Naoko Fujiwara

Stability of Corrosion-Resistant Magnéli-Phase Ti4O7-Supported PEMFC Catalysts at High Potentials

Substoichiometric titanium oxide (Ti 4 O 7 )-supported Pt catalysts were prepared and their electrochemical properties, particularly the effects of high-potential conditions on the activity and stability of Pt/Ti 4 O 7 catalysts, were compared to those of Pt/C catalyst. Polarization measurements using membrane electrode assemblies revealed that the Pt/Ti 4 O 7 cathode shows a similar activity for the oxygen reduction reaction as Pt/C catalyst at 80°C. A high-potential holding test (1 h holding at 1.0-1.5 V vs anode) demonstrated that the Pt/Ti 4 O 7 catalyst is quite stable against high potential up to 1.5 V. A single cell using a Pt/Ti 4 0 7 cathode was operated at 80°C, and voltage stability for >350 h with H 2 /O 2 was also demonstrated.

The effects of counter ions on characterization and performance of a solid polymer electrolyte actuator

Abstract A perfluorocarboxylic acid membrane was chemically plated with gold bends under electric stimuli in water. When exchanged with alkali metal ions as counter ions, the displacement is rapid, though charge-specific displacement, or ‘pumping’ efficiency, is small. The fast response is thought to be linked with the small radius of the hydrated ion relative to the hydrophilic channel size in the membrane. In contrast, the charge-specific displacement with alkyl ammonium ions increases, while the rate decreases, systematically with molecular size. The effects are interpreted in terms of an ‘ion-pumping’ model, in which the size of the hydrated ion relative to that of the hydrophilic channel is of paramount importance. A good ‘pumping’ ion inevitably effects only a slow displacement.

Platinum and molybdenum oxide deposited carbon electrocatalyst for oxidation of hydrogen containing carbon monoxide

Carbon-supported Pt/MoOx catalysts for use in PEFC anodes were prepared and their catalytic activity for the oxidation of CO-contaminated H2 was examined based on the fuel cell performance in PEFC single cell arrangements. Based on the XRD pattern and XPS measurements of the prepared Pt/MoOx/C catalysts, it was found that the deposited MoOx exists as an amorphous oxide phase. The MoOx phase shows a redox peak at around 0.45 V, which was revealed by the cyclic voltammogram of the Pt/MoOx/C in sulfuric acid solution. The PEFC performance of the cell with Pt/MoOx/C was improved under 100 ppm CO-contaminated H2 conditions compared to the Pt/C catalyst, and was almost comparable to the PtRu(1:1)/C catalyst.

Preparation of platinum–ruthenium onto solid polymer electrolyte membrane and the application to a DMFC anode

The ‘impregnation–reduction method’ has been investigated as a tool for the preparation of a direct methanol fuel cell (DMFC) anode. In this method, PtRu electrocatalysts were directly bonded onto a polymer electrolyte membrane by the chemical reduction of a mixture of Pt and Ru complexes impregnated in the membrane. The deposited PtRu particles were embedded in the 3–4 μm region of the membrane surface to form a porous and hydrophilic layer. The PtRu layers turned out to be applicable to the DMFC anode, despite their small active surface areas compared to PtRu nanoparticles used in the conventional method. Approximately, 3 mg cm−2 of the PtRu layer exhibited better catalyst utilization and facilitated the release of evolving CO2. This preparation technique is attractive for the application of various solid polymer electrolyte materials with low heat-resistance or various shapes, etc.

Enhanced CO-Tolerance of Carbon-Supported Platinum and Molybdenum Oxide Anode Catalyst

The activity of carbon-supported Pt/MoO x (Pt/MOO x /C) toward oxidation of 100 ppm CO in H 2 was investigated using a rotating disk electrode in 0.5 M H 2 SO 4 solution and by anodic polarization behavior in a single cell configuration. CO-stripping voltammetry of the Pt/MoO x /C catalyst showed a higher stripping peak potential compared to PtRu/C; however, the onset potential of the potentiodynamic oxidation of the CO/H 2 mixture was somewhat smaller than that of PtRu/C. Anodic polarization of a Pt/MoO x /C anode in a CO/H 2 mixture decreased with decreasing fuel flow rate and with decreasing thickness of the Nafion membrane, which indicated that part of the improved CO tolerance of the Pt/MoO x /C anode was due to O 2 that permeated from the cathode. This is supported by the anodic polarization of Pt/MoO x /C increasing and becoming independent of the fuel flow rate when the cathode gas was changed from Or to H 2 . Analyses of CO concentration in the exhaust gas from the anode side showed that part of the CO in the fuel gas stream was oxidized by electrochemical and nonelectrochemical processes. The CO tolerance of the Pt/MoO x /C anode was attributed to the intrinsic CO tolerance of the catalyst and nonelectrochemical CO oxidation by the permeated O 2 .

State of water and ionic conductivity of solid polymer electrolyte membranes in relation to polymer actuators

This paper studies the state of the water and the ionic conductivity of solid polymer electrolyte membranes (SPM) of various ionic forms relating to polymer actuators. Perfluorinated polymers in both sulfonic and carboxylic forms were studied. From differential scanning calorimetry (DSC) measurements, the freezable water content in the SPM was estimated. From impedance measurements, the membrane conductivity of the SPM was estimated by equivalent circuit analysis. The counter cation in the SPM can be categorized in three groups from the freezable water content and the ionic conductivity of the membrane. Group A includes small hydrophilic cations such as those of the alkali and alkaline earth metals, for which the membrane conductivity increases with an increase in the freezable water content of the membrane. Group B includes hydrophobic cations such as alkyl ammonium ions except tetrapropyl- and tetrabutyl-ammonium ions in the perfluorosulfonic acid membrane. The ionic conductivity depends on the size of the ion and the membrane has a relatively large freezable water content. Group C includes the large hydrophobic cations such as TPrA and TBA in perfluorosulfonic acid membrane, which have a low conductivity and low freezable water content. In the light of these results, the deformation properties of the SPM/metal composites are discussed.

Polymer actuator driven by ion current at low voltage, applied to catheter system

There is considerable present interest in developing mechanochemical materials which use the swelling of ion exchange membranes technologies suitable for the construction of electromechanical actuators of very small dimensions. Both sides of a film of perfluorocarboxylic acid were chemically plated with gold. A pulse voltage of 2.0 V between the gold electrodes on the polymer ribbon gave a quick bend 90 degree angle, 8 mm displacement toward the anode side of the ribbon in water. The displacement performance of this composite is five times larger than that of Nafion-Pt composite. This report describes in detail the remarkably large bending motion polymer-micro-actuator using perfluorocarboxylic acid film and gold plate composite.

Proton conductivity along interface in thin cast film of Nafion

Using a newly developed substrate with microelectrodes for the four-point method, the proton conductivity of a cast thin film of the Nafion® along the lateral (parallel to the interface) direction in a humidified atmosphere was measured. It was found to be much smaller than that of the as-received Nafion membrane. This difference should affect the simulation to design the gas diffusion electrodes for proton exchange membrane fuel cells (PEMFCs), because the ionic conductivity is one of the fundamental data for it.

Polymer electrolyte actuator with gold electrodes

A perfluorinated cation-exchange membrane plated with noble metals was found to bend with electric stimuli in water or a saline solution. The bent to anode is almost proportional to the applied voltage around 1.5 V, which is low enough to avoid electrolysis of water. The response is as quick as muscle. Composite of perfluorocarboxylic acid and electrodes gave larger displacement than that of perfluorosulfonic acid. Gold electrodes were deposited on the polymer electrolyte with large surface area by repeated plating, and showed larger displacement without gas evolution than platinum electrodes. Alkyl ammonium cation in the composite gave slower but larger displacement than alkali metal cations. The displacement of the strip of actuator in typical dimension of 0.2 mm thick and 10 mm long is more than 5 mm without gas evolution. A tubular actuator with four electrodes was fabricated with the newly developed components and bent more than 90 degree in 2 cm length to all directions.

Electrocatalytic oxidation of alcohols by a carbon-supported Rh porphyrin.

A Rh porphyrin on carbon black was shown to catalyze the electro-oxidation of several aliphatic alcohols (ethanol, 1-propanol, and 2-propanol) and benzyl alcohols. The overpotentials for alcohol oxidation were very low. The reaction mechanism and substrate specificity are discussed.