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Title: Electrochemical Hydrogen Evolution at Ordered Mo 7 Ni 7

Abstract

Ni–Mo alloys containing up to ~15 mol % Mo are excellent non-noble electrocatalysts for the hydrogen evolution reaction (HER) in alkaline aqueous electrolytes. To date, studies have not addressed the details of HER activity of ordered Ni–Mo intermetallic compounds, which can contain a significantly larger fraction of Mo (up to 50 mol %) than can be accessed through high-temperature alloying. Here, we present a straightforward and facile synthesis of three phase-pure electrocatalyst powders using a precipitation–reduction approach: ordered Mo7Ni7, disordered Ni0.92Mo0.08, and pure Ni. The Ni0.92Mo0.08 alloy exhibited a nearly 10-fold higher mass-specific HER activity than either pure Ni or Mo7Ni7, where much of the difference could be attributed to relative surface area. Therefore, we attempted to quantify and account for differences in surface areas using electron microscopy, impedance spectroscopy, and gas adsorption measurements. These data suggest that Ni–Mo alloys and intermetallic compounds exhibit substantial pseudocapacitance at potentials near the onset of hydrogen evolution, which can cause impedance spectroscopy to overestimate the interfacial capacitance, and thus the electrochemically active surface area, of these materials. From these observations, we postulate Mo redox activity as the chemical basis for the observed pseudocapacitance of Ni–Mo composites. Furthermore, using gas adsorption measurements, rather thanmore » capacitance, to estimate active surface area, we find that ordered Mo7Ni7 is more intrinsically active than the Ni0.92Mo0.08 alloy, implying that Mo7Ni7 intermetallics with high surface area will also give higher mass-specific activities than alloys with comparable roughness.« less

Authors:
 [1]; ORCiD logo [2]; ORCiD logo [3]; ORCiD logo [4];  [5];  [5]
  1. Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States
  2. Department of Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, United States
  3. Dow Electronic Materials, Marlborough Massachusetts 01752, United States
  4. Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
  5. Department of Chemistry and Chemical Biology, Cornell University, Ithaca New York 14853, United States
Publication Date:
Research Org.:
Energy Frontier Research Centers (EFRC) (United States). Energy Materials Center at Cornell (EMC2)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
1397225
DOE Contract Number:  
SC0001086
Resource Type:
Journal Article
Resource Relation:
Journal Name: ACS Catalysis; Journal Volume: 7; Journal Issue: 5; Related Information: Emc2 partners with Cornell University (lead); Lawrence Berkeley National Laboratory
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE

Citation Formats

Csernica, Peter M., McKone, James R., Mulzer, Catherine R., Dichtel, William R., Abruña, Héctor D., and DiSalvo, Francis J.. Electrochemical Hydrogen Evolution at Ordered Mo 7 Ni 7. United States: N. p., 2017. Web. doi:10.1021/acscatal.7b00344.
Csernica, Peter M., McKone, James R., Mulzer, Catherine R., Dichtel, William R., Abruña, Héctor D., & DiSalvo, Francis J.. Electrochemical Hydrogen Evolution at Ordered Mo 7 Ni 7. United States. doi:10.1021/acscatal.7b00344.
Csernica, Peter M., McKone, James R., Mulzer, Catherine R., Dichtel, William R., Abruña, Héctor D., and DiSalvo, Francis J.. Tue . "Electrochemical Hydrogen Evolution at Ordered Mo 7 Ni 7". United States. doi:10.1021/acscatal.7b00344.
@article{osti_1397225,
title = {Electrochemical Hydrogen Evolution at Ordered Mo 7 Ni 7},
author = {Csernica, Peter M. and McKone, James R. and Mulzer, Catherine R. and Dichtel, William R. and Abruña, Héctor D. and DiSalvo, Francis J.},
abstractNote = {Ni–Mo alloys containing up to ~15 mol % Mo are excellent non-noble electrocatalysts for the hydrogen evolution reaction (HER) in alkaline aqueous electrolytes. To date, studies have not addressed the details of HER activity of ordered Ni–Mo intermetallic compounds, which can contain a significantly larger fraction of Mo (up to 50 mol %) than can be accessed through high-temperature alloying. Here, we present a straightforward and facile synthesis of three phase-pure electrocatalyst powders using a precipitation–reduction approach: ordered Mo7Ni7, disordered Ni0.92Mo0.08, and pure Ni. The Ni0.92Mo0.08 alloy exhibited a nearly 10-fold higher mass-specific HER activity than either pure Ni or Mo7Ni7, where much of the difference could be attributed to relative surface area. Therefore, we attempted to quantify and account for differences in surface areas using electron microscopy, impedance spectroscopy, and gas adsorption measurements. These data suggest that Ni–Mo alloys and intermetallic compounds exhibit substantial pseudocapacitance at potentials near the onset of hydrogen evolution, which can cause impedance spectroscopy to overestimate the interfacial capacitance, and thus the electrochemically active surface area, of these materials. From these observations, we postulate Mo redox activity as the chemical basis for the observed pseudocapacitance of Ni–Mo composites. Furthermore, using gas adsorption measurements, rather than capacitance, to estimate active surface area, we find that ordered Mo7Ni7 is more intrinsically active than the Ni0.92Mo0.08 alloy, implying that Mo7Ni7 intermetallics with high surface area will also give higher mass-specific activities than alloys with comparable roughness.},
doi = {10.1021/acscatal.7b00344},
journal = {ACS Catalysis},
number = 5,
volume = 7,
place = {United States},
year = {Tue Apr 11 00:00:00 EDT 2017},
month = {Tue Apr 11 00:00:00 EDT 2017}
}