Impedance spectroscopy study of anodic growth of thick zirconium oxide films in H2SO4, Na2SO4 and NaOH solutions

Abstract

Anodic zirconium oxide films were grown potentiodynamically at a constant sweep rate up to the breakdown potential on rod electrodes made of 99.8% metallic zirconium. Different media of different pH were tested, namely 0.5 M H 2 SO 4 (pH 0.3), 0.1 M Na 2 SO 4 (pH 9) and 0.1 M NaOH (pH 13). By electrochemical impedance spectroscopy and scanning electron microscopy the oxide film thickness was monitored during the voltage scan. The behaviour was found to be different in the presence and absence of sulphate anions. In the presence of SO 4 2) , the films were dense but breakdown occurred at 300-340 nm. In NaOH, two relaxations appeared above 50 V and were ascribed to a bi-layered coating structure and the maximum layer thickness was 720 nm before breakdown.

Influence of surface disorder, oxygen defects and bandgap in TiO2 nanostructures on the photovoltaic properties of dye sensitized solar cells

“…However, the smaller current density (J sc ) in the hydrogenated samples imply an inefficient charge extraction which could be due to the decay of electrons by surface traps or oxygen vacancy defect levels in TiO 2 electronic structure. The interfacial capacitance, C int , due to the charge transfer and recombination at the sensitized-oxide/electrolyte interface is estimated from the resistance (R 3 ) and CPE parameters (C 3 and a) by the procedure described by Pauporté et al [66,67] using the following relation: Table 4 The fitted parameters extracted from the impedance spectra of dye sensitized solar cell. The interfacial capacitance C int and the electron relaxation time τ n (R 3 C int ) corresponding to the electron transfer and recombination at the TiO 2 /electrolyte interface is given for both as prepared and hydrogen treated samples.…”

Fabrication parameter-dependent morphologies of self-organized ZrO2 nanotubes during anodization

“…If the electric field across the layer was strengthened, the rate of migration of cations and/or anions would speed up accordingly. During the growth of zirconia, Zr 4+ movement is negligible whereas the growth occurs mostly at the metal/oxide interface via the inwards transport of F − and O 2− across the growing layer [26,27]. Upon reaching the opposite side of the oxide, F − and O 2− react with cations, forming additional fluoride and oxide phases at the oxide/metal interface.…”

The role of temperature in copper electrocrystallization in ammonia–chloride solutions

“…In this analysis, the model proposed by Milchev et al, could not account for the transient behavior at shorter times than 0.4 s. The capacitive effect generated by the oxide layer (Cr 2 O 3 )-chloride interactions, suggested by voltammetry, involves the contribution of two capacitances in series, namely the oxide film thicknesses barrier, and the double layer capacitance, which could be influenced by chloride adsorption and/or its reaction with oxide layer. A detailed study of this two capacitance contributions has been reported elsewhere [24,29]. Hence, taking into account the above described, the initial falling cathodic currents observed in the experimental current transients (I T ) obtained during copper deposition on SS electrode, may be described by the following equation: where I C = k 1 exp(−k 2 × t) is the current due to the capacitive effect of Cr 2 O 3 -Cl − interaction, being k 1 = k 2 Q C , where Q C is the charge density due to the overall capacitance effect.…”