ABSTRACT
The Li(+) ion diffusion coefficients (DLi+) in V2O5 (2.12 × 10(-12) cm(2) s(-1)) and in the intermediate α-, ε-, and δ-LixV2O5 phases (1.6 × 10(-14), 8.0 × 10(-15), and 8.5 × 10(-15) cm(2) s(-1), respectively), reversibly formed during charging/discharging processes of the crystalline-V2O5 and PEDOT (poly-3,4-ethylenedioxythiophene) composite-film electrode, are precisely determined by the galvanostatic intermittent titration technique. The specific surface area of the composite film is estimated to be 13.600 m(2) g(-1), where the external surface area and the nanopore area are 10.704 and 2.896 m(2) g(-1), respectively. The V2O5 crystals are coated and interconnected by a conductive polymer network in the composite film, thereby improving the electrode characteristics. V2O5 and PEDOT composite-film cathodes showed high specific capacities (290 mA h g(-1) at a 1 C rate), excellent rate capabilities (178 mA h g(-1) at a 10 C rate), and superior cycling stabilities (ca. 15% degradation after 500 consecutive cycles).
ABSTRACT
The electrochemical activities of PbO(2) thin-film electrodes were systematically studied with an oxygen-transfer reaction, i.e., the oxidation of thiourea. Five different types of PbO(2) film electrodes were prepared using various methods to investigate the influence of the interfacial oxide layer formed between the Ti substrate and the PbO(2) layer contacting the electrolyte. Among the electrodes tested, PbO(2) electrode prepared by minimizing the formation of the interfacial oxide by either the electrochemical or thermal decomposition method generally exhibited better electrochemical activity. From the results, it can be inferred that the enhanced electrochemical activity of the electrode is due to minimization of the interfacial resistance by the introduction of a metallic Pb layer between the Ti substrate and the PbO(2) layer, and to an increase in the roughness on the surface of the PbO(2) layer.
ABSTRACT
An instrumental setup has been configured for a simultaneous real time recording of electrochemical, spectroelectrochemical, and mass data on an electrode from a single measurement for studies of complex electrochemical reaction mechanisms. This was achieved by combining a few pieces of equipment: a potentiostat/galvanostat for electrochemical measurements, the near-normal incidence reflectance spectrometer for spectroelectrochemical measurements, and a quartz crystal analyzer (QCA) for mass changes on the electrode. The latter two were coupled through a bifurcated optical fiber on the reflective QCA electrode. The experimental setup thus assembled was demonstrated to be very powerful in elucidating reaction mechanisms of the reaction sequence for a complex reaction, for example, electrochemical oxidation of aniline, which accompanies spectral, as well as weight, changes upon oxidation. The system was also applied to the study of the lithium intercalation reaction of tungsten trioxide thin films in a nonaqueous solution.
