Copper Hexacyanoferrate Films Research Articles

Morphology and Conductivity of Copper Hexacyanoferrate Films

Films of conductive coordination network compounds are interesting as functional materials for charge storage, electrocatalysis, electrochromic switching, or conversion of light. The electrical con...

(Invited) Morphology and Conductivity of Copper Hexacyanoferrate Films

Metal hexacyanometallates (MHCMs) form a large family of coordination network compounds [1]. They have variable and tunable physical and chemical properties due to the three-dimensional framework of alternating metal knots connected by a non-innocent small bridging ligand forming interconnected channels that can accommodate solvent molecules and counter ions. Therefore, these materials have been comprehensively studied in several different fields, including, functional materials for charge storage, electrocatalysis, electrochromic devices or light harvesting. For the mentioned applications, conductivity is critical, to which i) electronic conductivity by electrons or holes [2], ii) ionic conductivity by mobile alkali ions in the channels of the MHCMs [3], and iii) proton conductivity [4] may contribute. In larger scale for real application, the conductivity depends not only on intrinsic material properties but also on the morphology. Morphology (particularly grain boundaries) plays an important role in determining the pathway of charge carrier transport (electrons and holes) in the film. From first principles it is expected that continuous compact crystalline films will have better electrical conductivity.Here, we present results on copper hexacyanoferrate which demonstrate particularly well the variation of film morphology and its influence on conductivity as a key functional property. We succeeded in devising a simple method for preparation of metal hexacyanoferrates as a thin continuous film by a combination of sonication-assisted casting and vapor-assisted conversion, without the need for surface pre-treatment. This is especially helpful for coating substrates composed of different materials. Films obtained in this way show conductivities higher than that of powder pellets with equivalent crystal structure. Temperature-dependent and humidity-dependent measurements on powder pellets revealed the activation energies for charge transport as well as the role of zeolitic water in facilitating the charge transfer. 1. Paolella, A.; Faure, C.; Timoshevskii, V.; Marras, S.; Bertoni, G.; Guerfi, A.; Vijh, A.; Armand, M.; Zaghib, K. A Review on Hexacyanoferrate-based Materials for Energy Storage and Smart Windows: Challenges and Perspectives. Mater. Chem. A 2017, 5, 18919–18932.2. Behera, J. N.; D’Alessandro, D. M.; Soheilnia, N.; Long, J. R. Synthesis and Characterization of Ruthenium and Iron−Ruthenium Prussian Blue Analogues. Mater. 2009, 21, 1922–1926.3. Ishizaki, M.; Ando, H.; Yamada, N.; Tsumoto, K.; Ono, K.; Sutoh, H.; Nakamura, T.; Nakao, Y.; Kurihara, M. Redox-Coupled Alkali-Metal Ion Transport Mechanism in Binder-Free Films of Prussian Blue Nanoparticles. Mater. Chem. A 2019, 7, 4777–4787.4. Ohkoshi, S.-I.; Nakagawa, K.; Tomono, K.; Imoto, K.; Tsunobuchi, Y.; Tokoro, H. High Proton Conductivity in Prussian Blue Analogues and the Interference Effect by Magnetic Ordering. Am. Chem. Soc. 2010, 132, 6620–6621.

Separation of cesium from wastewater with copper hexacyanoferrate film in an electrochemical system driven by microbial fuel cells

A electrochemical adsorption system driven by microbial fuel cell (MFC-adsorption) was developed based on copper(II) hexacyanoferrate(III) (CuHCF) film for cesium (Cs) removal from wastewater. Cs uptake and elution can be simply controlled by regulating the redox states of the CuHCF films. Chemical oxygen demand (COD) removal showed little difference as MFC was connected to adsorption system. Meanwhile, power density and coulombic efficiency of MFC were dramatically reduced. The efficiencies of Cs adsorption and desorption were undesirable. MFC-adsorption technology used for actual nuclear wastewater treatment still has far to go.

Fabrication and Investigation of Crystalline Non-Porous Conductive Coordination Network Compounds

During the last years, surface-bound coordination network compounds (CNCs) have found application for sensing purposes (electrical, optical, and magnetic read-out), charge storage, electrochromic and optoelectronic layers, transparent coatings, bipolar switches, thermoelectric materials, catalytic, photocatalytic and light harvesting applications [1]. However, most of these applications require electrically conductive coordination network compounds (CCNCs). This requirement severely limits the choice of CNCs for the above-mentioned applications. Hexacyanometallates are coordinative networks with high electrical and ion conductivity that possess interesting redox properties and tuneable electrochemical redox transitions associated with clear colour changes [2]. We developed and characterized CCNCs such as copper hexacyanoferrate as thin crystalline films and characterized their optical, magnetic, electrical and dielectric properties. Thin films of these compounds were fabricated on gold and silicon oxide coated by self-assembled, cyanide-terminated monolayers using alternating immersion in their precursor solutions. Atomic force microscopy (AFM) confirms the formation of copper hexacyanoferrate with cubic structure on the gold surface (Fig. 1). Fig. 1: AFM image of copper hexacyanoferrate film on a cyanide-terminated self-assembled monolayer on gold surface via layer-by-layer method. X-ray diffraction (XRD) analysis confirmed the crystalline nature of the films. The thin films can be switched by exploiting the redox chemistry of the metal centres. The modulation of the electrical transport properties provides great potential benefits for numerous future applications in microelectronic device technologies. Structural and electronic changes of the films were probed by X-ray photoelectron spectroscopy (XPS) and polarization modulation infrared reflection absorption spectroscopy (PM IRRAS) before and after electrochemical oxidation and reduction [3]. Results demonstrate the possibility for electrochemical switching of the material properties for each compound but also indicates the complications in those transitions originating in the existence of different structures and defects in which (mobile) alkali metal cations may or may not reside in the pores and provide charge compensation. Acknowledgement(s) Financial supports from DFG priority programme (SPP1928, Wi1617/24) is gratefully acknowledged.

Infrared spectroelectrochemical analysis of potential dependent changes in cobalt hexacyanoferrate and copper hexacyanoferrate films on gold electrodes

Metal hexacyanometallates represent coordination network compounds with a large variety of structurally similar substances. It is well established that they can undergo multiple redox transitions accompanied by cation insertion/ejection. However, the exact assignment of structural changes has remained complicated partially due to the structural variability resulting from different preparation methods and the lack of in situ tools to follow the redox transition and structural changes simultaneously. In this communication we prepared cobalt hexacyanoferrate (CoHCF) and copper hexacyanoferrate (CuHCF) by electrochemical deposition and, additionally, CuHCF by layer-by-layer deposition. These hexacyanoferrate films have a suitable thickness for their spectroelectrochemical characterization by means of polarization modulation infrared reflection-absorption spectroscopy with electrochemical control. Potential-dependent structural changes were followed in both HCF films using the cyanide stretching mode ν(CN) whose detailed position reveals coordination and symmetry around the cyanide bridging ligand. CoHCF undergoes two redox reactions. The spectral analysis of the ν(CN) mode provides clear evidence that oxidation of N-coordinated Co(II) to Co(III) takes place in the first redox process, at E1°′=0.530V. The second redox process at E2°′=0.685V is assigned to a partial oxidation of the C-coordinated Fe(II)/Fe(III). In CuHCF films, one redox process involves predominantly Fe(II)/Fe(III) centers. However, in the electrochemically deposited film a small fraction of the Cu(II) centers is oxidized to Cu(III). The species containing Cu(III) ions are unstable and undergo electron transfer reactions leading to the oxidation of the Fe(II) to Fe(III). In addition, CuHCF shows ‘annealing’ in which some cyanide groups change the coordination to C-coordinated Cu ions and N-coordinated Fe ions.

Column study on electrochemical separation of cesium ions from wastewater using copper hexacyanoferrate film

Nanoparticle film of copper hexacyanoferrate (CuHCFIII) was developed and coated on the rolled sheet electrodes for column cesium separation from wastewater. Results indicated well balance of Cs adsorption and desorption can be achieved switching the potentials between anodes and cathodes. XPS and isotherm studies indicated the electrochemical oxidation–reduction of Fe(II/III) on the monolayer of the CuHCFIII film made contributions to reversible Cs separation. Minimization of secondary waste, simple regeneration and uniformly coating for any size, suggest a promising column technology for sequential removal of Cs from actual wastewater.

Electrochemical Properties of Modified Carbon Paste with Copper Hexacyanoferrate Film on Nitric Oxide Reduction

Copper hexacyanoferate film was prepared electrochemically on carbon paste electrode and was tested for detection of nitric (II) oxide in comparison with unmodified electrodes. Modified electrode could be operated under physiological conditions (pH 7.5, 0.1 M phosphate buffer), with an operating potential of ﹣400 mV (vs. Ag/AgCl) in hydrodynamic amperometry. The amperometric response of the electrode showed good linearity up to 250 μM with a detection limit (3σ) of 8.32 μM. The relative standard deviation for the repeatability of measurements for 100 μM nitric (II) oxide was 4.1% (n = 10 measurements) and the corresponding reproducibility was 14% (n = 5 electrodes). The effect of investigated interferences (nitrite and nitrate ion) was not fatal and could be eliminated using the standard addition method. The modified electrode also seems promising to detect NO in car exhaust fumes.

Structural characterization of electrodeposited copper hexacyanoferrate films by using a spectroscopic multi-technique approach

A deep structural investigation predominantly by X-ray spectroscopic techniques is conducted on films of copper hexacyanoferrate (CuHCF) deposited under different conditions, aimed at establishing structure-properties relationships. We show that the potentiodynamic electrosynthesis of CuHCF on carbon-based surfaces produces a highly disordered material, with a variable amount of Prussian Blue (PB). The subsequent Cu(2+) intercalation induces the partial conversion of PB into CuHCF, which explains the improved electrocatalytic properties after the intercalation process. Both Cu and Fe K-edge data have been recorded. For the sample with the lower amount of PB, we could perform a multiple edge data analysis to determine the local atomic environment around both metal centres using the same set of structural parameters. The presence of high multiplicity Cu-N-C-Fe linear chains has allowed us to determine accurately the local environment of Fe while fitting the Cu K-edge data only. Using this approach we have retrieved structural information around Fe for those samples in which the concomitant presence of PB would have made impossible the analysis of the Fe K-edge. The Fe-C, C-N and Cu-N bond distances have been found in agreement with those of the bulk structures, but higher values of [Fe(CN)(6)] vacancies for the building blocks have been evidenced, reaching a value of ~45% in one sample. XANES, Raman and SEM data agree with the model proposed for each studied electrode.

Influence of copper hexacyanoferrate film thickness on the electrochemical properties of self-assembled 3-mercaptopropyl gold electrode and application as a hydrazine sensor

A copper hexacyanoferrate film was obtained on a modified electrode prepared by self-assembly of 3-mercaptopropyltrimethoxysilane on a gold surface. The film thickness was controlled using a layer-by-layer technique to tune the electrocatalytic properties of the electrode. Two electrodes with different hexacyanoferrate film thicknesses were prepared via three immersions (AuS/CuHCF3) and six immersions (AuS/CuHCF6) of the film in the precursor solutions. Cyclic voltammetry data were obtained to determine the adequate film thickness. Scanning electron microscopy images showed a roughness increase due to the growth of the film thickness at the electrode surface. Electrochemical impedance spectroscopy showed distinct behavior for the two electrodes prepared; while diffusion and charge transfer processes can be observed in both electrodes, an additional capacitive process at intermediary frequencies was observed for the AuS/CuHCF6 electrode. The charge transfer resistance (Rct) for the AuS/CuHCF3 electrode (19.6 Ω cm2) was lower than for AuS/CuHCF6 (27.9 Ω cm2) due to the hexacyanoferrate film thickness, since the charge transfer process demands the simultaneous diffusion of K+ into the surface. Cyclic voltammetry was used to evaluate the application of the AuS/CuHCF3 electrode as an electrochemical sensor, revealing a linear correlation for hydrazine concentrations.

Preparation of Bilayer Platinum and Copper Hexacyanoferrate Hybrid Film Modified Electrode and Its Electrocatalytic Properties

Bilayer platinum and copper hexacyanoferrate hybrid films have been prepared using repetitive cyclic voltammetry (CV). The deposition process and the films’ electrocatalytic properties have been investigated. The electrochemical quartz crystal microbalance and CV were used to study the deposition and growth mechanism of the copper hexacyanoferrate film and platinum/copper hexacyanoferrate hybrid films. Scanning electron microscopy was used to study the surface morphology of the film. In the platinum/copper hexacyanoferrate hybrid films, the peak potentials of the platinum component that demonstrates a proton effect in acidic aqueous solution as the redox couple attributed to copper hexacyanoferrate was found to be cation dependent but not pH dependent. The electrocatalytic reactions of , , and were carried out using the platinum/copper hexacyano- ferrate hybrid films.

Characterization of cobalt- and copper hexacyanoferrate-modified carbon film electrodes for redox-mediated biosensors

Cobalt and copper hexacyanoferrate films (CoHCF and CuHCF) were formed at carbon film electrodes by three different one-step processes: cycling the applied potential, application of a constant current, and chemically. All hexacyanoferrate films obtained were characterized electrochemically by cyclic voltammetry and electrochemical impedance spectroscopy. To evaluate their possible use as redox mediators for biosensors, they were applied to the determination of hydrogen peroxide in neutral phosphate buffer saline electrolyte. Chemically deposited CuHCF was found to be generally the most suitable as a mediator, although CoHCF made by potential cycling is the most useful when a very low detection limit is necessary.

A new, improved sensor for ascorbate determination at copper hexacyanoferrate modified carbon film electrodes

A new, improved sensor for the electrocatalytic determination of ascorbate has been developed that has both a low applied operating potential and a low detection limit. The sensor was constructed by depositing copper hexacyanoferrate film either electrochemically or chemically onto carbon film electrode, and it was then characterised by cyclic voltammetry and electrochemical impedance spectroscopy. Chemically deposited films were shown to be the best for ascorbate determination and were used as an amperometric sensor at +0.05 V versus SCE to determine ascorbate in wines and juice. The linear range extended to 5 mM with a limit of detection of 2.1 microM, the sensor was stable for more than four months, and it could be used continuously for at least 20 days.

Preparation, characterization, and electrocatalytic properties of copper hexacyanoferrate film and bilayer film modified electrodes

Copper(II)hexacyanoferrate films have been prepared from various electrolyte aqueous solutions using consecutive cyclic voltammetry. The cyclic voltammograms recorded the direct deposition of copper(II)hexacyanoferrate films from the mixing of Cu 2+ and Fe(CN) 6 3− ions from solutions of ten cations: Li +, Na +, K +, Rb +, Mg 2+, Ca 2+, Sr 2+, Ba 2+, H + and Al 3+. An electrochemical quartz crystal microbalance (EQCM) and cyclic voltammetry were used to study the in situ growth of the copper(II)hexacyanoferrate films. The copper(II)hexacyanoferrate film showed a single redox couple that exhibited a cation effect (Li +, Na +, K +, Rb + and Cs +) and an anion effect (F −, Cl − and Br −) in the cyclic voltammograms and formal potential of the redox couple. The electrochemical and EQCM properties of the film indicate that the redox process was confined to the immobilized copper(II)hexacyanoferrate, and the interaction between the copper(II)hexacyanoferrate film with K + (monovalent cation) and Ca 2+ (divalent cation). The electrocatalytic oxidation properties of NADH, NH 2OH, N 2H 4, SO 3 2− and S 2O 3 2− were also determined. The electrocatalytic reduction properties of SO 5 2− and S 2O 8 2− by monolayered iron, nickel, and cobalt hexacyanoferrate films, and by bilayered metal–copper hexacyanoferrate films were determined. Two-layered modified electrodes and hybrid films composed of a copper(II)hexacyanoferrate film with iron(II)hexacyanoferrate, cobalt(II)hexacyanoferrate, or nickel(II)hexacyanoferrate film were prepared, and these films caused the electrocatalytic reduction of SO 5 2− and S 2O 8 2−.

High Affinity of Thallium Ions to Copper Hexacyanoferrate Films

High affinity of thallium(I) ions with respect to a copper hexacyanoferrate (CuHCF) film was found. Interaction between the CuHCF film and thallium(I) ions was investigated using the electrochemical quartz crystal microbalance and cyclic voltammetric techniques. In 0.5 M solution, at submillimolar concentrations of Tl(I) ions, the CuHCF film reversibly transforms, during electrochemical experiments, from the potassium into the thallium form. For slightly higher (several millimoles) Tl(I) concentrations, the electrochemical and gravimetric responses prove that the CuHCF film behaves as the thallium form only. Its formal potential calculated from the dependence of the on [Tl(I)], is for 0.28 V more positive than that found for the potassium form. Experimental results obtained suggest that in both cases, potassium(I) and thallium(I) ions, exchange in interstitial positions takes place. Since the ionic radii and the hydration parameters of both ions are similar, we concluded that this high affinity of thallium(I) ions with respect to the CuHCF film, 250-100 times higher than that of potassium(I) ion, results from chemical interactions. In consequence, the solubility product of a thallium analogue of copper hexacyanoferrate is much smaller than that of the potassium form. For different forms they are equal to values): 37.8 46.3 and 17.2 © 2001 The Electrochemical Society. All rights reserved.

Preparation and characterization of Ag‐intercalated copper hexacyanoferrate films on electrodes

AbstractWe demonstrate the possibility of preparation of a mixed metal hexacyanoferrate system, silver‐containing copper hexacyanoferrate, in the form of a thin film on glassy carbon electrode substrate. This novel microstructure is characterized using conventional cyclic voltammetry, visible absorption spectrophotometry, as well as solid‐state electrochemistry in the absence of contact with liquid electrolyte. The results imply distinct physicochemical identity of the system in comparison to silver‐free copper hexacyanoferrate. Incorporation of Ag influences the selectivity of counter‐cation transport which supports redox reactions of the modified electrode in alkali metal supporting electrolytes. Thus the Ag‐intercalated material may be considered for ion‐exchange applications. Following in situ electroanalytical determinations, based on coulometry and stripping‐like voltammetry, we postulate stoichiometries, AgICuIIFeIII(CN)6 and KAgICuIIFeIII(CN)6, for the oxidized and reduced structures.

Electrocatalytic oxidation and amperometric determination of sulfhydryl compounds at a copper hexacyanoferrate film glassy carbon electrode in liquid chromatography

AbstractElectrocatalytic oxidation of sulfhydryl compounds was effective on a copper hexacyanoferrate (CuHCF) film glassy carbon electrode, at a significantly reduced overpotential (0.55 to 0.65 V) and for a broader pH range (2.0 to 7.0). The electrocatalysis was evaluated in terms of several preliminary experimental parameters, such as buffer pH, surface adsorbent concentration, operating potential, mobile‐phase flow rate, and concentration dependence in batch and flow systems. Electrochemical liquid chromatography (LCEC) of sulfhydryl compounds gave a linearity over two orders of magnitude and detection limits at picomole level. Overlaying the CuHCF film electrode surface with a Nafion layer is essential for improving the catalysis stability and offers enhancement of the liquid chromatography electro chemistry (LCEC) response.