1. Environmental priorities in the circular economy : examples from iron-based technologiesAndreea Oarga-Mulec, Uroš Luin, Keith R. Skene, Matjaž Valant, 2024, objavljeni znanstveni prispevek na konferenci Opis: The circular economy (CE) framework is crucial for promoting resource efficiency and minimizing waste, but it cannot achieve its sustainability goals alone. To achieve a truly sustainable future, broader social, environmental and economic aspects need to be taken into account. Rather than separating biological and technological cycles, as the CE principles are depicted in the Ellen MacArthur Foundation’s butterfly diagram (EMF, 2017), we propose an integrated approach that prioritises environmental aspects and includes a conceptual framework, socio-economic changes and implementation processes. It is crucial to re-evaluate the environmental aspects and strengthen their importance within the CE framework. Within this concept we present the case of iron, the most widely used metal, widely available compared to others and has been an essential part of societal development for more than 5,000 years. With its abundance, safety and electrochemical properties, iron is an ideal material for low-carbon energy technologies. We discuss how advanced iron-based technologies have a high potential to be successfully integrated into the CE, we evaluate different electrochemical energy storage systems and present advances in thermochemical Fe-Cl cycles for hydrogen production. An innovative thermal system for hydrogen production based on the thermochemical Fe-Cl cycle was evaluated in a life cycle assessment (LCA) study and shows the importance of choosing sustainable energy sources to minimise environmental impact. Sustainable production methods for iron are also analysed to demonstrate their potential to reduce the carbon footprint of the iron and steel industry. Finally, efforts should focus on minimising environmental impact and optimising resource recovery.
Ključne besede: circular economy, resource efficiency, sustainability, iron, hydrogen
Objavljeno v RUNG: 25.11.2024; Ogledov: 242; Prenosov: 0
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3. Chemistry of the iron-chlorine thermochemical cycle for hydrogen production utilizing industrial waste heatMatjaž Valant, Uroš Luin, 2024, izvirni znanstveni članek Opis: This research presents an inventive thermochemical cycle that utilizes a reaction between iron and HCl acid for hydrogen production. The reaction occurs spontaneously at room temperature, yielding hydrogen and a FeCl2 solution as a by-product. Exploring the thermal decomposition of the FeCl2 by-product revealed that, at conditions suitable for utilization of low-temperature industrial waste heat (250 °C), chlorine gas formation can be circumvented. Instead, the resulting by-product is HCl, which is readily soluble in water, facilitating direct reuse in subsequent cycles. The utilization of low-temperature industrial heat not only optimizes resource utilization and reduces operational costs but also aligns with environmentally sustainable production processes. From the kinetic studies the activation energy was calculated to be 45 kJ/mol and kinetics curves were constructed. They showed significant kinetics at room temperature and above but rapid decrease towards lower temperatures. This is important to consider during real-scale technology optimization. The theoretical overall energy efficiency of the cycle, with 100% and 70% heat recuperation, was calculated at 68.8% and 44.8%, respectively. In practical implementation, considering the efficiency of DRI iron reduction technology and free waste heat utilization, the cycle achieved a 41.7% efficiency. Beyond its energy storage capabilities, the Iron-chlorine cycle addresses safety concerns associated with large-scale hydrogen storage, eliminating self-discharge, reducing land usage, and employing cost-effective storage materials. This technology not only facilitates seasonal energy storage but also establishes solid-state energy reserves, making it suitable for balancing grid demands during winter months using excess renewable energy accumulated in the summer.
Ključne besede: chemical cycles, hydrogen production, thermal decomposition, reaction kinetics, iron, chlorine
Objavljeno v RUNG: 12.01.2024; Ogledov: 1901; Prenosov: 43
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4. Materials for sustainable electrochemical energy conversionSaim Emin, Takwa Chouki, Manel Machreki, 2023, objavljeni povzetek znanstvenega prispevka na konferenci (vabljeno predavanje) Opis: The process of hydrogen evolution reaction (HER) through water electrolysis is an important technology for
establishing the so called "hydrogen economy". Here we will cover different systems for electrocatalytic HER.
Transition metal carbides and metal phosphides are alternative to platinum (Pt) and offer excellent electrocatalytic
activity for HER. Pyrolysis of hexacarbonyl tungsten, W(CO)6, in 1-octadecene has been used to prepare colloidal
tungsten, W, nanoparticles (NPs) [1]. The obtained W NPs has been spin-coated on graphite (C) electrodes. Heat
treatment of the W/C electrodes at elevated temperatures (≥ 900°C) allows the preparation of metallic W and
tungsten carbide (W2C@WC) thin films. The obtained W2C@WC electrodes were used for hydrogen evolution
studies (HER) in 0.5M H2SO4. Cyclic voltammetry tests for 1000 cycles showed that W2C@WC exhibit long term
stability without significant drop in current density. The overpotential defined at 10 mA/cm2
is 310 mV vs. RHE
giving an excellent catalytic activity for HER. Iron phosphide electrocatalysts were synthesized using a
triphenylphosphine (TPP) precursor. Different iron phosphide phases were synthesized at 300°C (Fe2P) and at
350°C ( FeP ) [2]. To enhance the catalytic activities of obtained iron phosphide particles heat-treatments were
carried out at elevated temperatures. Annealing at 500°C under reductive atmosphere induced structural changes
in the samples: (i) Fe2P provided a pure Fe3P phase (Fe3P−500°C) and (ii) FeP transformed into a mixture of iron
phosphide phases (Fe2P/FeP−500°C). The lowest electrode potential of 110 mV vs. a reversible hydrogen electrode
(RHE) at 10 mA cm−2 was achieved with Fe2P/FeP−500°C catalyst
Ključne besede: Fe2P, electrocatalysis, hydrogen, ammonia
Objavljeno v RUNG: 13.12.2023; Ogledov: 1733; Prenosov: 4
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5. Composites of transition metal dichalcogenides and topological insulators as catalytic materials for HERJelena Rmuš, Blaž Belec, Igor Milanović, Mattia Fanetti, Sandra Gardonio, Matjaž Valant, Sandra V. Kurko, 2023, izvirni znanstveni članek Ključne besede: MoS2/Bi2Se3 composites, electrocatalyst, hydrogen evolution reaction, electron transfer
Objavljeno v RUNG: 01.06.2023; Ogledov: 2390; Prenosov: 4
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6. 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: 2482; Prenosov: 39 (1 glas)
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7. Iron phosphides as efficient electrocatalyst for hydrogen evolution and energy conversion : abstractSaim Emin, Takwa Chouki, 2021, objavljeni povzetek znanstvenega prispevka na konferenci Opis: Transition metal phosphides have been demonstrated as outstanding multifunctional catalysts in a broad range of energy conversion technologies. We developed a solvothermal synthesis approach for iron phosphide electrocatalystsusing a low-cost phosphorus precursor.The synthetic protocol allows for the preparation of a Fe2P phase at 300°C and FeP phase at 350°C. The obtained compounds were coated on conductive substrates to prepare catalysts thin films. Here, we exploited different phases of iron phosphide as counter electrodes (CEs) in dye-sensitized solar cells (DSSCs) with an I−/I3− based electrolyte [2]. The solar-to-current conversion efficiency of the solar cells assembled with the Fe2P material reached 3.96±0.06%,which is comparable to the device assembled with a platinum (Pt) CE. In addition to DSSC
applications, the iron phosphides were used as electrocatalyst for H2 evolution (Fig. 1). To enhance the catalytic activities of obtained iron phosphide particles, heat-treatments were carried out at elevated temperatures.Annealing at 500°C induced structural changes in the samples: (i) Fe2P provided a pure Fe3P phase (Fe3P−500°C) and (ii) FeP transformed into a mixture of iron phosphide phases (Fe2P/FeP−500°C). The electrocatalytic activities for H2 evolution of heat-treated catalysts were studied in 0.5 M sulfuric acid (H2SO4). The HER activities of the iron phosphide catalyst were found to be phase dependent. The lowest recorded overpotential of 110 mV at 10 mA cm−2 vs. a reversible hydrogen electrode was achieved with Fe2P/FeP−500°C catalyst. The developed procedure is an elegant approach to tune the composition of iron phosphide catalyst and control the morphology of particles.
Ključne besede: Iron phosphides
electrocatalyst
hydrogen evolution
energy conversion
Objavljeno v RUNG: 06.02.2023; Ogledov: 1974; Prenosov: 0
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8. Electrocatalytic Hydrogen Evolution with Transition Metal Based Compounds : abstractSaim Emin, Takwa Chouki, Manel Machreki, 2021, objavljeni povzetek znanstvenega prispevka na konferenci Opis: Electrocatalytic water splitting is one of the cleanest and sustainable way to generate hydrogen. Transition metal based electrocatalysts like iron phosphides (Fe2P, FeP), molybdenum diselenides (MoSe2), and tungsten carbides (W2C, WC) have unique advantages including competitive cost compared to platinum, controllable active sites, and electronic structures that could significantly enhance the hydrogen evolution reaction (HER). Here, we present a combination of approaches for preparing catalyst materials. As an elegant technique, colloidal synthesis was used to synthesize Mo and W nanoparticles. Combined with selenization and carbidation approaches at elevated temperature, it allowed to synthesize MoSe2, W2C, and WC thin films. The syntheses of Fe2P and FeP catalyst were achieved in one-stage using triphenylphosphine precursor. The obtained catalysts were applied in electrocatalytic HER studies.
Ključne besede: iron phosphides
molybdenum diselenide
tungtsen carbides
electrocatalysis
hydrogen evolution
Objavljeno v RUNG: 06.02.2023; Ogledov: 1941; Prenosov: 0
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9. Mechanochemically modified composites of molybdenum disulfide and graphene oxide for hydrogen evolution reactionJelena Rmuš, Blaž Belec, Željko Mravik, Sara Mijaković, Zoran Jovanović, Ivana Stojković Simantović, Sandra Kurko, 2022, objavljeni povzetek znanstvenega prispevka na konferenci Ključne besede: hydrogen evolution, mechanochemistry, MoS2
Objavljeno v RUNG: 16.12.2022; Ogledov: 1841; Prenosov: 0
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10. Plastic Waste Precursor-Derived Fluorescent Carbon and Construction of Ternary FCs@CuO@TiO2 Hybrid Photocatalyst for Hydrogen Production and Sensing ApplicationAkansha Metha, Rayees Ahmad Rather, Blaž Belec, Sandra Gardonio, Ming Fang, Matjaž Valant, 2022, izvirni znanstveni članek Opis: A sustainable nexus between renewable energy production and plastic abatement is imperative for overall sustainable development. In this regard, this study aims to develop a cheaper and environmentally friendly nexus between plastic waste management, wastewater treatment, and renewable hydrogen production. Fluorescent carbon (FCs) were synthesized from commonly used LDPE (low-density polyethylene) by a facile hydrothermal approach. Optical absorption study revealed an absorption edge around 300 nm and two emission bands at 430 and 470 nm. The morphological analysis showed two different patterns of FCs, a thin sheet with 2D morphology and elongated particles. The sheet-shaped particles are 0.5 μm in size, while as for elongated structures, the size varies from 0.5 to 1 μm. The as-synthesized FCs were used for the detection of metal ions (reference as Cu2+ ions) in water. The fluorescence intensity of FCs versus Cu2+ ions depicts its upright analytical ability with a limit of detection (LOD) reaching 86.5 nM, which is considerably lesser than earlier reported fluorescence probes derived from waste. After the sensing of Cu2+, the as-obtained FCs@Cu2+ was mixed with TiO2 to form a ternary FCs@CuO@TiO2 composite. This ternary composite was utilized for photocatalytic hydrogen production from water under 1.5 AM solar light irradiation. The H2 evolution rate was found to be ~1800 μmolg−1, which is many folds compared to the bare FCs. Moreover, the optimized FCs@CuO@TiO2 ternary composite showed a photocurrent density of ~2.40 mA/cm2 at 1 V vs. Ag/AgCl, in 1 M Na2SO4 solution under the illumination of simulated solar light. The achieved photocurrent density corresponds to the solar-to-hydrogen (STH) efficiency of ~0.95%. The efficiency is due to the fluorescence nature of FCs and the synergistic effect of CuO embedded in TiO2, which enhances the optical absorption of the composite by reaching the bandgap of 2.44 eV, apparently reducing the recombination rate, which was confirmed by optoelectronic, structural, and spectroscopic characterizations.
Ključne besede: plastic waste, fluorescent carbo, sensing of metal ions, photocatalytic hydrogen production
Objavljeno v RUNG: 25.02.2022; Ogledov: 2548; Prenosov: 49
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