| 1. |
- Ajpi, Cesario, et al.
(författare)
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Crystal structure and Hirshfeld surface analysis of poly[tris(mu(4)-benzene-1,4-dicarboxylato)tetrakis(di-methylformamide)tr inickel(II)] : a two-dimensional coordination network
- 2019
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Ingår i: Acta Crystallographica Section E. - : International Union of Crystallography. - 2056-9890. ; 75, s. 1839-1843
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Tidskriftsartikel (refereegranskat)abstract
- The crystal structure of the title compound, [Ni-3(C8H4O4)(3)(C3H7NO)(4)], is a two-dimensional coordination network formed by trinuclear linear Ni-3(tp)(3)(DMF)(4) units (tp = terephthalate = benzene-1,4-dicarboxylate and DMF = dimethyl-formamide) displaying a characteristic coordination mode of acetate groups in polynuclear metal-organic compounds. Individual trinuclear units are connected through tp anions in a triangular network that forms layers. One of the DMF ligands points outwards and provides interactions with equivalent planes above and below, leaving the second ligand in a structural void much larger than the DMF molecule, which shows positional disorder. Parallel planes are connected mainly through weak C-H center dot center dot center dot O, H center dot center dot center dot H and H center dot center dot center dot C interactions between DMF molecules, as shown by Hirshfeld surface analysis.
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| 2. |
- Ajpi, Cesario, et al.
(författare)
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Crystal structure and Hirshfeld surface analysis of poly[tris-(μ4-benzene-1,4-di-carboxyl-ato)tetra-kis-(di-methyl-formamide)-trinickel(II)] : a two-dimensional coordination network.
- 2019
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Ingår i: Acta Crystallographica Section E. - 2056-9890. ; 75:Pt 12, s. 1839-1843
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Tidskriftsartikel (refereegranskat)abstract
- The crystal structure of the title compound, [Ni3(C8H4O4)3(C3H7NO)4], is a two-dimensional coordination network formed by trinuclear linear Ni3(tp)3(DMF)4 units (tp = terephthalate = benzene-1,4-di-carboxyl-ate and DMF = di-methyl-formamide) displaying a characteristic coordination mode of acetate groups in polynuclear metal-organic compounds. Individual trinuclear units are connected through tp anions in a triangular network that forms layers. One of the DMF ligands points outwards and provides inter-actions with equivalent planes above and below, leaving the second ligand in a structural void much larger than the DMF mol-ecule, which shows positional disorder. Parallel planes are connected mainly through weak C-H⋯O, H⋯H and H⋯C inter-actions between DMF mol-ecules, as shown by Hirshfeld surface analysis.
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| 3. |
- Ajpi Condori, Cesario, et al.
(författare)
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Synthesis and Characterization of LiFePO4-PANI Hybrid Material as Cathode for Lithium-Ion Batteries
- 2020
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Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 13:12
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Tidskriftsartikel (refereegranskat)abstract
- This work focuses on the synthesis of LiFePO4-PANI hybrid materials and studies their electrochemical properties (capacity, cyclability and rate capability) for use in lithium ion batteries. PANI synthesis and optimization was carried out by chemical oxidation (self-assembly process), using ammonium persulfate (APS) and H3PO4, obtaining a material with a high degree of crystallinity. For the synthesis of the LiFePO4-PANI hybrid, a thermal treatment of LiFePO(4)particles was carried out in a furnace with polyaniline (PANI) and lithium acetate (AcOLi)-coated particles, using Ar/H(2)atmosphere. The pristine and synthetized powders were characterized by XRD, SEM, IR and TGA. The electrochemical characterizations were carried out by using CV, EIS and galvanostatic methods, obtaining a capacity of 95 mAhg(-1)for PANI, 120 mAhg(-1)for LiFePO(4)and 145 mAhg(-1)for LiFePO4-PANI, at a charge/discharge rate of 0.1 C. At a charge/discharge rate of 2 C, the capacities were 70 mAhg(-1)for LiFePO(4)and 100 mAhg(-1)for LiFePO4-PANI, showing that the PANI also had a favorable effect on the rate capability.
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| 4. |
- Ajpi Condori, Cesario, et al.
(författare)
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Synthesis and spectroscopic characterization of NiII coordination network : Poly-[tris(µ4-Benzene-1,4-dicarboxylato)-tetrakis(µ1-dimethylformamide-κ1O)-trinickel(II)] as material for lithium ion batteries
- 2022
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Ingår i: Journal of Molecular Structure. - : Elsevier B.V.. - 0022-2860 .- 1872-8014. ; 1265
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Tidskriftsartikel (refereegranskat)abstract
- The compound Ni3(C8H4O4)3(C3H7NO)3, poly-[tris(µ4-Benzene-1,4-dicarboxylato)-tetrakis(µ1-dimethylformamide-κ1O)-trinickel(II)], was synthesized by the solvothermal method prepared via reaction between NiCl2•6H2O and terephthalic acid using N,N-dimethylformamide (DMF) as solvent. The structure was characterized by powder X-ray diffraction and infrared spectroscopy analyses. The electrochemical properties as a potential active material in lithium-ion batteries were characterized by electrochemical impedance spectroscopy and galvanostatic charge-discharge curves in a battery half-cell. The characterization results show that the coordination network contains one independent structure in the asymmetric unit. It is constructed from Ni2+ ions, terephthalate bridges and in-situ-generated DMF ligands, forming two similar two-dimensional (2D) layer structures. These similar 2D layers are in an alternating arrangement and are linked with each other by dense H—H interactions (45%) to generate a three-dimensional (3D) supramolecular framework with ordered and disordered DMF molecules. The electrochemical measurements, conducted in the potential range of 0.5–3.5 V vs Li/Li+, show that Ni3(C8H4O4)3(C3H7NO)4 has good electrochemical properties and can work as anode in lithium-ion batteries. The material presents an initial specific capacity of ∼420 mAh g−1, which drops during consecutive scans but stabilizes at ∼50 mAh g−1. However, due to the wide potential range there are indications of a gradual collapse of the structure. The electrochemical impedance spectroscopy shows an increase of charge transfer resistance from 24 to 1190 Ohms after cycling likely due to this collapse.
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| 5. |
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| 6. |
- Benavente Araoz, Fabian Andres, 1985-, et al.
(författare)
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Effect of Partial Cycling of NCA/Graphite Cylindrical Cells in Different SOC Intervals
- 2020
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Ingår i: Journal of the Electrochemical Society. - : Institute of Physics Publishing. - 0013-4651 .- 1945-7111. ; 167:4
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Tidskriftsartikel (refereegranskat)abstract
- A quasi-realistic aging test of NCA/graphite lithium-ion 18650 cylindrical cells is performed during a long-term low c-rate cycling and using a new protocol for testing and studying the aging. This to emulate a characteristic charge/discharge profile of off-grid PV-battery systems. The cells were partially cycled at four different cut-off voltages and two state of charge ranges (ΔSOC) for 1000 and 700 cycles over 24 months. Differential voltage analysis shows that a combination of loss of active material (LAM) and loss of lithium inventory (LLI) are the causes of capacity loss. Cells cycled with high cut-off voltages and wide ΔSOC (20% to 95%) were severely affected by material degradation and electrode shift. High cut-off voltage and narrow ΔSOC (65% to 95%) caused greater electrode degradation but negligible cell unbalance. Cell impedance is observed to increase in both cells. Cells cycled with middle to low cut-off voltages and narrow ΔSOC (35%-65% and 20% to 50%) had comparable degradation rates to calendar-aged cells. Cycling NCA/graphite cells with low c-rate and high cut-off voltages will degrade the electrode in the same way high c-rate would do. However, low c-rate at low and middle cut-off voltages greatly decrease cell degradation compared to similar conditions at middle to high c-rate, therefore increasing battery lifetime. © 2020 The Author(s).
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| 7. |
- Benavente Araoz, Fabian Andres, et al.
(författare)
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Photovoltaic/battery system sizing for rural electrification in Bolivia : Considering the suppressed demand effect
- 2019
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 235, s. 519-528
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Tidskriftsartikel (refereegranskat)abstract
- Rural electrification programs usually do not consider the impact that the increment of demand has on the reliability of off-grid photovoltaic (PV)/battery systems. Based on meteorological data and electricity consumption profiles from the highlands of Bolivian Altiplano, this paper presents a modelling and simulation framework for analysing the performance and reliability of such systems. Reliability, as loss of power supply probability (LPSP), and cost were calculated using simulated PV power output and battery state of charge profiles. The effect of increasing the suppressed demand (SD) by 20% and 50% was studied to determine how reliable and resilient the system designs are. Simulations were performed for three rural application scenarios: a household, a school, and a health centre. Results for the household and school scenarios indicate that, to overcome the SD effect, it is more cost-effective to increase the PV power rather than to increase the battery capacity. However, with an increased PV-size, the battery ageing rate would be higher since the cycles are performed at high state of charge (SOC). For the health centre application, on the other hand, an increase in battery capacity prevents the risk of electricity blackouts while increasing the energy reliability of the system. These results provide important insights for the application design of off-grid PV-battery systems in rural electrification projects, enabling a more efficient and reliable source of electricity.
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| 8. |
- Benavente, Fabian, 1985-
(författare)
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Lithium-ion batteries for off-grid PV-systems
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis provides a comprehensive and detailed analysis on the effect ofthe battery operation strategy on the lifetime of commercial lithium-ionbatteries and on the economics of off-grid photovoltaic (PV)-batterysystems.Lithium-ion batteries play a key role in the transition to a fossil-freesociety. Compared to electric vehicles, stationary energy storage hasdifferent requirements for the performance and lifetime of batteries.Although optimal battery design is critical to achieve high energy densityand longer lifetime, operation plays an important role in preventingpremature performance degradation. Understanding the effects ofsuppressed demand, geographical location, and application on system lifecycle costs also enables optimal system design.Load profiles for three applications were estimated and implemented in asimulation model, along with meteorological data for three locations andthe suppressed demand (SD) effect. Using the hourly state of charge (SOC)profiles, four battery operation strategies were designed using partialcycling with different cut-off voltages and two state of charge windows(ΔSOC). Commercial cells were used for the experimental tests. After over1000 cycles a post-mortem characterization was performed.The experiments revealed the cause of premature degradation at high SOCoperation to be a combination of impedance rise in the positive electrodeand loss of lithium inventory at the negative electrode leading to decreaseof capacity. Studies on the impedance spectra of the cells using physicsbasedmodeling revealed a loss of conductivity between particles in thepositive electrode. At system level, as the SD increases, so does theoperational ΔSOC width, while the reliability of the system decreases. Wedefined the reliability as loss of power supply probability. Finally,optimization of cost and reliability, revealed that an optimal system designfavors a battery operation strategy with wider ΔSOC instead of batterylifetime.
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| 9. |
- Cardenas, Edgar, et al.
(författare)
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Microstructural evolution of condensed aggregates during the crystallization of ZSM-5 from a heterogeneous system
- 2021
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Ingår i: Journal of Crystal Growth. - : Elsevier. - 0022-0248 .- 1873-5002. ; 568–569
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Tidskriftsartikel (refereegranskat)abstract
- The microstructural evolution of precursors of ZSM-5 zeolite crystallized from a heterogeneous system using fumed silica, sodium aluminate and tetrapropylammonium ions as reagents is investigated. Entities previously described by Ren et al. (Chem. Mater. 2012, 24, 10, 1726–1737) as condensed aggregates, were extensively studied using scanning electron microscopy, and energy dispersive spectroscopy. It was observed that the condensed aggregates first comprise a core of nanocrystals that is enveloped by a shell of amorphous gel phase. During crystallization, the amorphous shell surrounding the core is converted into ZSM-5 crystals that grow to a film surrounding the core. The crystals in the film grow competitively with nutrients provided by the liquid phase from the surroundings, while the nanocrystals in the core show little or no signs of growth.
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| 10. |
- Cardenas, Edgar, 1990-
(författare)
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Synthesis of zeolites from economic raw materials
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Synthesis methods using economic raw materials, such as kaolin and diatomite have been developed for the production of zeolites in the present work. Zeolite Y and ZSM-5 have been synthetized successfully from diatomite and kaolin, respectively. The synthesis of zeolite Y was extensively studied (Paper I) in order to obtain final products with high crystallinity and an appropriate SiO2/Al2O3 ratio to be suitable for application as catalyst. Then, the influence of the alkalinity (in terms of SiO2/Na2O ratio) on the outcome of the synthesis was studied. Thus, an optimum range of alkalinity that satisfies the requirements stated before was found. Additionally, the results also showed that diatomite produce similar products as colloidal silica, which may be expected since both silica sources are highly polymerized forms of silica.The synthesized zeolite Y crystals were also ion-exchanged with Lanthanum to obtain a Rare Earth zeolite Y (REY) catalyst (Paper V). The REY catalyst was shown to be thermally stable up to 800°C as expected for this catalyst. The REY catalyst was also evaluated in the reaction of Catalytic Cracking of cumene. The results of catalytic tests shown that the REY catalyst synthetized from diatomite holds activity towards the catalytic cracking of cumene.In addition, studies of synthesis of ZSM-5 zeolite from kaolin have been performed to understand the crystal growth and morphology, crystal size, and aluminum distribution. In particular, the influence of the gel on the morphology of the crystals (Paper II) has been studied. It was observed that when the crystal surface is in contact with the gel phase, dendritic features appear at the crystal surface, that become smoother as the reaction proceeds. On the contrary, when only liquid phase is in contact with crystal surface there is no presence of dendritic features and the growth rate is higher.Further studies demonstrated that the ZSM-5 crystals possess a non-homogeneous aluminum distribution, a phenomenon known as Al-zoning. A thorough characterization at distinct stages of the reaction has been performed (Paper III), on the different reaction mixture phases such as solid part, gel phase and liquid phase. The main finding was that the gel phase consists of a nanoparticle skeleton rich in alumina, filled by a silica rich matrix. In the beginning of crystallization, the silica rich matrix is preferentially consumed to form the crystals, leaving behind the alumina rich nanoparticle skeleton that is consumed later, resulting in the non-homogeneous distribution of aluminum in the crystals.Finally, studies of the microstructure of a TPA-ZSM-5 system using fumed silica as silicon source have been performed (paper IV). In this system, three stages of crystallization were observed. Stage I, formation of amorphous gel phase. Stage II formation of XRD amorphous spherical entities denoted as Condensed Agregates (CAs). Stage III, Crystallization of CAs into ZSM-5. This study was focused only in the stage III. Findings showed that ZSM-5 nanocrystals are formed in the core of the CA (beginning of stage III), surrounded by an amorphous shell composed of alumino-silica. As the crystallization proceeds, the amorphous shell crystallizes into ZSM-5 by competitive growth, but the nanocrystals of the core remain intact. Moreover, compositional analysis results showed that the silicon from the liquid phase provided most of the nutrients for growth of the ZSM-5 crystals resulting in polycrystalline ZSM-5 aggregates with an Al rich core - Si rich shell morphology.
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