Elsevier

Nano Energy

Volume 68, February 2020, 104374
Nano Energy

Full paper
Understanding of nitrogen fixation electro catalyzed by molybdenum–iron carbide through the experiment and theory

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Highlights

A new Mo3Fe3C catalyst for electrocatalytic N2 reduction reaction (ENRR) is reported.

The prepared catalyst shows a faraday efficiency of 27% for N2 reduction to NH3.

Electron transfer in ENRR is explored by Fourier-transformed alternating current voltammetry.

The synergistic effect of the Mo–Fe site is revealed by density functional theory calculations.

Abstract

The electrochemical method is considered being a sustainable alternative to the industrial Haber-Bosch process (150–350 atm, 350–550 °C) because it can produce ammonia (NH3) from nitrogen (N2) and water (H2O) at room temperature and pressure. However, since the N≡N triple bond in N2 is one of the strongest bonds in nature, it requires a more negative potential for N2 reduction, which often leads to violent hydrogen evolution reaction (HER) in aqueous electrolysis systems. Therefore, it is a great challenge for the electrocatalytic N2 reduction reaction (ENRR) to find catalysts that can reduce the energy barrier of N2 fixation and inhibit the HER. Herein, inspired by the Mo–Fe site in the biological nitrogenase, we found that the catalyst containing Mo3Fe3C active material has excellent N2-fixing catalytic performance and can effectively inhibit the HER. At −0.05 V vs RHE, the Faraday efficiency (FE) of ENRR was as high as 27.0%. In addition, we innovatively used the Fourier-transformed alternating current voltammetry (FTACV) to explore the electron transfer process in ENRR, indicating that Mo3Fe3C is more conducive to reducing N2 at low potential. According to density functional theory (DFT) calculations, compared with Mo2C and Fe3C, Mo3Fe3C is more helpful in promoting N2 activation and hydrogenation. Due to the synergistic effect of the Mo–Fe site, N2 hydrogenation needs to overcome a lower energy barrier in potential-determining step (PDS). Our research extends the knowledge into bimetallic active sites in ENRR and provides a new insight for the subsequent synthesis of high selectivity catalysts.

Keywords

Nitrogen electroreduction
Electrocatalysis
Molybdenum-iron carbide
DFT calculation
Catalytic mechanism
Energy conversion

Binhao Qin received his M.S. degree (2018) in Industrial Catalysis from South China University of Technology, and he is currently a Ph.D. degree student in School of Chemistry and Chemical Engineering at South China University of Technology under the supervision of Prof. Feng Peng. His research has been focused on the application of electrochemical reactions to energy and environment.

Yuhang Li is currently a postdoctoral researcher in School of Chemistry at Sun Yat-sen University, China. He received his B.S. degree (2014) in Applied Chemistry and Ph.D. degree (2018) in Industrial Catalysis from South China University of Technology, under the supervision of Prof. Feng Peng. His researches are focused on the first principles calculations toward electrochemical reaction mechanism in energy conversion applications.

Qiao Zhang is an associate professor in School of Chemistry and Chemical Engineering at Guangzhou University. She received her B.S. degree in Applied Chemistry from Chang Jiang University in 2009 and her Ph.D. degree in Applied Chemistry from South China University of Technology in 2016. She did her postdoctoral work at Guangzhou Institute of Energy Conversion in 2016–2018. Her current research focuses on photocatalytic splitting of water and photocatalytic conversion of biomass.

Guangxing Yang received B.S. and M.S. degrees in Chemical Engineering from South China University of Technology, China. He received the Ph.D. degree in Chemical Engineering from University of New Hampshire-Durham, United States, in 2018. He is currently working at South China University of Technology as a postdoctoral researcher. He focuses on the electrooxidation of alcohols for fuel cells and CO2 conversion to valuable chemicals through electrochemistry and thermal chemistry.

Prof. Hong Liang received her B.S. degree (1984) in Organic Chemical Industry and received M.S degree (1987) and Ph.D. degree (2007) in Industrial Catalysis from South China University of Technology. She joined Guangzhou University in 1987 and was promoted to full professor of Chemical Engineering in 2005. Her research field is materials and catalysis for environment. She has contributed more than 50 peer-reviewed papers.

Prof. Feng Peng received his B.S. degree (1986) and M.S. degree (1990) in Chemical Engineering from Hunan University and his Ph.D. degree in Industrial Catalysis from South China University of Technology in 1996. His research field is nanomaterials and catalysis for energy and environment. He worked at South China University of Technology during 1996–2017. He is currently working in School of Chemistry and Chemical Engineering at Guangzhou University. He has contributed more than 280 peer-reviewed papers and 28 patents.

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These authors contributed equally to this work.

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