperatures are typically required for bond dissociation; however, the dissociation can be aided electrochemically as well.…”

Section: Results and Discussionmentioning

confidence: 99%

Electrode-Supported Protonic Ceramic Electrolysis Cells for Electrochemically Promoted Ammonia Synthesis at Intermediate Temperatures

Okazaki,

Otomo

2023

ACS Omega

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Protonic ceramic electrolysis cells (PCECs) have attracted attention for their applications in electrochemical ammonia synthesis, but their low Faradaic efficiency and thermodynamic constraints at high operating temperatures have led to low ammonia formation rates. In this work, electrode-supported PCECs with a noble-metal-free Ni-BaZr0.8Y0.2O3−δ cathode and a spin-coated proton-conducting electrolyte were developed for ammonia electrosynthesis, conducted in a single-chamber reactor cofed with N2 and H2. Ammonia formation rates increased non-Faradaically with applied voltage, reaching up to 1.1 × 10–8 mol s–1 cm–2 at 400 °C, which corresponds approximately to a 150 °C reduction in operating temperature compared to previously reported works conducted in mixed N2 and H2. The improved performance at intermediate temperatures by using a Ni catalyst is attributed to the electrochemical promotion of catalysis upon cathodic polarization. By fabrication of a cell with low Ohmic losses and improved contact resistance at the anode–electrolyte interface, sufficient cathodic polarization to accelerate ammonia formation was achieved, even at 400 °C. A combined water electrolysis and ammonia synthesis system is proposed, where the hydrogen byproduct from water electrolysis can be efficiently utilized via a recycling process; such a system requires enhanced ammonia formation in a mixed N2/H2 atmosphere, as demonstrated in this work.

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Hypes and hopes on the materials development strategies to produce ammonia at mild conditions

Singh

Mohammed

AlHammadi

et al. 2023

International Journal of Hydrogen Energy

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Kinetic and deuterium isotope analyses of ammonia electrochemical synthesis

Abstract: Electrochemical promotion of ammonia formation is mainly governed by surface reaction with N2 and H2 in the cathode.

Cited by 4 publications

References 40 publications

Iron-Based Electrode Structures for Ammonia Electrosynthesis Cells with Proton-Conducting Ceramic Electrolytes

Iron-Based Electrode Structures for Ammonia Electrosynthesis Cells with Proton-Conducting Ceramic Electrolytes

Electrode-Supported Protonic Ceramic Electrolysis Cells for Electrochemically Promoted Ammonia Synthesis at Intermediate Temperatures

Hypes and hopes on the materials development strategies to produce ammonia at mild conditions

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