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Partial oxidation of step-bound water leads to anomalous pH effects on metal electrode step-edges

Schwarz, Kathleen and Xu, Bingjun and Yan, Yushan and Sundararaman, Ravishankar (2016) Partial oxidation of step-bound water leads to anomalous pH effects on metal electrode step-edges. Physical Chemistry Chemical Physics, 18 (24). pp. 16216-16223. ISSN 1463-9076. doi:10.1039/c6cp01652a.

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The design of better heterogeneous catalysts for applications such as fuel cells and electrolyzers requires a mechanistic understanding of electrocatalytic reactions and the dependence of their activity on operating conditions such as pH. A satisfactory explanation for the unexpected pH dependence of electrochemical properties of platinum surfaces has so far remained elusive, with previous explanations resorting to complex co-adsorption of multiple species and resulting in limited predictive power. This knowledge gap suggests that the fundamental properties of these catalysts are not yet understood, limiting systematic improvement. Here, we analyze the change in charge and free energies upon adsorption using density-functional theory (DFT) to establish that water adsorbs on platinum step edges across a wide voltage range, including the double-layer region, with a loss of approximately 0.2 electrons upon adsorption. We show how this as-yet unreported change in net surface charge due to this water explains the anomalous pH variations of the hydrogen underpotential deposition (H_(upd)) and the potentials of zero total charge (PZTC) observed in published experimental data. This partial oxidation of water is not limited to platinum metal step edges, and we report the charge of the water on metal step edges of commonly used catalytic metals, including copper, silver, iridium, and palladium, illustrating that this partial oxidation of water broadly influences the reactivity of metal electrodes.

Item Type:Article
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URLURL TypeDescription
Xu, Bingjun0000-0002-2303-257X
Sundararaman, Ravishankar0000-0002-0625-4592
Additional Information:© 2016 the Owner Societies. Received 10th March 2016, Accepted 26th May 2016, First published online 26 May 2016. KAS thanks T. P. Moffat for helpful discussions. RS was supported by the Joint Center of Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award Number DE-SC0004993.
Funding AgencyGrant Number
Department of Energy (DOE)DE-SC0004993
Issue or Number:24
Record Number:CaltechAUTHORS:20160610-140536521
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Official Citation:Partial oxidation of step-bound water leads to anomalous pH effects on metal electrode step-edges Kathleen Schwarz, Bingjun Xu, Yushan Yan and Ravishankar Sundararaman Phys. Chem. Chem. Phys., 2016, Advance Article DOI: 10.1039/C6CP01652A
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:67847
Deposited By: Tony Diaz
Deposited On:10 Jun 2016 22:04
Last Modified:11 Nov 2021 03:55

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