Solid oxide fuel cell is a next generation energy conversion device that can efficiently convert the chemical energy of fuel into electrical energy. Fuel flexibility is one of the advantages of SOFCs over other types of fuel cells. SOFCs can operate with hydrocarbon type fuel. While nickel based composite is commonly used in direct methane fueled SOFC anode because of its great catalytic activity for methane reforming, the direct use of hydrocarbon fuels with pure Ni anode is usually insufficient for facile anode kinetics, and also deactivates the anode activity because of carbon deposition upon prolonged operation. In this report, the Ni based anodes with 20 nm thick catalytic functional layers, i.e., Pt, Ru, and Pt-Ru alloy, are fabricated by using the co-sputtering method to enhance the anode activity and power density of direct-methane SOFC operating at 500℃.
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A doped cobaltite for enhanced SOFCs fed with dry biogas Sebastian Vecino-Mantilla, Massimiliano Lo Faro Electrochimica Acta.2023; 464: 142927. CrossRef
In this study, Yttria-stabilized zirconia (YSZ) functional layers were applied with different thin-film fabrication process such as sputtering and atomic layer deposition (ALD) to enhance oxygen reduction reaction (ORR) for solid oxide fuel cells. We confirmed that the YSZ functional layer deposited with sputtering showed relatively low grain boundary density, while the YSZ functional layer deposited with the ALD technique clearly indicated high grain boundary density through scanning electron microscopy (SEM) and X-ray diffractometry (XRD) results. The YSZ functional layer coated with the ALD technique revealed that more ORR kinetics can occur using high grain boundary density than the functional layer deposited with sputtering. The peak power density of the SOFC deposited with ALD YSZ indicates 2-folds enhancement than the pristine SOFC.
A high temperature sintering process for solid electrolyte is the main cause of the increase in manufacturing costs of SOFCs. In this study, we developed a novel flash light sintering technique as an alternative sintering process of the conventional thermal sintering process. The YSZ electrolyte films were fabricated by conventional screen-printing method and the flash light sintering process and ESB sintering aid were applied to improve the flash light sinterability of the YSZ electrolyte. In the flash light sintering process, the effect of various pulse conditions such as energy density, and pulse interval were investigated and the microstructure, crystallinity, and sintering behavior of the sintered films were analyzed to demonstrate the effectiveness of the flash light sintering process. The flash light sintered YSZ electrolyte layer was used to fabricate the anode-supported SOFCs and its functionality is successfully demonstrated with the high open circuit voltage. The significance of this study includes minimization of the process time from tens of hours to just a few seconds, thus facilitating the commercialization of SOFCs.
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
The purpose of this study was to investigate the excitation force that generates the vibration of the reduction gear case for railroad vehicles. This excitation force is difficult to measure directly. The inverse stiffness method was used using the acceleration response measured in the experiment and the vibration response function derived from the finite element analysis. It was assumed that the excitation force acting on the reduction gear operates in the X, Y, and Z directions for each bearing, and a total of 12 excitation forces were investigated. When deriving the excitation force, singular value decomposition was applied to the vibration response function to increase the accuracy of the result. The results of the excitation force according to the number of degrees of freedom of the response were compared. Additionally, the magnitude of the estimated excitation force according to the singular value category used was compared, and it was confirmed that a too low singular value indicates a different excitation force.
Magnetic bearings are being actively adopted by the turbo-chiller industry because of their higher efficiency during partial load, quieter operation, and smaller footprint than that which machines with ball bearings provide. Since magnetic bearings are open-loop unstable, feedback control is necessary. In the industry, traditional PID-based control is preferred to model-based control, because of its simplicity. When traditional control algorithms are used, significant resources are required to obtain and tune control parameters, which is an impediment to the widespread use of magnetic bearing technology in the industry. In this paper, we propose a mixed optimization method by combining genetic algorithm and sequential quadratic programming. To obtain the initial guess to be used for the mixed optimization, a phase-margin maximization algorithm is also proposed, based on the rigid-body model of the system. Mixed optimization results in suitable control parameters in less than 2.8% of the time it takes a genetic algorithm only to find similar solutions. The proposed optimization also ensures the robustness of the control parameters. The output sensitivity measured from a prototype compressor with magnetic bearings confirms the validity of the control parameters.
In this study, a novel input signal transformer is introduced to remove an overshoot and steady-state error that hinder stable tracking and landing of an unmanned aerial vehicle (UAV) based on image recognition, and the performance is verified. The Input Signal Transformer (IST) is designed in the shape of a sigmoid function to attenuate or amplify the input signal to resolve the aforementioned problems. For the verification of the UAV control system based on the IST, the UAV, target, and sensors were implemented in a virtual environment using the robot operating system (ROS). And data exchange structure and control system were built by the ROS-based message communication. A simulation was performed to confirm the elimination of the overshoot and steady-state error when the UAV to which the above control system was applied tracks and lands a fixed target and a moving target. As a result of the simulation, when the IST was not used, the UAV performed an unstable because of the overshoot and could not land on the target by the steady-state error. Conversely, in the case of using IST, it was confirmed that the flight was stable and landed successfully.
This paper relates to the implementation of moving object position estimation by Pulsed LiDAR that can detect objects with high precision, speed, and spatial resolution. LiDAR measures the distance by calculating a return travel time when target is reflected. The retro-reflector, regardless of incident angle, can be reflected horizontally in the incident direction. This algorithm proposes a new approach method using LiDAR and retro-reflectors. According to the above algorithm, position can be determined by automatically detecting 90% of the reflected return beam intensity from moving objects to which the retro-reflector is attached. When this algorithm was applied indoors, it was possible to locate the position of the scanner accurately within ±5 mm error in 2,500 × 2,500 (mm) space. Also, it can detect a space of up to 5,000 × 5,000 (mm), making this an effective method for determining the position of a moving object in indoors.
Flexure hinges are widely used as joint linkages for precision stages applied to lithography processes. Among them, precision stages with 3 DOF (Degrees of Freedom) of x, y and θz prevail in semiconductor manufacturing and they have been adopting single directional flexure hinges as mechanical linkages without backlash and debris. However, new technologies including nano-imprinting, which replaces lithography, needs more than 3 DOF precision positioning stages that adopt cylindrical flexure hinges. In this study, the cylindrical flexure hinges with circular notches were analyzed using the Timoshenko beam theory and FEM (Finite Element Method), with focused on their directional stiffness. Based on the analysis and result comparison between theoretical equations and FEM, several practical suggestions for determining important design variables are provided in the conclusion of this study.
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Derivation and Verification of Novel Phenomenon-based Theoretical Formulas for the Axial Compliance of Circular Flexure Hinges Jun-Hee Moon, Hyun-Pyo Shin Journal of the Korean Society for Precision Engineering.2025; 42(1): 47. CrossRef
Analysis on Elliptic and Parabolic 2-DOF Flexure Hinges for Spatial Positioning Stages Hyun-Pyo Shin, Jun-Hee Moon Journal of the Korean Society for Precision Engineering.2023; 40(3): 229. CrossRef
In this paper, when the finishing process is performed on the additive by FDM type, the optimal parameter set of the additive-finishing design parameters to improve the surface quality and the verification of the finishing effect are described. Additive design parameters such as nozzle diameter and layer height and finishing design parameters such as depth of cut and feed rate have a significant influence on the printing time and surface roughness of the sculpture. So, we define the major additive-finishing design parameters expected to affect the results. So, we define the major additive-finishing design variables that expected to affect the experimental results. And to confirm how much they affect the results with the minimum number of experiments, the sensitivity analysis of the design parameters was performed through the level average analysis of the Taguchi method. As a result, compared to the surface roughness and additive time when only high-quality sculpture was performed, and it was confirmed that the printing time improved up to 70% and the surface roughness improved up to 87% for the additive-finishing sculpture performed with the optimal combination of design parameters.
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Advancements in polymer nanocomposite manufacturing: revolutionizing medical breakthroughs via additive manufacturing Sadaf Bashir Khan, Shenggui Chen, Xiaohong Sun Polymer Bulletin.2024; 81(11): 9465. CrossRef
Optimal Joint Path Planning of a New Virtual-Linkage-Based Redundant Finishing Stage for Additive-Finishing Integrated Manufacturing Jiwon Yu, Haneul Jeon, Hyungjin Jeong, Donghun Lee Mathematics.2023; 11(24): 4995. CrossRef
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