Separating the Faradaic and Non-Faradaic Contributions to the Total Capacitance for Different Manganese Dioxide Phases

Six different phases of manganese dioxide have been examined to determine the different contributions made by double layer capacitance and pseudo-capacitive redox reactions (or diffusion limited processes) to the total charge storage. These processes were separated using a novel combination of step potential electrochemical spectroscopy (SPECS), in which the electrode is charged and discharged in a series of small (±25 mV) potential steps, combined with modelling of the current response to determine the different charge storage processes occurring at the electrode. The manganese dioxide phases were all cycled in 0.5 M Na2SO4 between 0.0-0.8 V (vs SCE). The results indicate that the different properties of the samples, such as crystal structure, surface area and porosity affect the relative contributions from the each charge storage process.