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Title: Fe and Ni Dopants Facilitating Ammonia Synthesis on Mn4N and Mechanistic Insights from First-Principles Methods

Abstract

Cyclic step-catalysis enables intermittent, atmospheric ammonia production, and can be integrated with sustainable and renewable energy sources. By employing metal (e.g., Mn) nitride, a nitrogen carrier, the rate-limiting N2 activation step is bypassed. In this work, molecular-level pathways, describing the reduction of Mn4N by dissociatively adsorbed hydrogen, were investigated using periodic density functional theory (DFT). The established mechanism confirmed that Fe and Ni doped in the nitride sublayer and top layer can disturb local electronic structures and be exploited to tune the ammonia production activity. The strength of N–M (M = Mn, Fe, Ni) and H–M bonds both determine the overall reduction thermochemistry. DFT-based modeling further showed that the low concentration of Fe or Ni in the Mn4N sublayer facilitates N diffusion by lowering the diffusion energy barrier. Also, these heteroatom dopant species, particularly Ni, decrease the reduction endergonicity, thanks to the strong hydrogen binding with the surface Ni dopant. The Brønsted–Evans–Polanyi relationship and linear scaling relationships have been developed to reveal ammonia evolution kinetic and energetic trends for a series of idealized Fe- and Ni-doped Mn4N. Finally, deviations from the linear scaling relationship have been observed for certain doped systems, indicating potentially more complex behaviors of metal nitrides andmore » intriguing promises for greater ammonia synthesis materials design opportunities.« less

Authors:
ORCiD logo [1];  [2]; ORCiD logo [3]; ORCiD logo [1]
  1. Kansas State Univ., Manhattan, KS (United States). Dept. of Chemical Engineering
  2. Kansas State Univ., Manhattan, KS (United States). Dept. of Chemistry
  3. Kansas State Univ., Manhattan, KS (United States). Dept. of Chemical Engineering; Washington State Univ., Pullman, WA (United States). Dept. of Chemical Engineering and Bioengineering
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1483687
Grant/Contract Number:  
FOA-0001572; AC02-06CH11357; AC02-05CH11231
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 122; Journal Issue: 11; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Shan, Nannan, Chikan, Viktor, Pfromm, Peter, and Liu, Bin. Fe and Ni Dopants Facilitating Ammonia Synthesis on Mn4N and Mechanistic Insights from First-Principles Methods. United States: N. p., 2018. Web. doi:10.1021/acs.jpcc.7b12569.
Shan, Nannan, Chikan, Viktor, Pfromm, Peter, & Liu, Bin. Fe and Ni Dopants Facilitating Ammonia Synthesis on Mn4N and Mechanistic Insights from First-Principles Methods. United States. doi:10.1021/acs.jpcc.7b12569.
Shan, Nannan, Chikan, Viktor, Pfromm, Peter, and Liu, Bin. Mon . "Fe and Ni Dopants Facilitating Ammonia Synthesis on Mn4N and Mechanistic Insights from First-Principles Methods". United States. doi:10.1021/acs.jpcc.7b12569. https://www.osti.gov/servlets/purl/1483687.
@article{osti_1483687,
title = {Fe and Ni Dopants Facilitating Ammonia Synthesis on Mn4N and Mechanistic Insights from First-Principles Methods},
author = {Shan, Nannan and Chikan, Viktor and Pfromm, Peter and Liu, Bin},
abstractNote = {Cyclic step-catalysis enables intermittent, atmospheric ammonia production, and can be integrated with sustainable and renewable energy sources. By employing metal (e.g., Mn) nitride, a nitrogen carrier, the rate-limiting N2 activation step is bypassed. In this work, molecular-level pathways, describing the reduction of Mn4N by dissociatively adsorbed hydrogen, were investigated using periodic density functional theory (DFT). The established mechanism confirmed that Fe and Ni doped in the nitride sublayer and top layer can disturb local electronic structures and be exploited to tune the ammonia production activity. The strength of N–M (M = Mn, Fe, Ni) and H–M bonds both determine the overall reduction thermochemistry. DFT-based modeling further showed that the low concentration of Fe or Ni in the Mn4N sublayer facilitates N diffusion by lowering the diffusion energy barrier. Also, these heteroatom dopant species, particularly Ni, decrease the reduction endergonicity, thanks to the strong hydrogen binding with the surface Ni dopant. The Brønsted–Evans–Polanyi relationship and linear scaling relationships have been developed to reveal ammonia evolution kinetic and energetic trends for a series of idealized Fe- and Ni-doped Mn4N. Finally, deviations from the linear scaling relationship have been observed for certain doped systems, indicating potentially more complex behaviors of metal nitrides and intriguing promises for greater ammonia synthesis materials design opportunities.},
doi = {10.1021/acs.jpcc.7b12569},
journal = {Journal of Physical Chemistry. C},
number = 11,
volume = 122,
place = {United States},
year = {2018},
month = {2}
}

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Figures / Tables:

Figure 1 Figure 1: (a) Optimized bulk structure of the Mn4N phase of manganese nitride, two types of Mn atoms (I) and (II) are labelled. The lattice parameter of the cubic conventional cell is indicated. (b) The top (upper) and side (lower) views of N-terminated Mn4N close-packed (111) surface. Mn and Nmore » are in magenta and blue, respectively. Black lines represent the periodic boundaries of the p(1x1) unit cell of the Mn4N (111) facet.« less

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Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.