A thermogravimetric study of thermal dehydration of copper hexacyanoferrate by means of model-free kinetic analysis

Abstract

The kinetics of thermal dehydration of K 2x/3 Cu [Fe(CN) 6 ] 2/3 ÁnH 2 O was studied using thermogravimetry for x = 0.0 and 1.0. Data from both non-isothermal and isothermal measurements were used for model-free kinetic analysis by the Friedman and KAS methods. The water content was determined to be n = 2.9-3.9, plus an additional *10% of water, likely surface adsorbed, that leaves very fast when samples are exposed to a dry atmosphere. The determined average activation energy for 0.2 B a B 0.8 is 56 kJ mol -1 . The dehydration is adequately described as a diffusion-controlled single-step reaction following the D3 Jander model. The determined dehydration enthalpy is 11 kJ (mol H 2 O) -1 for x = 0.0 and 27 kJ (mol H 2 O) -1 for x = 1.0, relative to that of water. The increase with increasing x is evidence that the H 2 O molecules form bonds to the incorporated K ? ions.

Coprecipitation Temperature Effects of Morphology‐Controlled Nickel Hexacyanoferrate on the Electrochemical Performance in Aqueous Sodium‐Ion Batteries

“…In addition, the water molecules in the aqueous precursor would be contained as the zeolitic water at the interstitial sites of PBAs or coordinated with the vacant Fe(CN) 6 sites during the coprecipitation [6a,15a,26c] . Thus, the water amount within the coprecipitated NiHCF sample is directly proportional to the vacancy concentration within the NiHCF matrix [26b] . TGA/DSC analysis was conducted to determine the water content of all‐prepared NiHCF samples to ascertain the degree of crystallinity (Figure 4).…”

“…The adsorbed water weakly bound on the PBA surface was already removed since the as‐prepared NiHCF samples were dried at 80 °C in a vacuum before the TGA/DSC measurement [26d] . In the DSC profile, the endothermic peak between the room temperature and approximately 250 °C appears to evaporate the included water [26b–d] . Correspondingly, the weight loss experienced up to about 250 °C in the TGA curve indicates the water content within the NiHCF sample.…”

Influence of the Presence of Different Alkali Cations and the Amount of Fe(CN)6 Vacancies on CO2 Adsorption on Copper Hexacyanoferrates

“…The influence of the presence of A cations on the CO 2 adsorption for compounds A 2 / 3 Cu[Fe(CN) 6 ] 2/3 resemble the observed differences in thermal dehydration for cation free Cu[Fe(CN) 6 ] 2/3 ⋅ n H 2 O and K 2 / 3 Cu[Fe(CN) 6 ] 2/3 ⋅n H 2 O PBAs [9]. The dehydration enthalpy is larger for the latter compound, evidencing that the H 2 O molecules form bonds to the K + ions.…”

“…In previous work we have synthesized PBAs with a nominal formula K 2 x /3 Cu 2+ [Fe 2+ x Fe 3+ 1- x (CN) 6 ] 2/3 ⋅ n H 2 O and characterized the compounds by a variety of techniques [7]. The structures of the end-members with x = 0 and 1 were further studied by neutron powder diffraction and EXAFS [8], and the kinetics of their thermal dehydration studied by thermogravimetry [9]. The CO 2 adsorption capabilities of them were reported in [4].…”

Low-Potential Prussian Blue Analogues for Sodium-Ion Batteries: Manganese Hexacyanochromate

“…Between 30 o C and 150 o C there is the first mass loss step, corresponding to dehydration of the materials as seen through the m/z=18 mass spectrometry trace. Within this trace there are two distinct water evolutions steps which could correspond to water loss from two distinct environments, firstly the loosely bound zeolitic water and the second the coordinated water molecules at higher temperatures 22 . This is most clearly seen in the DSC trace as two distinguishable endothermic steps peaking at 80 o C and 124 o C. The second mass loss step shows CO2 release which is indictive of breakdown of the crystalline structure.…”