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Record-low sintering-temperature (600 <sup>o</sup>C) of solid-oxide fuel cell electrolyte
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. Elsevier Sequoia 2016 JOURNAL OF ALLOYS AND COMPOUNDS Vol.672 No.-
One of the major problems arising with Solid-Oxide Fuel Cell (SOFC) electrolyte is conventional sintering which requires a very high temperature (>1300 <SUP>o</SUP>C) to fully densify the electrolyte material. In the present study, the sintering temperature of SOFC electrolyte is drastically decreased down to 600 <SUP>o</SUP>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 <SUP>o</SUP>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 x 10<SUP>-2</SUP> S cm<SUP>-1</SUP> at 600 <SUP>o</SUP>C in air and from the conductivity plots the activation energy is found to be 0.53 eV.
Hydrogen production from water-splitting reaction based on RE-doped ceria-zirconia solid-solutions
Dasari, H.P.,Ahn, K.,Park, S.Y.,Ji, H.I.,Yoon, K.J.,Kim, B.K.,Je, H.J.,Lee, H.W.,Lee, J.H. Pergamon Press ; Elsevier Science Ltd 2013 INTERNATIONAL JOURNAL OF HYDROGEN ENERGY - Vol.38 No.14
The effect of rare earth (RE = Tb, Pr and La) dopant on the catalytic performance of RE-doped ceria-zirconia (CZRE) solid-solutions for oxygen storage capacity and hydrogen production activity has been successfully investigated. The sustainability of the solid-solutions even after the reduction was confirmed by XRD. Raman analysis showed that the addition of RE element in CZ system significantly decreased the intensity of the characteristic fluorite peak (462-474 cm<SUP>-1</SUP>) indicating a highly deformed structure than CZ system which can enhance the oxygen mobility and redox property of these materials and the order of the intensity decrease was Pr > Tb > La. The XPS measurements revealed that the CZPr sample has a homogeneous distribution of Ce/Zr and also showed a high enrichment of Pr on the particle surface than the others. Among the CZRE solid-solution catalysts tested, CZPr catalyst showed the best catalytic performance for high OSC and hydrogen production from water-splitting reaction.
Baral, A.K.,Dasari, H.P.,Kim, B.K.,Lee, J.H. Elsevier Sequoia 2013 Journal of alloys and compounds Vol.575 No.-
Electrical and dielectric properties of the nanocrystalline GDC materials co-doped with CoO (by deposition precipitation method) were studied in the temperature range of 150-600<SUP>o</SUP>C. CoO co-doped samples show higher grain interior conductivity than that of GDC. Dielectric loss tangent (tan δ) shows the presence of defect associates such as (Co-V<SUB>o@?</SUB>-Co) and (Co-V<SUB>o@?</SUB>) in co-doped samples in addition to the defects (Gd-V<SUB>o@?</SUB>-Gd) and (Gd-V<SUB>o@?</SUB>) that are present in GDC system. Dynamic parameters such as migration energy and association energy of oxygen vacancies do not vary significantly with co-doping CoO in the GDC materials. With higher content of CoO, excess of Co<SUP>2+</SUP> in the grain boundary regions leads to trapping of vacancies and/or depletion of vacancies in the space charge region. Therefore grain boundary activation energy increases and grain boundary conductivity decreases with CoO content above 1mol%, at lower temperatures. In the temperature range of 150-600<SUP>o</SUP>C overall conductivities in CoO co-doped samples increase two to three times than that of GDC material.
Kim, J.,Ji, H.I.,Dasari, H.P.,Shin, D.,Song, H.,Lee, J.H.,Kim, B.K.,Je, H.J.,Lee, H.W.,Yoon, K.J. Pergamon Press ; Elsevier Science Ltd 2013 International journal of hydrogen energy Vol.38 No.3
Degradation mechanism of the electrolyte and air electrode is reported for solid oxide electrolysis cells (SOECs). Symmetric cells composed of yttria-stabilized zirconia (YSZ) electrolyte, Sr-doped LaMnO<SUB>3+/-δ</SUB> (LSM)/YSZ composite working and counter electrodes, and Pt ring-type reference electrode are used to simulate the operating conditions of the air electrode. Degradation behavior in the impedance spectra is characterized as growth of mid-frequency arc at the initial stage, gradual increase of ohmic resistance throughout the operation, and sharp rise of low frequency resistance at the final stage, followed by catastrophic cell failure. Initial stage degradation is attributed to deactivation of LSM, resulting from reduction of oxygen vacancy concentration and/or segregation of passivation species on LSM surface under anodic current passage. Intergranular fracture, which occurs along the grain boundaries of the YSZ electrolyte, is responsible for gradual increase of ohmic resistance. Increase of low frequency arc at the final stage is caused by densification of the air electrode, leading to excessive pressure build-up and delamination of the air electrode. Cation migration, which is facilitated by oxygen excess nonstoichiometry of LSM and externally applied electric field, is considered to be the main cause of permanent damages.