Highly porous carbon-coated Si nanoparticles with canyon-like surfaces exhibit a stable cycle ret... more Highly porous carbon-coated Si nanoparticles with canyon-like surfaces exhibit a stable cycle retention of 59.1% after 200 cycles because of sufficient free volume for expansion upon lithiation from their unique canyon-like porous surfaces and cavities formed upon MgO etching.
We describe a fabrication strategy for preparing yttria-stabilized zirconia nanotube (YSZ-NT) arr... more We describe a fabrication strategy for preparing yttria-stabilized zirconia nanotube (YSZ-NT) arrays embedded in porous alumina membranes by means of template-directed atomic layer deposition (ALD) technique. The individual YSZ-NTs have a high aspect-ratio of well over 120, about ~ 110 nm in diameter, and ~ 14 µm in length. Interfacing the tube arrays with porous Pt was also introduced on the basis of partial etching technique in order to construct Pt/YSZ-NTs/Pt membrane electrode assembly (MEA) structures. The resulting YSZ-NTs MEAs show a 7 mm in diameter with a roughness factor of ~ 2. Area specific resistance was measured up to 1.84 Ω cm2 at 400 °C using H2 as fuel.
We report novel salami-like core-sheath composites consisting of Si nanoparticle assemblies coate... more We report novel salami-like core-sheath composites consisting of Si nanoparticle assemblies coated with indium tin oxide (ITO) sheath layers that are synthesized via coelectrospinning. Core-sheath structured Si nanoparticles (NPs) in static ITO allow robust microstructures to accommodate for mechanical stress induced by the repeated cyclical volume changes of Si NPs. Conductive ITO sheaths can provide bulk conduction paths for electrons. Distinct Si NP-based core structures, in which the ITO phase coexists uniformly with electrochemically active Si NPs, are capable of facilitating rapid charge transfer as well. These engineered composites enabled the production of high-performance anodes with an excellent capacity retention of 95.5% (677 and 1523 mAh g(-1,) which are based on the total weight of Si-ITO fibers and Si NPs only, respectively), and an outstanding rate capability with a retention of 75.3% from 1 to 12 C. The cycling performance and rate capability of core-sheath-structur...
Ni-based cermets have commonly been used as anode materials with good catalytic properties for hy... more Ni-based cermets have commonly been used as anode materials with good catalytic properties for hydrocarbon fuel.
We demonstrate 3D intra-stacked CoO/carbon nanocomposites welded by Ag nanoparticles with a capac... more We demonstrate 3D intra-stacked CoO/carbon nanocomposites welded by Ag nanoparticles with a capacity of 770 mA h g−1 at a current density of 2 A g−1, by reducing efficiently the irreversible capacity loss.
A Cu2ZnSnS4 solar cell with an efficiency of 8.17% was fabricated using a non-toxic solvent-based... more A Cu2ZnSnS4 solar cell with an efficiency of 8.17% was fabricated using a non-toxic solvent-based hybrid-ink without the involvement of a complex synthesis, toxic solvents or harmful post-selenization.
We propose a novel electrode design for co-planar single chamber solid oxide fuel cells. The conc... more We propose a novel electrode design for co-planar single chamber solid oxide fuel cells. The concentric electrodes as well as the controlled gas flow in perpendicular to the center of the electrode enable continuous laminar flow from the cathode to the anode, which leads optimal residence time of the gas near electrodes and in turn allows high-performance stable operation. The steady state gas flow without turbulence determines not only the local thermodynamic equilibrium, but also the kinetics of the electrochemical reactions. The cell with the concentric electrodes shows the maximum open circuit voltage (OCV) of 0.70 V, and the maximum power density is improved by 154%. In contrast, the conventional cell with linear-shaped electrodes exhibits the maximum OCV of 0.55 V. Impedance spectroscopy reveals that the polarization resistance is reduced by altering the electrode design from the linear-shape to the concentric design.
Electrochemical analysis allows in situ characterization of solid oxide electrochemical cells (SO... more Electrochemical analysis allows in situ characterization of solid oxide electrochemical cells (SOCs) under operating conditions. However, the SOCs that have been analyzed in this way have ill-defined or uncommon microstructures in terms of porosity and tortuosity. Therefore, the nano-scale characterization of SOCs with respect to three-phase boundaries has been hindered. We introduce novel in situ electrochemical analysis for SOCs that uses combined solid electrolyte potentiometry (SEP) and impedance measurements. This method is employed to investigate the oscillatory behavior of a porous Ni-yttria-stabilized zirconia (YSZ) anode during the partial oxidation of methane under ambient pressure at 8006C. The cyclic oxidation and reduction of nickel induces the oscillatory behavior in the impedance and electrode potential. The in situ characterization of the nickel surface suggests that the oxidation of the nickel occurs predominantly at the two-phase boundaries, whereas the nickel at the three-phase boundaries remains in the metallic state during the cyclic redox reaction. E lectrocatalysts are of key importance in solid oxide electrochemical cells (SOCs), such as solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs). SOCs provide the most promising technology for clean, efficient fuel generation and electric power production from both conventional and renewable energy sources 1-7. The electrodes in SOCs, where the electrochemical reactions occur, should be carefully designed with regard to the electrocatalytic activity and ionic-electronic conductivity. The state-of-the-art electrodes are composites of ion-conducting, electron-conducting, and catalytically active materials in which electrocatalytically active sites (i.e., three-phase boundaries (3PBs)) are maximized 8,9. However, the current understanding of the reaction mechanisms on a nano-scale is limited because of the scarcity of suitable in situ techniques. Therefore, three-dimensional reconstruction of the electrodes and a well-defined model system has been adopted to characterize the microstructural features and the reaction activity as a function of the 3PB site density 1,10-14. Although these previous efforts have provided valuable information about the electrocatalysts, the nano-scale elementary processes of the electrocatalytic reactions have not been clearly elucidated. Electrochemical analysis has been employed to elucidate the driving force and reaction kinetics of electrocatalytic reactions 15. In general, conventional solid electrolyte potentiometry (SEP) and impedance spectroscopy allow insight into electrochemical reactions by measuring global overpotentials and interfacial resistances 16-20. However, it is difficult to clarify how local distributions of overpotentials and resistances are related to the microstructural changes of nano-scale chemical states 21. In particular, the reaction mechanisms of electrocatalysis are very complex because of the dissociative adsorption of reactants that takes place concurrently with the electrochemical reactions. The electrocatalyst (i.e., the electrode) itself may undergo oxidation and reduction (redox) reactions, which results in variations in the resistance and potential of the electrodes. Recent advances in operando spectroscopy techniques, such as ambient pressure X-ray photoelectron spectroscopy (AP-XPS), in situ X-ray diffraction (XRD), and high temperature transmission electron microscopy (HT-TEM), have the potential to reveal nano-scale views of the electrocatalyst 22-24. However, unequivocal elucidation has not occurred because of the unrealistic measurement and specimen conditions required for operando spectroscopy 25. Therefore, a better in situ characterization technique employed under operating conditions with the real composite electrodes is needed. Herein, we demonstrate a novel in situ technique using electrochemical measurements that enables the characterization of the active surface sites on a yttria-stabilized zirconia (YSZ)-supported Ni catalyst during
Two-cell arrayed integrated planar solid oxide fuel cells (IP-SOFCs) were fabricated using a robo... more Two-cell arrayed integrated planar solid oxide fuel cells (IP-SOFCs) were fabricated using a robo-dispensing method. Special emphasis was placed on the influence of reduced shunting current on cell performance. The resistivity of the substrate increased according to a mixture rule of composites by adding Al 2 O 3 into the substrate of partially stabilized zirconia (PSZ). This strategy, which reduces shunting current through the substrate, enhances the power output. When the amount of Al 2 O 3 added was more than 26 vol%, however, the Ni anode migrated into the PSZ substrate to react with Al 2 O 3 , which led to performance degradation. In the case of the two-cell arrayed IP-SOFC with a 20 vol%-Al 2 O 3 added to the PSZ substrate, a reduced shunting current loss improved the power density by 30% compared to that of the Al 2 O 3 -free substrate. #
Influences of feeding gas compositions on the performance of co-planar, single chamber solid oxid... more Influences of feeding gas compositions on the performance of co-planar, single chamber solid oxide fuel cells (SC-SOFCs) are investigated with emphasis on the role of water vapor. The maximum open circuit voltage (OCV) and peak power density are obtained at a methane-to-oxygen ratio of 3.5 under the wet gas condition, and a stoichiometric ratio of 2.0 for methane partial oxidation under the dry gas condition. In addition to the partial oxidation of methane on the anode and electrocatalytic reactions, both steam reforming and methane combustion occur on the anode and cathode, respectively, in the presence of water vapor. Local volume expansion and a rise in temperature associated with these parasitic reactions intensify inter-mixing of the reactant and product gases by which the OCV and power density drastically deteriorate with decreasing anode-to-cathode gap distance, as confirmed by impedance analysis for the LSM-YSZ|YSZ|LSM-YSZ symmetrical cell.
Electrochemical impedance spectroscopy a b s t r a c t Sm 0.5 Sr 0.5 CoO 3 (SSC)eSm 0.2 Ce 0.8 O ... more Electrochemical impedance spectroscopy a b s t r a c t Sm 0.5 Sr 0.5 CoO 3 (SSC)eSm 0.2 Ce 0.8 O 1.9 (SDC) core-shell composite cathodes are synthesized via a polymerizable complex method, and the durability of a cell incorporating the cathodes is examined. Nanocrystalline SSC powders have been coated onto the surfaces of SDC cores to enable the formation of a rigid backbone structure, over which the catalyst phase is effectively dispersed. A symmetrical SSCeSDC jSDCj SSCeSDC half-cell exhibits a polarization resistance of 0.098 U cm 2 at 650 C. The durability and microstructure of the cathode are investigated by electrochemical impedance spectroscopy and thermo-cycle tests at temperatures in the range of 100 Ce650 C. After 30 cycles, the polarization resistance is found to increase by 9.04 Â 10 À2 U cm 2 , a 3.56% rise with respect to the initial resistance. Coarsening of the SSC catalyst phase has been prevented with the use of core-shell type powders, as confirmed by a nearly constant low frequency polarization resistance and a microstructural analysis. The performance of a unit cell comprised of the core-shell type cathode exhibits 1.07 W cm À2 at 600 C and 0.62 W cm À2 at 550 C. (J. Moon).
A double-layer dual-composite cathode is fabricated and has an ideal cathode microstructure with ... more A double-layer dual-composite cathode is fabricated and has an ideal cathode microstructure with large electrochemical active sites and enhanced the durability in solid oxide fuel cells (SOFCs). The insertion of a yttria-stabilized zirconia (YSZ)-rich functional layer between the electrolyte and the electrode allows for a graded transition of the YSZ phase, which enhances ionic percolation and minimizes the thermal expansion coefficient mismatch. Electrochemical measurements reveal that the double-layer composite cathode exhibits improved cathodic performance and long-term stability compared with a single-layer composite cathode. A cell with a well-controlled cathode maintains nearly constant interfacial polarization resistance during an 80 h accelerated lifetime test.
Electrospinning produces sub-micron sized continuous fibers from polymer solutions or melt by ele... more Electrospinning produces sub-micron sized continuous fibers from polymer solutions or melt by electric force. Due to its versatility and cost-effectiveness, this method has been recently adopted for the fabrication of one-dimensional materials. Here, we fabricated polyacrylonitrile (PAN) polymer fibers from which uniform nanoporous carbon fibers with diameters of 100e200 nm were obtained after carbonization at 800 C in Ar þ H 2 O. Water vapor was injected during carbonization to be utilized as a nanoscale pore former. Additionally, a direct coating method using palladium nanoparticles on the carbon fibers was developed. Palladium salt solution was electrosprayed during the electrospinning of the polymer fibers. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were used to confirm surface chemical composition and degree of carbonization. The specific surface area of the palladium coated carbon fibers was 815.6 m 2 /g. Reversible hydrogen adsorption capacity was determined to be 0.35 wt% at 298 K, 0.1 MPa.
Low-temperature solution-deposited thin film transistors (TFTs) involving sol-gel derived indium ... more Low-temperature solution-deposited thin film transistors (TFTs) involving sol-gel derived indium zinc oxide (IZO) as active layers is reported. Microwave annealing is shown to afford the fabrication of lowtemperature processable TFTs. Solution-processed IZO-TFTs prepared at 150 1C by microwave irradiation have shown enhanced device characteristics of 0.1 cm 2 V À 1 s À 1 mobility and a $ 10 6 on/off current ratio, a threshold voltage of 8.1, and a subthreshold slope of 3.3 V/decade. From the results of X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM), we confirmed that the device improvement originates from better crystallization at low temperature made possible by the use of microwave irradiation. Our findings suggest that solution-processable oxide semiconductors have potential for low-temperature and high-performance applications in transparent flexible devices.
Electrochemical impedance spectroscopy a b s t r a c t Sm 0.5 Sr 0.5 CoO 3 (SSC)eSm 0.2 Ce 0.8 O ... more Electrochemical impedance spectroscopy a b s t r a c t Sm 0.5 Sr 0.5 CoO 3 (SSC)eSm 0.2 Ce 0.8 O 1.9 (SDC) core-shell composite cathodes are synthesized via a polymerizable complex method, and the durability of a cell incorporating the cathodes is examined. Nanocrystalline SSC powders have been coated onto the surfaces of SDC cores to enable the formation of a rigid backbone structure, over which the catalyst phase is effectively dispersed. A symmetrical SSCeSDC jSDCj SSCeSDC half-cell exhibits a polarization resistance of 0.098 U cm 2 at 650 C. The durability and microstructure of the cathode are investigated by electrochemical impedance spectroscopy and thermo-cycle tests at temperatures in the range of 100 Ce650 C. After 30 cycles, the polarization resistance is found to increase by 9.04 Â 10 À2 U cm 2 , a 3.56% rise with respect to the initial resistance. Coarsening of the SSC catalyst phase has been prevented with the use of core-shell type powders, as confirmed by a nearly constant low frequency polarization resistance and a microstructural analysis. The performance of a unit cell comprised of the core-shell type cathode exhibits 1.07 W cm À2 at 600 C and 0.62 W cm À2 at 550 C. (J. Moon).
Influences of feeding gas compositions on the performance of co-planar, single chamber solid oxid... more Influences of feeding gas compositions on the performance of co-planar, single chamber solid oxide fuel cells (SC-SOFCs) are investigated with emphasis on the role of water vapor. The maximum open circuit voltage (OCV) and peak power density are obtained at a methane-to-oxygen ratio of 3.5 under the wet gas condition, and a stoichiometric ratio of 2.0 for methane partial oxidation under the dry gas condition. In addition to the partial oxidation of methane on the anode and electrocatalytic reactions, both steam reforming and methane combustion occur on the anode and cathode, respectively, in the presence of water vapor. Local volume expansion and a rise in temperature associated with these parasitic reactions intensify inter-mixing of the reactant and product gases by which the OCV and power density drastically deteriorate with decreasing anode-to-cathode gap distance, as confirmed by impedance analysis for the LSM-YSZ|YSZ|LSM-YSZ symmetrical cell.
Electrochemical analysis allows in situ characterization of solid oxide electrochemical cells (SO... more Electrochemical analysis allows in situ characterization of solid oxide electrochemical cells (SOCs) under operating conditions. However, the SOCs that have been analyzed in this way have ill-defined or uncommon microstructures in terms of porosity and tortuosity. Therefore, the nano-scale characterization of SOCs with respect to three-phase boundaries has been hindered. We introduce novel in situ electrochemical analysis for SOCs that uses combined solid electrolyte potentiometry (SEP) and impedance measurements. This method is employed to investigate the oscillatory behavior of a porous Ni-yttria-stabilized zirconia (YSZ) anode during the partial oxidation of methane under ambient pressure at 8006C. The cyclic oxidation and reduction of nickel induces the oscillatory behavior in the impedance and electrode potential. The in situ characterization of the nickel surface suggests that the oxidation of the nickel occurs predominantly at the two-phase boundaries, whereas the nickel at the three-phase boundaries remains in the metallic state during the cyclic redox reaction. E lectrocatalysts are of key importance in solid oxide electrochemical cells (SOCs), such as solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs). SOCs provide the most promising technology for clean, efficient fuel generation and electric power production from both conventional and renewable energy sources 1-7 . The electrodes in SOCs, where the electrochemical reactions occur, should be carefully designed with regard to the electrocatalytic activity and ionic-electronic conductivity. The state-of-the-art electrodes are composites of ion-conducting, electron-conducting, and catalytically active materials in which electrocatalytically active sites (i.e., three-phase boundaries (3 PBs)) are maximized . However, the current understanding of the reaction mechanisms on a nano-scale is limited because of the scarcity of suitable in situ techniques. Therefore, three-dimensional reconstruction of the electrodes and a well-defined model system has been adopted to characterize the microstructural features and the reaction activity as a function of the 3 PB site density 1,10-14 . Although these previous efforts have provided valuable information about the electrocatalysts, the nano-scale elementary processes of the electrocatalytic reactions have not been clearly elucidated.
Highly porous carbon-coated Si nanoparticles with canyon-like surfaces exhibit a stable cycle ret... more Highly porous carbon-coated Si nanoparticles with canyon-like surfaces exhibit a stable cycle retention of 59.1% after 200 cycles because of sufficient free volume for expansion upon lithiation from their unique canyon-like porous surfaces and cavities formed upon MgO etching.
We describe a fabrication strategy for preparing yttria-stabilized zirconia nanotube (YSZ-NT) arr... more We describe a fabrication strategy for preparing yttria-stabilized zirconia nanotube (YSZ-NT) arrays embedded in porous alumina membranes by means of template-directed atomic layer deposition (ALD) technique. The individual YSZ-NTs have a high aspect-ratio of well over 120, about ~ 110 nm in diameter, and ~ 14 µm in length. Interfacing the tube arrays with porous Pt was also introduced on the basis of partial etching technique in order to construct Pt/YSZ-NTs/Pt membrane electrode assembly (MEA) structures. The resulting YSZ-NTs MEAs show a 7 mm in diameter with a roughness factor of ~ 2. Area specific resistance was measured up to 1.84 Ω cm2 at 400 °C using H2 as fuel.
We report novel salami-like core-sheath composites consisting of Si nanoparticle assemblies coate... more We report novel salami-like core-sheath composites consisting of Si nanoparticle assemblies coated with indium tin oxide (ITO) sheath layers that are synthesized via coelectrospinning. Core-sheath structured Si nanoparticles (NPs) in static ITO allow robust microstructures to accommodate for mechanical stress induced by the repeated cyclical volume changes of Si NPs. Conductive ITO sheaths can provide bulk conduction paths for electrons. Distinct Si NP-based core structures, in which the ITO phase coexists uniformly with electrochemically active Si NPs, are capable of facilitating rapid charge transfer as well. These engineered composites enabled the production of high-performance anodes with an excellent capacity retention of 95.5% (677 and 1523 mAh g(-1,) which are based on the total weight of Si-ITO fibers and Si NPs only, respectively), and an outstanding rate capability with a retention of 75.3% from 1 to 12 C. The cycling performance and rate capability of core-sheath-structur...
Ni-based cermets have commonly been used as anode materials with good catalytic properties for hy... more Ni-based cermets have commonly been used as anode materials with good catalytic properties for hydrocarbon fuel.
We demonstrate 3D intra-stacked CoO/carbon nanocomposites welded by Ag nanoparticles with a capac... more We demonstrate 3D intra-stacked CoO/carbon nanocomposites welded by Ag nanoparticles with a capacity of 770 mA h g−1 at a current density of 2 A g−1, by reducing efficiently the irreversible capacity loss.
A Cu2ZnSnS4 solar cell with an efficiency of 8.17% was fabricated using a non-toxic solvent-based... more A Cu2ZnSnS4 solar cell with an efficiency of 8.17% was fabricated using a non-toxic solvent-based hybrid-ink without the involvement of a complex synthesis, toxic solvents or harmful post-selenization.
We propose a novel electrode design for co-planar single chamber solid oxide fuel cells. The conc... more We propose a novel electrode design for co-planar single chamber solid oxide fuel cells. The concentric electrodes as well as the controlled gas flow in perpendicular to the center of the electrode enable continuous laminar flow from the cathode to the anode, which leads optimal residence time of the gas near electrodes and in turn allows high-performance stable operation. The steady state gas flow without turbulence determines not only the local thermodynamic equilibrium, but also the kinetics of the electrochemical reactions. The cell with the concentric electrodes shows the maximum open circuit voltage (OCV) of 0.70 V, and the maximum power density is improved by 154%. In contrast, the conventional cell with linear-shaped electrodes exhibits the maximum OCV of 0.55 V. Impedance spectroscopy reveals that the polarization resistance is reduced by altering the electrode design from the linear-shape to the concentric design.
Electrochemical analysis allows in situ characterization of solid oxide electrochemical cells (SO... more Electrochemical analysis allows in situ characterization of solid oxide electrochemical cells (SOCs) under operating conditions. However, the SOCs that have been analyzed in this way have ill-defined or uncommon microstructures in terms of porosity and tortuosity. Therefore, the nano-scale characterization of SOCs with respect to three-phase boundaries has been hindered. We introduce novel in situ electrochemical analysis for SOCs that uses combined solid electrolyte potentiometry (SEP) and impedance measurements. This method is employed to investigate the oscillatory behavior of a porous Ni-yttria-stabilized zirconia (YSZ) anode during the partial oxidation of methane under ambient pressure at 8006C. The cyclic oxidation and reduction of nickel induces the oscillatory behavior in the impedance and electrode potential. The in situ characterization of the nickel surface suggests that the oxidation of the nickel occurs predominantly at the two-phase boundaries, whereas the nickel at the three-phase boundaries remains in the metallic state during the cyclic redox reaction. E lectrocatalysts are of key importance in solid oxide electrochemical cells (SOCs), such as solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs). SOCs provide the most promising technology for clean, efficient fuel generation and electric power production from both conventional and renewable energy sources 1-7. The electrodes in SOCs, where the electrochemical reactions occur, should be carefully designed with regard to the electrocatalytic activity and ionic-electronic conductivity. The state-of-the-art electrodes are composites of ion-conducting, electron-conducting, and catalytically active materials in which electrocatalytically active sites (i.e., three-phase boundaries (3PBs)) are maximized 8,9. However, the current understanding of the reaction mechanisms on a nano-scale is limited because of the scarcity of suitable in situ techniques. Therefore, three-dimensional reconstruction of the electrodes and a well-defined model system has been adopted to characterize the microstructural features and the reaction activity as a function of the 3PB site density 1,10-14. Although these previous efforts have provided valuable information about the electrocatalysts, the nano-scale elementary processes of the electrocatalytic reactions have not been clearly elucidated. Electrochemical analysis has been employed to elucidate the driving force and reaction kinetics of electrocatalytic reactions 15. In general, conventional solid electrolyte potentiometry (SEP) and impedance spectroscopy allow insight into electrochemical reactions by measuring global overpotentials and interfacial resistances 16-20. However, it is difficult to clarify how local distributions of overpotentials and resistances are related to the microstructural changes of nano-scale chemical states 21. In particular, the reaction mechanisms of electrocatalysis are very complex because of the dissociative adsorption of reactants that takes place concurrently with the electrochemical reactions. The electrocatalyst (i.e., the electrode) itself may undergo oxidation and reduction (redox) reactions, which results in variations in the resistance and potential of the electrodes. Recent advances in operando spectroscopy techniques, such as ambient pressure X-ray photoelectron spectroscopy (AP-XPS), in situ X-ray diffraction (XRD), and high temperature transmission electron microscopy (HT-TEM), have the potential to reveal nano-scale views of the electrocatalyst 22-24. However, unequivocal elucidation has not occurred because of the unrealistic measurement and specimen conditions required for operando spectroscopy 25. Therefore, a better in situ characterization technique employed under operating conditions with the real composite electrodes is needed. Herein, we demonstrate a novel in situ technique using electrochemical measurements that enables the characterization of the active surface sites on a yttria-stabilized zirconia (YSZ)-supported Ni catalyst during
Two-cell arrayed integrated planar solid oxide fuel cells (IP-SOFCs) were fabricated using a robo... more Two-cell arrayed integrated planar solid oxide fuel cells (IP-SOFCs) were fabricated using a robo-dispensing method. Special emphasis was placed on the influence of reduced shunting current on cell performance. The resistivity of the substrate increased according to a mixture rule of composites by adding Al 2 O 3 into the substrate of partially stabilized zirconia (PSZ). This strategy, which reduces shunting current through the substrate, enhances the power output. When the amount of Al 2 O 3 added was more than 26 vol%, however, the Ni anode migrated into the PSZ substrate to react with Al 2 O 3 , which led to performance degradation. In the case of the two-cell arrayed IP-SOFC with a 20 vol%-Al 2 O 3 added to the PSZ substrate, a reduced shunting current loss improved the power density by 30% compared to that of the Al 2 O 3 -free substrate. #
Influences of feeding gas compositions on the performance of co-planar, single chamber solid oxid... more Influences of feeding gas compositions on the performance of co-planar, single chamber solid oxide fuel cells (SC-SOFCs) are investigated with emphasis on the role of water vapor. The maximum open circuit voltage (OCV) and peak power density are obtained at a methane-to-oxygen ratio of 3.5 under the wet gas condition, and a stoichiometric ratio of 2.0 for methane partial oxidation under the dry gas condition. In addition to the partial oxidation of methane on the anode and electrocatalytic reactions, both steam reforming and methane combustion occur on the anode and cathode, respectively, in the presence of water vapor. Local volume expansion and a rise in temperature associated with these parasitic reactions intensify inter-mixing of the reactant and product gases by which the OCV and power density drastically deteriorate with decreasing anode-to-cathode gap distance, as confirmed by impedance analysis for the LSM-YSZ|YSZ|LSM-YSZ symmetrical cell.
Electrochemical impedance spectroscopy a b s t r a c t Sm 0.5 Sr 0.5 CoO 3 (SSC)eSm 0.2 Ce 0.8 O ... more Electrochemical impedance spectroscopy a b s t r a c t Sm 0.5 Sr 0.5 CoO 3 (SSC)eSm 0.2 Ce 0.8 O 1.9 (SDC) core-shell composite cathodes are synthesized via a polymerizable complex method, and the durability of a cell incorporating the cathodes is examined. Nanocrystalline SSC powders have been coated onto the surfaces of SDC cores to enable the formation of a rigid backbone structure, over which the catalyst phase is effectively dispersed. A symmetrical SSCeSDC jSDCj SSCeSDC half-cell exhibits a polarization resistance of 0.098 U cm 2 at 650 C. The durability and microstructure of the cathode are investigated by electrochemical impedance spectroscopy and thermo-cycle tests at temperatures in the range of 100 Ce650 C. After 30 cycles, the polarization resistance is found to increase by 9.04 Â 10 À2 U cm 2 , a 3.56% rise with respect to the initial resistance. Coarsening of the SSC catalyst phase has been prevented with the use of core-shell type powders, as confirmed by a nearly constant low frequency polarization resistance and a microstructural analysis. The performance of a unit cell comprised of the core-shell type cathode exhibits 1.07 W cm À2 at 600 C and 0.62 W cm À2 at 550 C. (J. Moon).
A double-layer dual-composite cathode is fabricated and has an ideal cathode microstructure with ... more A double-layer dual-composite cathode is fabricated and has an ideal cathode microstructure with large electrochemical active sites and enhanced the durability in solid oxide fuel cells (SOFCs). The insertion of a yttria-stabilized zirconia (YSZ)-rich functional layer between the electrolyte and the electrode allows for a graded transition of the YSZ phase, which enhances ionic percolation and minimizes the thermal expansion coefficient mismatch. Electrochemical measurements reveal that the double-layer composite cathode exhibits improved cathodic performance and long-term stability compared with a single-layer composite cathode. A cell with a well-controlled cathode maintains nearly constant interfacial polarization resistance during an 80 h accelerated lifetime test.
Electrospinning produces sub-micron sized continuous fibers from polymer solutions or melt by ele... more Electrospinning produces sub-micron sized continuous fibers from polymer solutions or melt by electric force. Due to its versatility and cost-effectiveness, this method has been recently adopted for the fabrication of one-dimensional materials. Here, we fabricated polyacrylonitrile (PAN) polymer fibers from which uniform nanoporous carbon fibers with diameters of 100e200 nm were obtained after carbonization at 800 C in Ar þ H 2 O. Water vapor was injected during carbonization to be utilized as a nanoscale pore former. Additionally, a direct coating method using palladium nanoparticles on the carbon fibers was developed. Palladium salt solution was electrosprayed during the electrospinning of the polymer fibers. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were used to confirm surface chemical composition and degree of carbonization. The specific surface area of the palladium coated carbon fibers was 815.6 m 2 /g. Reversible hydrogen adsorption capacity was determined to be 0.35 wt% at 298 K, 0.1 MPa.
Low-temperature solution-deposited thin film transistors (TFTs) involving sol-gel derived indium ... more Low-temperature solution-deposited thin film transistors (TFTs) involving sol-gel derived indium zinc oxide (IZO) as active layers is reported. Microwave annealing is shown to afford the fabrication of lowtemperature processable TFTs. Solution-processed IZO-TFTs prepared at 150 1C by microwave irradiation have shown enhanced device characteristics of 0.1 cm 2 V À 1 s À 1 mobility and a $ 10 6 on/off current ratio, a threshold voltage of 8.1, and a subthreshold slope of 3.3 V/decade. From the results of X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM), we confirmed that the device improvement originates from better crystallization at low temperature made possible by the use of microwave irradiation. Our findings suggest that solution-processable oxide semiconductors have potential for low-temperature and high-performance applications in transparent flexible devices.
Electrochemical impedance spectroscopy a b s t r a c t Sm 0.5 Sr 0.5 CoO 3 (SSC)eSm 0.2 Ce 0.8 O ... more Electrochemical impedance spectroscopy a b s t r a c t Sm 0.5 Sr 0.5 CoO 3 (SSC)eSm 0.2 Ce 0.8 O 1.9 (SDC) core-shell composite cathodes are synthesized via a polymerizable complex method, and the durability of a cell incorporating the cathodes is examined. Nanocrystalline SSC powders have been coated onto the surfaces of SDC cores to enable the formation of a rigid backbone structure, over which the catalyst phase is effectively dispersed. A symmetrical SSCeSDC jSDCj SSCeSDC half-cell exhibits a polarization resistance of 0.098 U cm 2 at 650 C. The durability and microstructure of the cathode are investigated by electrochemical impedance spectroscopy and thermo-cycle tests at temperatures in the range of 100 Ce650 C. After 30 cycles, the polarization resistance is found to increase by 9.04 Â 10 À2 U cm 2 , a 3.56% rise with respect to the initial resistance. Coarsening of the SSC catalyst phase has been prevented with the use of core-shell type powders, as confirmed by a nearly constant low frequency polarization resistance and a microstructural analysis. The performance of a unit cell comprised of the core-shell type cathode exhibits 1.07 W cm À2 at 600 C and 0.62 W cm À2 at 550 C. (J. Moon).
Influences of feeding gas compositions on the performance of co-planar, single chamber solid oxid... more Influences of feeding gas compositions on the performance of co-planar, single chamber solid oxide fuel cells (SC-SOFCs) are investigated with emphasis on the role of water vapor. The maximum open circuit voltage (OCV) and peak power density are obtained at a methane-to-oxygen ratio of 3.5 under the wet gas condition, and a stoichiometric ratio of 2.0 for methane partial oxidation under the dry gas condition. In addition to the partial oxidation of methane on the anode and electrocatalytic reactions, both steam reforming and methane combustion occur on the anode and cathode, respectively, in the presence of water vapor. Local volume expansion and a rise in temperature associated with these parasitic reactions intensify inter-mixing of the reactant and product gases by which the OCV and power density drastically deteriorate with decreasing anode-to-cathode gap distance, as confirmed by impedance analysis for the LSM-YSZ|YSZ|LSM-YSZ symmetrical cell.
Electrochemical analysis allows in situ characterization of solid oxide electrochemical cells (SO... more Electrochemical analysis allows in situ characterization of solid oxide electrochemical cells (SOCs) under operating conditions. However, the SOCs that have been analyzed in this way have ill-defined or uncommon microstructures in terms of porosity and tortuosity. Therefore, the nano-scale characterization of SOCs with respect to three-phase boundaries has been hindered. We introduce novel in situ electrochemical analysis for SOCs that uses combined solid electrolyte potentiometry (SEP) and impedance measurements. This method is employed to investigate the oscillatory behavior of a porous Ni-yttria-stabilized zirconia (YSZ) anode during the partial oxidation of methane under ambient pressure at 8006C. The cyclic oxidation and reduction of nickel induces the oscillatory behavior in the impedance and electrode potential. The in situ characterization of the nickel surface suggests that the oxidation of the nickel occurs predominantly at the two-phase boundaries, whereas the nickel at the three-phase boundaries remains in the metallic state during the cyclic redox reaction. E lectrocatalysts are of key importance in solid oxide electrochemical cells (SOCs), such as solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs). SOCs provide the most promising technology for clean, efficient fuel generation and electric power production from both conventional and renewable energy sources 1-7 . The electrodes in SOCs, where the electrochemical reactions occur, should be carefully designed with regard to the electrocatalytic activity and ionic-electronic conductivity. The state-of-the-art electrodes are composites of ion-conducting, electron-conducting, and catalytically active materials in which electrocatalytically active sites (i.e., three-phase boundaries (3 PBs)) are maximized . However, the current understanding of the reaction mechanisms on a nano-scale is limited because of the scarcity of suitable in situ techniques. Therefore, three-dimensional reconstruction of the electrodes and a well-defined model system has been adopted to characterize the microstructural features and the reaction activity as a function of the 3 PB site density 1,10-14 . Although these previous efforts have provided valuable information about the electrocatalysts, the nano-scale elementary processes of the electrocatalytic reactions have not been clearly elucidated.
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Papers by Daehee Lee