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Yoo Donggeun,Oh Sohyeong,Han Yuhan,Jeong Jihong,Jung Sunggi,박권필 한국화학공학회 2024 Korean Journal of Chemical Engineering Vol.41 No.8
In polymer electrolyte membrane fuel cell (PEMFC), the cost and durability are main challenges to commercialization. To achieve the long-term durability target, the durability of PEMFC materials should be further improved. In this paper, we investigated the chemical and electrochemical degradation of the expanded polytetrafl uoroethylene (e-PTFE) support and examined how it infl uences the mechanical properties of the e-PTFE support. We conducted the Fenton test and open circuit voltage (OCV) holding and analyzed the chemical and physical structural changes of the e-PTFE support by utilizing Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), and tensile test. After the chemical and electrochemical degradations, the molecular bonds of e-PTFE were broken, and the microstructures of e-PTFE were deformed. As the result the mechanical properties of e-PTFE showed signifi cant decrease. Consequently, our results show that the e-PTFE support is deteriorated chemically during PEMFC operation, and this chemical degradation lead reduction of mechanical strength.
Yoo Donggeun,Hwang Byungchan,Oh Sohyeong,박권필 한국화학공학회 2023 Korean Journal of Chemical Engineering Vol.40 No.8
During the durability tests for PEMFC membranes, performance characterization is conducted to determine the degree of degradation, the interval for which is different for each durability test protocol. Before performance characterization, activation is carried out to determine the reliability. Most activations are accompanied by voltage changes, which can lead to electrode degradation. However, this has largely been neglected because the activation time is shorter than the durability test time. In this study, activation was conducted at 24, 48, and 144 h intervals, during the membrane durability test of a PEMFC, and the effect of activation on the degradation of the membrane and electrode was investigated. For a shorter activation interval during the durability test, the lifetime of the membrane was reduced by up to 35%. For the same durability test time, more activations led to greater electrode and membrane degradation. Through scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM-EDS) analysis, it was found that for a shorter activation interval, more Pt was deposited into the membrane and then the membrane was thinner. During the durability test, frequent activation accelerated membrane and electrode degradation.
유동근 ( Donggeun Yoo ),김현석 ( Hyeonsuck Kim ),오소형 ( Sohyeong Oh ),박권필 ( Kwon-pil Park ) 한국화학공학회 2022 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.60 No.1
Cathode open-type PEMFC (Proton Exchange Membrane Fuel Cells) stacks, which are widely used in small transport-type PEMFC, have a problem with poor durability. Through the accelerated durability test of the 13-cell PEMFC stack, we tried to find the cause of the degradation of the stack and to contribute to the improvement of the durability of the cathode open stack. A hydrogen/air boundary is formed during start-up/shut-down (SU/SD) due to the structural problem of the cathode open stack in which the cathode is open to the atmosphere and it is difficult to maintain airtightness, thereby deteriorating the cathode. In this study, it was possible to evaluate the durability in a relatively short time by reducing the 54% of the initial performance by repeating SU/SD 1,800 times on the cathode open stack. After dismantling the stack, each cell was divided into two and the performance was analyzed. Overall, the anode outlet MEA, which facilitates air inflow, showed more severe electrode deterioration than the inlet MEA, confirming that the hydrogen/air boundary formation during SU/SD is the main cause of degradation.
고분자전해질 연료전지에서 고분자 막과 전극의 철 이온 오염 및 산 세척 효과
유동근 ( Donggeun Yoo ),박민정 ( Minjeong Park ),오소형 ( Sohyeong Oh ),박권필 ( Kwon-pil Park ) 한국화학공학회 2022 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.60 No.1
In the process of long-term use of PEMFC (Proton Exchange Membrane Fuel Cells), chemical degradation of membrane electrode assembly (MEA) occurs due to corrosion of stack elements and contamination of supply gas. In this study, we investigated whether chemically degraded MEA can be recovered by acid washing. The performance was measured and compared in a PEMFC cell after contamination with iron ions and washing with an aqueous sulfuric acid solution. The performance was reduced by about 25% by 0.5 ppm iron ion contamination, and 97.1% performance recovery was possible by washing of 0.15 M sulfuric acid. The membrane resistance was increased due to iron ion contamination of the polymer membrane, and the ionic conductivity was restored by washing the iron ions from the membrane while minimizing the loss of the electrode catalyst by washing with a low-concentration sulfuric acid aqueous solution. The possibility of solving the decrease in durability caused by chemical contamination of PEMFC MEA by the acid washing was confirmed.
PEMFC 고분자 막의 전기화학적 열화과정에서 OCV 감소 및 회복 거동을 통한 비가역적 열화 연구
유동근 ( Donggeun Yoo ),박권필 ( Kwon-pil Park ) 한국화학공학회 2022 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.60 No.2
It is very important to analyze the OCV change behavior during the open circuit potential holding (OCV holding) process, which accelerates the evaluation of the electrochemical durability of the PEMFC membrane. In this study, an empirical formula using the experimental data of three MEAs with different durability was created and compared. The durability evaluation time of the reinforced membrane MEA without radical scavenger inside the membrane was 383 h, and the durability evaluation time of the reinforced membrane MEA with radical scavenger inside the membrane was 1,000 and 1,650 h, respectively. The degradation of the membrane was divided into the reversible degradation that can be recovered by activation and the irreversible degradation that is not recovered. The irreversible degradation of the membrane was indicated by an increase in hydrogen permeability, and the change in hydrogen permeability was similar to the irreversible degradation constant c of all three MEAs. The initiation of irreversible deterioration without recovery is indicated by an increase in hydrogen permeability, and the OCV is not recovered due to an increase in hydrogen permeability, so the slope of the OCV recovery line (ORL) decreases, which can be confirmed by an increase in the constant c value of the empirical formula.
유동근 ( Donggeun Yoo ),박채훈 ( Chaehoon Park ),최유경 ( Yukyung Choi ),권인소 ( In So Kweon ) 한국정보처리학회 2012 한국정보처리학회 학술대회논문집 Vol.19 No.1
이 논문에서는 영상 검색(image retrieval) 및 영상 부류(image categorization)을 위하여 영상을 기술할 때 영상의 클레스(class)별로 서로 다른 주요 특징량(feature)에 가중치를 주는 방법론을 제안한다. 기존에 연구되어온 영상의 특징량 벡터에 가중치를 주는 방식은 모든 영상 클레스에 대하여 동일하게 가중치를 적용하기 때문에 영상이 클레스별로 서로 다른 특징량이 중요하다는 성질을 이용할 수 없다. 영상이 클레스별로 서로 다른 특징량이 중요하다는 성질을 이용하기 위하여 영상의 클레스별로 특징량 벡터에 서로 다른 가중치 벡터(weight vector)를 학습하였다. 그 후 질의 영상(query image)이 입력되면, 기존의 영상 검색 프레임워크(framework)를 통해 데이터베이스(database)로 부터 미리 정의된 서브 클레스(sub-class)의 수에 해당하는 영상부 집합(subset)을 만들었다. 그리고 영상 부 집합의 특징량 벡터들에 클레스별로 각각 학습된 가중치 벡터를 적용하여 특징량 벡터들 간의 거리를 다시 계산하여 리 랭킹(re-ranking)하였다. 이 방법론을 UKBench Dataset 에 적용하여 실험을 해보았으며 가중치를 주기 전과 비교 하였을 때 더 높은 정확도를 보였다.
Yoo, Hee-Bong,Oh, Donggeun,Song, Jae Yong,Kawaharasaki, Mamoru,Hwang, Jeeseong,Yang, In Chul,Park, Sang-Ryoul Springer-Verlag 2014 METROLOGIA -BERLIN- Vol.51 No.5
<P>This work demonstrates accurate measurement of the amount of substance concentration of low concentration plasmid DNA by counting individual DNA molecules using a high-sensitivity flow cytometric setup. Plasmid DNA is a widely used form of DNA, and its quantity often needs to be accurately determined. This work establishes a reference analytical method for direct quantification of low concentration plasmid DNA prepared as reference standards for polymerase chain reaction-based DNA quantification. The model plasmid DNA pBR322 (4361?bp) was stained with a fluorescent dye and was detected in a flow stream in a micro-fluidic channel with laser-induced fluorescence detection, for which the DNA flow was electro-hydrodynamically focused at the centre of the channel. 200 to 8000 DNA molecules in a ∼1??L sample volume were counted within 2?min in an ‘exhaustive counting’ manner, which facilitated quantitation without calibration. The sample volume was measured and validated from the close agreement of the results of two independent measurement methods, gravimetric determination of water filling the capillary and graphical estimation of actual cross sectional area of the capillary tubing with the image of calibrated scanning electron microscopy. Within the given concentration range, an excellent measurement linearity (<I>R</I><SUP>2</SUP>?=?0.999) was achieved with appropriate data processing for the correction of the events of double molecules (detection of double molecules opposed to single molecule detection assumed, which occurs due to their coincidental passing of the detection zone). The validity of the proposed method was confirmed from the close agreement with the results of quantitation of enzymatically released nucleotides using capillary electrophoresis.</P>