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Partial oxidation of Step-Bound Water Leads to Anomalous pH Effects on Metal Electrode Step-Edges | | Kathleen Schwarz
; Bingjun Xu
; Yushan Yan
; Ravishankar Sundararaman
; | | Date: |
Mon, 2 May 2016 16:30:42 GMT (1874kb,D) | | Abstract: | 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 the change in net surface charge due to
this water explains the anomalous pH variations of the hydrogen underpotential
deposition (Hupd) 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. | | Source: | arXiv, 1605.0550 | | Services: | Forum | Review | PDF | Favorites | |
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