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Operando Phonon Studies of the Protonation Mechanism in Highly Active Hydrogen Evolution Reaction Pentlandite Catalysts

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Zendegani,  Ali
Computational Phase Studies, Computational Materials Design, Max-Planck-Institut für Eisenforschung GmbH, Max Planck Society;

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Körmann,  Fritz
Computational Phase Studies, Computational Materials Design, Max-Planck-Institut für Eisenforschung GmbH, Max Planck Society;

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Neugebauer,  Jörg
Computational Materials Design, Max-Planck-Institut für Eisenforschung GmbH, Max Planck Society;

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Hickel,  Tilmann
Computational Phase Studies, Computational Materials Design, Max-Planck-Institut für Eisenforschung GmbH, Max Planck Society;

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Roldan Cuenya,  Beatriz
Interface Science, Fritz Haber Institute, Max Planck Society;
Department of Physics, Ruhr-University Bochum, 44780 Bochum, Germany;

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Citation

Zegkinoglou, I., Zendegani, A., Sinev, I., Kunze, S., Mistry, H., Jeon, H. S., et al. (2017). Operando Phonon Studies of the Protonation Mechanism in Highly Active Hydrogen Evolution Reaction Pentlandite Catalysts. Journal of the American Chemical Society, 139(41), 14360-14363. doi:10.1021/jacs.7b07902.


Cite as: http://hdl.handle.net/11858/00-001M-0000-002E-2985-2
Abstract
Synthetic pentlandite (Fe4.5Ni4.5S8) is a promising.electrocatalyst for hydrogen evolution, demonstrating high current densities, low overpotential and remarkable stability in bulk form. The depletion of sulfur from the surface of this catalyst during the electrochemical reaction has been proposed to be beneficial for its catalytic performance, but the role of sulfur vacancies and the mechanism determining the reaction kinetics are still unknown. We have performed electrochemical operando studies of the vibrational dynamics of pentlandite under hydrogen evolution reaction conditions using 57Fe nuclear resonant inelastic Xray scattering. Comparing the measured partial (Feprojected) vibrational density of states with density functional theory calculations, we have demonstrated that hydrogen atoms preferentially occupy substitutional positions replacing pre-existing sulfur vacancies. Once all vacancies are filled, the protonation proceeds interstitially, which slows down the reaction. Our results highlight the beneficial role of sulfur vacancies in the electrocatalytic performance of pentlandite and give insights into the hydrogen adsorption mechanism during the reaction.