Double Layer at the Pt(111)–Aqueous Electrolyte Interface: Potential of Zero Charge and Anomalous Gouy–Chapman Screening

Abstract

We report, for the first time, the observation of a Gouy–Chapman capacitance minimum at the potential of zero charge of the Pt(111)‐aqueous perchlorate electrolyte interface. The potential of zero charge of 0.3 V vs. NHE agrees very well with earlier values obtained by different methods. The observation of the potential of zero charge of this interface requires a specific pH (pH 4) and anomalously low electrolyte concentrations (<10−3 m). By comparison to gold and mercury double‐layer data, we conclude that the diffuse double layer structure at the Pt(111)‐electrolyte interface deviates significantly from the Gouy–Chapman theory in the sense that the electrostatic screening is much better than predicted by purely electrostatic mean‐field Poisson–Boltzmann theory.

Unexpectedly High Capacitance of the Metal Nanoparticle/Water Interface: Molecular‐Level Insights into the Electrical Double Layer

“…This demonstrates capacitances significantly exceeding classical assumptions also for gold in aqueous electrolytes,b ut roughly half of the value measured for platinum. As imilar conclusion has been reached from recent cyclic voltammetry experiments performed by Koper et al [6] at macroscopic single crystal electrodes.T hey reported anomalously high capacitance values for platinum, and to al ower extent for gold single crystals.T he authors proposed that these capacitance enhancements resulted from increased ion accumulation in the Helmholtz layer beyond purely electrostatic considerations,w hich leads to an appreciably more efficient electrostatic screening of the surface charge than predicted by mean-field theories.M erging these previous results with our experimental findings,t hus,s uggests that high capacitances are not specific to NPs. In the following,w ee xamine the role of the water networks formed in contact with Pt and Au for possibly promoting increased ion concentrations in the Helmholtz layer by means of classical MD simulations (computational details can be found in Supporting Information and Figure S10).…”

Unexpectedly High Capacitance of the Metal Nanoparticle/Water Interface: Molecular‐Level Insights into the Electrical Double Layer

“…This demonstrates capacitances significantly exceeding classical assumptions also for gold in aqueous electrolytes,b ut roughly half of the value measured for platinum. As imilar conclusion has been reached from recent cyclic voltammetry experiments performed by Koper et al [6] at macroscopic single crystal electrodes.T hey reported anomalously high capacitance values for platinum, and to al ower extent for gold single crystals.T he authors proposed that these capacitance enhancements resulted from increased ion accumulation in the Helmholtz layer beyond purely electrostatic considerations,w hich leads to an appreciably more efficient electrostatic screening of the surface charge than predicted by mean-field theories.M erging these previous results with our…”

Water at charged interfaces

“…Au(111)-aqueous HClO 4 (pH 3) solution with added NaClO 4 (ionic strength <10 −1 M) also showed the same behaviour. In all these cases, the electrostatic screening of the surface charge is appreciably more efficient than that predicted by mean-field theories (overscreening) 93 .…”