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Title: Temperature-Dependent Kinetics and Reaction Mechanism of Ammonia Oxidation on Pt, Ir, and PtIr Alloy Catalysts

Abstract

We report here a kinetic study of ammonia oxidation reaction (AOR) on carbon supported Pt, Ir, and PtIr (1:1) alloy catalysts using gas diffusion electrodes in 1 M KOH solution at temperatures up to 60°C. Ammonia concentration was kept constant by letting Ar gas bubbling through concentrated ammonia solution before entering the cell. At 0.5 V versus reversible hydrogen electrode, the currents normalized to the mass of platinum group metals are in the order of PtIr > Ir > Pt. Compared to Pt, Ir exhibited higher activity enhancement with increasing temperature, lower onset potential, and lower peak current. In correlation with previous theoretical studies, these differences are ascribed to Ir having lower activation barrier for the first one-electron deprotonation of NH3 to NH2*, but higher barrier for dimerization of two NH2* to N2H4*. The AOR current peaks at high potentials because the rate is limited by the potential-independent dimerization and formation of inactive N* that blocks the active surface. Below peak potentials, gradual deactivation occurs due to the accumulation of NH* that is harder to be dimerized than NH2*. PtIr alloy combines the virtues of Ir and Pt exhibiting the widest active potential window and the highest peak current.

Authors:
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Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences, and Biosciences Division; USDOE Advanced Research Projects Agency - Energy (ARPA-E)
OSTI Identifier:
1471769
Alternate Identifier(s):
OSTI ID: 1473653
Report Number(s):
BNL-209062-2018-JAAM
Journal ID: ISSN 0013-4651; /jes/165/15/J3095.atom
Grant/Contract Number:  
AR0000805; SC0012704
Resource Type:
Published Article
Journal Name:
Journal of the Electrochemical Society
Additional Journal Information:
Journal Name: Journal of the Electrochemical Society Journal Volume: 165 Journal Issue: 15; Journal ID: ISSN 0013-4651
Publisher:
The Electrochemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 36 MATERIALS SCIENCE; Ammonia oxidation; DAFC; Electrocatalysis

Citation Formats

Song, Liang, Liang, Zhixiu, Ma, Zhong, Zhang, Yu, Chen, Jingyi, Adzic, Radoslav R., and Wang, Jia X. Temperature-Dependent Kinetics and Reaction Mechanism of Ammonia Oxidation on Pt, Ir, and PtIr Alloy Catalysts. United States: N. p., 2018. Web. doi:10.1149/2.0181815jes.
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Song, Liang, Liang, Zhixiu, Ma, Zhong, Zhang, Yu, Chen, Jingyi, Adzic, Radoslav R., & Wang, Jia X. Temperature-Dependent Kinetics and Reaction Mechanism of Ammonia Oxidation on Pt, Ir, and PtIr Alloy Catalysts. United States. https://doi.org/10.1149/2.0181815jes
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Song, Liang, Liang, Zhixiu, Ma, Zhong, Zhang, Yu, Chen, Jingyi, Adzic, Radoslav R., and Wang, Jia X. Thu . "Temperature-Dependent Kinetics and Reaction Mechanism of Ammonia Oxidation on Pt, Ir, and PtIr Alloy Catalysts". United States. https://doi.org/10.1149/2.0181815jes.
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@article{osti_1471769,
title = {Temperature-Dependent Kinetics and Reaction Mechanism of Ammonia Oxidation on Pt, Ir, and PtIr Alloy Catalysts},
author = {Song, Liang and Liang, Zhixiu and Ma, Zhong and Zhang, Yu and Chen, Jingyi and Adzic, Radoslav R. and Wang, Jia X.},
abstractNote = {We report here a kinetic study of ammonia oxidation reaction (AOR) on carbon supported Pt, Ir, and PtIr (1:1) alloy catalysts using gas diffusion electrodes in 1 M KOH solution at temperatures up to 60°C. Ammonia concentration was kept constant by letting Ar gas bubbling through concentrated ammonia solution before entering the cell. At 0.5 V versus reversible hydrogen electrode, the currents normalized to the mass of platinum group metals are in the order of PtIr > Ir > Pt. Compared to Pt, Ir exhibited higher activity enhancement with increasing temperature, lower onset potential, and lower peak current. In correlation with previous theoretical studies, these differences are ascribed to Ir having lower activation barrier for the first one-electron deprotonation of NH3 to NH2*, but higher barrier for dimerization of two NH2* to N2H4*. The AOR current peaks at high potentials because the rate is limited by the potential-independent dimerization and formation of inactive N* that blocks the active surface. Below peak potentials, gradual deactivation occurs due to the accumulation of NH* that is harder to be dimerized than NH2*. PtIr alloy combines the virtues of Ir and Pt exhibiting the widest active potential window and the highest peak current.},
doi = {10.1149/2.0181815jes},
journal = {Journal of the Electrochemical Society},
number = 15,
volume = 165,
place = {United States},
year = {Thu Sep 20 00:00:00 EDT 2018},
month = {Thu Sep 20 00:00:00 EDT 2018}
}
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https://doi.org/10.1149/2.0181815jes
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