No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Synthesis, characterisation and in situ colorimetry of electrochromic Ruthenium purple thin films
Abstract
Ruthenium purple (RP) films on transmissive tin-doped indium oxide (ITO)/glass substrates have been synthesised by an electrochemical coagulation technique using an aqueous RP colloidal suspension prepared from separate very dilute aqueous solutions of iron(III) chloride and potassium hexacyanoruthenate(II), with dilute potassium chloride as supporting electrolyte solution. To aid stability of the RP films, ruthenium(III) chloride was added to the RP colloidal suspension. Using the CIE (Commission Internationale de l’Eclairage) system of colorimetry, the colour stimulus of the electrochromic RP films and the changes that take place on reversibly switching to the colourless form have been calculated from in situ visible spectra recorded under electrochemical control. On electrochemical reduction, the intensely absorbing bright purple mixed-valence iron(III) hexacyanoruthenate(II) chromophore is reduced to the colourless iron(II) hexacyanoruthenate(II) form. Sharp and reversible changes in the hue and saturation occur, as shown by the track of the CIE 1931 xy chromaticity coordinates. Concurrently, as the purple chromophore is bleached, a large increase in the relative luminance of the electrochromic film is observed. For the purple state, the CIELAB 1976 colour space coordinates were L* = 64, a* = 27 and b* = −36, with a complementary wavelength (λc) calculated as 555 nm, in excellent agreement with the absorption maximum (λmax) of 550 nm for the intervalence charge-transfer (IVCT) band.
... Inorganic-based EC devices are mainly constructed from transition metal oxide materials (e.g., iridium, tungsten, cobalt, manganese, nickel, palladium, cerium, rhodium, ruthenium, titanium, and molybdenum oxides), such as antimony EC film, three-dimensional ordered macroporous vanadium oxide EC film, and nickel oxide-based EC thin film. [113][114][115][116][117][118][119][120][121][122][123][124][125][126][127][128][129][130][131] Among inorganic-based EC materials, WO x offers better EC redox reaction effect, multi-color characteristics in reversible intercalation/deintercalation process, and fast switching response compared to other metal oxides. Moreover, WO x is a non-toxic, light-stable n-type semiconductor with a band gap of about 2.6 eV, enabling it to absorb a wide range of visible light. ...
Electrochromic (EC) glazing has garnered significant attention recently as a crucial solution for enhancing energy efficiency in future construction and automotive sectors. EC glazing could significantly reduce the energy usage of buildings compared to traditional blinds and glazing. Despite their commercial availability, several challenges remain, including issues with switching time, leakage of electrolytes, production costs, etc. Consequently, these areas demand more attention and further studies. Among inorganic-based EC materials, tungsten oxide nanostructures are essential due to its outstanding advantages such as low voltage demand, high coloration coefficient, large optical modulation range, and stability. This review will summarize the principal design and mechanism of EC device fabrication. It will highlight the current gaps in understanding the mechanism of EC theory, discuss the progress in material development for EC glazing, including various solutions for improving EC materials, and finally, introduce the latest advancements in photo-EC devices that integrate photovoltaic and EC technologies.
... In particular, green color is close to the most sensitive average wavelength for the human eye (555 nm) under daylight conditions. 43,48 In any digital image of an 8-bit color resolution, each color is quantized in 256 intensity levels where 255 is the fully bright color, and 0 means the color is turned off. This allows reaching 16777216 (256 × 256 × 256) combinations or colors. ...
Poly(Azure A) (PAA) films doped with sodium dodecyl sulfate (SDS) were grown on transparent indium tin oxide (ITO) glass substrates by cyclic voltammetry. The electrochromism of PAA was investigated by digital video-electrochemistry (DVEC). DVEC consists of the acquisition of sequential digital images during the electro-stimulated changes of PAA color. The evolution of red, green, and blue (R, G, B) colors intensity (I) of analyzed pixels provides enough sensitivity to detect changes of some nmol cm⁻² of electroactive centers. Besides, the different time evolution of these color intensities can serve to discern among different electroactive centers activated in the polymer. For the first time, contrast, coloration efficiency, and bleaching times of PAA are calculated by DVEC. The coloration efficiencies were between 15–25 cm² mC⁻¹ with short response times for the bleaching process between 2.9 and 5.5 s. PAA has good electrochromic performances to be used in electrochromic devices. Our present work provides an important insight into the design principles for a practical application of DVEC to characterize electrochromic devices in light-controlled conditions allowing us to find the best performances of these materials.
... Following the procedure described in [23], the RP solution for electrodeposition onto the CFM surface was prepared freshly on the day of experiment and used within 4 h. A solution of 1 mM K 4 [Ru II (CN) 6 ] prepared in 35 mM KCl (N 2 -purged) was mixed, under vigorous stirring, with a solution of 1 mM FeCl 3 / 35 mM KCl (N 2 -purged). ...
Microelectrodes coupled to fast electrochemical techniques are an attractive approach towards real time in vivo monitoring with minimal damage to living tissue. Here, carbon fiber microelectrodes (CFM) were modified by electrodeposition of ruthenium purple (RP) for monitoring of H2O2 concentration dynamics in brain tissue preparations. The RP-modified CFM (CFM-RP) showed catalytic activity for the reduction of H2O2 at −0.1 V vs. Ag/AgCl in aqueous electrolyte at neutral pH and in the presence of physiological concentration of sodium cation (154 mM). The CFM-RP displayed a linear response in the concentration range of 2−500 μM, with a sensitivity of 0.98 ± 0.37 μA cm⁻² μM⁻¹ and a limit of detection of 70 ± 40 nM. Coating the CFM-RP with a Nafion® layer greatly extended the operational stability of the RP film to 3 h in a medium containing a high sodium concentration at physiological pH 7.4. Validation of the CFM-RP- Nafion® sensor suitability for monitoring H2O2 concentration dynamics was achieved by measuring exogenously and locally applied H2O2 in rodent striatal slices. Together, these results support the excellent analytical performance of this new CFM-RP-Nafion® sensor design for sensitive and selective monitoring of H2O2 concentration dynamics in brain tissue.
... Dyes are commonly employed as tracer in the study of biochemical processes for several metabolic and biological studies. For this reason, a huge variety of methods such as colorimetry [1][2][3], electrochemistry [4][5][6][7][8], spectroelectrochemistry [9][10][11][12][13][14][15], fluorescence [16][17][18][19][20][21], chemiluminescence [22][23][24], photometry [25,26], etc. have been developed to analyse the behaviour of different systems used in clinical and biological applications. A redox indicator widely used for this purpose is resazurin (RZ), also known as Alamar Blue, a slightly fluorescent dye [27] used as chemical system for measuring the metabolic activity and the proliferation of living cells [28], and testing the cell viability and cytotoxicity in biological materials [29,30]. ...
Raman and fluorescence spectroelectrochemistry techniques have been used for the in-situ study of the reaction mechanism of resazurin/resorufin/dihydroresorufin system. Resazurin (RZ) is one of the most highly referenced substances used in studies on cell viability and cytotoxicity for a wide range of biological and environmental systems. Electrochemical behaviour of this tracer is based on the irreversible reduction of RZ, a slightly fluorescent compound, to resorufin (RS), a high fluorescent compound, while a subsequent and reversible reduction of RS generates dihydroresorufin (DHRS), a non-fluorescent compound. Time-resolved Raman spectroelectrochemistry has been used, for the first time, to perform dynamic studies of this system. The continuous optical acquisition provides a large number of spectra during the whole electrochemical reaction and not only at discrete potentials, offering a novel contribution to the literature related to this tracer. The characteristic Raman and fluorescence bands associated with each molecule as well as their evolution with potential allow us to obtain valuable information about the interconversion between RZ, RS and DHRS. In addition, spectroelectrochemistry demonstrates that experimental parameters play an essential role in the fluorescent response of this coloured system. In that way, operando multiresponse techniques shed more light for the complete understanding of RZ, RS and DHRS system, and they yield novel information to explain the electrochemical conversion of these compounds.
... Ruthenium purple (RP) is a PBA resulting from the substitution of Fe II by Ru II , with the formula KFe[Ru(CN) 6 ]·nH 2 O [10,11]. Similarly to PB, RP has an interesting electrochromic behavior, from colorless in its reduced state to deep purple in the oxidized one [12]. Besides, both PB and RP present a remarkable catalytic behavior towards hydrogen peroxide reduction in their reduced form, making them suitable for H 2 O 2 sensors [13]. ...
Thin films of iron-filled carbon nanotubes prepared through the liquid/liquid interfacial method were modified with a mixture of hexacyanometallates (HCMs) Prussian blue and ruthenium purple. Two different approaches were used in order to obtain both materials in the composites, based on a direct reaction starting from a mixture of both precursors or a step-by-step deposition of each compound. The modified films were characterized by cyclic voltammetry, Raman spectroscopy, X-ray diffraction, scanning electron microscopy, and UV-Vis spectroscopy, confirming the formation of a mixture of HCMs in both methods of synthesis. Stability studies were evaluated in different supporting electrolytes, and composites presented good performances due to carbon nanotube stabilization. Electrochromic properties were also evaluated for selected composites, showing high electrochromic efficiency and stability.
Graphical abstractᅟ
... 2, +a* is the red direction, −a* is the green direction, +b* is the yellow direction and −b* is the blue direction. The center (0, 0) of the chromaticity diagram is achromatic; as a* and b* values increase[14,15]. In the present work, chromaticity coordinates were calculated using a computer aided program and plotted as shown inFig. ...
In Dye-Sensitized Solar Cells (DSSC), the selection of the material used for the fabrication process plays a vital role in determining the performance of the cell. The fabrication and characterization of DSSC with Ruthenizer 620-1H3TBA also known as N749 or black dye as charge transfer sensitizer is discussed in this paper. The black dye exhibits a higher absorbance throughout the entire range of visible spectrum with a peak absorbance at 620 nm and also a good absorbance in ultraviolet region. The cell thus fabricated, with cell area 2.0 cm x 2.1 cm and 487.44 μm thick coating of Titanium dioxide nanoparticles, exhibits an open circuit cell voltage of 0.61 V and short circuit current of 48 μA. Further the morphological characterization of DSSC is carried out and the results were analysed.
All-inorganic halide perovskite nanocrystals with their fascinating optical properties have drawn increasing attention as promising nanoemitters. However, due to the intrinsic poor colloidal stability against the external environment, the practical applications are greatly limited. Herein, a facile and effective strategy for the in situ encapsulation of CsPbBr3 NCs into highly dense multichannel polyacrylonitrile (PAN) nanofibers via a uniaxial electrospinning strategy is presented. Such a facile uniaxial electrospinning strategy enables the in situ formation of CsPbBr3 NCs in PAN nanofibers without the introduction of stabilizers. Significantly, the obtained CsPbBr3 nanofibers not only display intense fluorescence with a high quantum yield (≈48%) but also present high stability when exposed to water and air owing to the peripheral protecting matrix of PAN. After immersing CsPbBr3@PAN nanofiber films in water for 100 days, the quantum yield of CsPbBr3@PAN nanofibers maintained 87.5% of the original value, which was much higher than that using CsPbBr3 NCs. Furthermore, based on the spectral overlap between the electrochromic material of ruthenium purple and fluorescence of CsPbBr3@PAN nanofiber films with excellent water stability, a reversible fluorescence switch is constructed with good fatigue resistance, suggesting their promising applications.
This work is the first one allowing the characterization of electrochromic devices simultaneously at various parts on their surface and different rates of color change. We describe a new proficient and affordable methodology for reporting electrochromic parameters such as coloration efficiency, optical contrast, and switching time based on the use of digital video-electrochemistry (DVEC) in the ac regime, namely RGB colorimetry impedance spectroscopy. Simultaneously with the electrochemical impedance spectroscopy, the RGB color changes of an electrochromic electrode were recorded by a CCD digital camera at 120 digital images per second. In such conditions, RGB electrochromic changes extracted from the digital images can be easily analyzed until 10 Hz using a potential perturbation amplitude of 50 mV rms. Electrochromic devices based on poly(3,4-ethylenedioxythiophene) films deposited on ITO electrodes were tested as examples. This new methodology does not require expensive instrumentation and it proves easy to be implemented in most of the specialized laboratories around the world.
In this study, a nanoparticulated synthesis based surface modification was applied to a Prussian blue analogue (PBA), ruthenium purple (Fe 4 [Ru(CN) 6 ] 3 , RP). The RP nanoparticles (nRP)with significantly enhanced electrical and ionic conductivities were compared to their micro-scale counterpart (mRP). By reducing the kinetic barriers during electrochemical cycling, nRP showed pronounced enhancement in the optical properties including higher transmittance change (ΔT), shorter response time, faster redox kinetics, and better cycling stability. A novel complementary electrochromic device (ECD)was proposed to utilize nRP as the anodically coloring material and Fe(II)-based metallo-supramolecular polymer (Fe(II)-MEPE)as the cathodically coloring material. Both anodically and cathodically coloring materials exhibited maximum optical modulation around 550 nm, which is the most sensitive light spectrum to human eyes in the visible region. Upon applying potential biases between 0.3 and 1.3 V to the Fe(II)-MEPE/nRP ECD, a large transmittance change of 50.7% at 580 nm, fast response times of 0.4 s both in coloring/bleaching, and a high coloration efficiency of 512.5 cm ² /C at 580 nm were observed. At the same operation condition, the proposed ECD retained 96.4% of its initial ΔT after 10,000 cycles of continuous switching.
Stoichiometric phosphors Sr2Ga3La1−xEuxGe3O14 (x = 0, 0.2, 0.4, 0.6, 0.8 and 1) were synthesized via traditional solid state reactions. The X-ray diffraction patterns of the samples reveal that Eu³⁺ can be successfully alloyed in Sr2Ga3La1−xEuxGe3O14 up to x = 1. Sr2Ga3LaGe3O14 and Sr2Ga3EuGe3O14 can form solid solution at any ratio. The composition of solid solution can be expressed as Sr2Ga3La1−xEuxGe3O14 (0 ≤ x ≤ 1). The photoluminescence properties of Sr2Ga3La1−xEuxGe3O14 are discussed in detail. Eu³⁺ doped phosphors can emit red light under the excitation of near ultraviolet light because of the emission from ⁵D0 → ⁷Fj (j = 0, 1, 2, 3, 4) transition. The typical chromaticity coordinates of Eu³⁺ doped phosphors are in red area, which are close to the standard values of red color chromaticity coordinate (0.67, 0.33) stipulated by National Television Standards Committee. The integral strength from 570 to 750 nm of Sr2Ga3EuGe3O14 is about 2.5 times of that of commercially obtained Y2O2S: 0.1Eu³⁺ under the excitation at 393 nm. Present research indicates that Sr2Ga3La1−xEuxGe3O14 is a promising phosphor for white light emitting diodes.
Ca2−xAl2SiO7:xEu3+ (0.03 ≤ x ≤ 0.21) and Sr2−xAl2SiO7:xEu3+ (0.03 ≤ x ≤ 0.15) phosphors are effectively excited by near-UV light (396 nm). The host composition and Eu3+ concentration of the two series phosphors substantially affect its emission characteristics. The calcium aluminosilicate Ca1.82Al2SiO7:0.18Eu3+ is 377% higher in red emission intensity than the Ca1.97Al2SiO7:0.03Eu3+, whereas the strontium aluminosilicate Sr1.88Al2SiO7:0.12Eu3+ is 343% higher in red emission intensity than the Sr1.97Al2SiO7:0.03Eu3+. In addition, the Eu3+ concentration of the Sr2−xAl2SiO7:xEu3+ (x = 0.12) showing the highest red emission intensity is much lower than that of the Ca2−xAl2SiO7:xEu3+ (x = 0.18). In spite of the low Eu3+ concentration, the red emission intensity and red color purity of Sr1.88Al2SiO7:0.12Eu3+ are much stronger and higher than those of the Ca1.82Al2SiO7:0.18Eu3+. Of the prepared phosphors, Sr1.88Al2SiO7:0.12Eu3+ is the optimal composition for obtaining strong and pure red light. Strontium aluminosilicate Sr2−xAl2SiO7:xEu3+ has distinct advantages including strong emission intensity, high color purity, and cost effectiveness.
This review deals with the basis and novel trends in electrochromism, describing the basic aspects and methodologies employed for the construction and analyses of different modified electrodes. The work presents the classic materials used for the construction of electrochromic electrodes, such as WO3 and a view on the basic concepts of chromaticity as a useful approach for analyzing colorimetric results. The report also addresses how the incorporation of nanomaterials and the consequent novel modification of electrodes have furthered this area of science, producing electrochromic electrodes with high performance, high efficiency and low response times.
This work reports the preparation, characterization and application as both electrochromic material and electrochemical sensor of novel materials: carbon nanotubes/ruthenium purple nanocomposites. Using an innovative route based on a heterogeneous electrochemical reaction involving iron oxide species encapsulated within the cavities of the carbon nanotubes, the composite materials were obtained as transparent thin films deposited over transparent electrodes. Several experimental parameters related to the nanocomposite synthesis were evaluated and related to the characteristics of the obtained materials, such as morphology and stability. The films were characterized by UV-Vis and Raman spectroscopy, scanning electron microscopy, X-ray diffraction, cyclic voltammetry and UV-Vis and Raman spectroelectrochemistry. Four different materials were applied as H2O2 sensors and exhibited impressive analytical parameters, including a limit of detection of 1.27 nmol L-1 and a sensitivity of 39.6 A M-1 cm-2. These nanocomposites also showed great electrochromic properties, with high stability and coloration efficiency over 95%, maintained during stability cycles.
A layer-by-layer (LbL) assembly of poly(butyl viologen) (PBV) and poly(peroxotungstate) was used for preparing a cathodically coloring dual electrochrome WO3-PBV film. A new formulation containing ferrocenecarboxaldehyde and potassium hexacyanoruthenate(II) was employed for the first time and anodically coloring ruthenium purple (RP) thin films were electrodeposited. X-ray photoelectron spectroscopy and Fourier transform infrared analyses confirmed the RP film structure to be an inorganic coordination polymer: K-x center dot Fe-x(III)[Ru-II(CN)(6)](y), wherein Fe3+ and Ru2+ color centers are flanked by CN- ligands. Nanoscale electrical conductivities determined by conducting atomic force microscopy were deduced to be 1.03 and 147.4 mS cm(-1), for the RP and WO3-PBV LbL films respectively, which confirmed their ability to function as mixed conductors, attributes pertinent during optical switching. Reversible bias induced transition between purple and colorless hues was attained in the RP film and between deep blue and colorless states was achieved for the WO3-PBV LbL film with coloration efficiencies of 188 and 380 cm(2) C-1 respectively. A complementarily coloring electrochromic device of WO3-PBV/RP was fabricated with an environmentally benign, inexpensive aqueous electrolyte, which switched between blue, purple, and colorless states. The device exhibited an electrochromic efficiency of 476 cm(2) C-1 at 580 nm, an outstanding transmission modulation of 49%, and short switching times (similar to 1 s); all under remarkably low operating voltages of +/- 1V. The WO3-PBV/RP device can deliver high optical contrast under low operating bias, and is highly scalable and durable, which demonstrates it to be ideal for practical optical switching devices like fast changing displays or smart windows.
In Dye-Sensitized Solar Cells (DSSC), the selection of the material used for the fabrication process plays a vital role in determining the performance of the cell. The fabrication and characterization of DSSC with Ruthenizer 620-1H3TBA also known as N749 or black dye as charge transfer sensitizer is discussed in this paper. The black dye exhibits a higher absorbance throughout the entire range of visible spectrum with a peak absorbance at 620 nm and also a good absorbance in ultraviolet region. The cell thus fabricated, with cell area 2.0 cm x 2.1 cm and 487.44 μm thick coating of Titanium dioxide nanoparticles, exhibits an open circuit cell voltage of 0.61 V and short circuit current of 48 μA. Further the morphological characterization of DSSC is carried out and the results were analysed.
A novel color-reinforcing electrochromic device (ECD) is described in which the anode and cathode reactions simultaneously exhibit reversible colorless to intense purple changes. Under coloration, the mixed-valence iron(III) hexacyanoruthenate(II) chromophore is formed on oxidation of iron(II) hexacyanoruthenate(II), with simultaneous reduction of the methyl viologen dication to form a mixture of the radical cation monomer/dimer. Using the CIE (Commission Internationale de l'Eclairage) system of colorimetry, the color stimulus of such ECDs and the changes that take place on reversibly switching between the colored and colorless states have been calculated from in situ visible spectra recorded under electrochemical control. On ECD color switching, with the excellent color-matching between the two purple states, sharp and reversible changes in the hue and saturation occur, as shown by the minimal hysteresis of the track of the CIE 1931 xy chromaticity coordinates. Extrapolation of the xy track to the color locus gave a complementary wavelength (λc) of 565 (±5) nm in close agreement with values obtained for the individual electrochromic materials. The concentration of the solution-phase methyl viologen and its diffusion to the cathode controlled both the proportion of surface-confined Ruthenium purple (RP) that is switched to the intense purple form and the overall ECD changes. For the ECDs' "on" states, the CIELAB 1976 color space coordinates were L* = 86, a* = 9, and b* =-15, and L* = 79, a* = 15, and b* =-22, respectively, for 5 and 10 mmol dm-3 methyl viologen solution concentrations. CIELAB 1976 color space coordinates showed that the ECDs were fully transparent and colorless in the "off" states, with L* = 100, a* = 0, and b* = 0. Switching times, as estimated for 95% of the total absorbance change, were 4 and 10 s respectively, for coloration and bleaching for the 5 mmol dm-3 methyl viologen ECD, and 8 and 16 s for the 10 mmol dm-3 methyl viologen ECD.
Electrochromic Ruthenium Purple-polymer nanocomposite films, fabricated by multilayer assembly, were found to exhibit sub-second switching speed and the highest electrochromic contrast reported to date for any inorganic material.
The role and effects of ruthenium on the electrochemical stabilisation of some metal-hexacyanometallate film electrodes was investigated by X-ray photoelectron spectroscopy (XPS). The following inorganic films were studied, cobalt(II)-hexacyanoferrate(II/III) (CoHCFe), nickel(II)-hexacyanoferrate(II/III) (NiHCFe), and iron(II/III)-hexacyanorutenate(II/III) (FeHCRu), and their corresponding ruthenium stabilised ones, Ru-CoHCFe, Ru-NiHCFe and Ru-FeHCRu. A mass increase of CoHCFe, NiHCFe, and FeHCRu, during continuous redox cycles (75–90 times) in a millimolar solution of RuCl3, was monitored by an electrochemical quartz crystal microbalance. Detailed XPS analysis of C 1s, O 1s, Fe 2p, Ni 2p, Co 2p, and Ru 3d peaks has allowed a comprehensive description of changes that occurred. The results obtained demonstrate that the insertion of ruthenium oxo species (e.g., Ru2O63+) was effective for the increase in lifetimes and for the electrocatalytic properties of ruthenium-modified metal-hexacyanometallate film electrodes. Three possible models of stabilisation are discussed.
A novel procedure that yields extremely stable ruthenium-modified inorganic film electrodes is presented. The following prussian blue (PB) analogues were investigated: indium(III)-hexacyanoferrate (InHCF), nickel(II)-hexacyanoferrate (NiHCF), cobalt(II)-hexacyanoferrate (CoHCF), and iron(III)-hexacyanorutenate also known as ruthenium purple (RP). The process includes electrochemical film deposition and subsequent voltammetric conditioning in a Ru(III)-containing solution at pH 2. Electrochemical and spectroscopic properties of each resulting modified film are better defined, redox and switching rates improved, and stability strongly enhanced. XPS supports the conclusions that the incorporation of ruthenium imparts an extensive crosslinking between hydrate microparticles through dinuclear [Fe, Ru] oxo (O) and cyanide (CN) bridges.
Thin films of ruthenium purple (RP) KFeRu(CN)6 or NH4FeRu(CN)6 are shown to be electrochromic. The compounds are reduced to a colorless state at 216 and 245 mV in 1 N K2SO4 and (NH4)2SO4, respectively. These reduction reactions are analogous to the reduction of Prussian blue (PB) but there is no corresponding oxidation to the analogue of Berlin green. The kinetics of the reduction of ruthenium purple and Prussian blue are examined in detail. It is shown that the scan rate dependence of voltammetric peak current and peak separation can be explained in terms of a concentration-dependent film resistance. The kinetic response to a potential step is explained in terms of migration and diffusion of charge carriers within the film. A simple transport model, which involves the assumption of electroneutrality within the film, leads to a special form of the Nernst-Planck equation which is solved for the current at the film-solution interface.
The intense color of the microcrystalline, inorganic dye Prussian blue, $KFe^{II} (CN)_{6} Fe^{III}$, is due to the transfer of an electron between iron ions, one of which is octahedrally surrounded by the carbon ends of the $CN^{-}$ ligands and assumes the strong field configuration while the other iron ion is octahedrally surrounded by the nitrogen ends of the $CN^{-}$ ligands and assumes a weak field configuration. Given the two types of iron ions, the problem then arises as to which ion anchors the optical electron orbital in the ground state and which anchors it in the excited state. The spectroscopic data can be rationalized using a simple orbital picture in which the iron ion in the carbon hole in the ground state is strong field $t_{2g}^{6}$ and in the transition, transfers an electron to the iron ion (weak field $t^{3}_{2g} e^{2}_{g}$) in the nitrogen hole. The unusually high intensity of the Prussian blue color band $(\epsilon = 9800)$ can be explained as due to a small amount of delocalization of the electrons in the ground state, brought about by configuration interaction.
Thin films of ferric-ruthenocyanide, also known as ruthernium purple (RP) can be readily prepared by repetitive potential cycling onto a number of different conducting materials such as glassy carbon, gold, platinum and indium-tin-oxide (ITO). This procedure is successfully accomplished provided that the supporting electrolyte, containing 0.5 mM FeCl3 + 0.5 mM K4Ru(CN)6, is moderately concentrated in potassium electrolytes, i.e. 40 mM KCl + HCl at pH 2. Electrode stability of RP films was found greatly enhanced by cycling the inorganic film in millimolar solutions of RuCl3. The resulting Ru(III)-RP film shows a single set of well-defined peaks with anodic and cathodic peak potentials at +0.26 V, and +0.14 V vs. SCE, respecsbvely. Its voltammetric profile remains unchanged after ca. 1500 oxidation-reduction cycles at 50 mV/s (14 h of potential cycling). The stabilisation process in RuCl3 solutions of as-grown RP films on platinum coated quartz crystals was followed concurrently by electrochemical quartz crystal microbalance (ECQM). The absorption spectra of the film on a ITO-covered glass electrode polarised to +0.50 V exhibits an absorption band at about 545 nm. The electrochemic activity and ease of preparation of Ru(III)
Electrochemical reactions of Ruthenium purple, Fe[RuII(CN)6]3 (RP; FeIII-RuII) were studied using a spectrocyclic voltammetry (SCV) technique. The SCV measurement for an RP film coated on an ITO electrode showed a reversible redox between RP and Ruthenium white (RW; FeII-RuII) at 0.14 V vs saturated calomel reference electrode (SCE). An RP film was electrodeposited on a hybrid film of tungsten trioxide (WO3)/tris(2,2′-bipyridine)ruthenium(II) ([Ru(bpy)3]2+; bpy = 2,2′-bipyridine)/poly(sodium 4-styrenesulfonate) (PSS) (denoted as WRP film) from a colloidal solution containing 0.5 mM FeCl3, 0.5 mM K4[Ru(CN)6] and 40 mM KCl using a potentiodynamic multi-sweep technique. In a cyclic voltammogram (CV) of a WRP/RP film, a redox response was observed at 0.61 V in addition to essential redox responses of WRP hybrid film (a [Ru(bpy)3]2+/[Ru(bpy)3]3+ redox at 1.03 V and a HxWO3/WO3 redox below 0.09 V), but a redox response of RW/RP was not observed at 0.14 V. The SCV measurement for the WRP/RP film suggested that the redox response at 0.61 V is attributed to a redox of [Ru(bpy)3]2+/[Ru(bpy)3]3+ interacted electrostatically with RP. It also showed that RW is oxidized to RP via [Ru(bpy)3]2+/[Ru(bpy)3]3+ redox and RP is reversibly reduced to RW via HxWO3/WO3 redox. This unique geared electrochemical reaction for the WRP/RP film leads to a hysteresis property of an RW/RP redox.
Electrochemistry of ferric ruthenocyanide (Ruthenium Purple, RP) was studied in acidic solutions containing a sodium salt (NaH2PO4 or NaCl). Two kinds of redox peaks for the FeIII/II couple were clearly seen in a Na+ solution, originating from a composite structure of both Fe4III[RuII(CN)6]3 (insoluble) and FeIII[RuII(CN)6]− (soluble). In repeated CV scans in a NaCl solution, it was found that only the couple of the redox peak assigned to the insoluble form remains unchanged under the steady state. The ratio of the insoluble form was estimated by coulometry as ca. 40% of the initial coated unit cells of the RP. Efficient electrocatalytic H2 formation was found to take place with the aid of the RP although this electrocatalysis was dependent on the type of sodium salt employed. In order to investigate the dominant factor affecting the overall kinetics in the H+ reduction catalysis, the dependences of both the catalytic activity and the electron transfer rate in the RP film were studied in a NaH2PO4 solution as a function of the coated amount. It was found that the overall kinetics are not dominated by electron transfer in the RP film.
Electrochemically prepared thin films of iron-hexacyanoruthenate(II) KFex[Ru{CN}6]y or Ruthenium purple (RP) were used as a surface modifier for the glassy carbon electrode (GCE). The redox behavior of the counter/central ions of RP has been investigated in aqueous electrolytes using CV, CC and electrochemical impedance spectroscopy (EIS). The effect of supporting electrolyte components on the electrochemical behavior was also investigated. In aqueous KClO4, RP showed three redox waves with Efo ≈0.2, 0.9 and 1.2 V versus Ag/AgCl. RP thin films were found to be either ionic size discriminatory or very sensitive to the level of doping with some organic solvents. Acetonitrile as a solvent and/or Li+ have a great distorting effect on these redox waves. The potential analytical application of these films was explored. The EC behavior was compared with that of related HCM (hexacyanometalate) compounds, such as KRux[Ru{CN}6]y, KRux[Fe{CN}6]y and KFex[Fe{CN}6]y. Kinetic studies corresponding to the iron and ruthenium centers in RP have been achieved. Obtained results indicated evidence for catalytic behavior of the RP towards water decomposition.
Variation of the colorimetric properties as a function of the film thickness and morphology has been investigated for two spray-coated electrochromic disubstituted 3,4-propylenedioxythiophene polymers. Changes in the luminance, hue, and saturation have been tracked using CIE 1931 Lxy chromaticity coordinates, with CIELAB 1976 color space coordinates, L*, a*, and b*, being used to quantify the colors. For (precycled) neutral PProDOT-(Hx)(2) films, with an increase in the thickness, L* is seen to decrease, with a* and b* coordinates moving in positive and negative directions, respectively, with quantification of the pink/purple (magenta) color as the summation of red and blue. For all thicknesses, L* is comparable, pre- and postcycling, with a* decreasing (less red) and b* becoming more negative (more blue) and the film now appearing as purple in the neutral state. Color coordinates for the reverse (reduction) direction exhibited hysteresis in comparison with the initial oxidation, with the specific choice of perceived color values depending not only on the film thickness but also on both the potential applied and from which direction the potential is changed. Neutral PProDOT-(2-MeBu)(2) films appear blue/purple to the eye both as-deposited and after potential cycling to the transparent oxidized state. For the neutral, colored state, with an increase in the thickness, L* is seen to decrease, with a* and b* coordinates moving in positive and negative directions, respectively. For PProDOT-(2-MeBu)(2) films, the a* coordinates are lower positive values and the b* coordinates are higher negative values, thus quantifying the high dominance of the blue color in the blue/purple films compared to the pink/purple PProDOT-(Hx)(2) films. As for the PProDOT-(Hx)(2) films, the tracks of the color coordinates show that the specific choice of perceived color values depends on the film thickness. Unlike the PProDOT-(Hx)(2) films, hysteresis is absent in the oxidation/reduction track of the x-y coordinates for the PProDOT-(2-MeBu)(2) films, although slight hysteresis is present in the luminance. Characterization of the film morphologies through atomic force microscopy reveals a much rougher, higher surface area morphology for the PProDOT-(2-MeBu)(2) films versus the PProDOT-(Hx)(2) films. The branched repeat unit in the PProDOT-(2-MeBu)(2) films provides a structure that allows ions to ingress/egress more effectively, thus removing hysteresis from the optical response.
An in situ colorimetric method, based on the CIE (Commission Internationale de l'Eclairage) system of colorimetry, has been successfully applied to the study of electrochromism in electrochemically deposited films of Prussian blue (iron(III) hexacyanoferrate(II), PB) on transmissive ITO/glass substrates for the first time. On electrochemical reduction of PB to Prussian white (iron(II) hexacyanoferrate(II), PW), sharp and reversible changes in the hue and saturation occur, as shown by the track of the CIE 1931 xy chromaticity coordinates. For PB, the CIELAB 1976 colour space coordinates were L*
= 73, a*
=
−26 and b*
=
−33, with a dominant wavelength calculated as 488 nm. Concurrently, as the intensely absorbing PB mixed-valence chromophore is ‘bleached’ to the transparent PW, a large increase in the relative luminance of the electrochromic film is observed. On oxidation of PB, the CIELAB 1976 colour space coordinates show the transition through intermediate green to the Prussian yellow (iron(III) hexacyanoferrate(III), PY) state (L*
= 94, a*
= 2 and b*
= 18), with a steady increase in relative luminance. To reliably compare the power requirement of PB films with other electrochromic systems, composite coloration efficiencies (CCE's) have been calculated, using a tandem chronoabsorptometry/chronocoulometry method, as previously developed for organic polymer systems. Using 95% of the total transmittance change at λmax as reference point, coloration efficiencies, η
=
ΔA(λmax)/Q, were calculated as 143 and 150 cm2 C−1 respectively for the PB/PW and PW/PB electrochromic transitions.
We introduce the concept of 'directed assembly' of multilayers on surfaces: the overall process involves the exposure of a surface to a series of solutions containing, alternately, adsorbable cations and adsorbable anions, and these are gradually built up into well-defined multilayer structures.
Ruthenium Purple (RP), an analogue of Prussian Blue, has potentially advantageous electrochemical characteristics. We now demonstrate its use in microelectrode biosensors for the first time. An RP layer was grown on, and remained stably anchored to, the surface of gold microelectrodes at physiological pH ranges. Crucially, it retained its electrochemical activity in sodium-based phosphate buffers. The RP microelectrodes displayed electrocatalytic reduction of hydrogen peroxide at 0 to -50 mV (vs Ag/AgCl). To fabricate biosensors on the RP microelectrodes, we used a sol-gel film electrodeposition technique to create ATP and hypoxanthine biosensors as examples of the methodology. These RP-mediated biosensors displayed excellent performance including the following: high selectivity against interferences such as 5HT, ascorbic acid, urate, and acetaminophen; high sensitivity with wide linear calibration range; and good stability. These attractive characteristics demonstrate that RP can be universally employed as an electron mediator in fabrication of highly selective oxidase-based microelectrode biosensors. Furthermore, given their ability to operate in the presence of physiological levels of Na+, the RP-mediated biosensors can be potentially applied to the in vitro and in vivo measurement of physiological signaling substances.
Electrochromism: fundamentals and applications. Weinheim: VCH
- Monk
- Pms
- Rj Mortimer
- Dr
Monk PMS, Mortimer RJ, Rosseinsky DR. Electrochromism: fundamentals and applications. Weinheim: VCH; 1995 [chapter 6].
Electrochromism and electrochromic devices
- Monk
- Pms
- Rj Mortimer
- Dr
Monk PMS, Mortimer RJ, Rosseinsky DR. Electrochromism and electrochromic devices. Cambridge: Cambridge University Press; 2007 [chapter 8].
Handbuch der anorganischen chemie, Frank-furt and Main: Deutsche Chemische Gesellschaft
- Diesbach
Diesbach (1704) cited in Gmelin, Handbuch der anorganischen chemie, Frank-furt and Main: Deutsche Chemische Gesellschaft, vol. 59; 1930. Eisen B p.671.