In-Su Park

A Pd-impregnated nanocomposite Nafion membrane for use in high-concentration methanol fuel in DMFC

Pd nanophases in a Nafion polymer membrane electrolyte were used to enhance DMFC performance by preventing or reducing methanol crossover through the electrolyte. Interestingly, the Pd-impregnated nanocomposite membrane showed a lower permeability for methanol and maintained a proton conductivity comparable to that of a pure Nafion membrane. Because of the modification of the membrane by the Pd nanophases, a high molar concentration of methanol could be applied for use in practical DMFC without any power loss.

New RuO2 and carbon–RuO2 composite diffusion layer for use in direct methanol fuel cells

Abstract A RuO 2 diffusion layer is examined for use in direct methanol fuel cells (DMFC) by comparison with acetylene black and Vulcan XC-72R. In the test with a DMFC unit cell, the RuO 2 diffusion layer is superior to the other two materials. The difference in performance is interpreted in terms of structural and electrical properties which are evaluated by porosity, scanning electron microscopy and resistance measurements. The RuO 2 diffusion layer displays different behaviors at the anode and cathode sides. These characteristics can be attributed to a reduced loss of catalyst in the active catalyst layer, which leads to increased methanol diffusion at the anode and prevention of water flooding in the cathode. The effect of the RuO 2 diffusion layer on cell performance becomes more pronounced at lower temperatures and during operation in the presence of air. Finally, a carbon–RuO 2 composite is evaluated as a diffusion layer material for a DMFC.

Promotional Effect of Palladium on the Hydrogen Oxidation Reaction at a PtPd Alloy Electrode

Although these factors arepivotal for the kinetics of the HOR, direct experimentalinspectionofthecontributionsofthesefactorshasrarelybeeninvestigated in electrochemical oxidation of hydrogen.There are more than enough signs that Pd catalysts havemany of the desired electrocatalytic properties for the HOR/hydrogen evolution reaction (HER), since the electrontransfer from the Pd surface into the antibonding orbital ofthe hydrogen molecule plays an important role in breakingthe hydrogen bonds, and this process lowers the associatedactivation energy.

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.

Surface Structures and Electrochemical Activities of Pt Overlayers on Ir Nanoparticles

Pt overlayers were deposited on carbon-supported Ir nanoparticles with various coverages. Structural and electrochemical characterizations were performed using transmission electron microscopy (TEM), X-ray diffraction, high-resolution powder diffraction (HRPD), X-ray photoelectron spectroscopy (XPS), X-ray absorption near-edge spectroscopy (XANES), cyclic voltammetry (CV), CO stripping voltammetry, and N2O reduction. The surface of Ir nanoparticles was covered with Pt overlayers with thickness varying from the submonolayer scale to more than two monolayers. Surface analyses such as CV and CO stripping voltammetry indicated that the Pt overlayers were uniformly deposited on the Ir nanoparticles, and the resultant Pt overlayers exhibited gradual changes in surface characteristics toward the Pt surface as the surface coverage increased. The distinct CO stripping characteristics and the enhanced Pt utilization affected electrocatalytic activities for methanol oxidation. The electrochemical stability of the Pt overlayer was compared with a commercial carbon-supported Pt catalyst by conducting a potential cycling experiment.

Synthesis of 3 nm Pt Nanowire Using MCM-41 and Electrocatalytic Activity in Methanol Electro-oxidation

A networked Pt nanowire electrocatalyst for methanol oxidation was prepared by way of a template confinement approach using MCM-41 (Mobil composition of matter), which is a mesoporous silicate with channel-like pores of rather uniform size. From the structural analysis, the prepared Pt nanowire showed an interconnected network structure and the diameter was about 3 nm. An electrochemical analysis indicated that the Pt nanowire electrocatalyst exhibited an increase in electrocatalytic activity over the Pt nanoparticle electrocatalyst for methanol oxidation reaction by 250 and 160%, respectively, when the area- and mass-normalized current densities were compared at 0.5 V vs a normal hydrogen electrode. These enhanced electrocatalytic activities of the Pt nanowire electrocatalyst might be related to its unique surface characteristics, which represent a mild surface roughness and favorable crystallographic Pt surface for methanol oxidation.

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.

Chemical State of Adsorbed Sulfur on Pt Nanoparticles

The chemical state of adsorbed sulfur (S) on a Pt surface was identified and investigated by a combination of detailed electrochemical (EC) measurements, in situ surface enhanced Raman scattering (SERS) and ab initio density functional theory (DFT) calculations. The SERS data of the adsorbed S coupled with the DFT calculations provide the first convincing evidence showing that the adsorbed sulfur is in a sulfide (S2-) state.

Synthesis of Pt and bimetallic PtPd nanostructures on Au nanoparticles for use as methanol tolerant oxygen reduction reaction catalysts

Core–shell structured Au–PtPd/C and Au–Pt/C nanoparticles (NPs) were prepared using a successive reduction process on carbon supported Au with PtPd and Pt particles. Structural analyses of the core–shell NPs revealed uniformly distributed fine particles (<5 nm in diameter) on carbon particles and selectively deposited Pt and bimetallic PtPd structures on the Au surface. The activity of the NPs was investigated for the oxygen reduction reaction (ORR) in both H2SO4 solutions with and without CH3OH. In Au–Pt and Au–PtPd NPs, the activities for the ORR decreased in the solution without CH3OH as the amount of Pd increased; moreover, Au–PtPd NPs showed higher activity than Au–Pt NPs in solution with CH3OH due to its enhanced tolerance for methanol oxidation. Thus, the high methanol oxidation reaction tolerance of Au–PtPd NPs is ascribed to the synergistic effect resulting from its thin structure and bimetallic PtPd composition.

A comparative in situ195Pt electrochemical-NMR investigation of PtRu nanoparticles supported on diverse carbon nanomaterials

This paper reports a detailed in situ 195Pt electrochemical-nuclear magnetic resonance (EC-NMR) study of PtRu nanoparticles (NPs) that had a nominal atomic ratio of Pt : Ru = 1 : 1 and were supported on carbon nanocoils and carbon black (Vulcan XC-72) respectively. The particle sizes of the two samples were determined by X-ray diffraction using the Sherrer equation: 3.6 nm for the former and 3.2 nm for the latter, which were further corroborated by transmission electron microscope measurements. By taking advantage of a unique correlation between the spectral frequency of the 195Pt NMR resonance and the radial atomic position in a particle, qualitatively- and spatially-resolved local Pt atomic fractions in the particles were deduced by using a Ruderman-Kittel-Kasuya-Yosida (RKKY) J-coupling-based method as a function of different electrode potentials. The results indicated that both samples had Pt-enriched cores and Pt-deprived surfaces and, most importantly, the local Pt concentration varied as the electrochemical environment changed. The spatially-resolved Fermi level local densities of states (E(f)-LDOS), which are a measure of the electronic frontier orbitals in metals, were deduced across the NMR spectrum and correlated with the EC activity in methanol electro-oxidation. The results were also compared to those obtained previously from Pt/Ru NPs supported respectively on carbon and graphite nanofibers.