Understanding the Electrochemistry of Ruthenium Complex Thin Films to Guide the Design of Improved Energy Storage Electrodes

Materials with fast charge transfer processes across electrochemical interfaces could exhibit a pseudocapacitive behavior, which is promising to achieve both high power and high energy density in energy storage devices. Therefore, the design of electrodes with highly exposed electroactive species and improved charge transport should lead to pseudocapacitive electrodes with high capacity at high rates. Herein, redox thin-film electrodes based on amphiphilic tri-ruthenium clusters are constructed and evaluated as energy storage electrodes. Cyclic voltammetry results are interpreted with the aid of a mathematical model, which describes the electrochemical response of layered films considering the stability of molecules and the charge transfer within the film. It is found that the interactions between tri-ruthenium cluster molecules within the film and the relatively fast electron transfer at the substrate/film interface lead to a wide redox peak with capacitive characteristics, achieving a specific capacitance of 204 F g–1 (1.02 mF cm2) for the electrode with 18 monolayers. However, the efficiency at high rates of thicker electrodes should be improved, and the model suggests that electron transfer at the substrate/film interface and the charge transport within the film are key factors to improving the energy storage efficiency at high rates in film electrodes.