Efficiency of the grid energy storage technology based on iron-chloride material cycleUroš Luin
, doktorska disertacija
Opis: Future high-capacity energy storage technologies are crucial for a highly renewable energy mix, and their mass deployment must rely on cheap and abundant materials, such as iron chloride. The iron chloride electrochemical cycle (ICEC), suitable for long-term grid energy storage using a redox potential change of Fe2+/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 maximizing the energy efficiency of the electrolysis process. The thesis presents a study of the influence of electrolysis parameters on energy efficiency, performed in an industrial-type electrolyzer system. We studied the conductivity of the FeCl2 solution as a function of concentration and temperature and correlated it with the electrolysis energy efficiency as a function of current density. 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 dm-3 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, calculated by extrapolating experimental results toward Eocell potential, was found to be 1.76 Wh g-1. For optimal long-duration electrolysis efficiency and performance, the optimal catholyte concentration range is
1-2 mol dm-3 FeCl2. We performed in situ X-ray absorption spectroscopy experimental studies to validate theoretical conclusions from literature related to the population and structure of Fe-species in the FeCl2 (aq) solution at different concentrations (1 - 4 mol dm-3) and temperatures (25 - 80 °C). This revealed 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 H2O 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 H2O is substituted by a Cl ion to yield a neutral Fe[Cl2(H2O)4]0. The transition from the 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 state-of-the-art conductivity models. An additional steric impediment of the electrolytic cell is caused by the predominant neutral species present in the catholyte solution at high concentration. This correlates with poor electrolysis performance at a very high catholyte concentration (4 mol dm-3 FeCl2), especially at high current densities (> 1 kA m-2). The neutral Fe[Cl2(H2O)4]0 complex negatively affects the anion exchange membrane ion (Cl-) transfer and lowers the concentration of electroactive species (Fe[Cl(H2O)5]+) at the cathode surface. The kinetics of hydrogen evolution from the reaction between Fe powder and HCl acid was studied under the first-order reaction condition. The activation energy was determined to be 55.3 kJ mol-1.
Ključne besede: ICEC, Power-to-Solid, energy storage, hydrogen, ferrous chloride, electrolysis, Fe deposition, efficiency, XAS, structure and population, ionic species, ion association, conductivity
Objavljeno v RUNG: 18.04.2023; Ogledov: 555; Prenosov: 20 (1 glas)
Celotno besedilo (4,34 MB)
Monitoring the success of the performance of a travel agency with the Power BI tool : diploma thesisRiste Ristov
, 2022, diplomsko delo
Opis: In today’s times, when digitalisation is advancing in all areas, travel agencies need to follow trends to optimise their work as much as possible and stay competitive. Business information systems provide a more detailed insight into business processes and their operation, which helps monitor progress and adapt to possible changes to achieve the best results in the business world. Travel agencies need a quality business information system that helps employees shift from using basic office tools to more modern and effective systems for reporting and monitoring work performance. Data is the basis on which agencies adjust, optimise and build their business. Data is available in huge quantities and a variety of formats. Raw data that is not organised into a meaningful whole cannot bring added value to the company. The thesis aims to use Power BI as a tool for editing and integrating databases in travel agencies, as well as their visualisation and display, which is understandable for the user. With the help of the tool, we will create a report which will help the travel agency improve its business and make critical decisions that are critical for success.
Ključne besede: Travel agency, business information system, data, database, Power BI, visualisation
Objavljeno v RUNG: 30.09.2022; Ogledov: 1040; Prenosov: 51
Celotno besedilo (1,26 MB)
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Correlation between FeCl2 electrolyte conductivity and electrolysis efficiencyLuin Uroš
, Valant Matjaz
, Arčon Iztok
, 2022, objavljeni povzetek znanstvenega prispevka na konferenci
Opis: The electrolysis efficiency is an important aspect of the Power-to-Solid energy storage technology (EST) based
on the iron chloride electrochemical cycle . This cycle employs an aqueous FeCl2 catholyte solution for the
electro-reduction of iron. The metal iron deposits on the cathode. The energy is stored as a difference in the
redox potential of iron species. Hydrogen, as an energy carrier, is released on demand over a fully controlled
hydrogen evolution reaction between metallic Fe0 and HCl (aq) . Due to these characteristics, the cycle is
suitable for long-term high-capacity and high-power energy storage. In a previous work  we revealed that
the electrolyte conductivity linearly increases with temperature. Contrary, the correlation between the
electrolyte concentration and efficiency is not so straightforward. Unexpectedly small efficiency variations were
found between 1 and 2.5 mol dm-3 FeCl2 (aq) followed by an abrupt efficiency drop at higher concentrations.
To explain the behavior of the observed trends and elucidate the role of FeCl2 (aq) complex ionic species we
performed in situ X-ray absorption studies. We made a dedicated experimental setup, consisting of a tubular
oven and PMMA liquid absorption cell, and performed the measurements at the DESY synchrotron P65
beamline. The XAS investigation covered XANES and EXAFS analyses of FeCl2 (aq) 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 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 .
 M. Valant, “Procedure for electric energy storage in solid matter. United States Patent and
Trademark Office. Patent No. US20200308715,” Patent No. US20200308715, 2021.
 U. Luin and M. Valant, “Electrolysis energy efficiency of highly concentrated FeCl2 solutions
for power-to-solid energy storage technology,” J. Solid State Electrochem., vol. 26, no. 4, pp.
929–938, Apr. 2022, doi: 10.1007/S10008-022-05132-Y.
 U. Luin, I. Arčon, and M. Valant, “Structure and Population of Complex Ionic Species in
FeCl2 Aqueous Solution by X-ray Absorption Spectroscopy,” Molecules, vol. 27, no. 3, 2022,
Ključne besede: Iron chloride electrochemical cycle, Power-to-Solid energy storage, XANES, EXAFS, electrical
conductivity, electrolyte complex ionic species structure and population
Objavljeno v RUNG: 26.09.2022; Ogledov: 768; Prenosov: 0 (1 glas)
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