Heigo ERS1, Iuliia VOROSHYLOVA2, Liis SIINOR1, Piret PIKMA1, Vladislav IVANISTSEV1,3
1Institute of Chemistry, University of Tartu, Tartu, Estonia
2LAQV@REQUIMTE, Faculdade de Ciências, Universidade do Porto, Departamento de Química e Bioquímica, Porto, Portugal
3Department of Chemistry, University of Copenhagen, Copenhagen, Denmark
Ionic liquids are of fundamental interest, as their properties and composition differ from other common solvents. Long and short-range interactions between the ions give rise to the electrode’s charge overscreening, layered interfacial structure, and camel- or bell-shaped capacitance-potential dependence. Numerous present and potential applications have highlighted the significance of ionic liquids while establishing a better understanding of their characteristics is necessary for improving their design and contributing to exploitation in novel energy storage devices.
To shed light on the interfacial processes occurring during the charging of an electrical double layer capacitor, we have conducted molecular dynamics simulations, which offer an atomic-scale insight into the ionic liquid’s interfacial structure. We have focused on analysing the capacitance-potential dependence to draw parallels between simulations and experimental results. The results of the simulations have given an insight into the dependence of capacitance on the temperature, electrode’s charge plane position, and potential scan direction, along with the reasons behind the occurrence of capacitance peaks.
Furthermore, we have also developed a bilayer interfacial model for describing the characteristic features of the capacitance-potential dependence and relating them to the interfacial structure changes. The given electrical double layer model uses the parameters of only two first ionic liquid layers to provide the estimate of interfacial capacitance and characterise the impact of different structural parameters on it. Although simplistic, this model helps describe the observed features of capacitance more systematically and provides practical for the analysis of capacitance-structure dependence.