Electrochemical oxidation of CH4 is known to be inefficient in aqueous electrolytes. The lower activity of methane oxidation reaction (MOR) is primarily attributed to the dominant oxygen evolution reaction (OER) and the higher barrier for CH4 activation on transition metal oxides (TMOs). However, a satisfactory explanation for the origins of such lower activity of MOR on TMOs, along with the enabling strategies to partially oxidize CH4 to CH3OH, have not been developed yet. We report here the activation of CH4 is governed by a previously unrecognized consequence of electrostatic (or Madelung) potential of metal atom in TMOs. The measured binding energies of CH4 on 12 different TMOs scale linearly with the Madelung potentials of the metal in the TMOs. The MOR active TMOs are the ones with higher CH4 binding energy and lower Madelung potential. Out of 12 TMOs studied here, only TiO2, IrO2, PbO2, and PtO2 are active for MOR, where the stable active site is the O on top of the metal in TMOs. The reaction pathway for MOR proceeds primarily through *CHx intermediates at lower potentials and through *CH3OH intermediates at higher potentials. The key MOR intermediate *CH3OH is identified on TiO2 under operando conditions at higher potential using transient open-circuit potential measurement. To minimize the overoxidation of *CH3OH, a bimetallic Cu2O3 on TiO2 catalysts is developed, in which Cu reduces the barrier for the reaction of *CH3 and *OH and facilitates the desorption of *CH3OH. The highest faradaic efficiency of 6% is obtained using Cu-Ti bimetallic TMO.
|Original language||English (US)|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Feb 23 2021|
Bibliographical noteFunding Information:
ACKNOWLEDGMENTS. This material is based on the work performed in the Materials and Systems Engineering Laboratory at the University of Illinois at Chicago, in collaboration with Goodpaster Laboratory at the University of Minnesota. B.A.C. and J.D.G. acknowledge the Minnesota Supercomputing Institute at the University of Minnesota and the National Energy Research Scientific Computing Center, a Department of Energy (DOE) Office of Science User Facility supported by the Office of Science of the US DOE under Contract No. DE-AC02-05CH11231, for providing resources that contributed to the results reported within this paper. This work made use of the Electron Probe Instrumentation Center (EPIC) and Keck-II facility of North-western University’s Northwestern University Atomic and Nanoscale Characterization Experimental Center, which has received support from the Soft and Hybrid Nanotechnology Experimental Resource (NSF ECCS-1542205), the Institute of Integrative Nutrition, and Northwestern’s Materials Research Science and Engineering Center program (NSF DMR-1720139).
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- Binding energy measurement
- Density functional theory
- Electrochemical oxidation of methane
- Methanol synthesis
- Transient open-circuit potential
PubMed: MeSH publication types
- Journal Article