Electrochemistry of ruthenium dioxide composite electrodes in diethylmethylammonium-triflate protic ionic liquid and its mixtures with acetonitrile

Ruthenium dioxide electrodes store charge via faradaic reactions involving proton exchange with the electrolyte, thereby achieving very high specific capacitance values that make it a very interesting material for electrochemical capacitors. We demonstrated earlier that these faradaic reactions occur for RuO2 in non-aqueous electrolytes based on protic ionic liquids, but the specific capacitance were limited due to the high degree of crystallinity of the material prepared in thin films by thermal decomposition. In order to increase the specific capacitance and to evaluate the impact of proton transport and transfer in high load electrodes, RuO2 was prepared by a conventional sol-gel route and used as the active material in a composite electrode to evaluate its electrochemical response in the protic ionic liquid diethymethylammonium-trifluoromethanesulfonate (DEMA-TfO). Cyclic voltammetry was carried out in the pure DEMA-TfO as well as in mixtures of the ionic liquid with acetonitrile. The results showed a significant impact of the electrolyte viscosity and conductivity at high potential scan rates and a limitation of the proton transfer rate at low scan rates. The specific capacitance can be improved at low scan rates by increasing temperature, reaching a value of 338 F/g at 120 °C with a 2 mV/s scan rate. This value is by far the highest reported for RuO2 in a non-aqeuous electrolyte.