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Structure and population of complex ionic species in FeCl[sub]2 aqueous solution by X-ray absorption spectroscopy
Matjaž Valant, Iztok Arčon, Uroš Luin, 2022, izvirni znanstveni članek

Opis: Technologies for mass production require cheap and abundant materials such as ferrous chloride (FeCl2). The literature survey shows the lack of experimental studies to validate theoretical conclusions related to the population of ionic Fe-species in the aqueous FeCl2 solution. Here, we present an in situ X-ray absorption study of the structure of the ionic species in the FeCl2 aqueous solution at different concentrations (1–4 molL−1) and temperatures (25–80 ◦C). We found that at low temperature and low FeCl2 concentration, the octahedral first coordination sphere around Fe is occupied by one Cl ion at a distance of 2.33 (±0.02) Å and five water molecules at a distance of 2.095 (±0.005) Å. The structure of the ionic complex gradually changes with an increase in temperature and/or concentration. The apical water molecule is substituted by a chlorine ion to yield a neutral Fe[Cl2(H2O)4]0. The observed substitutional mechanism is facilitated by the presence of the intramolecular hydrogen bonds as well as entropic reasons. The transition from the single charged Fe[Cl(H2O)5]+ to the neutral Fe[Cl2(H2O)4]0 causes a significant drop in the solution conductivity, which well correlates with the existing conductivity models.
Najdeno v: ključnih besedah
Povzetek najdenega: ...require cheap and abundant materials such as ferrous chloride (FeCl2). The literature survey shows the...
Ključne besede: structure, population, ionic species, aqueous ferrous chloride, in situ X-ray absorption spectroscopy
Objavljeno: 24.01.2022; Ogledov: 733; Prenosov: 19
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Electrolysis energy efficiency of highly concentrated FeCl[sub]2 solutions for power-to-solid energy storage technology
Matjaž Valant, Uroš Luin, 2022, izvirni znanstveni članek

Opis: An electrochemical cycle for the grid energy storage in the redox potential of Fe involves the electrolysis of a highly concentrated aqueous FeCl2 solution yielding solid iron deposits. For the high overall energy efficiency of the cycle, it is crucial to maximize the energy efficiency of the electrolysis process. Here we present a study of the influence of electrolysis parameters on the energy efficiency of such electrolysis, performed in an industrial-type electrolyzer. We studied the conductivity of the FeCl2 solution as a function of concentration and temperature and correlated it with the electrolysis energy efficiency. The deviation from the correlation indicated an important contribution from the conductivity of the ion-exchange membrane. Another important studied parameter was the applied current density. We quantitatively showed how the contribution of the resistance polarization increases with the current density, causing a decrease in overall energy efficiency. The highest energy efficiency of 89 ± 3% was achieved using 2.5 mol L−1 FeCl2 solution at 70 °C and a current density of 0.1 kA m−2. In terms of the energy input per Fe mass, this means 1.88 Wh g−1. The limiting energy input per mass of the Fe deposit was found to be 1.76 Wh g−1.
Najdeno v: ključnih besedah
Povzetek najdenega: ...electrolysis, ferrous chloride, iron deposition, energy efficiency...
Ključne besede: electrolysis, ferrous chloride, iron deposition, energy efficiency
Objavljeno: 16.02.2022; Ogledov: 641; Prenosov: 36
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