Journal of the Korean Society for Precision Engineering

A Review of in Operando Measurements of Local Temperature for Lithium-ion Batteries: Soyoung Park, Woosung Park; J. Korean Soc. Precis. Eng. 2025;42(12):1021-1035.
Published online December 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.00024

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Sensing the internal temperature of lithium-ion batteries is particularly useful for reliable battery operation as both electrochemistry and mass transport are dictated by local temperature. In this article, we review in operando techniques to monitor the internal temperature of lithium-ion batteries during charging and discharging. We categorize existing techniques into two groups: invasive and non-invasive approaches. Invasive techniques include optical fibers, thermocouples, and resistance temperature detectors as a thermometer. Non-invasive methods cover the temperature estimation techniques, namely electrochemical impedance spectroscopy as well as X-ray thermometry. For both approaches, we review working principle of thermometry, pros and cons of each thermometry, and recent studies to tackle relevant technical challenges. This review provides useful information for internal temperature measurements, offering chances for thermally reliable battery operation.

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Electrochemical Evaluation of PrO_x Capping Layer in LT-SOFCs via Sputtering Process: Ji Woong Jeon, Geon Hyeop Kim, Hyeon Min Lee, Jun Geon Park, Gu Young Cho; J. Korean Soc. Precis. Eng. 2025;42(12):1003-1010.
Published online December 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.00014

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Solid Oxide Fuel Cells (SOFCs) are energy conversion devices known for their significantly higher power density compared to other fuel cell types. However, their high operating temperatures pose challenges related to thermal stability. To address this, research is focusing on Low-Temperature SOFCs (LT-SOFCs), which function at lower temperatures and exhibit enhanced electrochemical performance. While various electrode materials are utilized in SOFCs, platinum (Pt) stands out for its excellent electronic conductivity and catalytic activity. Unfortunately, at the operating temperatures of SOFCs, Pt tends to agglomerate, leading to a rapid reduction in the triple phase boundary (TPB) and a subsequent decline in electrochemical reactions. In this study, LT-SOFCs were fabricated with a Praseodymium Oxide (PrOx) capping layer applied to a porous Pt cathode using sputtering, with various thicknesses achieved by adjusting the deposition time. The electrochemical performance of the LT-SOFCs was measured at 500^oC. Additionally, the degradation behavior of the LT-SOFCs was assessed by applying a constant voltage of 0.5 V for 48 hours. Scanning Electron Microscopy (SEM) analysis was also conducted on the PrOx capping layer thin films under the same operating conditions.

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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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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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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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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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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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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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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

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Effects of Current Collecting Methods for Polymer Bipolar Plate of Ultra-Light Polymer Electrolyte Membrane Fuel Cells: Gye Eun Jang, Young Jo Lee, Gu Young Cho; J. Korean Soc. Precis. Eng. 2022;39(2):109-114.
Published online February 1, 2022; DOI: https://doi.org/10.7736/JKSPE.021.118

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In this study, polymer bipolar plates for ultra-light polymer electrolyte membrane fuel cells (PEMFCs) were fabricated. Various methods for current collecting were applied to ensure electron conductivity of the polymer bipolar plates. Direct wire contact and Ag sputter process were applied. The Ag current collecting layer fabricated by the sputter process showed a well-covered and defectless surface. After preparations of bipolar plates, the effects of current collecting methods of bipolar plates on the electrochemical properties of PEMFCs were systematically investigated. The maximum power density of PEMFCs with the Ag current collecting of layered polymer bipolar plates decreased 37.39% because of increased ohmic resistance. However, the power/weight of PEMFCs with the Ag current collecting of layered polymer bipolar plates increased 27.23% because of the dramatically reduced weight (-50.63%) of bipolar plates compared to the graphite bipolar plates. We affirm that results in this report can provide meaningful insight for portable electrochemical energy devices.

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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
Journal of the Korean Society for Precision Engineering.2023; 40(7): 539. CrossRef

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A Study on the Selection of Failure Factors for Transient State Lithium-Ion Batteries based on Electrochemical Impedance Spectroscopy: Miyoung Lee, Seungyun Han, Jinhyeong Park, Jonghoon Kim; J. Korean Soc. Precis. Eng. 2021;38(10):749-756.
Published online October 1, 2021; DOI: https://doi.org/10.7736/JKSPE.021.040

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Lithium-ion batteries are one of the main parts of electrical devices and are widely used in various applications. To safely use lithium-ion batteries, fault diagnosis and prognosis are significant. This paper analyzes resistance parameters from electrochemical impedance spectroscopy (EIS) to detect the fault of lithium-ion batteries. The internal fault mechanisms of batteries are so complex; it is difficult to detect abnormalities by direct current-based methods. However, by using alternating-current-based impedance by EIS, the internal degradation processes of the batteries can be detected. Impedance variation from EIS is verified under accelerated degradation test conditions and normal cycling test conditions. The results showed a significant relationship between fault and increase in resistance.

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Research into the Detection of Faulty Cells in Battery Systems Using BMS Cell Balancing Counts
Hyunjun Kim, Woongchul Choi
Transaction of the Korean Society of Automotive Engineers.2025; 33(8): 637. CrossRef
PEDOT:PSS‐Based Prolonged Long‐Term Decay Synaptic OECT with Proton‐Permeable Material, Nafion
Ye Ji Lee, Yong Hyun Kim, Eun Kwang Lee
Macromolecular Rapid Communications.2024;[Epub] CrossRef
Lithium-Ion Batteries (LIBs) Immersed in Fire Prevention Material for Fire Safety and Heat Management
Junho Bae, Yunseok Choi, Youngsik Kim
Energies.2024; 17(10): 2418. CrossRef