Preparation of Carbon Paper for Anodic Porous Trans...

Jo Apr 29, 2025

The exhaustion of fossil fuel resources and constant evil effect of the global warming due to greenhouse gas emission needs the introduction of new kinds of energy system. Now, hydrogen energy system is attracting a great deal of attention as a reasonable energy system that can solve almost all kinds of environmental problems.

Proton exchange membrane (PEM) water electrolysis is considered as a main option to integrate and to miniaturize hydrogen energy systems. An advantage of PEM water electrolysis is short start-up time, high current density, high pressurized hydrogen production possibility and no use of corrosive solutions like alkali.

The kinds and properties of an anodic porous transport layer (PTL) play an important role in water management and ohmic resistance reduction. Some materials such as porous carbon materials (carbon fiber or carbon paper) and metals (Ti or Ni) can be used as the PTLs of PEM water electrolyzers.

Jang Tae Il, a researcher at the Institute of Nano Science and Technology, has concluded that the hot-pressed carbon paper is a superior PTL for improving the conductivity of the catalyst coated layer (CCL), and intensified his research to use carbon paper as an anodic PTL.

First, he found that anti-oxidized and hydrophilically treated carbon paper could be used as anodic PTL. Then, during the formation of a micro protective layer (MPL) by protective agents, he conducted plasma treatment of the hydrophobized carbon paper followed by impregnation with the hydrophilic polymer Nafion solution before repeating immersion-drying processes several times and heat treatment at 140℃ for 30 min to use carbon paper as anodic PTL.

PEM water electrolyzer prepared with the hydrophilic anodic PTL displayed desirable performance; initial voltage at 1.2A·cm^-2 of current density at 80℃ was 1.76±0.02V, and finally measured voltage 1.84±0.02V after 6 270h of testing.

For more information, please refer to his paper “Hydrophilic treatment of carbon paper for anodic porous transport layer in proton exchange membrane water electrolyzer” in “Reaction Kinetics, Mechanisms and Catalysis” (SCI).

Selection of Titanium Alloy by Integrated Multi-att...

Jo Apr 28, 2025

Commercial pure titanium (Cp Ti) and Ti alloys have good mechanical properties, excellent biocompatibility, corrosion resistance and specific strength, and most suitable characteristics required for biomedical applications. So, they have been widely used in many biomedical applications including hip joints, dental implants, etc. Especially, the alloys with lower modulus are desired because the moduli of alloys are required to be much more similar to bone.

There are many kinds of Ti alloys applicable to biomedical applications. To evaluate the performance of Ti alloys, it is necessary to consider the multiple biomedical and mechanical properties comprehensively, not individually. Therefore, Ti alloy selection becomes a multi-attribute decision-making (MADM) problem for evaluating the multiple candidate Ti alloys in consideration of their multiple conflicting attributes and selecting the best one among them, and it could be solved using the MADM methods.

Many works have applied the multiple MADMs to solve the biomaterials selection problems. However, the previous works have the following shortcomings: (1) they do not reflect the preference-weights of each MADM in the integrated ranks, and (2) they determine only the integrated evaluation ranks of candidates, and do not determine the integrated evaluation values of candidates.

Yang Won Chol, a researcher at the Faculty of Materials Science and Technology, has proposed a new integrated MADM methodology based on the integrated comprehensive evaluation index (ICEI) of candidates: ICEI-MADM.

The ICEIs are the preference-weighted averages of comprehensive evaluation indices (CEIs) of candidates obtained from individual MADMs, and the preference-weights are calculated by the normalized average correlation coefficients between rankings from the individual MADMs.

To demonstrate the effectiveness of the proposed method, he applied the method to the comprehensive evaluation of the performance of biomedical Ti alloys and the selection of the best of them.

For more information, please refer to his paper “Integrated multi-attribute decision-making methodology based on integrated comprehensive evaluation index: application to titanium alloy selection” in “Applied Physics A” (SCI).

Winding Design and Lead-Angle Control for Maximum S...

Jo Apr 26, 2025

The Interior Permanent-Magnet Brushless DC Motor (IPMBLDCM) without exciting winding and exciting source is widely used to replace traditional DC motors for subway locomotives. IPMBLDCM is gaining a great deal of interest for subway locomotive applications due to its high efficiency, simple control mode and small size.

PMBLDCM has a wide speed regulation range and its start current, start torque and starting time are small. Also, PMBLDCM generates enough torque and speed by the combination mode of motor/generator. From zero to base speed, it is dependent on applied voltage, and above the base speed, it is dependent on flux weakening by torque angle.

Cha Myong Song, a section head at the Faculty of Electrical Engineering, has proposed a winding design and lead angle control method for the maximum speed of an IPMBLDCM for subway locomotives.

The maximum speed of the IPMBLDCM is regulated by the linkage flux and armature reaction by lead angle control because permanent magnet magnetomotive force (mmf) cannot be regulated directly. The maximum speed of IPMBLDCM for the subway locomotive is 2.34 times the rated speed. As the speed regulation ratio is larger than 2, the maximum speed of motor must be ensured by lead angle and conductors per slot. If the lead angle is regulated, no-load speed is increased by changing linkage flux at no-load state and the rated speed is increased by armature reaction.

He simulated the relation between the speed, torque, output power and efficiency for the lead-angle and conductors per slot by means of Ansoft Maxwell/RMxprt. The simulation results verified that the speed, torque, output power and efficiency are constant in the range of 47°-68° and the maximum speed is 1948r/min. The experimental results indicated that the operation of the IPMBLDCM is stable at the maximum speed.

For more information, please refer to his paper “Winding Design and Lead-Angle Control for the Maximum Speed of an Interior Permanent-Magnet Brushless DC Motor” in “Journal of Electrical Power & Energy Systems” (SCI).