Namgee Jung

Tailoring the Electronic Structure of Nanoelectrocatalysts Induced by a Surface-Capping Organic Molecule for the Oxygen Reduction Reaction.

Capping organic molecules, including oleylamine, strongly adsorbed onto Pt nanoparticles during preparation steps are considered undesirable species for the oxygen reduction reaction due to decreasing electrochemical active sites. However, we found that a small amount of oleylamine modified platinum nanoparticles showed significant enhancement of the electrochemical activity of the oxygen reduction reaction, even with the loss of the electrochemically active surface area. The enhancement was correlated with the downshift of the frontier d-band structure of platinum and the retardation of competitively adsorbed species. These results suggest that a capping organic molecule modified electrode can be a strategy to design an advanced electrocatalyst by modification of electronic structures.

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.

Chemical tuning of electrochemical properties of Pt-skin surfaces for highly active oxygen reduction reactions

Pt-skin surfaces were successfully fabricated by the chemical deposition of additional Pt on corrugated Pt-Ni nanoparticles with Pt-skeleton surfaces. Compared to the Pt-skin formed by heat annealing, the chemically-tuned Pt-skin had a higher Pt coordination number and surface crystallinity, which resulted in superior ORR activity and durability.

High Alloying Degree of Carbon Supported Pt-Ru Alloy Nanoparticles Applying Anhydrous Ethanol as a Solvent

Alloying degree is an important structural factor of PtRu catalysts for direct methanol fuel cells (DMFC). In this work, carbon supported PtRu catalysts were synthesized by reduction method using anhydrous ethanol as a solvent and NaBH4 as a reducing agent. Using anhydrous ethanol as a solvent resulted in high alloying degree and good dispersion. The morphological structure and crystallanity of synthesized catalysts were characterized by X-ray diffraction (XRD), high resolution transmission electron microscope (HR-TEM). CO stripping and methanol oxidation reaction were measured. Due to high alloying degree catalyst prepared in anhydrous ethanol, exhibited low onset potential for methanol oxidation and negative peak shift of CO oxidation than commercial sample. Consequently, samples, applying ethanol as a solvent, exhibited not only enhanced CO oxidation, but also increased methanol oxidation reaction (MOR) activity compared with commercial PtRu/C (40 wt%, E-tek) and 40 wt% PtRu/C prepared in water solution.

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