Hexacyanoferrate Anions Research Articles

(Digital Presentation) Prussian Blue Analogs – a Wide Variety of Promising Cathode Materials with Peculiar Electrochemical Properties

Today, post-lithium energy storage technologies are now rapidly progressing due to the high price of a net Li-ion battery, which also depends on the desired capacity and power. Among sodium, potassium, calcium, magnesium, and even aluminum-based alternatives, young potassium-ion batteries demonstrate high capacity and energy density, notable ionic transport in electrolytes, the possibility to employ graphite anodes, and a wide variety of possible electrode materials: layered oxides, polyanionic, organic compounds, Prussian Blue analogs. However, the latter ones are generally considered as the most promising and practically viable.Prussian Blue analogs form a big family of electrode materials with the general formula KxM1[M2(CN)6]∙nH2O, where x=0...2, and Mi are any possible 3d transition metals. The most well-known and commercially available is based on a hexacyanoferrate anion [Fe(CN)6]n-, while other transition metals can also form hexacyanometallate complexes, but are poorly studied or not known at all. The most part of published works shed light on the morphology and low content of water defects inside crystallites counting the lack of hexacyanoferrate, and their influence on realized capacity and capacity fades, while the fundamental principles and real water position presence which guide the electrochemical activity of high- and low-spin cations in these materials are totally missed.In our work, we also started with the intrinsic water defects and their impact on crystal and physicochemical properties in K2Mn[Fe(CN)6]∙nH2O but with sensitive to light atoms neutron diffraction technique. We observed that water content does not effect the whole crystal symmetry but slightly amend unit cell parameters. Besides the fact of decreasing a decomposition temperature in “watered” Prussian Blue analog, electrochemical properties were found close. Therefore, we concluded that intrinsic water does not notably influence material properties. Continuing with potassium manganese hexacyanoferrate and electronic structure impact to the compound properties, to reveal the best synergetic stabilizing agent during cycling, we synthesized and studied the system K2-γMn1-xCox[Fe(CN)6]∙nH2O with x=0, 0.05,...1. In addition to symmetry and composition transformations, magnetic and electrochemical properties also significantly differ, while higher cobalt content increases the redox potential of iron, but drastically decreases total capacity due to the inability of reaching iron oxidation. The fact of notable changing of redox potentials in K2-γMn1-xCox[Fe(CN)6]∙nH2O is inspiring, and we have been extending with other hexacyanometallates. Hexacyanomanganate-ion [Mn(CN)6]n- is one of the promising pathways to investigate such systems with a more fundamental point of view, and the obtained experimental results confirm the hypothesis. We discovered that cation position exchange totally alters the electrochemistry of the Prussian Blue cathode materials, and the interpretation still raises a lot of questions and assumptions, and together with computational chemistry, we will try to answer the fundamental questions about electronic, crystal structures and electrochemical properties. In this report we will present the new correlations of redox potential in Prussian Blue analogs depending on transition metal position and electronic structure, evaluate diffusion of potassium in these materials, and try to answer the possibility to use these compounds in potassium-ion batteries.

Quantification of Tyrosine in Pharmaceuticals with the New Biosensor Based on Laccase-Modified Polypyrrole Polymeric Thin Film.

Stress, a state of body tension, sometimes caused by increased levels of tyrosine (Tyr) in the body, can lead to serious illnesses such as depression, irritability, anxiety, damage to the thyroid gland, and insomnia. The body can be provided with an adequate concentration of tyrosine by taking pharmaceutical products or by dietary intake. Therefore, this study presents the development of a new enzyme sensor for the quantification of Tyr in pharmaceuticals. A screen-printed carbon electrode (SPCE) was modified with the conductive polymer (CP) polypyrrole (PPy) doped with hexacyanoferrate (II) anion (FeCN), the polymer having been selected for its excellent properties, namely, permeability, conductivity, and stability. The enzyme laccase (Lacc) was subsequently immobilized in the polymer matrix and cross-linked with glutaraldehyde, as this enzyme is a thermostable catalyst, greatly improving the performance of the biosensor. The electrochemical method of analysis of the new device, Lacc/PPy/FeCN/SPCE, was cyclic voltammetry (CV), and chronoamperometry (CA) contributed to the study of changes in the biosensor with doped PPy. CV measurements confirmed that the Lacc/PPy/FeCN/SPCE biosensor is a sensitive and efficient platform for Tyr detection. Thus, this enzyme sensor showed a very low limit of detection (LOD) of 2.29 × 10−8 M, a limit of quantification (LOQ) of 7.63 × 10−8 M, and a very high sensitivity compared to both devices reported in the literature and the PPy/FeCN/SPCE sensor. Quantitative determination in pharmaceuticals was performed in L-Tyr solution of different concentrations ranging from 0.09 to 7 × 10−6 M. Validation of the device was performed by infrared spectrometry (FT-IR) on three pharmaceuticals from different manufacturers and with different Tyr concentrations.

The effect of halogen bonding on protonated hexacyanoferrate networks in hexacyanoferrates of halogenopyridines

Hydrogen bonded network of protonated hexacyanoferrate anions is determined by geometry and halogen bonding proclivity of the halogenopyridinium cation.

Reaction kinetics of sonochemical oxidation of potassium hexacyanoferrate(II) in aqueous solutions.

We studied sonochemical reactions resulting from ultrasonic treatment of potassium hexacyanoferrate(II) in aqueous solutions using a custom-built apparatus working at 536kHz. We concluded that primary reactions are completely dominated by oxidation of Fe(II) to Fe(III) and did not find any evidences for degradation of cyanide. At the highest concentration used in the present study (0.1M) we detected formation of pentacyanoaquaferrate(II) complex, which is most probably formed in reactions between hexacyanoferrate(III) anions and hydrogen atoms or hydrated electrons formed in sonochemical processes. We also determined that hydroxyl radicals formation rate in our system, (8.7±1.5)∙10-8 M∙s-1, is relatively high compared to other reported experiments. We attribute this to focusing of the ultrasonic wave in the sample vessel. Finally, we suggest that oxidation rate of hexacyanoferrate(II) anions can be a convenient benchmark of efficiency of sonochemical reactors.

Slow Magnetic Relaxation, Antiferromagnetic Ordering, and Metamagnetism in MnII (H2 dapsc)-FeIII (CN)6 Chain Complex with Highly Anisotropic Fe-CN-Mn Spin Coupling.

Reactions of [Mn(H2 dapsc)Cl2 ]⋅H2 O (dapsc=2,6- diacetylpyridine bis(semicarbazone)) with K3 [Fe(CN)6 ] and (PPh4 )3 [Fe(CN)6 ] lead to the formation of the chain polymeric complex {[Mn(H2 dapsc)][Fe(CN)6 ][K(H2 O)3.5 ]}n ⋅1.5n H2 O (1) and the discrete pentanuclear complex {[Mn(H2 dapsc)]3 [Fe(CN)6 ]2 (H2 O)2 }⋅4 CH3 OH⋅3.4 H2 O (2), respectively. In the crystal structure of 1 the high-spin [MnII (H2 dapsc)]2+ cations and low-spin hexacyanoferrate(III) anions are assembled into alternating heterometallic cyano-bridged chains. The K+ ions are located between the chains and are coordinated by oxygen atoms of the H2 dapsc ligand and water molecules. The magnetic structure of 1 is built from ferrimagnetic chains, which are antiferromagnetically coupled. The complex exhibits metamagnetism and frequency-dependent ac magnetic susceptibility, indicating single-chain magnetic behavior with a Mydosh-parameter φ=0.12 and an effective energy barrier (Ueff /kB ) of 36.0 K with τ0 =2.34×10-11 s for the spin relaxation. Detailed theoretical analysis showed highly anisotropic intra-chain spin coupling between [FeIII (CN)6 ]3- and [MnII (H2 dapsc)]2+ units resulting from orbital degeneracy and unquenched orbital momentum of [FeIII (CN)6 ]3- complexes. The origin of the metamagnetic transition is discussed in terms of strong magnetic anisotropy and weak AF interchain spin coupling.

Ultra-slow diffusion of hexacyanoferrate anions in poly(diallyldimethyl ammonium chloride)-poly(acrylic acid sodium salt) multilayer films

Polyelectrolyte multilayer (PEM) films display either a linear or an exponential increase of their thickness with increasing the number of polycation/polyanion deposition cycles. Each of these growth regimes is further associated with a specific mode of internal PEM charge compensation: either intrinsic in the case of linearly growing films, or extrinsic for exponentially growing films with incorporation of small ions from the neighbouring electrolyte solution. In this report, we investigate by electrochemistry the charge compensation mechanism operational for poly(diallyldimethyl ammonium chloride)-poly(acrylic acid sodium salt) (PDAMAC-PAA)n films recently found to be out-of-equilibrium immediately after the deposition process despite of their exponential growth mode. It is found here that these films are defined by a negative Donnan potential drop (ca. −160 mV), thus evidencing an extrinsic charge compensation process, and most importantly, by a remarkably slow kinetics for loading of hexacyanoferrate anions, a very unusual property for PEMs with exponential growth. Depending on the film thickness, the diffusion coefficient of the redox probe in the film is found to be of the order of 10−13 − 10−15 cm2 s−1, i.e. about 8 to 10 orders of magnitude less than that typically measured in aqueous solution. This results in a steady state filling of e.g. a 2.8 µm thick PEM film with the redox probe that is achieved after more than 40 h, a feature in line with the typical 4 to 5 days relaxation timescale of the film structure previously determined by atomic force microscopy and Raman micro-spectroscopy analyses.

Thin layer films of copper hexacyanoferrate: Structure identification and analytical applications

Thin films of copper hexacyanoferrate (CuHCF) have been reproducibly electrodeposited on conductive substrates according to two different potentiostatic methods, here denoted as A and B. For both methods two consecutive steps are involved, the first being the electrodeposition of a thin Cu layer, the second its partial dissolution and formation of CuHCF in presence of hexacyanoferrate anion, giving as result a two layers film (CuHCF on Cu metal). The main difference, instead, consists in the applied potential values and their application times, featuring Method A lower potentials but longer processing times. Structural insights have been achieved by means of X-ray Diffraction (XRD) and X-ray Absorption Fine Structure (XAFS) measurements, from which we can deduce the presence of Prussian blue (PB) impurities in Method A, while Method B leads to a pure CuHCF phase. Two analytical applications have been considered, ion exchange and H2O2 sensing. Ion exchange has been first assayed and, although CuHCF-A shows a higher stability towards multivalent cations, CuHCF-B is suitable for small hydrated ions. PB impurities in CuHCF-A boost its sensing towards H2O2, making it more adapted to this employment.

Study of binary self-assembled monolayers of a novel anchoring thiol (11-mercaptoundecyl-N′,N″,N‴-trimethylammonium) in the electron transfer with glucose oxidase enzyme

In this study, we explore the fabrication and properties of a sensing electrochemical platform that is based on a novel 11-mercaptoundecyl-N′,N″,N‴-trimethylammonium hexacyanoferrate (MAH) and 6-(ferrocenyl)hexanethiol (FT)/glucose oxidase (GOx) on gold substrate. The hexacyanoferrate and ferrocene moieties that were immobilized on the gold surface were examined as electron transfer mediators with the oxidase glucose. The sensing platform, based on 11-mercaptoundecyl-N′,N″,N‴-trimethylammonium hexacyanoferrate (MAH) and 6-(ferrocenyl)hexanethiol (FT)/GOx modified gold electrode, shows the potential to work with two distinct mechanisms for electrochemical response. The hexacyanoferrate anion that was anchored at positive edge charge of the 11-mercaptoundecyl-N′,N″,N‴-trimethylammonium on the gold surface provided an efficient electron transfer. It was demonstrated that in the design of the GOx/MAH, the FT/Au electrode is facilitating the electron transfer from GOx toward the gold substrate. We believe that this study adds a new facet to nanobioelectronics with applications for biofuels and sensorial platforms.

Supramolecular inter-ionic charge-transfer complexes between derivatives of pyridinium-4-oxime cations and hexacyanoferrate(ii) anions

Mono- and bis-pyridinium-4-oxime compounds are introduced as new electron acceptors for the formation of colored, supramolecular, inter-ionic charge-transfer complexes with hexacyanoferrate(ii) as a donor.

New Tricks by Old Anions: Hydrogen Bonded Hexacyanoferrous Anionic Networks

Hexacyanoferrates are well-known to form metal–organic frameworks by coordination to metal atoms or acting as hydrogen bond acceptors. In this paper we report a new type of hexacyanoferrate self-assembly, based on direct hydrogen bonding of partially protonated hexacyanoferrate anions. By preparing a series of 15 hexacyanoferrates with various organic bases, we have found that protonated hexacyanoferrates (present in 10 structures) readily form chains (two structures), two-dimensional (four structures), or three-dimensional networks (four structures), whereby the dimensionality of the network generally increases with the protonation degree of the hexacyanoferrates. The exact mode of the self-assembly, including the network type, depends on fine interplay of the pKa value of the base, its steric properties, and the stoichiometry of the formed solid.

Electrochemical behaviors of iron-based layered double hydroxide thin-films

The ordered ultrathin films based on the fabrication of Mg/Fe-LDHs ([Mg6Fe2(OH)16CO3·(H2O)4.5]0.375) nanosheets and hexacyanoferrate(III) anions via the self-assembly procedure were prepared. The electrodes modified by the films demonstrated a couple of well-defined reversible redox peaks attributed to [Fe(CN)6]3−/4− and Fe2+/3+ couples. The effects of cycle number, scan rate and Mg/Fe molar ratio on the CV performance of the thin-film electrodes were observed in K3[Fe(CN)6] electrolyte. The [Fe(CN)6]3− pillared Mg/Fe-LDHs with Mg/Fe molar ratio of 3 (LDH-(CN)-3) demonstrated an excellent electrochemical behavior with a potential window between − 0.2 and 1.0 V, high specific capacitance and sensitivity, indicating that the high crystallinity, large specific surface area and plentiful [Fe(CN)6]3− anions in interlayer spaces were necessary. Especially, the interlayer [Fe(CN)6]3− anions significantly affected the electrochemical behavior of the electrode, where the electrode reaction was controlled by the diffusion of [Fe(CN)6]3−/4− and Fe2+/3+ couples. Under current density of 2.5 A g−1, the optimized LDH-(CN)-3 electrode exhibited high specific capacitance of 250.81 F g−1 with good cycling stability. This facile synthesis strategy and the good electrochemical properties indicated that the LDH-(CN)-3 was a potential economical alternative material for supercapacitor application.

Thermal behavior of binary complex сompounds сontaining the hexacyanoferrate anion

The thermal behavior of compounds with the general formula [MA6] x [Fe(CN)6] y (M = Со, Cu, Ni, A = NH3, 1/2 C3H10N2) in air, argon, nitrogen, and hydrogen at temperatures between 20 to 1000°C was studied. The study involved measurement of TG–DSC–DTG curves and analysis of solid and gaseous thermolysis products. It was found that the process is not affected by the nature of the atmosphere up to about 200°C. The coordinated cyanide ion partially releases as hydrogen cyanide. The destruction of diamines forms NH3, and a large amount of carbon remains in the solid phase.

Electrooxidation of Hexacyanoferrate(II) Anions and Electroreduction of Oxygen in the Microfabricated Electrochemical Sensor-Array System

The microfabrication technique was used to prepare a six-channel sensor-array chip. The sensor-array has been fabricated using borosilicate wafer containing Pt electrodes and connection pads and the silicon wafer with through holes, which were bonded with SU-8 using adhesion bonding method. To characterize the prepared sensor-array chips the cyclic voltammetry and electrochemical impedance experiments were carried out in a three-electrode electrochemical system. The electrooxidation of ferrocyanide and electroreduction of oxygen were studied. It was shown that the measured current density depends on the electrode potential sweep rate however, both linear and radial diffusion mass transfer components are important at high electrode potential scanning rate. The pseudo steady-state conditions were achieved at slow potential sweep rates (>0.01 V s‒1) and the electrodes behaved as the microelectrodes. The pseudo steady-state current density is proportional to the concentration of electroactive species. The recessed microdisc electrode model has been used to describe the system.

Supramolecular complexes involving non-symmetric viologen cations and hexacyanoferrate(ii) anions. A spectroscopic, crystallographic and computational study

We have investigated spectrally, crystallographically as well as computationally charge transfer complexes involving synthesizedN-aryl-N′-methyl non-symmetric viologen cations and hexacyanoferrate(ii) anions.

Is the Hexacyanoferrate(II) Anion Stable in Aqueous Solution? A Combined Theoretical and Experimental Study.

A combined theoretical and experimental study was performed to elucidate the structural and dynamical properties of the isolated aqueous hexacyanoferrate(II) ion as well as in the presence of potassium counterions. It is shown that in absence of counterions, the highly negatively charged hexacyanoferrate(II) complex is not stable in aqueous solution. However, if the high negative charge is compensated by potassium counterions, a stable complex is observed, which is proven by theoretical simulations as well as by extended X-ray absorption fine structure (EXAFS) experiments. From the simulation it is found that potassium ions surrounding the complex are highly mobile and thus cannot be observed via EXAFS experiments. The structure of aqueous hexacyanoferrate(II) in the presence of potassium ions is identical to that of the solid-state structure, but the mobility of potassium ions is significantly increased in the liquid. These highly mobile potassium ions circulating the complex are the reason for the very short lifetime of hydrogen bonds between solvent water molecules and cyanide ligands being on the femtosecond scale.

Effective removal of hexacyanoferrate anions using quaternary amine type ion exchange resin

Styrene-ethylstyrene divinylbenzene type copolymer modified with methyl chloride and trimethylamino chloride moieties was studied for its potential application for the removal of hexacyanoferrate anions [Fe(CN)6]α−, HCF, from various waste waters. The material is found to be highly effective on recovering both ferrous-, HCF(II), and ferric-, HCF(III), hexacyanide ions. Based on the difference observed in the presence of either NO3− or SO42− ions, the selectivity order is found to be NO3−>HCF(III)>SO42−>HCF(II), which is not in agreement with the number of charged units required for binding the given ion. In a complex solution system like a fly ash extract, the selectivity for HCF(II) has dropped but the material was highly effective for HCF(III), which does not possess adverse impact as oxidation of ferrous ions is a spontaneous phenomenon. Therefore, the resin offered peculiar selectivity and strong potential as a counter-measure for HCF decontamination.

Permeabilty of silver cations through (PAH–PSS)m polyelectrolyte multilayer films to deposit silver in underlying (PAH–tannic acid)n film without external reducing agent at pH 5.0

Polyelectrolyte multilayer films made from the alternated deposition of poly(allylamine) as the polycation (PAH) and from poly(styrene-4-sulfonic acid) as the polyanion are known to be very compact and impermeable to multivalent ions and to display a strong selectivity for monovalent cations with respect to multilvalent ones. Herein, the particular case of the diffusion of silver cations at pH 5.0 through (PAH–PSS)m films of variable thickness is investigated using an original detection method of the silver cations. In this method, the (PAH–PSS)m multilayer films are deposited on films made from the alternated adsorption of PAH and tannic acid (TA). When those (PAH–TA)n films are put in contact with Ag+ cations, the TA allows for the reduction of Ag+ cations in silver particles easily detectable by means of UV–vis spectroscopy. The deposition of (PAH–PSS)m multilayers on top of (PAH–TA)6 films does not imped the deposition of silver up to m = 10 (PAH–PSS) bilayers, corresponding to a thickness of 25 nm. The high permeability of (PAH–PSS)m films is not due to a lack of homogeinity because hexacyanoferrate anions are not able to react with Fe3+ cations encapsulated in (PAH–TA)6 films when those films are capped with a (PAH–PSS)5 film known to be impermeable to Fe(CN)64− in the absence of defects in the film. It is also found that the reduction of Ag+ cations on a (PAH–TA)4 film is a slow process needing more than 1 h to be achieved.

An electrochemical DNA-based biosensor to study the effects of CdTe quantum dots on UV-induced damage of DNA

A DNA-based biosensor is presented that can be applied to the detection of DNA damage caused by UV-C radiation (254 nm) in the presence of CdTe quantum dots (QDs). The sensor is composed of a glassy carbon electrode whose surface was modified with a layer of dsDNA and an- other layer of CdTe QDs. The response of this sensor is based on (a) the intrinsic anodic signal of the guanine moiety in the DNA that is measured by square-wave voltammetry, and (b) thecyclicvoltammetricresponseoftheredoxindicatorsystem hexacyanoferrate(III/II). Depending on the size of the QDs, they exert a significant effect on the rate of the degradation of dsDNA by UV-C light, and even by visible light. Time- dependent structural changes of DNA include opening of the doublehelix (as indicated byanincrease inthe redox response of the guanine moiety due to easy electron exchange with the electrode when compared to the original helix state and by an increase in the voltammetric peak current of the hexacyanoferrate(III/II) anion after degradation of the nega- tively charged DNA backbone on the electrode). The effects of QDs were verified for salmon sperm DNA and calf thymus DNA,andfurthercorroboratedbyexperimentsinwhichDNA solutions were irradiated in the presence of QDs.

Layer-by-layer deposition of tannic acid and Fe3+ cations is of electrostatic nature but almost ionic strength independent at pH 5

The step-by-step assembly of tannic acid (TA) and of Fe3+ cations allows to produce films of controlled thickness using exclusively small multivalent ions. In the present investigation, it is shown that even if electrostatic interactions are dominant over ligand to metal charge transfer interactions in stabilizing such films, those electrostatic interactions display a small sensitivity to concentration in NaCl used as a supporting electrolyte as well as to the concentration in sodium acetate in the absence of NaCl. This finding highlights the strong stability of the films obtained through the step-by-step deposition of TA and Fe3+ cations. Complementarily, the films made from 6 deposition cycles of TA and Fe3+ cations do not form Prussian Blue when put in contact with hexacyanoferrate anions. This shows that Fe3+ is so tightly bound to the film that it is not able to form a coordination polymer with Fe(CN)64− anions.

Phase Diagram of Sodium Hexametaphosphate and Poly(allylamine hydrochloride) Mixtures and In Situ Monitoring of Step‐by‐Step Deposition in This Polyelectrolyte System

The step‐by‐step deposition of poly(allylamine hydrochloride) (PAH) and sodium hexameta­phosphate (PSP) leads to coatings displaying interesting intumescent properties and is a fascinating model system to understand the fundamental mechanism behind such a deposition process. In this investigation, the deposition kinetics of (PAH‐PSP)n is followed in situ by means of a quartz crystal microbalance with dissipation monitoring, as a function of NaCl concentration. The evolution of the film deposition is analyzed in detail and the data are compared with previous data obtained by ellipsometry on dried films. These results are also compared with the expectations from the PAH/PSP phase diagram. The (PAH‐PSP)n films are also able to incorporate hexacyanoferrate anions with an amount of an incorporated redox probe reflecting the film thickness as obtained in the presence of eletrolyte solutions of increasing ionic strength. The in situ measurements and the electrochemical probe experiments reveal details of the film deposition mechanism that are not accessible by dry‐state characterization methods. image