Suzana Sopčić

Anodic deposition of lead dioxide at Nafion covered gold electrode

Anodic electrodeposition of lead dioxide at the bare and Nafion® covered gold electrode was studied by cyclic voltammetry and chronoamperometry. The results showed that Nafion® layer has a favourable effect on the efficiency of the deposition process which was caused by both thermodynamic and kinetic reasons. Electrodeposition process at Nafion® covered gold electrode goes via Pb(III) intermediate species which are stabilized within Nafion® membrane. The final PbO2 deposit crystallizes in tetragonal β-PbO2 form.

Influence of supporting electrolyte on the pseudocapacitive properties of MnO2/carbon nanotubes

The aim of this study was to prepare MnO2 from a MnCl2 solution by electrode polarisation at a constant potential. MnO2 was deposited at platinum and platinum modified by carbon nanotubes (CNTs) with a varying degree of oxidation. The mass of the electrodeposited MnO2 was calculated from the current transient. An electrochemical quartz crystal microbalance (EQCM) enabled the determination of the correction factor which considers the presence of the equivalent amount of water within the MnO2 layer. The obtained electrodes (MnO2, MnO2/CNT, MnO2/CNT-EO1 and MnO2/CNT-EO2) were tested in NaCl, LiCl and MnCl2 electrolytes by cyclic voltammetry, demonstrating the best pseudocapacitive properties in the MnCl2 solution. It was proven that the electrolyte cation size, its valence and the hydration shell significantly influence the MnO2 pseudocapacitive redox reaction. The pseudocapacitive properties of MnO2 were improved by MnO2 deposition onto CNTs and oxidised CNT electrodes. The oxidation of CNTs was accomplished by a simple electrochemical procedure in a Na2SO4 solution (CNT-EO1 and CNT-EO2 electrodes). Electrochemical impedance spectroscopy has shown that charge transfer resistance has increased by oxidation process. However, it did not influence the overall pseudocapacitive properties significantly.

Supercapacitors based on graphene/pseudocapacitive materials

In this work composites of graphene and SnO 2 were successfully prepared by single step simultaneous synthesis of SnO 2 and reduction of graphene oxide (GO). Three different compositions of precursor solution resulted with different composite materials containing graphene and SnO 2 . The reaction was carried out by using microwave-assisted hydrothermal synthesis. Scanning electron microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDX) gave insight into morphology and composition of the obtained materials. Good capacitive/pseudocapacitive properties of the obtained material suitable for supercapacitor application were registered by using cyclic voltammetry from where specific capacitance values up to 93 F g -1 were determined.