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41.
Coevaporation of doped inorganic carrier-selective layers for high-performance inverted planar perovskite solar cells
Jiexuan Jiang, Andraž Mavrič, Nadiia Pastukhova, Matjaž Valant, Qiugui Zeng, Zeyu Fan, Beibei Zhang, Yanbo Li, 2022, original scientific article

Abstract: Inorganic carrier selective layers (CSLs), whose conductivity can be effectively tuned by doping, offer low-cost and stable alternatives for their organic counterparts in perovskite solar cells (PSCs). Herein, we employ a dual-source electron-beam co-evaporation method for the controlled deposition of copper-doped nickel oxide (Cu:NiO) and tungsten-doped niobium oxide (W:Nb2O5) as hole and electron transport layers, respectively. The mechanisms for the improved conductivity using dopants are investigated. Owing to the improved conductivity and optimized band alignment of the doped CSLs, the all-inorganic-CSLs-based PSCs achieves a maximum power conversion efficiency (PCE) of 20.47%. Furthermore, a thin titanium buffer layer is inserted between the W:Nb2O5 and the silver electrode to prevent the halide ingression and improve band alignment. This leads to a further improvement of PCE to 21.32% and a long-term stability (1200 h) after encapsulation. Finally, the large-scale applicability of the doped CSLs by co-evaporation is demonstrated for the device with 1 cm2 area showing a PCE of over 19%. Our results demonstrate the potential application of the co-evaporated CSLs with controlled doping in PSCs for commercialization.
Keywords: carrier selective layers, Cu-doped nickel oxide, electron-beam evaporation, perovskite solar cells, W-doped niobium oxide
Published in RUNG: 17.03.2022; Views: 1695; Downloads: 121
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42.
Plastic Waste Precursor-Derived Fluorescent Carbon and Construction of Ternary FCs@CuO@TiO2 Hybrid Photocatalyst for Hydrogen Production and Sensing Application
Akansha Metha, Rayees Ahmad Rather, Blaž Belec, Sandra Gardonio, Ming Fang, Matjaž Valant, 2022, original scientific article

Abstract: 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.
Keywords: plastic waste, fluorescent carbo, sensing of metal ions, photocatalytic hydrogen production
Published in RUNG: 25.02.2022; Views: 1556; Downloads: 42
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43.
Electrolysis energy efficiency of highly concentrated FeCl[sub]2 solutions for power-to-solid energy storage technology
Uroš Luin, Matjaž Valant, 2022, original scientific article

Abstract: 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.
Keywords: electrolysis, ferrous chloride, iron deposition, energy efficiency
Published in RUNG: 16.02.2022; Views: 1639; Downloads: 75  (1 vote)
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44.
Structure and population of complex ionic species in FeCl[sub]2 aqueous solution by X-ray absorption spectroscopy
Uroš Luin, Iztok Arčon, Matjaž Valant, 2022, original scientific article

Abstract: 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.
Keywords: structure, population, ionic species, aqueous ferrous chloride, in situ X-ray absorption spectroscopy
Published in RUNG: 24.01.2022; Views: 1666; Downloads: 42  (1 vote)
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Spectroscopic investigation of oxygen vacancies in CeO[sub]2 : dissertation
Thanveer Thajudheen, 2021, doctoral dissertation

Abstract: A unique material, ceria (CeO2), which is widely applied in automobile exhaust catalysts, is functional due to presence of defects in its crystal structure. Furthermore, the structural defects dictate electrical and chemical properties of ceria. The creation of intrinsic oxygen vacancies in ceria is responsible for oxygen-ion conductivity in solid oxide fuel cells. This unfolds the keen interest in ceria defects. Using the analytical technique cathodoluminescence spectroscopy (CLS) we can characterize ceria for its band gap and the defect states within the band gap. Since CLS has a high spatial resolution, high sensitivity to low concentration of defects and ability to obtain depth resolved information it is an obvious technique of choice. The first part of the thesis is an introduction to the topic and description of the experimental techniques. Importance of ceria as a multifaceted material finding applications in areas spanning from energy production and conversion to biomedical applications is detailed. CLS as a tool to understand defect-related optical properties and advancement in the CL detection systems are discussed. To study the relationship between local structure and its impact on CL emission spectra, an X-ray absorption spectroscopy techniques were used. The X-ray absorption near edge structure (XANES) and the Extended x-ray absorption fine structure (EXAFS) techniques are summarized. The second part discusses CL emission from ceria. Initially, CL emission from reduced ceria and its dependence on oxygen vacancy concentration are presented. The origin of emission was attributed to different configurations of the oxygen vacancies and polarons. The recent F center description in ceria was adopted here. The intriguing observation of CL emission quenching as a function of oxygen vacancy concentration was explained on the basis of a relative change in population of F centers in ceria. This demonstrated the relevance of local structure for the CL emission in ceria. In order to have a better understanding of the system, La-doped ceria was proposed as a model system. A precise control over the stoichiometry helped to achieve a desired oxygen vacancy concentration. The CL emission behavior, as observed in reduced ceria, was replicated in the case of La-doped ceria and the analysis revealed that F+ centers favor CL emission whereas F0 centers are disadvantageous. The local structure investigation using EXAFS analysis of both cations Ce and La (K-Edge) showed distortion from the fluorite symmetry and corroborated the F center description of oxygen vacancies in ceria. Our results provide an experimental evidence for F center description involving oxygen vacancies and polarons.
Keywords: ceria, cathodoluminescence spectroscopy, local structure distortion, EXAFS analysis, La doped ceria, luminescence quenching, F centers, dissertations
Published in RUNG: 25.11.2021; Views: 2390; Downloads: 103
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49.
Unravelling the P[sub]3 centers origin in alkali phosphate glasses
Luigi Giacomazzi, Nikita S. Shcheblanov, Layla Martin-Samos, Matjaž Valant, Nadege Ollier, Nicolas Richard, 2021, published scientific conference contribution abstract

Keywords: EPR, DFT, NaPO3, LiPO3, alkali phosphate glasses, point defects
Published in RUNG: 29.09.2021; Views: 1741; Downloads: 7
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50.
Unravelling the P[sub]3 centers origin in alkali phosphate glasses
Luigi Giacomazzi, Nikita S. Shcheblanov, Layla Martin-Samos, Matjaž Valant, Nadege Ollier, Nicolas Richard, 2021, published scientific conference contribution abstract

Keywords: EPR, DFT, NaPO3, LiPO3, alkali phosphate glasses, point defects
Published in RUNG: 29.09.2021; Views: 1764; Downloads: 0
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