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In this paper, we report the preparation of highly active and durable ordered intermetallic PdFe catalyst supported on carbon black for formic acid oxidation reaction (FAOR) by high-temperature hea...

Metal nanoparticles (NPs) have been extensively investigated owing to their unique properties attributing to their high surface/bulk ratio and finite number of atoms. However, the thermodynamic instability of NPs, which originates from their finite size, limits their practical applications. Hence, carbon-supported Pt NPs are synthesized onto carbon-containing liquid substrates via direct one-step sputtering. In order to successfully produce uniform Pt NPs via sputtering using various ionic liquids as non-volatile liquid substrates, special conditions are required, and the relationship between ionic liquids and particle surfaces should be investigated. It has been reported that anions and carbon supports of ionic liquids significantly affect the dispersion and synthesis of Pt NPs. In this study, we proposed a mechanism underlying the chemical bonding between anions and carbon supports and verified it using X-ray photoelectron spectroscopy and infrared spectroscopy.

Despite the advantage of chemical vapor deposition (CVD) for realization of large area epitaxial growth of graphene on transition metal catalysts, both etching and transfer process of CVD-grown graphene sheets still remain a big challenge. Here we demonstrate the formation of multilayer graphene (MLG) sheets tailored from C60 thin films on the top of Si/Ni substrate without etching and transfer steps based on Ni films. This self-assembled process separates the MLG sheets from the conductive Ni catalyst, embarking a possibility for direct characterizations of MLG sheets. The fine-tuned C60 films (30 nm) are transformed into approximately 17 MLG sheets, thus making it large-area MLG sheets for a variety of direct applications.

A Rh–Sn nanoparticle is achieved by combinatorial approaches for application as an active and stable electrocatalyst in the oxygen reduction reaction. Both metallic Rh and metallic Sn exhibit activities too low to be utilized for electrocatalytic reduction of oxygen. However, a clean and active Rh surface can be activated by incorporation of Sn into a Rh nanoparticle through the combined effects of lateral repulsion, bifunctional mechanism, and electronic modification. The corrosion-resistant property of Rh contributes to the construction of a stable catalyst that can be used under harsh fuel cell conditions. Based on both theoretical and experimental research, Rh–Sn nanoparticle designs with inexpensive materials can be a potential alternative catalyst in terms of the economic feasibility of commercialization and its facile and simple surfactant-free microwave-assisted synthesis.

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.

An anode electrode with the carbon buffer layer is fabricated to increase the performance of direct methanol fuel cell (DMFC). The carbon buffer layer is located in the middle of the anode catalyst layers, consists of porous carbon and Nafion ionomer. Since the porous and relatively hydrophilic carbon buffer layer absorbs methanol, the flux of the methanol solution in the anode electrode can be controlled. And methanol crossover is decreased by the effect of the carbon buffer layer. Consequently, methanol can be oxidized more efficiently and the performance of DMFC increases. Therefore, the membrane electrode assembly (MEA) with the carbon buffer layer on the anode electrode exhibits higher open circuit voltage (OCV) and maximum power density compared to those of conventional MEA. Especially with 3.0 M methanol solution, the maximum power density is increased by ∼60%.

E-mail: ysung@snu.ac.krReceived November 7, 2012, Accepted January 26, 2013Nickel hexacyanoferrate supported palladium nanoparticles (Pd-NiHCF NPs) were synthesized and studied foroxygen reduction reactions in direct methanol fuel cell. The NiHCF support was readily synthesized by a co-mixing of Ni(OCOCH

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

Pd-based nanoparticles, such as 40 wt.% carbon-supported Pd50Pt50, Pd75Pt25, Pd90Pt10 and Pd95Pt5, for anode electrocatalyst on polymer electrolyte membrane fuel cells (PEMFCs) were synthesized by the borohydride reduction method. PdPt metal particles with a narrow size distribution were dispersed uniformly on a carbon support. The membrane electrode assembly (MEA) with Pd95Pt5/C as the anode catalyst exhibited comparable single-cell performance to that of commercial Pt/C at 0.7 V. Although the Pt loading of the anode with Pd95Pt5/C was as low as 0.02 mg cm−2, the specific power (power to mass of Pt in the MEA) of Pd95Pt5/C was higher than that of Pt/C at 0.7 V. Furthermore, the single-cell performance with Pd50Pt50/C and Pd75Pt25/C as the anode catalyst at 0.4 V was approximately 95% that of the MEA with the Pt/C catalyst. This indicated that a Pd-based catalyst that has an extremely small amount of Pt (only 5 or 50 at.%) can be replaced as an anode electrocatalyst in PEMFC.

To understand the difference in degradation characteristics between carbon-supported platinum (Pt/C) and platinum–nickel alloy (Pt1Ni1/C) cathode catalysts in membrane electrode assemblies (MEAs) of a polymer electrolyte membrane fuel cell (PEMFC), constant current operation of MEA in a single cell was conducted for 1100 h. A significant change in cell potential for the Pt1Ni1/C MEA was observed throughout the test. High-resolution transmission electron microscopy showed that sintering and detachment of metal particles in the Pt1Ni1/C catalyst occurred more sparingly than in the Pt/C catalyst. Instead, X-ray photoelectron spectroscopy element mapping revealed dissolution of Ni atoms in the Pt1Ni1 catalysts even when the Pt1Ni1/C catalyst used in the MEA was well synthesized.

A methanol-tolerant cathode electrode composed of heterogeneous composites was developed to overcome CO poisoning and large O2 mass transfer overpotential generated by methanol crossover as well as the limitation of a single alloy catalyst with methanol-tolerance in direct methanol fuel cells (DMFCs). Two additives, PtRu black and PTFE particles, were well distributed in the Pt/C matrix of the cathode electrode, and had significant effects upon open circuit voltage (OCV) and performance. A small amount of PtRu black protected the Pt surface during the oxygen reduction reaction (ORR) by decreasing CO poisoning. In addition, hydrophobic PTFE particles reduced the O2 mass transfer overpotential induced by water and permeated methanol in the cathode. Despite only 0.5 mg cm−2 of metal catalysts in the cathode, the membrane electrode assembly (MEA) with 3 M methanol showed high performance (0.117 W cm−2), which was larger than that of the traditional MEA (0.067 W cm−2).

Water management is one of the most important factors for improving the performance in polymer electrolyte membrane fuel cells (PEMFCs). The micro-porous layers (MPLs) in the membrane-electrode assembly provide proper pores and paths for mass transport, thereby allowing for the control of the water balance. In this study, a copolymer containing hydrophilic functional groups is introduced into the binder materials of the MPL instead of a highly hydrophobic binder. When 10 wt.% of the binder is incorporated in the MPL on the cathode side, the best performance is exhibited and the ohmic resistance is decreased. Although the charge transfer resistance at low potential is higher than that of the hydrophobic treated MPL, due to the flooding effects, the charge transfer resistance at high potential becomes smaller. This indicates that excess liquid absorption from the catalyst layer to the hydrophilic MPL occurs more strongly than in the case of the hydrophobic MPL. This may bring about an increase in the accessibility of oxygen to the active sites, because the excess liquid near the catalyst agglomerates is expelled as fast as possible. Consequently, the hydrophilicity control in the MPL has a positive effect on the water management in PEMFCs.

In this work, a surface modified Nafion 212 membrane was fabricated by plasma etching in order to enhance the performance of a membrane electrode assembly (MEA) in a polymer electrolyte membrane fuel cell. Single-cell performance of MEA at 0.7 V was increased by about 19% with membrane that was etched for 10 min compared to that with untreated Nafion 212 membrane. The MEA with membrane etched for 20 min exhibited a current density of 1700 mA cm−2 at 0.35 V, which was 8% higher than that of MEA with untreated membrane (1580 mA cm−2). The performances of MEAs containing etched membranes were affected by complex factors such as the thickness and surface morphology of the membrane related to etching time. The structural changes and electrochemical properties of the MEAs with etched membranes were characterized by field emission scanning electron microscopy, Fourier transform-infrared spectrometry, electrochemical impedance spectroscopy, and cyclic voltammetry.

A catalyst-coated membrane (CCM) as used in the membrane electrode assembly (MEA) of a polymer electrolyte membrane fuel cell is treated by dilute sulfuric acid solution (0.5 M) at boiling temperature for 1 h. This treatment improves the single-cell performance of the CCM without further addition of Pt catalyst. The changed microstructure and electrochemical properties of the catalyst layer are investigated by field emission scanning electron microscopy with energy dispersive X-ray, mercury intrusion porosimetry, waterdrop contact angle measurement, Fourier transform-infrared spectrometry in attenuated total reflection mode, electrochemical impedance spectroscopy, and cyclic voltammetry. The results indicate that this pretreatment enhances MEA performance by changing the microstructure of the catalyst layer and thus changing the degree of hydration, and by modifying the Pt surface, thus enhancing the oxygen reduction reaction.

Nickel hexacyanoferrate supported palladium nanoparticles are synthesized from mixtures of nickel hexacyanoferrate nanoparticles, L-ascorbic acid, and Pd(NO3)2 in EtOH (Ar, 80 °C, 3 h).

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.

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.

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.