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S. H. Chan - One of the best experts on this subject based on the ideXlab platform.
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Development of LSm/YSZ Composite Electrodes for Thin Film Solid Oxide Fuel Cells
ECS Proceedings Volumes, 2020Co-Authors: Yongjun Leng, S. H. Chan, K. A. Khor, San Ping JiangAbstract:The effects of cathodic current passage, (La,Sr)MnO 3 (LSm) stoichiometry and the surface treatment of YSZ electrolyte on the performance of LSm/YSZ composite cathode were investigated. The cathodic current passage had an enhancing/activation effect on the composite cathode made of stoichiometric LSm powder (LSm-A) and YSZ powder, while it had little effect on the composite cathode made of A-site sub-stoichiometric LSm powder (LSm-B) and YSZ powder. An A-site deficiency (∼0.1) is effective in inhibiting the formation of the resistive layer such as La 2 Zr 2 O 7 /SrZrO 3 between LSm and YSZ. Also, surface treatment of YSZ electrolyte had a major effect on the cathode performance. After polishing the YSZ surface, the measured interfacial resistance of LSm-B/YSZ (50:50 wt%) decreased to 0.27 ohm cm 2 from 0.50 ohm cm 2 on as-sintered YSZ surface at 800°C in air. The results showed that LSm/YSZ composite cathode performance can be significantly improved by using A-site deficient LSm and thorough surface treatment of YSZ electrolyte.
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(La_0.8Sr_0.2)_0.9MnO_3–Gd_0.2Ce_0.8O_1.9 composite cathodes prepared from (Gd, Ce)(NO_3)_ x -modified (La_0.8Sr_0.2)_0.9MnO_3 for intermediate-temperature solid oxide fuel cells
Journal of Solid State Electrochemistry, 2006Co-Authors: Y. J. Leng, S. H. Chan, K. A. Khor, S. P. JiangAbstract:Development of high performance cathodes with low polarization resistance is critical to the success of solid oxide fuel cell (SOFC) development and commercialization. In this paper, (La_0.8Sr_0.2)_0.9MnO_3 (LSm)–Gd_0.2Ce_0.8O_1.9(GDC) composite powder (LSm ~70 wt%, GDC ~30 wt%) was prepared through modification of LSm powder by Gd_0.2Ce_0.8(NO_3)_ x solution impregnation, followed by calcination. The electrode polarization resistance of the LSm–GDC cathode prepared from the composite powder was ~0.60 Ω cm^2 at 750 °C, which is ~13 times lower than that of pure LSm cathode (~8.19 Ω cm^2 at 750 °C) on YSZ electrolyte substrates. The electrode polarization resistance of the LSm–GDC composite cathode at 700 °C under 500 mA/cm^2 was ~0.42 Ω cm^2, which is close to that of pure LSm cathode at 850 °C. Gd_0.2Ce_0.8(NO_3)_ x solution impregnation modification not only inhibits the growth of LSm grains during sintering but also increases the triple-phase-boundary (TPB) area through introducing ionic conducting phase (Gd,Ce)O_2-δ, leading to the significant reduction of electrode polarization resistance of LSm cathode.
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Electrochemical behavior of La(Sr)MnO3 electrode under cathodic and anodic polarization
Solid State Ionics, 2004Co-Authors: X J Chen, Khiam Aik Khor, S. H. ChanAbstract:Electrochemical behavior of the strontium doped lanthanum manganite (LSm) electrode under cathodic and anodic current treatment was investigated by a.c. impedance spectroscopy and cyclic voltammetry. The reversible behavior of the LSm electrode may be related to the partial reduction and oxidation of the Mn ions under cathodic and anodic polarization. The performance of the LSm electrode was found to depend on the oxygen vacancies at the LSm surface, which would promote the transport of oxygen intermediate species at LSm surface close to the three-phase boundary (TPB) region. Results show that the impedance resistance of LSm electrode reduces with the increase of cathodic DC bias. The exponential dependence of QH and QL on the cathodic overpotential suggests that the reaction processes associated with the high- and low-frequency arcs to be chemical or physical processes. © 2003 Elsevier B.V. All rights reserved.
Henry Likyuen Chan - One of the best experts on this subject based on the ideXlab platform.
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factors associated with unreliable liver stiffness measurement and its failure with transient elastography in the chinese population
Journal of Gastroenterology and Hepatology, 2011Co-Authors: Grace Laihung Wong, Vincent Waisun Wong, Angel M L Chim, Mia K P Li, Henry Likyuen ChanAbstract:Background and Aim: Liver stiffness measurement (LSm) with transient elastography is a non-invasive and reliable test for liver fibrosis. However a small proportion of patients may have unreliable LSm or LSm failure. The aim of the present study was to investigate the factors associated with unreliable LSm or LSm failure in Chinese patients. Methods: We prospectively recruited liver patients for LSm. Unreliable LSm was defined as 30%, or a success rate < 60%. LSm failure was defined as zero valid shots. Results: Among 3205 patients with LSm, 371 (11.6%) and 88 (2.7%) had unreliable LSm and LSm failure, respectively. The rates started to increase when body mass index (BMI) ≥ 28.0 kg/m2. Comparing patients with BMI ≥ 28.0–29.9 kg/m2 versus those with BMI ≥ 30.0 kg/m2, the rates of unreliable LSm (16.4% vs 18.9%; P = 0.62) and LSm failure (11.8% vs 17.8%; P = 0.16) were similar. BMI ≥ 28.0 kg/m2 was the most important factor associated with unreliable LSm (odds ratio [OR] = 2.9, 95% confidence interval [CI] = 2.1–3.9, P 80 cm in women and > 90 cm in men, was another independent risk factor of unreliable LSm (OR = 1.3, 95% CI = 1.0–1.6, P = 0.04) and LSm failure (OR = 5.8, 95% CI = 2.9–11.5, P < 0.0001). Conclusion: BMI ≥ 28.0 kg/m2 and central obesity were the independent risk factors of unreliable LSm and LSm failure in Chinese, and these rates were significantly higher in patients with extreme BMI.
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on treatment monitoring of liver fibrosis with transient elastography in chronic hepatitis b patients
Antiviral Therapy, 2011Co-Authors: Grace Laihung Wong, Vincent Waisun Wong, P C L Choi, Anthony Wh Chan, Francis K L Chan, Joseph J Y Sung, Angel Meiling Chim, Henry Likyuen ChanAbstract:Background: The performance of liver stiffness measurement (LSm) to monitor the changes in the severity of liver fibrosis in chronic hepatitis B (CHB) patients on antiviral treatment is uncertain. Methods: We prospectively studied CHB patients undergoing paired liver biopsy and transient elastography before and at week 48 of antiviral treatment. Based on our previously reported LSm algorithm, advanced liver fibrosis (F3-4) could be excluded or confirmed at >90% confidence. Results: A total of 71 CHB patients were studied. The median alanine aminotransferase (ALT) level decreased from 991 U/I to 331 U/I, and the median LSm decreased from 8.8 kPa to 6.6 kPa, respectively, from baseline to week 48. Overall, 17 and 11 patients had regression and progression of histological fibrosis, respectively. Areas under the receiver operating characteristics curves of the LSm algorithm at baseline and week 48 for advanced fibrosis were 0.80 (95% confidence interval [CI] 0.69-0.90) and 0.78 (95% CI 0.64-0.92), respectively. The sensitivity of LSm algorithm to exclude advanced fibrosis was 100% at baseline and 75% at week 48. The specificity of the LSm algorithm to diagnose advanced fibrosis was 84% at baseline and 91% at week 48. Overall, 11/28 (39%) patients with LSm that decreased by >30%, 28/41 (68%) of patients with LSm that changed within 30% and 1/2 (50%) patients with LSm that increased by >30% had decreased, unchanged and increased histological fibrosis stages, respectively. Conclusions: LSm could predict advanced fibrosis during antiviral therapy according to the ALT-based algorithm. Decrease in absolute LSm value, which could be related to ALT normalization, was unreliable to indicate regression of liver fibrosis.
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increased liver stiffness measurement by transient elastography in severe acute exacerbation of chronic hepatitis b
Journal of Gastroenterology and Hepatology, 2009Co-Authors: Grace Lh Wong, Vincent Waisun Wong, Angel M L Chim, P C L Choi, Anthony Wh Chan, Francis K L Chan, Joseph J Y Sung, Henry Likyuen ChanAbstract:Background and Aims: The proposed cut-off values for the degree of fibrosis as assessed by liver stiffness measurement (LSm) might not be applicable in severe acute exacerbation of chronic hepatitis B (CHB). We aimed to assess the effect of necroinflammatory activity on LSm in this condition. Methods: We prospectively recruited consecutive patients with severe acute exacerbation of CHB (alanine aminotransferase or ALT > 10× upper limit of normal). The relationship of ALT levels and LSm were serially assessed and liver biopsy was carried out after ALT normalization. Results: Eleven patients (10 male, median age 43 years) were followed up for 25 weeks; nine patients received antiviral therapy. Overall, LSm was positively correlated with ALT levels (r = 0.67, P < 0.001). At initial presentation, the median serum ALT and LSm was 1136 (581–2210) IU/L and 26.3 (11.1–33.3) kPa. A progressive reduction in LSm was observed during subsequent visits in parallel with the reduction of ALT levels. At the last visit, the median ALT was 27 (11–52) IU/L and LSm was 7.7 (4.7–10.8) kPa. Among the five patients who had liver biopsy carried out at week 25, four patients had F2 fibrosis (LSm 5.7–8.1 kPa) and one patient had F3 fibrosis (LSm 8.6 kPa). Conclusions: LSm using transient elastography with the current proposed cut-off values might misdiagnose liver cirrhosis in patients suffering from severe acute exacerbation of CHB. LSm should be assessed after normalization of ALT levels in order to accurately assess the degree of fibrosis.
San Ping Jiang - One of the best experts on this subject based on the ideXlab platform.
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Identification of oxygen reduction processes at (La,Sr)MnO3 electrode/La9.5Si6O26.25 apatite electrolyte interface of solid oxide fuel cells
International Journal of Hydrogen Energy, 2013Co-Authors: Xiao Guo Cao, San Ping JiangAbstract:Oxygen reduction reaction of (La,Sr)MnO3 (LSm) cathode on La9.5Si6O26.25 apatite (LSO) electrolyte is studied over the temperature range 750-900 ??C and the oxygen partial pressure range 0.01-1 atm by electrochemical impedance spectroscopy. The impedance responses show two separable arcs and are analyzed in terms of two different equivalent circuits with comparable information on the electrode processes at high and low frequencies. The electrode process associated with the high frequency arc (??1) is basically independent of oxygen partial pressure. The activation energy of ??1 is 188 ?? 15 kJ mol-1 for the O2 reduction reaction on the LSm electrode sintered at 1150 ??C, and decreases to 120 kJ mol-1 for the O2 reduction reaction on the LSm electrode sintered at 850 ??C, which is close to 80-110 kJ mol-1 observed for the same electrode process at LSm/YSZ interface. The reaction order with respect to PO2 and the activation energy of the electrode process associated with low frequency arc (??2) are generally close to that of ??2 at the LSm/YSZ interface. The activation process of the cathodic polarization treatment is noticeably slower for the reaction at LSm/LSO interface as compared to that at LSm/YSZ interface. The impedance responses of O2 reduction reaction at the LSm/LSO interface are significantly higher than that at the LSm/YSZ interface due to the silicon spreading. The impedance responses decrease with the decrease of the sintering temperature of LSm electrode on LSO electrolyte. At the sintering temperature of 1000 ??C, the impedance responses of O2 reduction reaction is 1.74 ?? cm2 at 900 ??C, which is significantly smaller than that of LSm electrode sintered at 1150 ??C. Copyright ?? 2012, Hydrogen Energy Publications, LLC.
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fabrication and performance of gdc impregnated la sr mno3 cathodes for intermediate temperature solid oxide fuel cells
Journal of The Electrochemical Society, 2005Co-Authors: San Ping Jiang, Wei WangAbstract:High-performance (La,Sr)MnO 3 (LSm) cathodes for intermediate temperature solid oxide fuel cells were fabricated by the ion impregnation of oxygen ion conducting Gd-doped CeO 2 (GDC) oxide. The microstructure of the GDC-impregnated LSm electrode was characterized by the uniform dispersion of very fine GDC particles in the LSm porous framework. The particle size of the impregnated GDC phase was in the range of 100-200 nm. Uniform distribution of the nanosized ionic conducting GDC phase significantly enhanced the electrode activities for the O 2 reduction reaction. In the case of the 5.8 mg cm - 2 GDC-impregnated LSm electrode, electrode polarization resistance was 0.21 Ω cm 2 at 700°C, 56 times lower than that of the pure LSm at the same temperature. GDC-impregnated LSm electrode showed lower activation energy and low reaction order with respect to the partial pressure of oxygen, as compared to that on the pure LSm electrodes. The results indicate that GDC impregnation has significant electrocatalytic effect on the O 2 reduction reactions on the LSm electrodes.
Kwang-leong Choy - One of the best experts on this subject based on the ideXlab platform.
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The electrochemical properties of LSm-based cathodes fabricated by electrostatic spray assisted vapour deposition
Journal of Power Sources, 2008Co-Authors: Kwang-leong ChoyAbstract:Abstract La 0.8 Sr 0.2 MnO 3− δ (LSm) and LSm–8 mol% yttria-stabilized zirconia (YSZ) composite cathodes were fabricated using electrostatic spray assisted vapour deposition (ESAVD) method. The porous cathode layers of LSm and LSm–YSZ with high specific surface areas were obtained by optimizing the deposition parameters. It was found that the introduction of YSZ into LSm decreased the electrochemical impedance significantly. The activation effect of passing current on the electrochemical activity of the LSm–YSZ composite cathodes was much lower than that of the LSm cathodes. For the LSm–YSZ composite cathodes, there was a saturation of current with increasing applied potential at higher temperatures (from 900 to 1000 °C). The LSm–YSZ composite cathode fabricated by ESAVD exhibited high electrochemical activity at high and intermediate temperatures (from 800 to 1000 °C). This suggests that ESAVD is a promising technique for the fabrication of solid oxide fuel cell (SOFC) cathodes.
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The electrochemical properties of LSm-based cathodes fabricated by electrostatic spray assisted vapour deposition
Journal of Power Sources, 2008Co-Authors: Jingwang Yan, Xianghui Hou, Kwang-leong ChoyAbstract:La0.8Sr0.2MnO3-?? (LSm) and LSm-8 mol% yttria-stabilized zirconia (YSZ) composite cathodes were fabricated using electrostatic spray assisted vapour deposition (ESAVD) method. The porous cathode layers of LSm and LSm-YSZ with high specific surface areas were obtained by optimizing the deposition parameters. It was found that the introduction of YSZ into LSm decreased the electrochemical impedance significantly. The activation effect of passing current on the electrochemical activity of the LSm-YSZ composite cathodes was much lower than that of the LSm cathodes. For the LSm-YSZ composite cathodes, there was a saturation of current with increasing applied potential at higher temperatures (from 900 to 1000 ??C). The LSm-YSZ composite cathode fabricated by ESAVD exhibited high electrochemical activity at high and intermediate temperatures (from 800 to 1000 ??C). This suggests that ESAVD is a promising technique for the fabrication of solid oxide fuel cell (SOFC) cathodes. ?? 2008 Elsevier B.V. All rights reserved.
Wei Wang - One of the best experts on this subject based on the ideXlab platform.
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fabrication and performance of gdc impregnated la sr mno3 cathodes for intermediate temperature solid oxide fuel cells
Journal of The Electrochemical Society, 2005Co-Authors: San Ping Jiang, Wei WangAbstract:High-performance (La,Sr)MnO 3 (LSm) cathodes for intermediate temperature solid oxide fuel cells were fabricated by the ion impregnation of oxygen ion conducting Gd-doped CeO 2 (GDC) oxide. The microstructure of the GDC-impregnated LSm electrode was characterized by the uniform dispersion of very fine GDC particles in the LSm porous framework. The particle size of the impregnated GDC phase was in the range of 100-200 nm. Uniform distribution of the nanosized ionic conducting GDC phase significantly enhanced the electrode activities for the O 2 reduction reaction. In the case of the 5.8 mg cm - 2 GDC-impregnated LSm electrode, electrode polarization resistance was 0.21 Ω cm 2 at 700°C, 56 times lower than that of the pure LSm at the same temperature. GDC-impregnated LSm electrode showed lower activation energy and low reaction order with respect to the partial pressure of oxygen, as compared to that on the pure LSm electrodes. The results indicate that GDC impregnation has significant electrocatalytic effect on the O 2 reduction reactions on the LSm electrodes.
