Minjeh Ahn

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.

Improved electrocatalytic stability in ethanol oxidation by microwave-assisted selective deposition of SnO2 and Pt onto carbon

Pt/SnO2/C nanostructures with SnO2/Pt molar ratios ranging from 2.5 to 0.6 were synthesized by simple and fast microwave-assisted routes. The materials are composed of 3–5 nm SnO2 and Pt nanoparticles dispersed on the carbon support, with the morphology of the coating depending on the SnO2/Pt ratio: a homogenous layer of nanoparticles coating the carbon surface is obtained for SnO2/Pt of 2.5, whereas small Pt–SnO2 clusters are formed for lower ratios. The electrocatalytic activity of the composites on the ethanol oxidation reaction (EOR) was studied by cyclic voltammetry and chronoamperometry. All the binary catalysts exhibited lower onset potentials for the EOR and slower decay of the current density with time than a commercial Pt/C catalyst. However, improved peak current densities were only observed for the composites with ratios 1.6, 1.0 and 0.6, indicating that the formation of metal and metal oxide nanoparticles clusters is favorable for the EOR. This morphology facilitates the hydroxyl groups transfer from the metal oxide to the platinum at low potentials and also the electron transfer between carbon and platinum. The best overall performance was found for the catalyst with SnO2/Pt = 1, on which the number of three-phase boundaries is maximized. Moreover, the catalyst with SnO2/Pt = 1 continued to exhibit significantly better catalytic performance on the EOR than the commercial catalyst after potential cycling.

Facile synthesis of carbon supported metal nanoparticles via sputtering onto a liquid substrate and their electrochemical application

Synthesis of electrochemically active carbon supported nanoparticles (NPs) was achieved via direct one-step sputtering onto a carbon containing liquid substrate. Platinum (Pt) and platinum–nickel (PtNi) NPs of approximately 2 nm in size were uniformly deposited onto carbon supports via a sputtering method with polyethylene glycol (PEG) being used as a liquid substrate. Unlike expensive ionic liquids, this experiment leads to direct application for the electrocatalyst, due to the absence of the surface absorbable ions which can hinder electrochemically active surfaces. The fabricated carbon supported Pt NPs had comparable activity to commercial Pt/C catalysts, and PtNi NPs on carbon synthesized by co-sputtering exhibited 1.9 times higher mass activity at 0.95 V for the oxygen reduction reaction relative to the conventional catalyst. Synthesis via a sputtering process onto the PEG is beneficial due to repeatable results, has easy scalability for mass production as well as a simple and convenient preparation method for NPs.

Heterogeneous rhodium–tin nanoparticles: highly active and durable electrocatalysts for the oxidation of ethanol

Facile synthesis of Rh–Sn catalysts for the electrocatalytic oxidation of ethanol is carried out via a surfactant-free microwave-assisted method. The bifunctional mechanism and electronic modification with C–C bond splitting enable this electrocatalyst to be remarkably active and durable at high fuel concentrations, which allows for a significant reduction in the volume and weight of the fuel cell system.

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