The effect of solution pH on the electrochemical performance of nanocrystalline metal ferrites MFe2O4 (M=Cu, Zn, and Ni) thin films

Abstract

Nanocrystalline metal ferrite MFe 2 O 4 (M=Cu, Zn, and Ni) thin films have been synthesized via electrodeposition-anodization process. Electrodeposited (M)Fe 2 alloys were obtained from aqueous sulfate bath. The formed alloys were electrochemically oxidized (anodized) in aqueous (1 M KOH) solution, at room temperature, to the corresponding hydroxides. The parameters controlling the current efficiency of the electrodeposition of (M)Fe 2 alloys such as the bath composition and the current density were studied and optimized. The anodized (M)Fe 2 alloy films were annealed in air at 400°C for 2 h. The results revealed the formation of three ferrite thin films were formed. The crystallite sizes of the produced films were in the range between 45 and 60 nm. The microstructure of the formed film was ferrite type dependent. The corrosion behavior of ferrite thin films in different pH solutions was investigated using open circuit potential (OCP) and potentiodynamic polarization measurements. The open circuit potential indicates that the initial potential E im of ZnFe 2 O 4 thin films remained constant for a short time, then sharply increased in the less negative direction in acidic and alkaline medium compared with Ni and Cu ferrite films. The values of the corrosion current density I corr were higher for the ZnFe 2 O 4 films at pH values of 1 and 12 compared with that of NiFe 2 O 4 and CuFe 2 O 4 which were higher only at pH value 1. The corrosion rate was very low for the three ferrite films when immersion in the neutral medium. The surface morphology recommended that Ni and Cu ferrite films were safely used in neutral and alkaline medium, whereas Zn ferrite film was only used in neutral atmospheres.

Mesoporous CuFe2O4 Photoanodes for Solar Water Oxidation: Impact of Surface Morphology on the Photoelectrochemical Properties**

“…Considering the Pourbaix diagram for iron, [67] the reduction of iron (III) to iron (II) is likely, which is close to 0 V vs. RHE. We note that the reduction of copper ions occurs electrochemically in the range of cathodic sweeps and that the reductive species are reported to be soluble in alkaline media [68] . These findings explain the instability of CFO photocathodes for cathodic potentials already in the absence of light (dark), which was additionally proven through 20 consecutive CV scans at 50 mV/s (Figure S7).…”

Mesoporous CuFe2O4 Photoanodes for Solar Water Oxidation: Impact of Surface Morphology on the Photoelectrochemical Properties

“…We note that the reduction of copper ions occurs electrochemically in the range of cathodic sweeps and that the reductive species are reported to be soluble in alkaline media. [64] These findings explain the instability of CFO photocathodes for cathodic potentials already in the absence of light (dark), which was additionally proven through 20 consecutive CV scans at 50 mV/s (Figure S7). The data show that the corresponding reduction and oxidation peaks become less prominent in following cycles, indicating dissolution of films.…”

Simple Portable Voltammetric Sensor Using Anodized Screen-Printed Graphene Electrode for the Quantitative Analysis of p-Hydroxybenzoic Acid in Cosmetics

“…The changes in pH influence the stability of the oxide film. 31 Therefore, the pH of 1.0 mol/L PB was also varied from 5.5 to 8.0 to achieve a high performance of the sensor. As shown in Figure 4 a, the current response increased with the increase of pH until pH 6.5.…”

“…The changes in pH influence the stability of the oxide film . Therefore, the pH of 1.0 mol/L PB was also varied from 5.5 to 8.0 to achieve a high performance of the sensor.…”