Yoon-Hwan Cho

Modified Decal Method and Its Related Study of Microporous Layer in PEM Fuel Cells

A modified version of the conventional decal transfer method for the fabrication of electrodes for polymer electrolyte membrane fuel cells is introduced. This modified method makes use of a carbon breaking layer to ensure a high catalyst transfer ratio during the process. In order to optimize this method, the effect of the thickness of the microporous layer was also studied using a thin-film/flooded agglomerate model. The structural features of the electrodes made by the modified decal method were investigated by field-emission scanning electron microscopy, electrochemical impedance spectroscopy, mercury intrusion porosimetry, and current-voltage polarization measurements. The results indicate that the modified decal method has the potential to be a reliable and facile method of fabricating electrodes with high performance.

PtRu-Modified Au Nanoparticles as Electrocatalysts for Direct Methanol Fuel Cells

PtRu-modified Au nanoparticles on a carbon support were prepared using a polyol reduction process with various Pt/Ru ratios. The prepared nanoparticles were characterized using transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, cyclic voltammetry, and chronoamperometry. The surfaces of most Au nanoparticles were covered with bimetallic PtRu overlayers with a thickness of 1-2 monolayers. The thin PtRu overlayers represented distinct CO stripping characteristics, which may be attributable to the unique surface structures of the PtRu overlayers on the Au nanoparticles. PtRu utilization was enhanced by as much as two times compared to that of PtRu/C, which can be attributed to the PtRu overlayers that were deposited only on the surface of the Au nanoparticles. The distinct CO stripping characteristics and the enhanced PtRu utilization affected the electrocatalytic activities of methanol oxidation. Pt 2 Ru 1 overlayers exhibited the highest CO tolerance and the highest methanol oxidation activity. The unique electrocatalytic characteristics of the PtRu overlayer structures on the Au nanoparticles are expected to provide methods for reducing the use of active elements.

Realization of Both High-Performance and Enhanced Durability of Fuel Cells: Pt-Exoskeleton Structure Electrocatalysts.

Core-shell structure nanoparticles have been the subject of many studies over the past few years and continue to be studied as electrocatalysts for fuel cells. Therefore, many excellent core-shell catalysts have been fabricated, but few studies have reported the real application of these catalysts in a practical device actual application. In this paper, we demonstrate the use of platinum (Pt)-exoskeleton structure nanoparticles as cathode catalysts with high stability and remarkable Pt mass activity and report the outstanding performance of these materials when used in membrane-electrode assemblies (MEAs) within a polymer electrolyte membrane fuel cell. The stability and degradation characteristics of these materials were also investigated in single cells in an accelerated degradation test using load cycling, which is similar to the drive cycle of a polymer electrolyte membrane fuel cell used in vehicles. The MEAs with Pt-exoskeleton structure catalysts showed enhanced performance throughout the single cell test and exhibited improved degradation ability that differed from that of a commercial Pt/C catalyst.

The Operation Characteristics of MEAs with Pinholes for Polymer Electrolyte Membrane Fuel Cells

We conducted performance tests on a polymer electrolyte membrane fuel cell containing a catalyst-coated membrane in which artificial pinholes were introduced. The membrane electrode assembly (MEA) with the punctured membrane showed similar performance behavior to an unblemished MEA in the lower current density region. However, the performance of the pinhole MEA with the punctured membrane in the higher current density region was inferior and unstable. The structures of the defective membrane and the MEA were analyzed by field-emission scanning electron microscopy, and their electrochemical characteristics were investigated by electrochemical impedance spectroscopy and single-cell testing.

Improved methanol tolerance using Pt/C in cathode of direct methanol fuel cell

Membrane-electrode assemblies (MEAs) were prepared using PtRu black and 60 wt% carbon-supported platinum (Pt/C) as their anode and cathode catalysts, respectively. The cathode catalyst layers were fabricated using various amounts of Pt (0.5, 1.0, 2.0 and 3.0 mg/cm 2 ). To study the effect of carbon support on performance, an MEA in which Pt black was used as the cathode catalyst was fabricated. In addition, the effect of methanol crossover on the Pt/C on the cathode side of a direct methanol fuel cell (DMFC) was investigated. The performance of the single cell that used Pt/C as the cathode catalyst was higher than that of the single cell that used Pt black, and this result was pronounced when highly concentrated methanol (above 2.0M) was used as the fuel.

Comparison between CFD Analysis and Experiments According to Various PEMFC Flow-field Designs

Flow-field design has much influence over the performance of proton exchange membrane fuel cell (PEMFC) because it affects the pressure magnitude and distribution of the reactant gases. To obtain the pressure magnitude and distribution of reactant gases in five kinds of flow-field designs, computational fluid dynamics (CFD) analysis was performed. After the CFD analysis, a single cell test was carried out to obtain the performance values. As expected, the pressure differences due to different flow-field configurations were related to the PEMFC performance because the actual performance results showed the same tendency as the results of the CFD analysis. A large pressure drop resulted in high PEMFC performance. The single serpentine configuration gave the highest performance because of the high pressure difference magnitudes of the inlet/outlet. On the other hand, the parallel flow-field configuration gave the lowest performance because the pressure difference between inlet and outlet was the lowest.

CO Tolerance Improvement of MEA Using Metal Thin Film by Sputtering Method in PEM Fuel Cell

When reformer for fuel cell is used, CO in hydrogen gas leads to a seriously decreased membrane electrode assembly (MEA) performance by catalyst poisoning. The effect of CO on performance of modified MEA by sputtering method is studied in this paper. The experimental results show that sputtered Pt and Ru thin film improve a single cell performance of MEA and sputtered metal thin film has a CO tolerance. The air injection process on anode show improved CO tolerance test result. Moreover, Pt, Ru and PtRu thin film by sputtering had influence on the CO tolerance with air injection process.

Pulsed VUV synchrotron radiation source

The conceptual design of the pulsed VUV synchrotron radiation (SR) source is reported. This machine has a modified racetrack shape (diamond shape) and consists of two superconducting bending magnets, two normal conducting bending magnets, iron yokes, quadrupole magnets and an injection system. The maximum magnetic flux density is 7 T. The injector is a 100 MeV racetrack microtron and a 100 MeV, 10 pps electron beam is directly injected to this SR source. The bending radius is 4.8 cm and critical wavelength is 27 nm.

Morphology Controlled Cathode Catalyst Layer with AAO Template in Polymer Electrolyte Membrane Fuel Cells

고분자전해질 연료전지 (PEMFC)의 공기극을 양극산화 알루미늄 (AAO) 템플레이트를 이용하여제조하고 촉매층의 구조적 특성을 주사현미경 (SEM) 측정과 BET (Brunauer-Emmett-Teller)분석을 통해 알아보았다. SEM 측정을 통해 일정한 크기와 모양의 Pt nanowire 가 규칙적으로형성된 것을 확인할 수 있었다. BET 분석을 통해 AAO 템플레이트로 인하여 20-100 nm 크기의 기공 분포가 증가한 것을 확인하였다. 단위전지 성능평가와 임피던스 측정을 통하여 막-전극접합체 (MEA)의 전기화학적 특성을 분석하였다. 그 결과, AAO 템플레이트를 이용하여 제조한MEA는 촉매층의 구조 개선으로 인하여 물질 전달 저항을 감소시킬 수 있었으며, 25%의 단위전지 성능이 향상되었다. Abstract: The cathode catalyst layer in polymer electrolyte membrane fuel cells (PEMFCs)was fabricated with anodic aluminum oxide (AAO) template and its structure was characterizedwith scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) analysis. TheSEM analysis showed that the catalyst layer was fabricated the Pt nanowire with uniform shapeand size. The BET analysis showed that the volume of pores in range of 20-100 nm wasenhanced by AAO template. The electrochemical properties with the membrane electrodeassembly (MEA) were evaluated by current-voltage polarization measurements and electrochem-ical impedance spectroscopy. The results showed that the MEA with AAO template reducedthe mass transfer resistance and improved the cell performance by approximately 25% throughcontrolling the structure of catalyst layer. Keywords : Polymer electrolyte membrane fuel cell (PEMFC), Membrane-electrode assembly,Cathode catalyst layer; AAO template