jz7b02383_si_001.pdf (374.11 kB)
Electrochemical Capacitance of CO-Terminated Pt(111) Dominated by the CO–Solvent Gap
journal contribution
posted on 2017-10-17, 00:00 authored by Ravishankar Sundararaman, Marta C. Figueiredo, Marc T. M. Koper, Kathleen A. SchwarzThe distribution of electric fields
within the electrochemical double layer depends on both the electrode
and electrolyte in complex ways. These fields strongly influence chemical
dynamics in the electrode–electrolyte interface but cannot
be measured directly with submolecular resolution. We report experimental
capacitance measurements for aqueous interfaces of CO-terminated Pt(111).
By comparing these measurements with first-principles density functional
theory (DFT) calculations, we infer microscopic field distributions
and decompose contributions to the inverse capacitance from various
spatial regions of the interface. We find that the CO is strongly
electronically coupled to the Pt and that most of the interfacial
potential difference appears across the gap between the terminating
O and water and not across the CO molecule, as previously hypothesized.
This “gap capacitance” resulting from hydrophobic termination
lowers the overall capacitance of the aqueous Pt–CO interface
and makes it less sensitive to electrolyte concentration compared
to the bare metal.