Cation-Surface Interactions During Electrocatalytic Hydrogen Evolution Probed by Surface X-ray Diffraction

ACS Physical Chemistry Au, vol. 6, pp. 503–513

Abstract

High Resolution Image Download MS PowerPoint Slide The electrocatalytic production of hydrogen is pivotal for the sustainable generation of hydrogen fuel and hydrogen as reducing agent. Metal cations in alkaline electrolytes can facilitate or significantly impede this reaction, depending on electrolyte pH, catalyst surface, cation identity, and concentration. Still, the underlying mechanisms governing these effects remain elusive, in part due to the lack of direct characterization of how cations interact with the electrocatalyst surface and interfacial water. Here, using Surface X-ray Diffraction combined with ab initio Molecular Dynamics, we elucidate the formation of a cation layer at the electrochemical interface during hydrogen evolution on a hexagonally reconstructed Au(100) model catalyst under varying pH, potential, cation concentration, and electrolyte composition. Specular Crystal Truncation Rod measurements show that as the potential becomes more negative, Cs + cations increase in surface coverage and move progressively closer to the interface, revealing that the positions of the inner- and outer-Helmholtz planes continuously shift with potential. Slightly smaller cation-to-surface distances and higher coverages are observed in alkaline media compared to acidic environments. Ab initio Molecular Dynamics simulations reveal that the Cs + ions move into the first water layer as they approach the surface at more negative potentials. No water molecules can then reside between the ions and the Au surface, leading to a broken solvation symmetry and an opening angle. This opening is initially established by an orientation and slight distortion of the solvation shell, while at shorter ion-surface distances the ion sheds ∼10% of its solvation, enabling a closer approach to the surface. Finally, in Li + /Cs + electrolyte mixtures at pH 3, we observe the preferential accumulation of Cs + at the electrochemical interface, albeit in a more disordered fashion compared to the Li + -free situation. This is expected to enhance interfacial mobility and influence electrocatalytic activity beyond traditional “structure making/breaking” descriptions.

Authors 13

1. Mariana C. O. Monteiro corresponding Aachen Leiden Institute of Chemistry

   Leiden University · Fritz Haber Institute of the Max Planck Society

   Affiliation as printed

   Department of Interface Science, Fritz-Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany

   Leiden Institute of Chemistry

   Leiden University

2. Leon Jacobse

   Fritz Haber Institute of the Max Planck Society · Deutsches Elektronen-Synchrotron DESY

   Affiliation as printed

   Centre for X-ray and Nano Science CXNS, Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, D-22607 Hamburg, Germany

   Department of Interface Science, Fritz-Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany

3. Arthur M. V. Hagopian Aachen Leiden Institute of Chemistry

   Leiden University

   Affiliation as printed

   Leiden Institute of Chemistry

   Leiden University

4. Vedran Vonk

   Deutsches Elektronen-Synchrotron DESY

   Affiliation as printed

   Centre for X-ray and Nano Science CXNS, Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, D-22607 Hamburg, Germany

5. Simon Chung

   Deutsches Elektronen-Synchrotron DESY · Rice University

   Affiliation as printed

   Centre for X-ray and Nano Science CXNS, Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, D-22607 Hamburg, Germany

   Electrical and Computer Engineering, Rice University, 6100 Main Street, Houston, Texas 77005, United States

6. Sheena Louisia Aachen Leiden Institute of Chemistry

   Leiden University

   Affiliation as printed

   Leiden Institute of Chemistry

   Leiden University

7. Alexander Meinhardt

   Deutsches Elektronen-Synchrotron DESY

   Affiliation as printed

   Centre for X-ray and Nano Science CXNS, Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, D-22607 Hamburg, Germany

8. Elif Öykü Alagöz

   Fritz Haber Institute of the Max Planck Society

   Affiliation as printed

   Department of Interface Science, Fritz-Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany

9. Xin Deng

   Deutsches Elektronen-Synchrotron DESY

   Affiliation as printed

   Centre for X-ray and Nano Science CXNS, Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, D-22607 Hamburg, Germany

10. Beatriz Roldán Cuenya

    Fritz Haber Institute of the Max Planck Society

    Affiliation as printed

    Department of Interface Science, Fritz-Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany

11. Katharina Doblhoff-Dier corresponding Aachen Leiden Institute of Chemistry

    Leiden University

    Affiliation as printed

    Leiden Institute of Chemistry

    Leiden University

12. Marc T. M. Koper Aachen Leiden Institute of Chemistry

    Leiden University

    Affiliation as printed

    Leiden Institute of Chemistry

    Leiden University

13. Andreas Stierle

    Universität Hamburg · Deutsches Elektronen-Synchrotron DESY

    Affiliation as printed

    Centre for X-ray and Nano Science CXNS, Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, D-22607 Hamburg, Germany

    Fachbereich Physik, Universität Hamburg, Jungiusstraße 11, 20355 Hamburg, Germany