Abstract
Based on a mean-field description of thermodynamic cyclic voltammograms (CVs), we analyze here in full generality, how CV peak positions and shapes are related to the underlying interface energetics, in particular when also including electrostatic double layer (DL) effects. We show in particular, how non-Nernstian behaviour is related to capacitive DL charging, and how this relates to common adsorbate-centered interpretations such as a changed adsorption energetics due to dipole-field interactions and the electrosorption valency – the number of exchanged electrons upon electrosorption per adsorbate. Using Ag(111) in halide-containing solutions as test case, we demonstrate that DL effects can introduce peak shifts that are already explained by rationalizing the interaction of isolated adsorbates with the interfacial fields, while alterations of the peak shape are mainly driven by the coverage-dependence of the adsorbate dipoles. In addition, we analyze in detail how changing the experimental conditions such as the ion concentrations in the solvent but also of the background electrolyte can affect the CV peaks via their impact on the potential drop in the DL and the DL capacitance, respectively. These results suggest new routes to analyze experimental CVs and use of those for a detailed assessment of the accuracy of atomistic models of electrified interfaces e.g. with and without explicitly treated interfacial solvent and/or approximate implicit solvent models.
Highlights
Cyclic voltammetry is a standard experimental technique for studying electrochemical interfaces that allows to infer surface compositions and interface reactions as a function of the applied electrode potential
Based on a mean-field description of thermodynamic cyclic voltammograms (CVs), we analyse here in full generality, how CV peak positions and shapes are related to the underlying interface energetics, in particular when including electrostatic double layer (DL) effects
Using Ag(111) in halidecontaining solutions as test case, we demonstrate that DL effects can introduce peak shifts that are already explained by rationalizing the interaction of isolated adsorbates with the interfacial fields, while alterations of the peak shape are mainly driven by the coverage-dependence of the adsorbate dipoles
Summary
Cyclic voltammetry is a standard experimental technique for studying electrochemical interfaces that allows to infer surface compositions and interface reactions as a function of the applied electrode potential. At low scan rates and in potential windows without faradaic side reactions this asymmetry typically vanishes as does the scan-rate dependence (when currents are appropriately normalized) In this case, CV peak positions and shapes are related directly to the underlying thermodynamics of the electrified interface [3], and such CV experiments provide invaluable contributions to the understanding of the latter. The derived equations can naturally explain Non-Nernstian behaviour and introduce a sensitive dependence of CV peaks to the electrolyte, via its impact on the interfacial capacitance [17, 18] We hope, these results might help in the future to better understand according experiments and help to validate and improve theoretical models. Peak positions and shapes, can be affected in a non-trivial way by the ion concentrations in solution as well as the electrolyte composition, and estimate according effects for halide solutions and selected metallic electrodes based on theoretical density functional theory (DFT) calculations
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