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Ahn, Junsung,Choi, Sungjun,Yoon, Kyung Joong,Son, Ji-Won,Kim, Byung-Kook,Lee, Jong-Ho,Jang, Ho Won,Kim, Hyoungchul American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.49
<P>We explored oxygen-ion transport in highly doped CeO2 through density-functional theory calculations. By applying biaxial strain to 18.75 mol % Ceo(2):Gd, we predicted the average migration-barrier energy with six different pathways, with results in good agreement with those of experiments. Additionally, we found that the migration-barrier energy could be lowered by increasing the tetrahedron volume,, including the space occupied by the oxygen vacancy. Our results indicate that the tetrahedron volume can be expanded by larger codoliants, as well as biaxial tensile strain: Thus, the combination of thin-film structure and codoping could offer a new approach to accelerate oxygen-ion transport.</P>
Identification of an Actual Strain-Induced Effect on Fast Ion Conduction in a Thin-Film Electrolyte
Ahn, Junsung,Jang, Ho Won,Ji, Hoil,Kim, Hyoungchul,Yoon, Kyung Joong,Son, Ji-Won,Kim, Byung-Kook,Lee, Hae-Weon,Lee, Jong-Ho American Chemical Society 2018 NANO LETTERS Vol.18 No.5
<P>Strain-induced fast ion conduction has been a research area of interest for nanoscale energy conversion and storage systems. However, because of significant discrepancies in the interpretation of strain effects, there remains a lack of understanding of how fast ionic transport can be achieved by strain effects and how strain can be controlled in a nanoscale system. In this study, we investigated strain effects on the ionic conductivity of Gd<SUB>0.2</SUB>Ce<SUB>0.8</SUB>O<SUB>1.9−δ</SUB> (100) thin films under well controlled experimental conditions, in which errors due to the external environment could not intervene during the conductivity measurement. In order to avoid any interference from perpendicular-to-surface defects, such as grain boundaries, the ionic conductivity was measured in the out-of-plane direction by electrochemical impedance spectroscopy analysis. With varying film thickness, we found that a thicker film has a lower activation energy of ionic conduction. In addition, careful strain analysis using both reciprocal space mapping and strain mapping in transmission electron microscopy shows that a thicker film has a higher tensile strain than a thinner film. Furthermore, the tensile strain of thicker film was mostly developed near a grain boundary, which indicates that intrinsic strain is dominant rather than epitaxial or thermal strain during thin-film deposition and growth via the Volmer-Weber (island) growth mode.</P> [FIG OMISSION]</BR>
Designing a nanocrystal-based temperature and strain multi-sensor with one-step inkjet printing
( Junsung Bang ),( Junhyuk Ahn ),( Soong Ju Oh ) 한국센서학회 2021 센서학회지 Vol.30 No.4
Wearable multi-sensors based on nanocrystals have attracted significant attention, and studies on patterning technology to implement such multi-sensors are underway. Conventional patterning processes may affect material properties based on high temperatures and harsh chemical conditions. In this study, we developed an inkjet printing technique that can overcome these drawbacks through the application of patterning processes at room temperature and atmospheric pressure. Nanocrystal-based ink is used to adjust properties efficiently. Additionally, the viscosity and surface tension of the solvents are investigated and optimized to increase patterning performance. In the patterning process, the electrical, electrothermal, and electromechanical properties of the nanocrystal pattern are controlled by the ligand exchange process. Experimental results demonstrate that a multi-sensor with a temperature coefficient of resistance of 3.82 × 10<sup>-3</sup> K<sup>-1</sup> and gauge factor of 30.6 can be successfully fabricated using one-step inkjet printing.
Praseodymium doped ceria as electrolyte material for IT-SOFC applications
Shajahan, Irfana,Ahn, Junsung,Nair, Parvathi,Medisetti, Srikar,Patil, Sunaina,Niveditha, V.,Uday Bhaskar Babu, G.,Dasari, Hari Prasad,Lee, Jong-Ho Elsevier 2018 Materials chemistry and physics Vol.216 No.-
<P><B>Abstract</B></P> <P>Praseodymium-doped ceria (PDC, Ce<SUB>0.9</SUB>Pr<SUB>0.1</SUB>O<SUB>2</SUB>) 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<SUP>−1</SUP> and with a secondary peak at 550 cm<SUP>−1</SUP>. 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 m<SUP>2</SUP>/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<SUP>−1</SUP> along with an activation energy of 1.28eV. Instead of a single fluorite structure, XRD of sintered PDC pellet showed multiple structures (Fluorite structure (CeO<SUB>2</SUB>) and cubic structure (PrO<SUB>2</SUB>).</P> <P><B>Highlights</B></P> <P> <UL> <LI> Praseodymium doped ceria (PDC) electrolyte was synthesised by EDTA citrate method. </LI> <LI> Dilatometer study revealed multiple shrinkage behaviour of PDC. </LI> <LI> PDC showed an ionic conductivity of 1.213E-03 S cm<SUP>−1</SUP> at 700 °C. </LI> <LI> XRD at 1500 °C revealed that they crystallize as fluorite CeO<SUB>2</SUB> + cubic PrO<SUB>2</SUB> phase. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Jeon, Sanghyun,Ahn, Junhyuk,Kim, Haneun,Woo, Ho Kun,Bang, Junsung,Lee, Woo Seok,Kim, Donggyu,Hossain, Md Ashraf,Oh, Soong Ju American Chemical Society 2019 The Journal of Physical Chemistry Part C Vol.123 No.17
<P>Ligand exchange processes have been attracting tremendous interest and are necessary when fabricating nanocrystal (NC) thin films for various applications. As ligand exchange processes are based on solution treatment processes, understanding solvents’ effects on the ligand exchange process is necessary. Herein, we investigated the effects of exchanging solvents and rinsing solvents on silver (Ag) NC thin films during the ligand exchanging and rinsing steps. We studied the relationships between solvent properties, such as polarity and steric hindrance, and the structural, electronic, and electromechanical properties of NC thin films. A model system was proposed to explain the obtained relationships. We found that exchanging solvents and rinsing solvents during the ligand exchange process should be separated to regulate the ligand exchange process so that films with desired properties can be obtained. Films optimized for different purposes (highly conductive/highly electromechanically sensitive) were fabricated with the same materials and ligands using different solvents for each process. On the basis of these films, we fabricated a flexible strain sensor using an all-solution process at room temperature. This device exhibits excellent performance, including a high gauge factor up to 400, and high reliability, and stability; furthermore, it can detect minute human motion and sound.</P> [FIG OMISSION]</BR>
Choi, Sung Min,Ahn, Junsung,Son, Ji-Won,Lee, Jong-Ho,Kim, Byung-Kook,Yoon, Kyung Joong,Ji, Ho-Il American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.46
<P>Degradation of oxygen electrode in reversible solid oxide cells operating in both electrolysis and fuel-cell modes is a critical issue that should be tackled. However, origins and mechanisms thereof have been diversely suggested mainly due to the difficulty in precise analysis of microstructural/compositional changes of porous electrode, which is a typical form in solid oxide cells. In this study, we investigate the degradation phenomena of oxygen electrode under electrolysis and fuel-cell long-term operations for 540 h, respectively, using a geometrically well-defined, nanoscale La<SUB>0.6</SUB>Sr<SUB>0.4</SUB>Co<SUB>0.2</SUB>Fe<SUB>0.8</SUB>O<SUB>3−δ</SUB> (LSCF) dense film with a thickness of ∼70 nm. Based on assessments of electrochemical properties and analyses of microstructural and compositional changes after long-term operations, we suggest consolidated degradation mechanisms of oxygen electrode, including the phenomena of kinetic demixing/decomposition of LSCF, which is not readily observable in the typical porous-structured electrode.</P> [FIG OMISSION]</BR>
Choi, Sungjun,Jeon, Minjae,Ahn, Junsung,Jung, Wo Dum,Choi, Sung Min,Kim, Ji-Su,Lim, Jaemin,Jang, Yong-Jun,Jung, Hun-Gi,Lee, Jong-Ho,Sang, Byoung-In,Kim, Hyoungchul American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.28
<P>The composite cathode of an all-solid-state battery composed of various solid-state components requires a dense microstructure and a highly percolated solid-state interface different from that of a conventional liquid-electrolyte-based Li-ion battery. Indeed, the preparation of such a system is particularly challenging. In this study, quantitative analyses of composite cathodes by three-dimensional reconstruction analysis were performed beyond the existing qualitative analysis, and their microstructures and reaction interfaces were successfully analyzed. Interestingly, various quantitative values of structure properties (such as the volume ratio, connectivity, tortuosity, and pore formation) associated with material optimization and process development were predicted, and they were found to result in limited electrochemical charge/discharge performances. We also verified that the effective two-phase boundaries were significantly suppressed to ∼23% of the total volume because of component dispersion and packing issues.</P> [FIG OMISSION]</BR>