Determining the hydronium pKα at platinum surfaces and the effect on pH-dependent hydrogen evolution reaction kinetics
Abstract
Electrocatalytic hydrogen evolution reaction (HER) is critical for green hydrogen generation and exhibits distinct pH-dependent kinetics that have been elusive to understand. A molecular-level understanding of the electrochemical interfaces is essential for developing more efficient electrochemical processes. Here we exploit an exclusively surface-specific electrical transport spectroscopy (ETS) approach to probe the Pt-surface water protonation status and experimentally determine the surface hydronium pKa = 4.3. Quantum mechanics (QM) and reactive dynamics using a reactive force field (ReaxFF) molecular dynamics (RMD) calculations confirm the enrichment of hydroniums (H3O+*) near Pt surface and predict a surface hydronium pKa of 2.5 to 4.4, corroborating the experimental results. Importantly, the observed Pt-surface hydronium pKa correlates well with the pH-dependent HER kinetics, with the protonated surface state at lower pH favoring fast Tafel kinetics with a Tafel slope of 30 mV per decade and the deprotonated surface state at higher pH following Volmer-step limited kinetics with a much higher Tafel slope of 120 mV per decade, offering a robust and precise interpretation of the pH-dependent HER kinetics. These insights may help design improved electrocatalysts for renewable energy conversion.
Additional Information
© 2022 the Author(s). Published by PNAS. This article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND). X.D. acknowledges support from NSF Award 1800580. Y.H. acknowledges the gracious support by NewHydrogen, Inc. W.A.G. received support from the Liquid Sunlight Alliance, which is supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Fuels from Sunlight Hub under Award DE-SC0021266. T.C. acknowledges support from the National Natural Science Foundation of China (21903058 and 22173066),the Natural Science Foundation of Jiangsu Higher Education Institutions(BK20190810), and the Priority Academic Program Development of Jiangsu Higher Education Institutions and partial support from the Collaborative Innovation Center of Suzhou NanoScience & Technology. Portions of this paper were used in the PhD thesis of G.Z. DATA, MATERIALS, AND SOFTWARE AVAILABILITY. All study data are included in the article and/or SI Appendix. The authors declare no competing interest.Attached Files
Published - pnas.202208187.pdf
Supplemental Material - pnas.2208187119.sapp.pdf
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Additional details
- PMCID
- PMC9522355
- Eprint ID
- 117364
- Resolver ID
- CaltechAUTHORS:20221011-984569000.2
- CHE-1800580
- NSF
- DE-SC0021266
- Department of Energy (DOE)
- 21903058
- National Natural Science Foundation of China
- 22173066
- National Natural Science Foundation of China
- BK20190810
- Natural Science Foundation of Jiangsu Province
- Priority Academic Program Development of Jiangsu Higher Education Institutions
- Collaborative Innovation Center of Suzhou NanoScience & Technology
- NewHydrogen, Inc.
- Created
-
2022-10-12Created from EPrint's datestamp field
- Updated
-
2023-07-21Created from EPrint's last_modified field
- Caltech groups
- Liquid Sunlight Alliance
- Other Numbering System Name
- WAG
- Other Numbering System Identifier
- 1539