Transition between electric double-layer and Faradaic charge storage phenomena at nanoconfined electrochemical interfaces

• Applicant: Dr. Simon Fleischmann
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation ; Solid State and Surface Chemistry, Material Synthesis
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 513327636

For decades, electrochemical charge storage processes have been separated into either electric double-layer capacitance or Faradaic redox reactions, depending on whether charges are separated or transferred, respectively, at the electrochemical interface. However, a blurring between the two mechanisms has been observed when the charge storage process takes place at a nanoconfined electrochemical interface, where spatial constraints for the electrolyte are in the order of the solvated ion size, around 1 nanometer. This manifests in novel electrochemical properties that combine characteristics of electric double-layer capacitance and Faradaic reactions. The origins of these processes - they are sometimes referred to as “pseudocapacitance” – are still unresolved. The main objective of this project is to create a fundamental understanding of electrochemical charge storage processes at nanoconfined interfaces. Model layered host electrode materials will be employed to study the impact of nanoconfinement geometry on the electrochemical process of lithium ion intercalation. The goal is to observe and understand whether charge storage phenomena can deviate in nanoconfinement from the strict binary of either electric double-layer capacitance or Faradaic reaction. The main hypothesis of this proposal is that there can be a continuous transition between double-layer capacitance and Faradaic charge storage phenomena based on the degree of solvation of the intercalated ions. It is expected that there exists a transition region in which ions are partially solvated and pseudocapacitive processes can occur. To experimentally analyze the hypothesis, the interlayer spacing of a model layered host material, TiS2, is varied via chemical functionalization approaches to systematically define the nanoconfinement environment in the interlayer space. It is hypothesized that larger interlayer spacings can lead to the electrochemical intercalation of more solvated ions, rather than fully desolvated ions, leading to a change of electrochemical properties. Diffraction and spectroscopic measurements during electrochemical cycling will provide information on the mechanistic origin as a function of the nanoconfinement environment. The results of the project will create fundamental understanding of electrochemical processes in nanoconfinement and provide design criteria for layered electrode materials which can exhibit pseudocapacitive charge storage properties. These are especially valuable for electrochemical intercalation reactions, as they offer a path towards combined high charge storage capacity with high power.

• DFG Programme: Research Grants