Herein the semiconducting nature of electrodeposited manganese dioxide (γ-MnO2) is examined for its effects on pseudo-capacitive electrode behaviour in neutral electrolytes. Electrochemical analysis of the manganese dioxide electrode is achieved using a combination of cyclic voltammetry (CV), step potential electrochemical spectroscopy (SPECS) and electrochemical impedance spectroscopy (EIS), in particular the combination of SPECS and EIS in a single experiment, enabling the determination of electronic properties across the full potential window. After establishing stable cycling with CV, electrode performance is examined using SPECS. EIS data, recorded under quasi-equilibrium conditions at the end of each potential step rest period, is then analyzed using the Mott-Schottky equation, leading to the identification of both n-type and p-type behaviour for the manganese dioxide electrode. Flat band potentials are determined (Vfb,n = −0.34 V vs SCE and Vfb,p = 0.98 V vs SCE), and conclusions about the electrochemically active surface area being more closed related to the geometric surface area were reached.
Herein the charge storage capabilities of a planar non-porous glassy carbon electrode (GCE) in electrolytes of aqueous 0.5 M Na2SO4 and 1 M tetraethylammonium tetrafluoroborate (TEABF4) in acetonitrile are compared using a combination of cyclic voltammetry (CV), step potential electrochemical spectroscopy (SPECS) and electrochemical impedance spectroscopy (EIS). In all techniques the resultant capacitance was substantially higher for the GCE in 1 M TEABF4 compared to 0.5 M Na2SO4, with the differences due to solvation of the adsorbing electrolyte ions. Adsorbing Na+ cations in the aqueous system have a substantial solvation sheath that increases the resistance associated with capacitive charge storage, decreases the capacitance, as well as inhibits the packing of similar electrolyte ions in the vicinity of the GCE. Conversely, the adsorbing BF4− ions in the acetonitrile-based electrolyte exhibit a low resistance to charge storage, a greatly enhanced capacitance, as well as exhibit an improved ability to pack at the electrode-electrolyte interface. The impact of this behaviour on electrode performance has also been discussed.
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