Faculty Publications
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Item Performance analysis of a variable-speed wind and fuel cell-based hybrid distributed generation system in grid-connected mode of operation(Taylor and Francis Inc. 325 Chestnut St, Suite 800 Philadelphia PA 19106, 2016) Ayyappa, S.K.; Gaonkar, D.N.This article presents the performance study of a variable-speed wind and solid oxide fuel cell-based hybrid distributed generation system, along with the energy storage devices in the grid connected mode of operation. The developed model has a salient feature of utilizing fluctuating output power of wind systems to produce hydrogen and also to charge the ultra capacitor. The presented model in the article also uses the stored energy in the ultra capacitor to compensate for the slow response time of the fuel cell. The distributed generation systems and energy storage devices considered in this study are integrated at common distributed generation links to form the hybrid system. The hybrid system is interfaced to the grid through the three-phase voltage source inverter in this article. The detailed modeling of the individual components of the hybrid distributed generation system, along with the necessary power electronic converter control schemes, are presented. The simulation results reported in this article show the effective performance of the hybrid model to produce reliable, low-cost electricity and hydrogen from the variable wind generation system. © 2016 Taylor & Francis Group, LLC.Item Record-low sintering-temperature (600 °c) of solid-oxide fuel cell electrolyte(Elsevier Ltd, 2016) Prasad Dasari, H.P.; Ahn, K.; Park, S.-Y.; Hong, J.; Kim, H.; Yoon, K.J.; Son, J.-W.; Kim, B.-K.; Lee, H.-W.; Lee, J.-H.One of the major problems arising with Solid-Oxide Fuel Cell (SOFC) electrolyte is conventional sintering which requires a very high temperature (>1300 °C) to fully densify the electrolyte material. In the present study, the sintering temperature of SOFC electrolyte is drastically decreased down to 600 °C. Combinational effects of particle size reduction, liquid-phase sintering mechanism and microwave sintering resulted in achieving full density in such a record-low sintering temperature. Gadolinium doped Ceria (GDC) nano-particles are synthesized by co-precipitation method, Lithium (Li), as an additional dopant, is used as liquid-phase sintering aid. Microwave sintering of this electrolyte material resulted in decreasing the sintering temperature to 600 °C. Micrographs obtained from Scanning/Transmission Electron Microscopy (SEM/TEM) clearly pointed a drastic growth in grain-size of Li-GDC sample (?150 nm) than compared to GDC sample (<30 nm) showing the significance of Li addition. The sintered Li-GDC samples displayed an ionic conductivity of ?1.00 × 10-2 S cm-1 at 600 °C in air and from the conductivity plots the activation energy is found to be 0.53 eV. © 2016 Elsevier B.V. All rights reserved.Item Low-temperature sonochemical synthesis of high dielectric Lanthanum doped Cerium oxide nanopowder(Elsevier Ltd, 2018) Kishor Kumar, M.J.; Kalathi, J.T.Lanthanum (La) doped Cerium Oxide (CeO2) nanopowder was synthesized at a relatively lower temperature (70°C), without calcination in a simple, faster, and efficient way through sonochemical method. X-ray diffraction (XRD) results confirmed the formation of a cubic fluorite structure of nanocrystalline CeO2 and lattice deformation due to La-doping in CeO2. TEM analysis revealed that the size of La-doped CeO2 particles is in the range of 20?50 nm. In addition, selective area electron diffraction (SAED) and high-resolution TEM (HRTEM) analyses portrayed the nano-crystallinity, lattice fringe pattern, and d-spacing details of La-doped CeO2 powder. Lanthanum doping in CeO2 was further confirmed by a shift in Raman band towards the lower frequency (from 464 cm?1 to 457cm?1) along with peak intensity increase. Photoluminescence (PL) emission spectra showed that emission intensity of the La-doped CeO2 at 510 nm is increased due to oxygen vacancy mediated charge transfer. All these results confirm the successful doping of La in CeO2. The La-doped CeO2 powder possesses a high dielectric constant (?r) of 106 and a low dielectric loss (tan ?) of < 0.4 % at 1 kHz. The La-doped CeO2 finds potential applications on developing devices in the field of a thin film capacitor, transistors, and solid oxide fuel cells. © 2018 Elsevier B.V.Item Praseodymium doped ceria as electrolyte material for IT-SOFC applications(Elsevier Ltd, 2018) Shajahan, I.; Ahn, J.; Nair, P.; Medisetti, S.; Patil, S.; Niveditha, V.; Uday Bhaskar Babu, G.; Prasad Dasari, H.P.; Lee, J.-H.Praseodymium-doped ceria (PDC, Ce0.9Pr0.1O2) electrolyte material for intermediate temperature solid oxide fuel cells (IT-SOFCs) has been successfully synthesised by EDTA-citrate method. From X-Ray diffraction (XRD), fluorite structure along with a crystallite size of 5.4 nm is obtained for PDC nanopowder calcined at 350 °C/24 h. Raman spectroscopy confirmed the structure, presence of oxygen vacancies with the manifestation of the main peak at 457 cm?1 and with a secondary peak at 550 cm?1. From Transmission Electron Microscopy (TEM) analysis, the average particle size is around 7–10 nm and selected area electron diffraction (SAED) patterns further confirmed the fluorite structure of PDC nanopowder. The PDC nanopowder displayed a BET surface area of 65 m2/g with a primary particle size of ?13 nm (calculated from BET surface area). Dilatometer studies revealed a multi-step shrinkage behaviour with the multiple peaks at 522, 1171 and 1461 °C which may be originated due to the presence of multiple size hard agglomerates. The PDC electrolyte pellet sintered at 1500 °C displayed an ionic conductivity of 1.213E-03 S cm?1 along with an activation energy of 1.28eV. Instead of a single fluorite structure, XRD of sintered PDC pellet showed multiple structures (Fluorite structure (CeO2) and cubic structure (PrO2). © 2018 Elsevier B.V.Item Optical and structural properties of BCBS glass system with and without alumina(Elsevier B.V., 2018) Bhattacharya, S.; Shashikala, H.D.BaO–CaO–Al2O3–SiO2 (BCAS) glass and their derivatives have gained extreme importance for their high endurance to elevated temperatures and being suitable for various electrochemical applications. Two glass systems, one being 50mol% [SiO2–B2O3]-xBaO-(45-x)CaO–5Al2O3 called as BCBSA and another without Al2O3 termed as BCBS were synthesized using melt quenching technique in the present work. Addition of ZnO and MgO as flux helped in melting them at 1300 °C which is much lower than the usual melting temperature of these glasses [1–4]. Density of the quenched glasses was measured by Archimedes method and structural bond vibrations were confirmed through FTIR. UV Visible spectroscopy was used to determine band gap energy and confirm the insulating nature of the synthesized glasses. The samples were isothermally heated at 700 °C, 800 °C for 50 h and at 900 °C for 50 and 100 h duration in air to allow the devitrification process to take place. The heat treated samples were analyzed by X-ray diffraction to identify the developed phases. Five Al2O3 free samples synthesized at 1300 °C by regular melt quenching technique were found to be devoid of the monocelsian phase. This is a detrimental phase for high temperature sealant applications as it has a very low coefficient of thermal expansion (CTE). Al2O3 free BCBS glasses, properties of which are being reported for the first time and glasses with low BaO concentrations are found to meet the requirements for high temperature applications as sealants in Solid Oxide Fuel Cell (SOFC). © 2018 Elsevier B.V.Item Studies on the Solid Oxide Cell Perovskite Electrode Materials for Soot Oxidation Activity(Springer, 2019) Shenoy, C.S.; Patil, S.S.; Govardhan, P.; Shourya, A.; Prasad Dasari, H.P.; Saidutta, M.B.; Harshini, H.Solid oxide cell (SOC) perovskite electrode materials (BSCF (Ba0.5Sr0.5Co0.8Fe0.2O3-?), LSCF (La0.6Sr0.4Co0.2Fe0.8O3-?) and LSCM (La0.75Sr0.25Cr0.5Mn0.5O3-?)) were synthesised using microwave-assisted reverse-strike co-precipitation method and tested for soot oxidation activity. The calcined perovskite materials were characterized using FT-IR, XRD, SEM and BSE, BET and BJH and XPS analysis. The mean activation energy for soot oxidation was calculated from Ozawa plots at various heating rates (5, 10, 15 and 20 K/min) at different levels of soot conversions (T10 to T90) for BSCF, LSCM and LSCF perovskite materials and was around 133 ± 11.5, 138 ± 9.9 and 152 ± 7.2 kJ/mol, respectively. Irrespective of the heating rates, BSCF material showed the lowest T50 temperature than compared to other samples, and it is correlated to the presence of Fe3O4 as a secondary phase. © 2019, Springer Nature Switzerland AG.Item Dilatometer studies of praseodymium doped ceria: Effect of synthesis methods on sintering behaviour(Elsevier Ltd, 2020) Shajahan, I.; Prasad Dasari, H.P.; Govardhan, P.Praseodymium-doped ceria (Ce0.9Pr0.1O2, PDC), as an electrolyte material for IT-SOFCs, is investigated with respect to the effect of synthesis method and a detailed analysis was carried out to understand the effect on crystallite size, morphology, specific surface area and sintering behaviour. The various synthesis routes such as microwave assisted co-precipitation method, room temperature co-precipitation method and EDTA-citrate complexing method was adopted for the synthesis of praseodymium doped ceria-based nano-materials. XRD pattern confirms the fluorite-type crystal structure of ceria and Raman spectroscopy analysis confirms the structure with the presence of oxygen vacancies. PDC synthesised by microwave assisted co-precipitation method using isopropyl alcohol as solvent exhibited better sintering activity, reduced the sintering temperature and promoted the densification rate when compared to other synthesis methods with uni-model shrinkage behaviour with shrinkage maxima at 765 °C. Based on two sintering models (CHR/Dorn method), the initial stage sintering mechanism was investigated in the present study and confirmed that the grain boundary diffusion (m = 2) as the dominant mechanism and the activation energy was found to be 116 kJ/mol (CHR model) and 176 kJ/mol (Dorn Method) for initial stages of sintering for PDC material synthesised by microwave assisted co-precipitation method using isopropyl alcohol as solvent. © 2019 Elsevier B.V.Item Effect of sintering aids on sintering kinetic behavior of praseodymium doped ceria based electrolyte material for solid oxide cells(Elsevier Ltd, 2020) Shajahan, I.; Prasad Dasari, H.P.; Saidutta, M.B.The present study investigates the effect of sintering additives (Li, Co, Fe, and Mg) on the sintering kinetic behavior of the praseodymium-doped-ceria (PDC) electrolyte of solid oxide electrolyzer cell. 3Li-PDC, 3Co-PDC, 3Fe-PDC, and 3 Mg-PDC pellets were obtained from the synthesis of PDC nano-powder by microwave-assisted co-precipitation method using isopropyl alcohol as a solvent and followed by sintering additive wetness impregnation method. Linear shrinkage and shrinkage rate data suggest a positive sintering effect for 3Li-PDC and 3Co-PDC pellets and a negative sintering effect for 3 Mg-PDC and 3Fe-PDC pellets than compared to PDC pellets alone. The addition of lithium as a sintering additive (3Li-PDC) had reduced the sintering temperature of PDC from 1100 °C to 850 °C. For PDC, 3Li-PDC, 3Co-PDC, 3Fe-PDC and 3 Mg-PDC pellets sintered at 1100 °C, 850 °C, 1000 °C, 1200 °C, 1100 °C for 2 h resulted in a relative density of 93.6 ± 0.25, 95.8 ± 0.45, 95.0 ± 0.20, 92.7 ± 0.10, and 94.5 ± 0.10%, respectively. The XRD patterns of the sintered PDC pellets suggested a secondary phase formation (PrO2) in 3Co-PDC, 3Fe-PDC, and 3 Mg-PDC pellets indicating that the addition of these sintering aids results in poor solubility limit of Pr in CeO2. On the other hand, XRD patterns of PDC and Li-PDC sintered pellets displayed no secondary peak indicating good solid-solution formation. The activation energy of the 3Li-PDC pellet is obtained from CHR and Dorn methods and was found to be 182 kJ/mol and 196 kJ/mol. From the CHR method, for the 3Li-PDC pellet, the initial sintering behavior is by the grain boundary diffusion mechanism (m = ~2). © 2020 Hydrogen Energy Publications LLCItem Dilatometer studies on LAMOX based electrolyte materials for solid oxide fuel cells(Elsevier Ltd, 2021) Das, A.; Lakhanlal, u.; Shajahan, I.; Prasad Dasari, H.P.; Saidutta, M.B.; Harshini, H.The present study deals with the citrate complexion synthesis of LAMOX-based Solid Oxide Fuel Cell (SOFC) electrolyte materials (La1.8Dy0.2Mo2-xWxO9 (x = 0, 0.1, 0.2, 0.5, and 1), La1.8Dy0.2Mo2-xGaxO9 (x = 0.1 and 0.2), and La1.8Dy0.2Mo2-xVxO9 (x = 0.025, 0.05, 0.1, and 0.2)) and their characterization to understand the sintering behaviour and phase stability. From the dilatometer studies, the linear shrinkage and shrinkage rate of the LDMW (x = 0, and 0.1) showed better shrinkage than LM and LDM. Gallium addition (LDMG) and Vanadium addition (LDMV) showed a negative impact on shrinkage behaviour. In the temperature range of 500–580 °C, the abrupt change in shrinkage rate showed the transition of phase from ? to ? for the LM. The modification of LM to LDM, LDMW, and LDMV suppressed the formation of the ? phase. During thermal expansion behaviour study in the temperature range of 100–500 °C and 550–800 °C, the LM sintered pellet showed the coefficient of thermal expansion (CTE) values of 13.3 ? 10?6/°C and 21.6 ? 10?6/°C respectively. The LDM and LDMW sintered pellets showed the CTE values in the range of 14–15 ? 10?6/°C and 16–19 ? 10?6/°C, respectively. The relative density of the sintered pellets (1100 °C/5 h in air) (LM, LDM, LDMW, and LDMG (x = 0.1)) is found to be >90%. It provides the suitability of these materials for further investigation as electrolytes of SOFCs/SOECs. © 2020 Elsevier B.V.Item Electrical conductivity studies on LAMOX based electrolyte materials for solid oxide fuel cells(Elsevier Ltd, 2022) Srijith; Lakhanlal, u.; Das, A.; Prasad Dasari, H.P.; Saidutta, M.B.In this study, the electrical conductivity of the LAMOX based electrolytes (La1.8Dy0.2Mo2-xWxO9 (x = 0, 0.1, 0.2, 0.5, and 1), and La1.8Dy0.2Mo2-xGaxO9 (x = 0.1)) synthesized by the citrate complexion method has been studied using DC four-probe method. The electrical conductivity of the electrolytes is measured in the temperature range of 800–400 °C in the air (∼100 ml min−1). The effect of W and Ga substitution at the Mo site on the electrical conductivity is evaluated. The long-term electrical conductivity stability test (time on stream) (5 h) is conducted at 650, 580, and 520 °C to study the effect of possible phase transition on electrical conductivity. A high-temperature XRD study is also conducted in the temperature range of 500–650 °C (during heating and cooling) on selected electrolyte materials (La1.8Dy0.2Mo2-xWxO9 (x = 0 and 0.1) and La1.8Dy0.2Mo2-xGaxO9 (x = 0.1)) to study the α↔β phase transition. The electrical conductivity of these electrolytes in the air at 800 °C is in the range of 5.3 × 10−2 – 14 × 10−2 S cm−1. The activation energy (EA) of these electrolytes is in the range of 1.11–1.62 eV. The VTF parameters σo, B, and To are in the range of 67.46–395.88 S cm−1 K0.5, 0.122–0.254 eV, and 247–347 °C, respectively. The La1.8Dy0.2Mo2-xWxO9 (x = 0.1) shows highest electrical conductivity (14 × 10−2 S cm−1, EA = 1.54 eV) among all electrolytes in air at 800 °C and for this material the VTF parameters σo, B, and To are 170.32 S cm−1 K0.5, 0.153 eV, and 302 °C, respectively. © 2022 Elsevier Ltd and Techna Group S.r.l.