PEMFC에서 막 열화가 전극 열화에 미치는 영향

송진훈 ( Jin Hoon Song ),정재진 ( Jae Jin Jeong ),정재현 ( Jae Hyeun Jeong ),김세훈 ( Sae Hoon Kim ),안병기 ( Byung Ki Ahn ),고재준 ( Jai Joon Ko ),박권필 ( Kwon Pol Park ) 한국화학공학회 2013 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.51 No.3

실제 고분자 전해질 연료전지(PEMFC) 운전조건에서는 전극과 전해질 막은 동시에 열화된다. 그런데 고분자전해질연료전지의 전극 열화와 전해질 열화의 상호 작용에 대해 연구되지 않았다. 본 연구에서는 전해질 막 열화가 전극 열화에 미치는 영향에 대해 연구하였다. 전해질 막 열화 후 전극을 열화시켜 전해질 막 열화없이 전극을 열화시켰을 때와 비교하였다. 열화전후의 I-V 성능, 수소투과전류, 순환 전압측정(CV), 임피던스, TEM 등을 측정하였다. 전해질 막열화에 의해 수소투과도가 증가하고, 이에 따라 백금 입자 성장속도가 감소함으로써 전극 열화속도가 감소함을 보였다. The membrane and electrode were degraded coincidentally at real PEMFC(Proton Exchange Membrane Fuel Cells) operation condition. But the interaction membrane degradation between electrode degradation has not been studied. The effect of membrane degradation on electrode degradation was studied in this work. We compared electrode degradation after membrane degradation and electrode degradation without membrane degradation. I-V performance, hydrogen crossover current, impedance and TEM were measured after and before degradation of MEA. Membrane degradation enhanced hydrogen crossover, and then Pt particle growth rate was reduced. Increase of hydrogen crossover by membrane degradation reduced the electrode degradation rate.

Mapping and assessing land degradation vulnerability in Kangra district using physical and socio-economic indicators

Satya Prakash,Milap Chand Sharma,Rajesh Kumar,P. S. Dhinwa,K. L. N. Sastry,A. S. Rajawat 대한공간정보학회 2016 Spatial Information Research Vol.24 No.6

Land degradation is a major problem in the fragile ecosystem of the Himalayan region. The steep slope with low forest cover and increasing human interference are the major factors of land degradation. Therefore, identification of severe degradation prone areas is necessary for implementing conservation strategies to retard the present rate of degradation processes. The aim of this study is to assess the vulnerable land degradation areas based on Space Application Centre (SAC/ISRO) guidelines and MEDALUS model. Indicators used to calculate the degradation vulnerability are geology, slope, aspect, soil type, rainfall, temperature, land use/land cover, population density, non-worker population and illiteracy. The results reveal that the areas with higher rainfall, less forest cover and large population are highly vulnerable to degradation in spite of moderate slope. The degradation vulnerability index values have been classified into five land degradation categories. The Pong dam is a large water body where the land degradation is nil. The low, moderate, high and very high land degradation categories account for 19.01, 22.79, 31.49 and 17.37% area of the district, respectively.

Preliminary Safety Evaluation for Cellulose Disposal at 1st Phase Disposal Facility

Hyun Woo Song,Moonoh Kim,Sang June Park,Suil Bang 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.1

Recently, concern regarding disposal of cellulosic material is growing as cellulose is known to produce complexing agent, isosaccharinic acid (ISA), upon degradation. ISA could enhance mobility of some radionuclides, thus increasing the amount of radionuclide released into the environment. Evaluation on the possible impact of the cellulose degradation would be an important aspect in safety evaluation. In this paper, the maximum safe disposal amount cellulose is evaluated considering the disposal environment of silos of 1st phase disposal facility. The key factor governing the impact of cellulose degradation is pH of disposal environment, as cellulose is known to degrade partially at pH above 12.5, and completely at pH above 13. Thus, disposal environment should be analyzed as to determine the extent of degradation. As silos are constructed with large amount of cement, porewater within concrete walls would be of very high pH. However, for high pH porewater to be released into the pores of crushed rock, which is filling up the silos, lower pH groundwater (commonly pH 7) should flow into the silos through the concrete walls. This causes dilution of the high pH concrete porewater, resulting in a lower pH as the silos are filled, reaching to expected pH of 11.8–12.3, which is below cellulose degradation condition. Thus, cellulose degradation is not expected, but to quantitatively evaluate safe disposal amount of cellulose, partial degradation is assumed. Upon literature review, the most conservative ISA concentration, enhancing radionuclide mobility, is determined to be 1.0×10?4 M and to reach this concentration, cellulose mass equivalent to 6wt% of cement of the repository, is required to be degraded. However, this ratio is derived based on complete degradation of cellulose into ISA, so for partial degradation, degradation ratio and yield ratio of ISA should be considered. Commonly, cellulosic material (e.g. cotton, paper, etc.) has degree of polymerization (DP) between 1,000–2,000, and with this DP, degradation ratio is estimated to be about 10%. Furthermore, yield ratio of ISA is known to be 80%. Considering all these aspects, about 1.79×107 kg of cellulose could be disposed, which if converted into number of drums, considering cellulose content of dry active waste, more than 100,000 drums (200 L) could be disposed with negligible impact on safety. Based on the result, negligible impact of cellulose degradation is expected for safety of 1st phase disposal facility. In future, this study could be used as fundamental data for revising waste acceptance criteria.

PEMFC에서 전극 열화가 전해질 막 열화에 미치는 영향

박권필 ( Kwon Pil Park ),송진훈 ( Jin Hoon Song ),김세훈 ( Sae Hoon Kim ),안병기 ( Byung Ki Ahn ),고재준 ( Jai Joon Ko ) 한국화학공학회 2013 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.51 No.1

Until a recent day, degradation of PEMFC MEA (membrane and electrode assembly) has been studied, separated with membrane degradation and electrode degradation, respectively. But membrane and electrode were degraded coincidentally at real PEMFC operation condition. During simultaneous degradation, there was interaction between membrane degradation and electrode degradation. The effect of electrode degradation on membrane degradation was studied in this work. We compared membrane degradation after electrode degradation and membrane degradation without electrode degradation. I-V performance, hydrogen crossover current, fluoride emission rate (FER), impedance and TEM were measured after and before degradation of MEA. Electrode degradation reduced active area of Pt catalyst, and then radical/H2O2 evolution rate decreased on Pt. Decrease of radical/H2O2 reduced the velocity of membrane degradation.

Field degradation prediction of potential induced degradation of the crystalline silicon photovoltaic modules based on accelerated test and climatic data

Oh, Wonwook,Bae, Soohyun,Chan, Sung-Il,Lee, Hae-Seok,Kim, Donghwan,Park, Nochang Elsevier 2017 Microelectronics and reliability Vol.76 No.-

<P>We investigated the field degradation modeling of potential-induced degradation (PID) in crystalline silicon photovoltaic modules. Five accelerated tests using four-cell mini modules were conducted to derive the hourly degradation rate of the potential induced degradation. The voltage-Peck model was used for predicting the hourly degradation rate. The field degradation modeling was performed at Busan and Miami. The annual degradation rate in field based on the temperature, humidity, and solar irradiance was calculated as the sum of the hourly degradation rate for one year. The annual degradation rates in Busan and Miami were recorded as 6.93% and 11.23% under 72cells and 18 modules series-connected string configuration, respectively. The annual degradation rate induced by PID in the solar power plant in Busan showed similar result to 8.8%. (C) 2017 Elsevier Ltd. All rights reserved.</P>

A Study on the Factors Required to Be Considered for Safety Assessment of Cellulose Degradation

Hyun Woo Song,Moonoh Kim,Sang June Park,Suil Bang 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.1

Recently, concern regarding disposal of cellulosic material is growing as cellulose is known to produce complexing agent, isosaccharinic acid (ISA), upon degradation. ISA could enhance mobility of some radionuclides, thus increasing the amount of radionuclide released into the environment. Thus, evaluation on the possible impact of the cellulose degradation would be an important aspect in safety evaluation. In this paper, safety assessments conducted in Sweden and UK are studied, and the factors required to be considered for appropriate safety assessment of cellulose is analyzed. SKB (Sweden) conducted safety assessment of cellulose degradation as a part of long-term safety assessment of SFR. SKB determined that ISA would impact sorption of trivalent and tetravalent radionuclides (Eu, Am, Th, Np, Pa, Pu, U, Tc, Zr and Nb) at concentration higher than 10?4–10?3 M, and impact sorption of divalent radionuclides (Ni, Co, Fe, Be and Pb) at concentration higher than 10?2 M. Then, SKB conservatively set the upper limit of ISA concentration to be 10?4 M and conducted cellulose degradation evaluation on each waste package type, considering the expected disposal environment of SFR. Based on the calculated results, some of the waste packages showed concentration of ISA to be higher than 10?4 M, so SKB conservatively developed waste acceptance criteria to prevent ISA being produced to an extent of affecting the safety of the repository. SKB conducted safety assessment only for the repositories with pH above 12.5 and excluded 1BLA from the safety assessment as the expected pH of 1BLA is around 12, which is insufficient for cellulose to degrade. However, SKB set disposal limit for 1BLA as well, to minimize potential impact in future. Serco (UK) conducted safety assessment of cellulose degradation for the conceptual repository, which is a concrete vault with cementitious backfill. Serco estimated that the pH of repository would maintain around 12.4. Serco conservatively assumed that the pH would be sufficient for cellulose degradation to occur partially, and suggested application of appropriate degradation ratio for safety assessment of cellulose degradation. To conduct appropriate safety assessment of cellulose degradation, an appropriate ISA concentration limit based on radionuclide inventory list, and an appropriate cellulose degradation ratio based on the pH of disposal environment should be determined. As for guidance, below pH 12.5, cellulose degradation is not expected, and between pH 12.5–13, partial cellulose degradation is expected. In future, this study could be used as fundamental data to evaluate safety of the repository.

Aqueous phase degradation of methyl paraben using UV-activated persulfate method

Dhaka, Sarita,Kumar, Rahul,Khan, Moonis Ali,Paeng, Ki-Jung,Kurade, Mayur B.,Kim, Sun-Joon,Jeon, Byong-Hun Elsevier 2017 Chemical Engineering Journal Vol.321 No.-

<P><B>Abstract</B></P> <P>Methyl paraben (MP), a widely used preservative, exhibits endocrine-disrupting properties with estrogenic activities. The aqueous phase degradation of MP, using UV-activated persulfate method, was investigated in the present study. The combination of UV irradiation and persulfate anion successfully degraded MP showing 98.9% removal within 90min. A quenching experiment using ethanol (EtOH) and <I>tert</I>-butyl alcohol (TBA) showed the presence of both radicals (OH<SUP> </SUP> and SO<SUB>4</SUB> <SUP> –</SUP>) in the system; near neutral pH SO<SUB>4</SUB> <SUP> –</SUP> radical was the major species. The influence of various factors such as persulfate dose, initial MP concentration, solution pH, and water matrix components on the degradation kinetics was examined in view of the practical applications of the developed process. The degradation rate of MP was considerably increased as the amount of persulfate increased. The degradation of MP in the UV/persulfate system was pH dependent and more promising near neutral pH (6.5) conditions. The presence of anions such as Cl<SUP>−</SUP>, HPO<SUB>4</SUB> <SUP>2−</SUP> and HCO<SUB>3</SUB> <SUP>−</SUP> showed inhibitory effect towards MP degradation. The presence of humic acid also suppressed the degradation efficiency of MP. The reaction rate followed pseudo-first-order kinetics for all of the degradations. The degradation of MP by UV/persulfate treatment led to the production of seven transformation byproducts, which were identified using ultra-high-performance liquid chromatography-mass spectrometry (UPLC-MS). A degradation pathway for MP degradation was also proposed. The results of the present study reveal that the UV/persulfate process could be an effective approach to remove MP from aqueous solutions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Aqueous phase MP degradation using UV/persulfate method was investigated. </LI> <LI> Degradation rate of MP followed pseudo-first-order kinetics. </LI> <LI> MP degradation was pH dependent. </LI> <LI> HCO<SUB>3</SUB> <SUP>−</SUP>, HPO<SUB>4</SUB> <SUP>2−</SUP> and humic acid exhibited inhibitory effect on MP degradation. </LI> <LI> Hydroxylation and hydrolysis were possible pathways of degradation of MP. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Proposal on the Cellulose Degradation Model for the Domestic 1st Phase Underground Repository

Hyun Woo Song,Moonoh Kim,Sang June Park,Sungjun Kim,Jun-gi Yeom 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.1

With the recent concern regarding cellulose enhancing radionuclide mobility upon its degradation to ISA, disposal of cellulosic wastes is being held off until the disposal safety is vindicated. Thus, a rational assessment should be conducted, applying an appropriate cellulose degradation model considering the disposal environment and cellulose degradation mechanisms. In this paper cellulose degradation mechanisms and the disposal environment are studied to propose the best-suitable cellulose degradation model for the domestic 1st phase repository. For the cellulose to readily degrade, the pH should be greater than 12.5. As in the case of SKB, 1BLA is excluded from the safety assessment because the pH of 1BLA remains below 12.5. Furthermore, despite cellulose degradation occurring, it does not always produce ISA. At low Ca2+ concentration, the ISA yield rate is around 25%, but at high Ca2+ concentration, the ISA yield rate increases up to 90%. Thus, for the cellulose to be a major concern, both pH and Ca2+ concentration conditions must be satisfied. To satisfy both conditions, the cement hydration must be in 2nd phase, when the porewater pH remains around 12.5 and a significant amount of Ca2+ ion is leaching out from the cement. However, according to the safety evaluation and domestic research, 2nd phase of cement hydration for silo concrete would achieve a pH of around 12.4, dissatisfying cellulose degradation condition like in 1BLA. Thus, cellulose degradation would be unlikely to occur in the domestic 1st phase repository. To derive waste acceptance criteria, a quantitative evaluation should be conducted, conservatively assuming cellulose is degraded. To conduct a safety evaluation, an appropriate degradation model should be applied to determine the degradation rate of cellulose. According to overseas research, despite the mid-chain scission being yet to be seen in the experiments, the degradation model considering mid-chain scission is applied, resulting in an almost 100% degradation rate. The model is selected because the repositories are backfilled with cement, achieving a pH greater than 13, so extensive degradation is reasonably conservative. However, under the domestic disposal condition, where cellulose degradation is unlikely to occur, applying such model would be excessively conservative. Thus, the peeling and stopping model derived by Van Loon and Haas, which suggests 10~25% degradation rate, is reasonably conservative. Based on this model, cellulose would not be a major concern in the domestic 1st phase repository. In the future, this study could be used as fundamental data for planning waste acceptance criteria.

Variations of tunneling properties in poly (lactic acid) (PLA)/poly (ethylene oxide) (PEO)/carbon nanotubes (CNT) nanocomposites during hydrolytic degradation

Kim, Sanghoon,Zare, Yasser,Garmabi, Hamid,Rhee, Kyong Yop Elsevier 2018 Sensors and actuators. A, Physical Vol.274 No.-

<P><B>Abstract</B></P> <P>The combination of poly (lactic acid) (PLA) with water-soluble poly (ethylene oxide) (PEO) and carbon nanotubes (CNT) presents interesting results during hydrolytic degradation. This paper investigates the conductivity of PLA/PEO/CNT nanocomposites during degradation in phosphate-buffered saline (PBS) solution. A simple model is suggested to express the conductivity of samples during degradation by CNT properties, degradation fraction, interphase thickness and tunneling properties. The calculations of developed model are compared to the experimental data and the variations of tunneling resistivity and tunneling distance are explained. Moreover, the parametric examinations are applied to confirm the developed model. The predictions of conductivity acceptably agree with the experimental data during degradation. The degradation reduces the tunneling resistivity and tunneling distance between neighboring CNT, due to the exclusion of polymer matrix. The results demonstrate the positive effects of high degradation fraction, thick interphase, large tunneling diameter, slight tunneling resistivity and short tunneling distance between adjacent CNT on the conductivity of degraded nanocomposites. The current study can provide useful guidelines for analysis of conductivity in nanocomposites during degradation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> This paper studies the conductivity of PLA/PEO/CNT nanocomposites during degradation. </LI> <LI> A simple model is suggested for conductivity of nanocomposites during degradation. </LI> <LI> The degradation fraction, interphase and tunneling properties are considered for modeling. </LI> <LI> The degradation reduces the tunneling resistivity and tunneling distance between CNT. </LI> <LI> The tunneling properties largely manipulate the conductivity of degraded nanocomposites. </LI> </UL> </P>

Investigation of the Degradation-Retarding Effect Caused by the Low Swelling Capacity of a Novel Hyaluronic Acid Filler Developed by Solid-Phase Crosslinking Technology

( Sunyoung Park ),( Kui Young Park ),( In Kwon Yeo ),( Sung Yeon Cho ),( Young Chang Ah ),( Hyun Ju Koh ),( Won Seok Park ),( Beom Joon Kim ) 대한피부과학회 2014 Annals of Dermatology Vol.26 No.3

Background: A variety of hyaluronic acid (HA) fillers demonstrate unique physical characteristics, which affect the quality of the HA filler products. The critical factors that affect the degradation of HA gels have not yet been determined. Objective: Our objective was to determine the characteristics of HA gels that affect their resistance to the degradation caused by radicals and enzymes. Methods: Three types of HA fillers for repairing deep wrinkles, Juvederm Ultra Plus (J-U), Restylane Perlane (Perlane), and Cleviel, were tested in this study. The resistance of these HA fillers to enzymatic degradation was measured by carbazole and displacement assays using hyaluronidase as the enzyme. The resistance of these fillers to radical degradation was measured by the displacement assay using H2O2. Results: Different tests for evaluating the degradation resistance of HA gels can yield different results. The filler most susceptible to enzymatic degradation was J-U, followed by Perlane and Cleviel. The HA filler showing the highest degree of degradation caused by H2O2 treatment was Perlane, followed by J-U, and then Cleviel. Cleviel showed higher enzymatic and radical resistances than J-U and Perlane did. Furthermore, it exhibited the highest resistance to heat and the lowest swelling ratio among all the fillers that were examined. Conclusion: The main factor determining the degradation of HA particles is the gel swelling ratio, which is related to the particle structure of the gel. Our in vitro assays suggest that the decrease in the swelling ratio will lead to a retarding effect on the degradation of HA fillers. (Ann Dermatol 26(3) 357∼362, 2014)