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Materials Chemical Point of View for Durability Issues in Solid Oxide Fuel Cells
Yokokawa, Harumi,Horita, Teruhisa,Yamaji, Katsuhiko,Kishimoto, Haruo,Brito, M.E. The Korean Ceramic Society 2010 한국세라믹학회지 Vol.47 No.1
Degradation in Solid Oxide Fuel Cell performance can be ascribed to the following fundamental processes from the materials chemical point of view; that is, diffusion in solids and reaction with gaseous impurities. For SOFC materials, diffusion in solids is usually slow in operation temperatures $800\sim1000^{\circ}C$. Even at $800^{\circ}C$, however, a few processes are rapid enough to lead to some degradations; namely, Sr diffusion in doped ceria, cation diffusion in cathode materials, diffusion related with metal corrosion, and sintering of nickel anodes. For gaseous impurities, chromium containing vapors are important to know how the chemical stability of cathode materials is related with degradation of performance. For LSM as the most stable cathode among the perovskite-type cathodes, electrochemical reduction reaction of $CrO_3$(g) at the electrochemically active sites is crucial, whereas the rest of the cathodes have the $SrCrO_4$ formation at the point where cathodes meet with the gases, leading to rather complicated processes to the degradations, depending on the amount and distribution of reacted Cr component. These features can be easily generalized to other impurities in air or to the reaction of nickel anodes with gaseous impurities in anode atmosphere.
Degradation of SOFC Cell/Stack Performance in Relation to Materials Deterioration
Yokokawa, Harumi,Horita, Teruhisa,Yamaji, Katsuhiko,Kishimoto, Haruo,Brito, M.E. The Korean Ceramic Society 2012 한국세라믹학회지 Vol.49 No.1
The characteristic features of solid oxide fuel cells are reviewed from the viewpoint of the thermodynamic variables to be developed inside cells/stacks particularly in terms of gradients of chemical potential, electrical potential and temperature and corresponding flows of air, fuel, electricity and heat. Examples of abrupt destruction of SOFC systems were collected from failures in controlling their steady flows, while continuous degradation was caused by materials behaviors under gradients of chemical potentials during a long operation. The local equilibrium approximation has been adopted in NEDO project on the durability/reliability of SOFC stacks/systems; this makes it possible to examine the thermodynamic stability/reactivity as well as mass transfer under the thermodynamic variable gradients. Major results of the NEDO project are described with a focus on degradation/deterioration of electrolyte and electrode materials.
Degradation of SOFC Cell/Stack Performance in Relation to Materials Deterioration
Harumi Yokokawa,Teruhisa Horita,Katsuhiko Yamaji,Haruo Kishimoto,M. E. Brito 한국세라믹학회 2012 한국세라믹학회지 Vol.49 No.1
The characteristic features of solid oxide fuel cells are reviewed from the viewpoint of the thermodynamic variables to be developed inside cells/stacks particularly in terms of gradients of chemical potential, electrical potential and temperature and corresponding flows of air, fuel, electricity and heat. Examples of abrupt destruction of SOFC systems were collected from failures in controlling their steady flows, while continuous degradation was caused by materials behaviors under gradients of chemical potentials during a long operation. The local equilibrium approximation has been adopted in NEDO project on the durability/reliability of SOFC stacks/systems; this makes it possible to examine the thermodynamic stability/reactivity as well as mass transfer under the thermodynamic variable gradients. Major results of the NEDO project are described with a focus on degradation/deterioration of electrolyte and electrode materials.
Materials Chemical Point of View for Durability Issues in Solid Oxide Fuel Cells
Harumi Yokokawa,Teruhisa Horita,Katsuhiko Yamaji,Haruo Kishimoto,M. E. Brito 한국세라믹학회 2010 한국세라믹학회지 Vol.47 No.1
Degradation in Solid Oxide Fuel Cell performance can be ascribed to the following fundamental processes from the materials chemical point of view; that is, diffusion in solids and reaction with gaseous impurities. For SOFC materials, diffusion in solids is usually slow in operation temperatures 800~1000oC. Even at 800oC, however, a few processes are rapid enough to lead to some degradations; namely, Sr diffusion in doped ceria, cation diffusion in cathode materials, diffusion related with metal corrosion, and sintering of nickel anodes. For gaseous impurities, chromium containing vapors are important to know how the chemical stability of cathode materials is related with degradation of performance. For LSM as the most stable cathode among the perovskitetype cathodes, electrochemical reduction reaction of CrO3(g) at the electrochemically active sites is crucial, whereas the rest of the cathodes have the SrCrO4 formation at the point where cathodes meet with the gases, leading to rather complicated processes to the degradations, depending on the amount and distribution of reacted Cr component. These features can be easily generalized to other impurities in air or to the reaction of nickel anodes with gaseous impurities in anode atmosphere.
Taiju Miyagami,Hirohide Yokokawa,Kazutoshi Fujibayashi,Hiroshi Fukuda,Teruhiko Hisaoka,Toshio Naito 대한골다공증학회 2020 Osteoporosis and Sarcopenia Vol.6 No.1
Objectives: To investigate the correlation between imbalance of muscle mass to body weight and lifestyle-related diseases using bioelectrical impedance analysis (BIA) among Japanese population. Methods: This was a retrospective, cross-sectional study conducted at Juntendo University Hospital in Tokyo, Japan, from May 2015 to November 2017. Their muscle-to-weight ratio were stratified into “muscle-to-weight ratio” quartiles as follows: men, Q1 (0.79), Q2 (0.75 to <0.79), Q3 (0.72 to <0.75), and Q4 (<0.72); women, Q1 (0.73), Q2 (0.68 to <0.73), Q3 (0.63 to <0.68), and Q4 (<0.63). The primary outcome was prevalence of 2 lifestyle-related diseases, including hypertension, dyslipidemia, type 2 diabetes mellitus, and hyperuricemia. Results: Data from 2009 individuals (men, 55%; mean age, 62 years) were analyzed. Compared to the lowest quartile, risk for the presence of2 lifestyle-related diseases, in a multivariable regression model for men was as follows: Q2 (odds ratio [OR],1.93; 95% confidence interval [CI],1.31e2.87), Q3 (OR, 2.85; 95% CI, 1.89e4.29), and Q4 (OR, 6.00; 95% CI, 4.07e8.84). For women, an increased risk was seen in Q2 (OR, 2.31; 95% CI, 1.20e4.46), Q3 (OR, 4.45; 95% CI, 2.40e8.26), and Q4 (OR, 12.6; 95% CI, 6.80e23.5). Cutoff values of muscle-to-weight ratio correlated with lifestyle-related diseases (2) were 0.76 for men and 0.68 for women. Conclusions: Our results showed that an imbalance of muscle mass to body weight confers an independent and stepwise increased risk for lifestyle-related diseases.
강천수,고영일,Fujisawa Kazunori,Yokokawa Taiki,김진희,한종훈,위재형,김융암,Muramatsu Hiroyuki,Hayashi Takuya 한국탄소학회 2020 Carbon Letters Vol.30 No.5
Free-standing hybridized electrode consisting of double-walled carbon nanotubes (DWNTs) and activated carbon have been fabricated for fexible supercapacitor applications. The xanthan-gum, used in our methodology, showed high ability in dispersing the strongly bundled DWNTs, and was then efectively converted to activated carbon with large surface area via chemical activation. The homogeneously dispersed DWNTs within xanthan-gum derived activated carbon acted as both electrical path and mechanical support of electrode material. The hybridized flm from highly dispersed DWNTs and activated carbon was mechanically strong, has high electrical conductivity, and exhibited high specifc capacitance of 141.5 F/g at the current density of 100 mV/s. Our hybridized flm is highly promising as electrode material for fexible supercapacitors in wearable device.