Indium Hexacyanoferrate Films Research Articles

Stability-enhanced indium hexacyanoferrate electrodes: Morphological characterization, in situ EQCM analysis in nonaqueous electrolytes and application to a WO 3 electrochromic device

This paper presents a promising transparent counterelectrode system for a WO 3 electrochromic device (ECD) on the basis of a stability-enhanced indium hexacyanoferrate (InHCF) electrode and a NaClO 4/propylene carbonate (PC) electrolyte. Through SEM characterization it was found that clusters of granular InHCF nanoparticles (ca. 80–140 nm) were deposited on ITO substrates in HCl and KCl-stabilized plating solutions, and uniform micrometer thick films with high charge capacity could be obtained. From in situ electrochemical quartz crystal microbalance study, it was discovered that Na + would enter or move out from the InHCF film in the “desolvated” form during the redox process in a PC electrolyte. Besides, NaClO 4/PC resulted in higher electrochemical activity and reversibility than LiClO 4/PC. With these discoveries, a durable WO 3-InHCF ECD featuring blue-to-colorless electrochromism was fabricated successfully. The device remained 73.6 and 88.7% of its initial Δ T values at 600 and 800 nm after 40,000 rapid and successive coloring/bleaching cycles, respectively. Moreover, the cycling-induced loss of electrochromic performance almost completely restored after 1-month rest and kept unchanged for another month. Thus, the applicability of this nonaqueous InHCF counterelectrode system to ECDs was verified.

Indium hexacyanoferrate films, voltammetric and impedance characterization

Charge transfer processes within indium hexacyanoferrate (InHCF) films have been studied by using mainly cyclic voltammetry and faradaic impedance methods. Cyclic voltammetry reveals the existence of two types of InHCF films deposited from solutions of high and low potassium concentrations, respectively. The difference in the electrochemical behavior of these films disappears after their cyclic processing in the range of electrode potentials from 0.0 to 1.3 V with respect to Ag/AgCl electrode. The obtained data are strongly dependent on the nature of supporting electrolyte cations. However, in all the cases, the obtained impedance spectra are qualitatively the same. In the region of high a.c. frequencies, they contain a semi-circular part, the parameters of which depend on both the substrate nature and the mechanical pre-treatment (polishing) of the used substrate (platinum, glassy carbon). This allows one to assign that part of impedance spectra to the film/electrode interface. The next part of the spectra corresponds to the Warburg impedance that is somewhat masked by the subsequent increase of the imaginary part of the film impedance under decreasing a.c. frequency. Effective diffusion coefficients calculated from the Warburg dependence for different supporting electrolytes change their values in the series: D K+≥ D Na+≫ D Li+. Such a great difference between D Li+ and D K+≥ D Na+ is confirmed by the results of chronoamperometric measurements. It is assumed that the above difference originates from different binding of the compared counter-ions with anion film fragments. This assumption is in agreement with the results derived from low frequency parts of the impedance spectra.

Enhanced electrodeposition of indium hexacyanoferrate thin films through improved plating solution stability

An ordinary plating solution for indium hexacyanoferrate (InHCF) thin film deposition, mainly composed of equal concentrations of In3+ and [Fe(CN)6]3–, usually forms precipitates rapidly when either concentration is higher than few millimolar. This contributes to the plating solution's instability. Moreover, electrodeposited capacities are limited accordingly. In this work, the plating solution's stability and the electrodeposition of InHCF were greatly enhanced by adding a large amount of K+ and/or H+. It was found that a 10-mM plating solution added with 1 M HCl and 1 M KCl could be stored as fresh over a one-week period, whereas an unmodified plating solution became useless within a couple of minutes. Also, such cationic additions, especially adding H+, increased the electrodeposited capacity ca. 18 times at least, as compared with that obtained from the unmodified plating solution. Furthermore, related enhancing mechanisms were proposed and verified. To sum up, this study offers a means for better InHCF electrodeposition and should promote the applications of InHCF films.

Optical beam deflection study of indium-hexacyanoferrate films

Optical beam deflection technique was employed to follow the ion transport and ion exchange processes taking place in the course of redox transformations of indium-hexacyanoferrate surface layers. The data analysis by the help of a convolution method attested that the principal charge compensating ions are cations and the contribution of anions to the charge neutralization inside the film is less than a few percents in the range [0, 0.85 V].

Electrocatalysis and Amperometric Detection at a Ruthenium-Modified Indium-Hexacyanoferrate Film Electrode

The electrocatalytic activity of a glassy carbon electrode modified with electrochemically deposited indium(III)-hexacyanoferrate (InHCF) film, which has been subsequently cycled in a solution of ruthenium(III), is described. Although the resulting ruthenium-modified InHCF thin film electrode behaves in a manner analogous to the parent InHCF film, its stability was found to be greatly improved. Such a modified electrode was characterized, in acidic (pH 2) 0.5 M KCl solutions, by cyclic voltammetry and flow injection analysis. It exhibits a high catalytic activity for the electrooxidation of some inorganic and organic compounds of analytical interest, such as As(III), S2O2–3, cysteine, and 2-furaldehyde. The analytical applicability of this novel ruthenium-modified InHCF film electrode for the amperometric detection in flowing streams is discussed. Repetitive sample injections with amperometric detection of thiosulfate at +0.8 V (vs. Ag/AgCl) as applied potential produced a stable response over 8 h of operation, making it very attractive for practical applications.

Probe beam deflection study of the transport of ions during the redox reaction of indium-hexacyanoferrate films

The probe beam deflection technique was employed to follow the ion transport and ion exchange processes taking place in the course of redox transformations of indium-hexacyanoferrate surface layers. In accordance with the results of quartz crystal microbalance studies it was established that the principal charge compensating ions are cations. The data analysis by the help of a convolution method attested that the contribution of anions to the charge neutralization inside the film below 0.9 V versus SCE is less than 7%, if any at all.

Spectroelectrochemical Studies of Indium Hexacyanoferrate Electrodes Prepared by the Sacrificial Anode Method

Indium hexacyanoferrate (InHCF) thin films have been successfully deposited on the ‐coated surface of conductive float glass by the sacrificial anode (SA) method. It was found that InHCF films prepared in such a way possess relatively smooth surface morphology, presumably influenced by the anodic dissolution current. The films have been characterized and discussed in terms of their electro‐optical properties. The compositions of as‐deposited InHCF films prepared by the SA method were analyzed by atomic absorption (AA) spectroscopy and can actually be expressed as , with 0 ⩽ x ⩽ 0.38. Cyclic voltammetry (CV) done in various electrolytes supports the double injection/extraction mechanism during switching. It is concluded that ion permeability in an InHCF film follows the order of . A one‐electron transfer reaction is proposed for the switching of the InHCF film according to the absorption spectra. The film is shown to be electrochromic, and the redox reaction can be summarized as where is the metal cation in supporting electrolytes. The coloration efficiency for the InHCF film switching involving , measured at 410 nm, is 47.6 cm2/C for coloring and is 47.3 cm2/C for bleaching, indicating nearly ideal electrochromic behaviors.

Microgravimetric monitoring of transport of cations during redox reactions of indium(III) hexacyanoferrate(III,II)

We demonstrate here that, primarily, electrolyte cations but also, to some extent, anions are capable of penetrating indium hexacyanoferrate films during redox reactions. We find from electrochemical quartz crystal microbalance measurements that the electrolyte cation (K+) undergoes sorption and desorption during the system's reduction and oxidation, respectively. The formal potential, which has been determined from the system's well-defined voltammetric peaks recorded with the use of an ultramicroelectrode, decreases ∼40 mV per decade of decreasing K+ concentration. The latter value is lower than the 60 mV change expected for the involvement of a cation in the reaction mechanism according to the ideal Nernstian dependence. We also demonstrate, using 35-S labelled sulfate, that anion penetrates the reduced film and its concentration markedly increases during oxidation. Careful examination of cyclic voltammetric responses of the system shows that, in addition to the well-defined peaks, capacitance-like currents appear during oxidation. During reduction anion is largely expelled from the film. This complex ionic penetration and transport in indium hexacynoferrate may be explained in terms of formation of two forms: ‘soluble’, KInIII[FeII(CN)6], and ‘insoluble’ (‘normal’), InIII4[FeII(CN)6]3, during the electrochemical growth or potential cycling of the films. These forms would require cations and anions, respectively, to provide charge balance during reactions. Regardless of the actual mechanism, penetration of anions cannot be neglected completely in the discussion of charging of indium hexacyanoferrate.

Quartz crystal microbalance study of the growth of indium hexacyanoferrate films during electrodeposition and coagulation

An electrochemical quartz crystal microbalance and cyclic voltammetry have been used to monitor fabrication of indium(III) hexacyanoferrate(III,II) films by electrodeposition through potential cycling and by interfacial coagulation during ageing in the modification solution containing potassium electrolyte, indium(III) and hexacyanoferrate(III). We have chosen indium hexacyanoferrate as a model system since its cyclic voltammetry shows a single set of reversible, well-defined peaks significantly separated from the solution responses. Simultaneous estimations of charge and mass have been used to characterize the efficiency of the deposition processes. Microgravimetry is particularly attractive for monitoring the film growth due to interfacial coagulation (at open circuit). Electrodeposition by potential cycling permits fast preparation of thin films. The coagulation method is useful for fabrication of thick films. We also discuss the response of the resulting indium hexacyanoferrate film in the supporting electrolyte. The data are consistent with the insertion and exclusion of K + countercations during the system's reduction and oxidation respectively.

Novel photochemical/photoelectrochemical systems based on metal hexacyanoferrates

Abstract Electrolyte modification is realized to be a promising route to achieve better efficiencies in solar energy conversion in photoelectrochemical cells. Recent reports by Bocarsly et al. [1,2] and Licht et al. [3,4] have amply demonstrated this aspect wherein maximum efficiency received so far viz. 16.4% has been reported using chalcogenides of Cd as semiconductors in contact with a solution of a mixture of ferro/ferricyanide containing added cyanide ions. Surface modification of the semiconductor, cadmium sulphide/selenide, that takes place as a result of interaction with the redox, giving rise to cadmium hexacyanoferrate, has been considered important in yielding the improved energy efficiency. But interestingly, no attempt to ascertain the role of modifying hexacyanoferrate film formed as a possible photo-energy converter (also) has been made. Many metal hexacyanoferrates themselves semiconductors, being intervalent compounds, are subjects of intensive current research as they hold promise in several applications of sensors, electrochromic devices, catalysis, and most importantly in photo-energy conversion. In this context we report the results of photoresponse studies on indium hexacyanoferrate films on conducting carbon in contact with solutions of Fe(CN) −3 6 . We conclude from these studies that such interfaces under light irradiation indeed give rise to measurable and significant photocurrents whose nature is distinctly different from that obtained in the absence of a redox in solution. The article describes the observations and explains them taking into account photo/photoelectrochemical effects.

Spectroelectrochemical studies of indium hexacyanoferrate film modified electrodes

Abstract Spectroelectrochemical methods were used to study the electrochemical behaviour of a novel Prussian blue analogue indium hexacyanoferrate (InHCF) film modified electrodes. It was determined that a one-electron transfer electrode reaction took place for InHCF film modified electrodes. It was found that ion permeability in an InHCF film followed the order: Na+, K+ > NH+4, Li+.

Electrochemistry of indium hexacyanoferrate film modified electrodes

A thin film of prussian blue analogues containing indium was first electrodeposited on platinum electrode surfaces. The modified electrode surface has been characterized by means of X-ray diffraction method as well as ir spectra. The result shows that the electroactive white film firmly attached to the platinum substrate is really composed of indium hexacyanoferrate (InHCF). The electrochemical behaviour of InHCF modified electrodes was studied by cyclic voltammetry (CV). Ion effects of the supporting electrolyte suggest that both anions and cations have a considerable effect on the electrochemical behaviour of the modified electrode. InHCF film modified electrodes are very stable under CV scanning.