Journal of the Korean Society for Precision Engineering

Development of Transformer-based Model for Prediction of PEMFC Remaining Useful Life: Da Hye Geum, Hyeon Do Han, Hyunjun Yang, Heejun Shin, Suk Won Cha, Gu Young Cho; J. Korean Soc. Precis. Eng. 2025;42(12):981-986.
Published online December 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.00015

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A Transformer model to predict the remaining useful life of a fuel cell, which has demonstrated superior performance in analyzing time series data. The dataset was created from long-term performance evaluation experiments conducted in rated power mode, with measurements taken every 10 hours. We preprocessed the raw data using a moving average, allocating 70% for training and 30% for evaluation. The model's performance, evaluated through MAE, MSE, and MAPE, was excellent. The fuel cell's critical voltage, defined as 94.5% of its initial voltage, was measured at 0.719 V. During the experimental run, the actual critical time was 106.6 hours, while the model predicted 106.8 hours, resulting in a 0.19% error. Since the predictions were based on data collected up to 93 hours, the estimated remaining life was 13.8 hours.

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Dendrite Growth Suppression in Lithium Metal Batteries with Composite Quasi-solid Electrolytes: Jeongeun Park, Jinhyeong An, Jiwoong Bae; J. Korean Soc. Precis. Eng. 2025;42(12):1037-1043.
Published online December 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.00010

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Secondary batteries are crucial for eco-friendly systems, but existing technologies struggle with energy density and safety issues. This study aims to develop a next-generation battery utilizing quasi-solid electrolytes (QSE), which combine the advantages of both liquid and solid electrolytes. However, QSEs often lack the mechanical strength necessary to prevent lithium dendrite growth. To address this challenge, two strategies were proposed and experimentally validated. The first strategy involves creating a QSE-separator composite (QSE-PI) by integrating QSE with a polyimide (PI) separator. Among the various options, PI with a thickness greater than 20 μm and a pore size of 2-5 μm exhibited superior electrolyte absorption and dendrite suppression. This configuration allowed for rapid lithium plating/stripping, high ionic conductivity (1.7 × 10^-3 S cm^-1), and excellent Coulombic efficiency (99.94%).The second strategy incorporates silica (SiO₂) as a ceramic filler in the QSE-PI to enhance mechanical strength and ion transport. The addition of SiO₂ disrupted polymer crystallinity, increased the amorphous regions, and effectively suppressed dendrite formation. Notably, SiO₂ particles larger than 10 μm improved cycle stability, with the composite maintaining performance for over 50 cycles, compared to only 30 cycles for the version without filler.

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Parametric Studies of Ionomer Content in PEMFC MEA with Different Humidity: Byung Gyu Kang, Hyeon Min Lee, Ye Rim Kwon, Sun Ki Kwon, Ki Won Hong, Seoung Jai Bai, Gu Young Cho; J. Korean Soc. Precis. Eng. 2025;42(12):975-980.
Published online December 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.00006

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The ionomer content in the catalyst layer is a crucial design factor that affects the performance of polymer electrolyte membrane fuel cells (PEMFCs). However, the optimal ionomer content can vary based on the surrounding humidity levels. This study systematically evaluated the influence of the ionomer-to-carbon (I/C) ratio (0.00, 0.55, and 0.91) on PEMFC performance under fully humidified (RH 100%) and low-humidity (RH 25%) conditions. Membrane-electrode assemblies (MEAs) were fabricated using a spray coating technique, and their electrochemical properties were analyzed through polarization curves and electrochemical impedance spectroscopy (EIS). Under RH 100%, the MEA with an I/C ratio of 0.55 achieved the highest peak power density of 519.8 mW/cm², indicating a successful balance between proton conductivity and gas transport. Conversely, under RH 25%, the best performance of 203.9 mW/cm² was observed at an I/C ratio of 0.91. This shift is attributed to improved water retention at higher ionomer content, which reduced membrane dehydration and lowered both ohmic and Faradaic resistances. These findings highlight the dual role of the ionomer in facilitating proton transport and managing water balance, emphasizing the necessity of optimizing the I/C ratio according to operating conditions for stable and high-performing PEMFC operation.

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Electrochemical Impedance Analyses of ePTFE-reinforced Polymer Electrolyte Membrane-based PEMFC with Varying Thickness and Relative Humidity: Gyutae Park, Subin Jeong, Youngjae Cho, Junseo Youn, Jiwon Baek, Jooyoung Lim, Dongjin Kim, Taehyun Park; J. Korean Soc. Precis. Eng. 2025;42(11):901-907.
Published online November 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.052

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The polymer electrolyte membrane fuel cell (PEMFC) generates electrical energy through electrochemical reactions and is a key technology for sustainable energy. The electrolyte membrane significantly affects performance under varying conditions. This study examines the impact of membrane thickness and relative humidity (RH) on PEMFC performance using j-V curves and electrochemical impedance spectroscopy (EIS). Experiments were conducted with membrane thicknesses of 30, 15, and 5 μm under RH conditions of 100%-100% and 100%-0%. Under RH 100%-100%, performance improved as the membrane thickness decreased, with values of 954, 1050, and 1235 mW/cm² for the 30, 15, and 5 μm membranes, respectively. The 5 μm membrane demonstrated a 23% performance improvement over the 30 μm membrane. Under RH 100%-0%, performances were 422, 642, and 852 mW/cm², with degradation rates of 55.8%, 39.0%, and 32.1%. The 5 μm membrane exhibited the lowest degradation rate, indicating superior performance under low humidity. These results suggest that thinner membranes generally enhance performance and maintain efficiency even in dry conditions.

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Development of Droplet Sliding Control Surfaces on Multiscale Hierarchical Polymeric Structures: Min Ji Kim, Seong Min Kim, Ji Seong Choi, Seong Min Kang; J. Korean Soc. Precis. Eng. 2025;42(10):825-832.
Published online October 1, 2025; DOI: https://doi.org/10.7736/JKSPE.D.25.00005

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In this paper, we propose a novel method for controlling the anisotropic sliding behavior of droplets using multiscale hierarchical structures. First, we employed a silicon wafer mold containing micro-pillars and directional micro-line structures to induce the directional sliding of droplets. Additionally, we fabricated micro-cone patterns and integrated them into the structures to precisely control droplet movement. These two structures were replicated in polymer and subsequently fused into a single multiscale hierarchical mold through a partial curing process. The completed multiscale hierarchical surface was then replicated with PDMS to create anisotropy that governs the direction of droplet movement. We experimentally confirmed that the degree of sliding is influenced by the cone pattern. Our proposed structural design demonstrates that anisotropic wettability control is achievable even on surfaces made from a single material, indicating potential applications in various fields such as microfluidics, sensors, and functional surfaces.

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Recent Advances in Ionic Polymer-Metal Composite Sensors: Gwon Min Kim, Seong-Jun Jo, Jaehwan Kim; J. Korean Soc. Precis. Eng. 2025;42(5):367-379.
Published online May 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.012

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This paper extensively explores and analyzes the latest research trends in Ionic Polymer-Metal Composites (IPMC) sensors. IPMC sensors are known for their flexibility, lightness, and high responsiveness. They show great promise across different fields. They can respond sensitively to various stimuli such as mechanical deformation, humidity, and pressure, making them ideal for bio-responsive detection, health monitoring, and energy harvesting. This paper introduces actuation and sensing mechanisms of IPMCs, discusses their manufacturing processes, and explores how these processes can influence the responsiveness and stability of sensors. Moreover, through case studies of IPMC-based research that can perform self-sensing functions, it presents possibilities brought by the integration of sensors and actuators. This paper emphasizes the potential for research and development of IPMC sensors to expand into various industrial fields and explores ways to continuously improve the accuracy and reliability of sensors. IPMC-based sensors are expected to play a significant role in advancing medical devices and wearable technologies, thereby facilitating innovation in the field.

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Evaluation of Electrochemical Performance of PEMFCs with Decontamination Devices at Marine Environments: Ye rim Kwon, Ho Jun Yoo, Byung Gyu Kang, Ki Won Hong, Sun Ki Kwon, Sanghoon Lee, Gu Young Cho; J. Korean Soc. Precis. Eng. 2025;42(1):57-63.
Published online January 1, 2025; DOI: https://doi.org/10.7736/JKSPE.024.109

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In this study, we developed and evaluated a simple device for removing ionic impurities that affect the performance of a polymer electrolyte membrane fuel cell (PEMFC) in a marine environment. In such environments, PEMFCs may experience performance degradation due to the presence of Na+ and Cl- in the air. To address this issue, the decontamination device was designed with both heating and cooling components. This device was positioned between a humidifier containing NaCl solution and a humidifier containing deionized water, both connected on the cathode side. The decontamination device effectively removed impurities (Na+ and Cl-) during experiments. As a result, the electrochemical performance of the fuel cell with the decontamination device improved compared to that of the fuel cell without it. Notably, the activation resistance and electrochemical surface area were significantly enhanced, and the ohmic resistance also improved when compared to the fuel cell without the decontamination device.

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Effects of NaCl Solution on Proton Exchange Membrane Fuel Cell with Serpentine Flow Channel of Different Depths
Dong Kun Song, Ho Jun Yoo, Jung Soo Kim, Ki Won Hong, Do Young Jung, George Ilhwan Park, Gu Young Cho
Journal of the Korean Society for Precision Engineering.2025; 42(5): 399. CrossRef

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Micro-hole Array Ceria Functional Layer Embedded Membrane for Durable Polymer Electrolyte Membrane Fuel Cell: Changwook Seol, Segeun Jang, Sang Moon Kim; J. Korean Soc. Precis. Eng. 2024;41(7):533-539.
Published online July 1, 2024; DOI: https://doi.org/10.7736/JKSPE.024.041

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For the commercialization of polymer electrolyte membrane fuel cells (PEMFCs), it is essential to achieve high performance while improving the durability of the membrane electrode assembly. In particular, the durability of PEMFCs can be improved by adding radical scavengers, such as CeO2 (ceria), to the membrane. Though it is desirable to insert the ceria at the interface between the membrane and electrode, where the generated radical attack initiates, this increases interfacial resistance and ionic resistance, thereby inducing a probable reduction in initial performance, compared to that of a conventional membrane. Here, we developed modified Nafion electrolyte membranes with a spatially located patterned ceria containing Nafion ionomer to improve durability while minimizing performance degradation. The fabrication process includes an etching process to pattern the electrolyte membrane, and the ceria nanoparticle layer is selectively deposited by spray coating onto the membrane. The synergetic effect of the structural modification of the electrolyte membranes and the introduction of the functional ceria layer exhibited improved chemical durability, while maintaining the initial performance of the PEMFC.

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Additional Ionomer-coated Layer for Self-humidifying Polymer Electrolyte Membrane Fuel Cells: Gyutae Park, Dongjin Kim, Junseo Youn, Junghyun Park, Hyoun-Myoung Oh, Taehyun Park; J. Korean Soc. Precis. Eng. 2023;40(12):997-1001.
Published online December 1, 2023; DOI: https://doi.org/10.7736/JKSPE.023.097

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In this study, we aim to develop a self-humidifying polymer electrolyte membrane fuel cell (PEMFC) by depositing platinum (Pt) on a membrane using sputtering. After we coated it with a Nafion^® ionomer solution. This is considered a solution that can prevent membrane degradation in low humidity conditions. By introducing this self-humidifying concept, we can expect improved performance compared to conventional PEMFCs. By managing the water content of Nafion^®, we aim to improve both the stability and performance of the PEMFCs. This research contributes to the development of more efficient and reliable PEMFC systems, showing promise for advances in this field.

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A Study of Effects of the Repetition of Assembly and the Addition of Activation on Electrochemical Characteristics of PEMFCs: Ji Woong Jeon, Gye Eun Jang, Young Jo Lee, Dong Kun Song, Ho Jun Yoo, Seung Hyeok Hong, Jung Soo Kim, Ye Rim Kwon, Da Hye Geum, Gu Young Cho; J. Korean Soc. Precis. Eng. 2023;40(11):867-872.
Published online November 1, 2023; DOI: https://doi.org/10.7736/JKSPE.023.026

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In this study, the effects of repetition of assembly and disassembly of polymer electrolyte membrane fuel cells on electrochemical performance were systematically investigated. Additionally, the effects of additional activation on polymer electrolyte membrane fuel cells were evaluated. All fuel cells were measured every three days. For the disassembled polymer electrolyte membrane fuel cells, membrane electrode assemblies were stored in a vacuum desiccator. For the maintained assembly, fuel cells were stored at room temperature. The performance and electrochemical characteristics of the fuel cell were analyzed by electrochemical impedance spectroscopy. As a result, the addition of activation to maintained assembly fuel cells showed the best performance among fuel cells with other assembly and activation conditions. Repetition of assembly and disassembly, as well as insufficient activation, caused degradation of the performance of fuel cells.

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A Study on Electrochemical Resistance Change through the Pressurization Process of MEA for PEMFC: Ye Rim Kwon, Dong Kun Song, Ho Jun Yoo, Gye Eun Jang, Young Jo Lee, Jung Soo Kim, Ji Woong Jeon, Da hae Guem, Gu Young Cho; J. Korean Soc. Precis. Eng. 2023;40(7):539-544.
Published online July 1, 2023; DOI: https://doi.org/10.7736/JKSPE.022.150

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In this study, the electrochemical characteristics of fuel cell were evaluated after applying a compressive load to the activation area of membrane electrode assembly (MEA) in polymer electrolyte membrane fuel cells. The effects of the pressed area under the compressive load were systematically investigated using polarization curves and electrochemical impedance spectroscopies (EIS) of the fuel cell. Interestingly, the performance of the fuel cell was improved as the pressed area of the MEA was increased from 25.2% to 100% of the active area. In addition, the increased pressed area led to a decrease in the ohmic resistance and the activation resistance of fuel cells.

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The Improvement of Roundness and Surface of Sheath & Dilator Catheter Tube: Gyu Ik Lee, Howon Lee, Gyu Man Kim, Woojin Kim, 이은택; J. Korean Soc. Precis. Eng. 2023;40(6):457-465.
Published online June 1, 2023; DOI: https://doi.org/10.7736/JKSPE.023.024

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As the market for minimally invasive procedures developed rapidly, there was an increase in the demand for high-precision, high-performance catheter fabrication technology. Sheath and dilator tubes are essential intervention devices for procedures, in which catheters are used and require precise dimensional accuracy, and uniform roundness and surface roughness. Polyethylene is used in sheath and dilator limitation for processability, which causes low melt flow index and side effects. Therefore, in the extrusion process using polyethylene, it is important to study the manufacturing of tubes with improved roundness and surface roughness. In this study, we proposed a calibrator for precise production with an aim to manufacture 5Fr micro-puncture tubes, and studied the changes in the roundness and surface roughness of tubes by changing the cooling water temperature and water disk thickness. As a result, it was found that the cooling water temperature and wafer disk thickness had an effect on the roundness and surface roughness, and the roundness had an effect on the formation of the wall thickness. Therefore, these experimental results were used as a study for the production of improved Sheath and Dilator tubes.

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Analysis of Electrochemical Behavior of PEMFC Humidified with NaCl Solution Mist Using an Ultrasonic Vibrator: Ho Jun Yoo, Gye Eun Jang, Young Jo Lee, Dong Kun Song, Heeyun Lee, Gu Young Cho; J. Korean Soc. Precis. Eng. 2022;39(12):939-946.
Published online December 1, 2022; DOI: https://doi.org/10.7736/JKSPE.022.096

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Durability evaluations were conducted using polymer electrolyte membrane fuel cells in a marine environment. Deionised water and 3.5 wt% of NaCl solution were supplied to the cathode using an ultrasonic vibrator. Performance and electrochemical impedance spectroscopy of fuel cells were measured to evaluate the electrochemical behaviors. Additionally, long-term stability evaluations of PEMFCs were carried out at 0.65 V for 20 h. Following the experiments, scanning electron microscope analysis was conducted to confirm the presence of NaCl on membrane electrode assembly and micro porous layer of fuel cells.

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Citations to this article as recorded by

Effects of NaCl Solution on Proton Exchange Membrane Fuel Cell with Serpentine Flow Channel of Different Depths
Dong Kun Song, Ho Jun Yoo, Jung Soo Kim, Ki Won Hong, Do Young Jung, George Ilhwan Park, Gu Young Cho
Journal of the Korean Society for Precision Engineering.2025; 42(5): 399. CrossRef
Evaluation of Electrochemical Performance of PEMFCs with Decontamination Devices at Marine Environments
Ye rim Kwon, Ho Jun Yoo, Byung Gyu Kang, Ki Won Hong, Sun Ki Kwon, Sanghoon Lee, Gu Young Cho
Journal of the Korean Society for Precision Engineering.2025; 42(1): 57. CrossRef
A Study of Effects of the Repetition of Assembly and the Addition of Activation on Electrochemical Characteristics of PEMFCs
Ji Woong Jeon, Gye Eun Jang, Young Jo Lee, Dong Kun Song, Ho Jun Yoo, Seung Hyeok Hong, Jung Soo Kim, Ye Rim Kwon, Da Hye Geum, Gu Young Cho
Journal of the Korean Society for Precision Engineering.2023; 40(11): 867. CrossRef
A Study on Electrochemical Resistance Change through the Pressurization Process of MEA for PEMFC
Ye Rim Kwon, Dong Kun Song, Ho Jun Yoo, Gye Eun Jang, Young Jo Lee, Jung Soo Kim, Ji Woong Jeon, Da hae Guem, Gu Young Cho
Journal of the Korean Society for Precision Engineering.2023; 40(7): 539. CrossRef

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Fabrication of Nanopatterned Metal Mold based on Zirconia Nanoparticle and its Application into Thermal Replication of Thermoplastic Materials: Selim Park, Kyoung Chan Min, Sowon Jang, Yujin Ha, Wook-Bae Kim; J. Korean Soc. Precis. Eng. 2022;39(7):501-508.
Published online July 1, 2022; DOI: https://doi.org/10.7736/JKSPE.022.059

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Fabrication of a durable and strong nanopatterned mold insert using metal sheet and plate is important for molding of thermoplastic materials. Conventionally, the nickel stamper replicating a master pattern by electroforming process has been used for injection molding of nanotextured products such as Blu-ray media. However, a more facile and cheaper mold fabrication process is highly required for manufacturing of functional products based on nanostructured surface. In this study, zirconia nanoparticles were blended with UV curing polymer to fabricate a polymer nanocompositebased nanopattern mold. Compared to the cured pure Ormostamp, the modulus of elasticity of the nanocomposite filled with approximately 54 vol% of zirconia nanoparticles increased by 160 times. Additionally, the modulus of elasticity reached 197 ㎬ by thermal decomposition of the UV-Cured polymer and post-annealing at 800°C of the nanoparticle layer. The nanopatterns were formed on stainless steel sheet and block, and applied to hot embossing of the PMMA films and injection molding of the COC materials, respectively. No deterioration of the mold occurred during the hot embossing 30 times and the injection molding 600 shots. Nanoparticle-enhanced UV curing nanocomposites or post-heat treatment methods are cost-efficient and easy, because many molds can be manufactured from one master pattern.

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Effects of NaCl Solution Humidification on Electrochemical Characteristics of PEMFCs: Ho Jun Yoo, Hye Gang Noh, Gye Eun Jang, Young Jo Lee, Dong Kun Song, Gu Young Cho; J. Korean Soc. Precis. Eng. 2022;39(6):451-456.
Published online June 1, 2022; DOI: https://doi.org/10.7736/JKSPE.022.030

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In this study, polymer electrolyte membrane fuel cells (PEMFCs) were humidified with NaCl solutions. NaCl solutions were provided to the cathode side of fuel cells by bubbling. De-Ionized water, 3.5 wt% NaCl solution, and 20 wt% NaCl solution were used to evaluate the effects of NaCl. Current density-voltage curves and electrochemical impedance spectroscopies (EIS) of fuel cells were measured. Additionally, the constant-voltage mode long-term stability of PEMFCs humidified with NaCl solution were investigated. Constant-voltage measurements and EIS results imply that the degradation of fuel cells is clearly related with the concentration of NaCl solutions.

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Citations to this article as recorded by

Effects of NaCl Solution on Proton Exchange Membrane Fuel Cell with Serpentine Flow Channel of Different Depths
Dong Kun Song, Ho Jun Yoo, Jung Soo Kim, Ki Won Hong, Do Young Jung, George Ilhwan Park, Gu Young Cho
Journal of the Korean Society for Precision Engineering.2025; 42(5): 399. CrossRef
Analysis of Electrochemical Behavior of PEMFC Humidified with NaCl Solution Mist Using an Ultrasonic Vibrator
Ho Jun Yoo, Gye Eun Jang, Young Jo Lee, Dong Kun Song, Heeyun Lee, Gu Young Cho
Journal of the Korean Society for Precision Engineering.2022; 39(12): 939. CrossRef