Electrochemical Charging, Countercation Accommodation, and Spectrochemical Identity of Microcrystalline Solid Cobalt Hexacyanoferrate

Abstract

Oxidized and reduced cobalt(II) hexacyanoferrates were fabricated and characterized in the presence of alkali metal (Li+, Na+, K+, Cs+) and Co2+ countercations. Formal potentials of hexacyanoferrate(III,II) redox reactions are sensitive to the choice of electrolyte cation, and they correlate well with the sizes of hydrated Li+, Na+, and K+. Electrochemical quartz crystal microbalance measurements clearly indicate that countercations, presumably in partially dehydrated form, are incorporated into reduced cobalt(II) hexacyanoferrate(II). The color of the system reflects primarily the oxidation state of iron sites. But the color of the reduced form is also affected by the nature of an intercalated hydrated countercation. This observation is correlated with the reversible continuous thermochromism of K2CoII[FeII(CN)6]*nH2O that shall be attributed to the release of structural water molecules interacting with CoII during heating in the temperature range 25−85 °C. It is apparent from X-ray absorption near-edge structure (XANES) experiments that the chemical environment of cobalt(II) sites is influenced by the presence of hydrated alkali metal countercations. The results are consistent with the accommodation of countercations in the lattice cavities at interstitial positions. The structural environment of iron ions was the same in all systems studied except that a chemical shift was observed due to change of the oxidation state of iron.

Th(IV)-hexacyanoferrate modified carbon paste electrode as a new electrocatalytic probe for simultaneous determination of ascorbic acid and dopamine from acidic media

“…The anodic peak current increased with the increase in the concentration of AA. The significant negative shift in the peak potential about 330 mV and the enhanced current response observed with the THMCPE compared to bare CPE indicate a strong electrocatalytic effect of Fe(CN) 6 3-/Fe(CN) 6 4-redox couple in the THMCPE towards the oxidation of AA.…”

“…19, No. 7, 2008 as Th[Fe(CN) 6 ] by the chemical analysis. The carbon paste electrode was prepared by hand-mixing of graphite powder, paraffin and Th-HCF ion-pair.…”

Cubic Copper Hexacyanoferrates Nanoparticles: Facile Template-Free Deposition and Electrocatalytic Sensing Towards Hydrazine

“…The good permeability of Li + can be reasonably explained in terms of a partial dehydration of hydrated Li + that reduces the cation to an appropriate size to enter the lattice. [20,21] The radii of naked ions Li + , Na + , K + , NH 4 and those of hydrated ions are 2.1, 1.8, 1.25, and 1.25Å, respectively; after complete dehydration, naked Li + has the smallest radius, which may be a prerequisite for it to be incorporated into the CuHCF lattice [12]. Figure 2(a) shows cyclic voltammetric responses of the CuHCF-modified electrode recorded in KNO 3 electrolytes with K + concentrations varied from 0.01 to 0.15 M. With increasing K + concentration, the voltammetric peak potentials were shifted to more positive potentials, and the result is in good agreement with the involvement of potassium ions in the redox reaction [21].…”

New Developments in Electrochemical Sensors Based on Poly(3,4-ethylenedioxythiophene)-Modified Electrodes

“…Conducting organic polymers also constitute a category of materials showing suitable reversible redox chemistry. On the other hand, considerable interest has been also devoted to the preparation and characterisation of polynuclear transition metal hexacyanoferrates by virtue of their characteristics which include electrochromic properties [29], ability to mediate redox reactions [30][31][32][33]. The transition metal hexacyanoferrates represent an important class of insoluble mixed valence compounds.…”