Metal-organic framework-derived nitrogen-doped highly disordered carbon for electrochemical ammonia synthesis using N2 and H2O in alkaline electrolytes

Shreya Mukherjee; David A. Cullen; Stavros Karakalos; Kexi Liu; Hao Zhang; Shuai Zhao; Hui Xu; Karren L. More; Guofeng Wang; Gang Wu

doi:10.1016/j.nanoen.2018.03.059

Metal-organic framework-derived nitrogen-doped highly disordered carbon for electrochemical ammonia synthesis using N₂ and H₂O in alkaline electrolytes

Shreya Mukherjee, David A. Cullen, Stavros Karakalos, Kexi Liu, Hao Zhang, Shuai Zhao, Hui Xu, Karren L. More, Guofeng Wang, Gang Wu

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

416 Scopus citations

Abstract

Ammonia (NH₃) is considered an important chemical for both agriculture fertilizer and renewable energy. The conventional Haber-Bosh process to produce NH₃ is energy intensive and leads to significant CO₂ emission. Alternatively, electrochemical synthesis of ammonia (ESA) through the nitrogen reduction reaction (NRR) by using renewable electricity has recently attracted significant attention. Herein, we report a metal-organic framework-derived nitrogen-doped nanoporous carbon as an electrocatalyst for the NRR. It exhibits a remarkable production rate of NH₃ up to 3.4 × 10⁻⁶ mol cm⁻² h⁻¹ with a Faradaic efficiency (FE) of 10.2% at −0.3 V vs. RHE under room temperature and ambient pressure using aqueous 0.1 M KOH electrolyte. Increasing the temperature to 60 °C further improves production rates to 7.3 × 10⁻⁶ mol cm⁻² h⁻¹. The stability of the nitrogen-doped carbon electrocatalyst was demonstrated during an 18-h continuous test with constant production rates. First principles calculations were used to elucidate the possible active sites and reaction pathway. The moiety, which consists of three pyridinic N atoms (N₃) adjacent with one carbon vacancy embedded in a carbon layer, is able to strongly adsorb N₂ and further realize N≡N triple bond dissociation for the subsequent protonation process. The rate-determining step of the NRR is predicted to be the adsorption and bond activation of N₂ molecule. Increasing overpotentials is favorable for the protonation process during NH₃ generation. Further doping Fe into the nitrogen-doped carbon likely blocks the N₃ active sites and facilitates the hydrogen evolution reaction, a strong competitor to the NRR, thus yielding negative effect on ammonia production. This work provides a new insight into the rational design and synthesis of nitrogen-doped and defect-rich carbon as efficient NRR catalysts for NH₃ synthesis at ambient conditions.

Original language	English
Pages (from-to)	217-226
Number of pages	10
Journal	Nano Energy
Volume	48
DOIs	https://doi.org/10.1016/j.nanoen.2018.03.059
State	Published - Jun 2018

Funding

Guofeng Wang is currently an associate professor in the Department of Mechanical Engineering and Materials Science at the University of Pittsburgh. He receives his Ph.D. in Materials Science from California Institute of Technology. His research focuses on development and application of advanced computational methods for rational design of high-performance electrocatalysts with use in energy conversion and energy storage technologies. His research has been supported by National Science Foundation (NSF) and Department of Energy (DOE). He has published more than 80 journal articles, book chapters, and refereed conference proceedings. This work was financially supported by start-up funding from the University at Buffalo , SUNY along with U.S. Department of Energy 's Advanced Research Projects Agency-Energy (ARPA-E) office's REFUL program. Electron microscopy conducted at Oak Ridge National Laboratory's Center for Nanophase Materials Sciences, which is a U.S. Department of Energy, Office of Science User Facility. The computation were carried out on the computer facility at Center for Simulation and Modeling of the University of Pittsburgh and at the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1053575 .

Funders	Funder number
U.S. Department of Energy 's Advanced Research Projects Agency-Energy
National Science Foundation	ACI-1053575
U.S. Department of Energy
Advanced Research Projects Agency - Energy
State University of New York
University of Pittsburgh
University at Buffalo

Keywords

Electrocatalysis
First principle calculation
MOFs
NH synthesis
Nanocarbon

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

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10.1016/j.nanoen.2018.03.059

Cite this

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title = "Metal-organic framework-derived nitrogen-doped highly disordered carbon for electrochemical ammonia synthesis using N2 and H2O in alkaline electrolytes",

abstract = "Ammonia (NH3) is considered an important chemical for both agriculture fertilizer and renewable energy. The conventional Haber-Bosh process to produce NH3 is energy intensive and leads to significant CO2 emission. Alternatively, electrochemical synthesis of ammonia (ESA) through the nitrogen reduction reaction (NRR) by using renewable electricity has recently attracted significant attention. Herein, we report a metal-organic framework-derived nitrogen-doped nanoporous carbon as an electrocatalyst for the NRR. It exhibits a remarkable production rate of NH3 up to 3.4 × 10−6 mol cm−2 h−1 with a Faradaic efficiency (FE) of 10.2% at −0.3 V vs. RHE under room temperature and ambient pressure using aqueous 0.1 M KOH electrolyte. Increasing the temperature to 60 °C further improves production rates to 7.3 × 10−6 mol cm−2 h−1. The stability of the nitrogen-doped carbon electrocatalyst was demonstrated during an 18-h continuous test with constant production rates. First principles calculations were used to elucidate the possible active sites and reaction pathway. The moiety, which consists of three pyridinic N atoms (N3) adjacent with one carbon vacancy embedded in a carbon layer, is able to strongly adsorb N2 and further realize N≡N triple bond dissociation for the subsequent protonation process. The rate-determining step of the NRR is predicted to be the adsorption and bond activation of N2 molecule. Increasing overpotentials is favorable for the protonation process during NH3 generation. Further doping Fe into the nitrogen-doped carbon likely blocks the N3 active sites and facilitates the hydrogen evolution reaction, a strong competitor to the NRR, thus yielding negative effect on ammonia production. This work provides a new insight into the rational design and synthesis of nitrogen-doped and defect-rich carbon as efficient NRR catalysts for NH3 synthesis at ambient conditions.",

keywords = "Electrocatalysis, First principle calculation, MOFs, NH synthesis, Nanocarbon",

author = "Shreya Mukherjee and Cullen, {David A.} and Stavros Karakalos and Kexi Liu and Hao Zhang and Shuai Zhao and Hui Xu and More, {Karren L.} and Guofeng Wang and Gang Wu",

note = "Publisher Copyright: {\textcopyright} 2018 Elsevier Ltd",

year = "2018",

month = jun,

doi = "10.1016/j.nanoen.2018.03.059",

language = "English",

volume = "48",

pages = "217--226",

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T1 - Metal-organic framework-derived nitrogen-doped highly disordered carbon for electrochemical ammonia synthesis using N2 and H2O in alkaline electrolytes

AU - Mukherjee, Shreya

AU - Cullen, David A.

AU - Karakalos, Stavros

AU - Liu, Kexi

AU - Zhang, Hao

AU - Zhao, Shuai

AU - Xu, Hui

AU - More, Karren L.

AU - Wang, Guofeng

AU - Wu, Gang

PY - 2018/6

Y1 - 2018/6

N2 - Ammonia (NH3) is considered an important chemical for both agriculture fertilizer and renewable energy. The conventional Haber-Bosh process to produce NH3 is energy intensive and leads to significant CO2 emission. Alternatively, electrochemical synthesis of ammonia (ESA) through the nitrogen reduction reaction (NRR) by using renewable electricity has recently attracted significant attention. Herein, we report a metal-organic framework-derived nitrogen-doped nanoporous carbon as an electrocatalyst for the NRR. It exhibits a remarkable production rate of NH3 up to 3.4 × 10−6 mol cm−2 h−1 with a Faradaic efficiency (FE) of 10.2% at −0.3 V vs. RHE under room temperature and ambient pressure using aqueous 0.1 M KOH electrolyte. Increasing the temperature to 60 °C further improves production rates to 7.3 × 10−6 mol cm−2 h−1. The stability of the nitrogen-doped carbon electrocatalyst was demonstrated during an 18-h continuous test with constant production rates. First principles calculations were used to elucidate the possible active sites and reaction pathway. The moiety, which consists of three pyridinic N atoms (N3) adjacent with one carbon vacancy embedded in a carbon layer, is able to strongly adsorb N2 and further realize N≡N triple bond dissociation for the subsequent protonation process. The rate-determining step of the NRR is predicted to be the adsorption and bond activation of N2 molecule. Increasing overpotentials is favorable for the protonation process during NH3 generation. Further doping Fe into the nitrogen-doped carbon likely blocks the N3 active sites and facilitates the hydrogen evolution reaction, a strong competitor to the NRR, thus yielding negative effect on ammonia production. This work provides a new insight into the rational design and synthesis of nitrogen-doped and defect-rich carbon as efficient NRR catalysts for NH3 synthesis at ambient conditions.

AB - Ammonia (NH3) is considered an important chemical for both agriculture fertilizer and renewable energy. The conventional Haber-Bosh process to produce NH3 is energy intensive and leads to significant CO2 emission. Alternatively, electrochemical synthesis of ammonia (ESA) through the nitrogen reduction reaction (NRR) by using renewable electricity has recently attracted significant attention. Herein, we report a metal-organic framework-derived nitrogen-doped nanoporous carbon as an electrocatalyst for the NRR. It exhibits a remarkable production rate of NH3 up to 3.4 × 10−6 mol cm−2 h−1 with a Faradaic efficiency (FE) of 10.2% at −0.3 V vs. RHE under room temperature and ambient pressure using aqueous 0.1 M KOH electrolyte. Increasing the temperature to 60 °C further improves production rates to 7.3 × 10−6 mol cm−2 h−1. The stability of the nitrogen-doped carbon electrocatalyst was demonstrated during an 18-h continuous test with constant production rates. First principles calculations were used to elucidate the possible active sites and reaction pathway. The moiety, which consists of three pyridinic N atoms (N3) adjacent with one carbon vacancy embedded in a carbon layer, is able to strongly adsorb N2 and further realize N≡N triple bond dissociation for the subsequent protonation process. The rate-determining step of the NRR is predicted to be the adsorption and bond activation of N2 molecule. Increasing overpotentials is favorable for the protonation process during NH3 generation. Further doping Fe into the nitrogen-doped carbon likely blocks the N3 active sites and facilitates the hydrogen evolution reaction, a strong competitor to the NRR, thus yielding negative effect on ammonia production. This work provides a new insight into the rational design and synthesis of nitrogen-doped and defect-rich carbon as efficient NRR catalysts for NH3 synthesis at ambient conditions.

KW - Electrocatalysis

KW - First principle calculation

KW - MOFs

KW - NH synthesis

KW - Nanocarbon

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DO - 10.1016/j.nanoen.2018.03.059

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