Abstract
The kinetics of thermal dehydration of K2x/3Cu[Fe(CN)6]2/3·nH2O 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 ≤ α ≤ 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 H2O)−1 for x = 0.0 and 27 kJ (mol H2O)−1 for x = 1.0, relative to that of water. The increase with increasing x is evidence that the H2O molecules form bonds to the incorporated K+ ions.
Highlights
Rechargeable battery systems manufactured from low-cost materials are needed to support current intermittent power sources, e.g. the sun and wind [1]
Water-based systems with Prussian blue analogues (PBAs), e.g. copper hexacyanoferrate (CuHCF), as electrodes exhibit a number of merits; they can be synthesized in large quantities from cheap precursors and show long cycle lives, fast kinetics, high power operations, and good energy efficiencies [2]
We have investigated the characteristics and kinetics of the thermal dehydration of the two end compositions of K2x/3Cu[Fe(CN)6]2/3ÁnH2O with nominally x = 0.0 and x = 1.0, using model-free kinetic analysis, as well as determined the degree of hydration as a function of x
Summary
Rechargeable battery systems manufactured from low-cost materials are needed to support current intermittent power sources, e.g. the sun and wind [1]. Water contents were determined for nominal x values 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0 from TG runs in air and at heating rates of 10 °C min-1. Isoconversional methods rest on the assumption that the reaction models are independent of temperature and can be considered constant at fixed values of conversion. As isoconversional kinetic analyses are carried out over a set of measurements at specific values of a, the reaction rate will be a function of temperature only [23]. Different pairs of the Arrhenius parameters, Aj and Ej, are obtained by substituting expressions of g(a) for different reaction models j and fitting them to experimental data according to gðaÞ ln T2. By plotting the parameters lnAj and Ej, for a single heating run and different models, the compensation effect constants can be determined. The predictions work as verification that the obtained results are able to adequately describe the reaction behaviour
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