DMFC is one of the fuel cells that generate electricity using aqueous methanol solution as a fuel and oxygen or air as an oxidizing agent. By operation of DMFC, methanol is oxidized by oxygen to produce carbon dioxide and water. A single cell of DMFC is composed of an MEA that is held between separators. MEA is manufactured by laminating anode and cathode on both sides of polymer electrolyte membrane which is made of sulfonized perfluorocarbon polymer or hydrocarbon polymer. Recently limiting current has increased up to 600 mA/cm² owing to the advance in MEA technology. DMFC can be downsized because they use liquid fuel directly, which is more preferable for applications such as portable and mobile use. However, there are many technological problems that should be overcome to realize DMFC system to be used for those applications. Especially, a breakthrough in materials research should be necessary in order to decrease methanol crossover and to improve catalytic activity.

Proton conducting electrolyte membranes are key elements for advanced PEFC technologies, which are promised to reduce emissions from fossil fuels because of their higher efficiency. Technological options such as high temperature cell operation and/or direct methanol fuel cells (DMFC) encourage the development of more functionalized membranes. In this report, new class of amphiphilic organic/inorganic nano-hybrid membranes have been synthesized through sol-gel processing of bridged polysilsesquioxanes. The membrane doped with acidic moieties such as 12-phosphotungstic acid (PWA) show large protonic conductivities and was found to be flexible as well as thermally stable due to the temperature tolerant inorganic frameworks in the macromolecules. The hybrid membranes with the proton conductivity exceeding 10^{- 2} S/ cm can be used for an application in the PEFC electrolyte membrane.

A Micro-Polymer Electrolyte Fuel Cell (µ-PEFC) with “alternating structure” was demonstrated. The alternating structure has a series of single cells formed in one plane, and the polarization of each single cell is alternately inverted. This structure has self-assembled cell interconnection on micromachined silicon substrates. The µ-PEFC has a size of 20 × 27 mm, and consists of 9 cells with a size of 1.2 × 15 mm connected in series. The voltage of a single cell was about 0.4 V, when a 10 MΩ load was connected to the cell. The potential of a six-stacked cell was, however, only 0.18 V under the same testing condition as used in the single cell test. This is probably caused by cross-talk and hydrogen leakage between the electrodes which are formed on the same substrate.

The performance of the liquid-feed DMFC system at near-ambient temperature was investigated for mobile applications. The open circuit voltage and the current density at 0.4 V of the liquid-feed DMFC system decreased with the increasing methanol flow rate because of methanol crossover. The open circuit voltage of the liquid-feed DMFC system monotonously decreased with the increasing methanol concentration. At a temperature of 300 K and a methanol flow rate of 0.1 mL/min, the open circuit voltage of 0.58 V at the methanol concentration of 0.5 mol/L decreased to 0.46 V at the concentration of 5 mol/L. Meanwhile, the current density was a maximum at 1.5 mol/L but dropped at the concentration of 0.5 mol/L due to a methanol deficiency.

The effect of Nafion loading with spray treatment in the catalyst layer for the Direct Methanol Fuel Cell (DMFC) was investigated. The spray treatment of the membrane electrode assembly (MEA) was effective, and improved the short circuit current up to 378 mA/cm² at a 0.05 mg/cm² loading when compared to 307 mA/cm² for the untreated MEA. The impedance of the MEA was determined by ac impedance spectroscopy. The diameter of the arc at low frequency was decreased by increasing the Nafion loading. The optimum Nafion loading value was 0.05 mg/cm². The cell performance was dependent on the mass-transfer resistance was caused by the methanol chemisorption.

A composite membrane consisting of three-dimensionally ordered macroporous silica and ion exchange gel polymer electrolyte was successfully prepared in this study. Firstly, the macroporous silica was prepared by a filtration of a mixed suspension of colloidal silica and monodispersed polystyrene beads followed by a heat treatment. Then, a gel electrolyte was injected into pores to form the composite membrane. The obtained membrane had 1.7 cm in a diameter and exhibited 1 × 10⁻⁴ S cm⁻¹ ion conductivity at 40°C under 80% humidity. This low conductivity of the composite membrane may be strongly related to a skin layer of the prepared composite membrane.

A fabrication of membrane electrode assembly (MEA) was conducted by using an electrophoretic deposition process. In this process, carbon particles and Nafion^® polymer were moved according to the potential gradient and deposited on the Nafion^® membrane with strong adhesion. The polarization curve for the prepared MEA was measured using humidified oxygen and hydrogen at 80°C. The result exhibited that the MEA prepared by the EPD was comparable with that produced by a conventional hot-pressing process.

A glassy carbon electrode modified with bilirubin oxidase (BOD) cross-linked to an Os redox polymer functions as a bio-cathode for a 4-electron reduction of O₂ under neutral conditions. On the other hand, a glassy carbon electrode modified with pyrroloquinoline quinone-dependent soluble glucose dehydrogenase (sGDH) or glucose oxidase cross-linked to an Os redox polymer functions as a bio-anode for a 2-electron oxidation of glucose. A prototype of a one-compartment glucose/O₂ biofuel cell without a separator was constructed by using the BOD-modified cathode and the sGDH-modified anode. The maximum power density was 0.058 mW cm⁻². The loss in the power is discussed in terms of thermodynamics and kinetics.

Poly(2,5-benzimidazole) (ab-PBI) membranes were characterized for use as electrolytes in fuel cells operating at elevated temperatures (100 to 200°C). The conductivity of phosphoric acid-doped ab-PBI was as high as 0.12 S cm⁻¹ at temperatures below 120°C, but it decreased to 0.025 S cm⁻¹ above 150°C due to a dehydration of the doped acid. Using the H₃PO₄-doped ab-PBI, H₂/O₂ fuel cell could be operated at 120°C with a low humidification of reactant gases, although it was necessary to keep the acid-doping level high in both the membrane and the electrodes.

Gas evolution rate at the anode of a direct methanol fuel cell with liquid feeding was measured at low temperatures below 353 K, and also gas analysis was made by means of gas chromatography and mass spectroscopy. It was confirmed that the main component of the gas was CO₂ and the evolution rate, at relatively high current density where CO₂ dissolving rate could be neglected, was agreed well with that calculated with the assumption of complete oxidation of methanol.

A pore-filling electrolyte membrane was prepared by plasma-graft filling polymerization as an electrolyte membrane for a direct methanol fuel cell. The pores of a porous poly(tetrafluoroethylene) substrate were filled with poly(acrylic acid) grafted polymer. Grafted polymer formation through the substrate was homogeneous and the pore-filling membrane was obtained by this technique. The membrane showed low methanol permeability, and, in addition, heat resistance to 180°C was achieved during the operation period.

We synthesised a new mesoporous carbon consisting of aggregates of uniformly sized spherical particles are aggregated. The structure is directed by the carbonisation of sucrose in the pores of mesocellular foam silica. The BET specific surface area and the transmission electron micrograph demonstrate that the carbon particles are not solid spheres but hollow ones whose diameter and the thickness of the wall are 30 and 3 nm, respectively.

A composite of zirconium hydrogen phosphate, HZr₂(PO₄)₃·nH₂O (HZP), and proton conducting glass was investigated as an inorganic solid-state proton conductor for a direct methanol fuel cell (DMFC) working at higher temperatures around 200°C. It was possible to prepare a composite of HZP and 5P₂O₅-95SiO₂ glass with porosity of 12-15%. The apparent proton conductivity of HZP/5P₂O₅-95SiO₂ glass composite was about 10⁻⁴-10⁻³ S cm⁻¹ under 100°C and 10⁻⁸-10⁻⁷ S cm⁻¹ at 200°C.

The quick startup/shutdown operation of solid oxide fuel cells (SOFC) was demonstrated. It took only 15 seconds to startup with butane as fuel. The demonstration confirmed that a small tubular cell could endure thermal stress caused by rapid heating up to operating temperature. A new stack concept of small tubular cells was also proposed for quick startup application. A three-cell prototype stack equipped with a rapid heating burner was examined.

We have studied the electrochemical performance of a direct 2-propanol fuel cell (D2PFC) having a Pt5:Ru5 anode comparatively with those using primary alcohols at room temperature. First, cyclic voltammograms of the alcohols were recorded in aqueous solution at a Pt-Ru sputtered electrode in an atomic ratio of 50:50. As a result, 2-propanol exhibited (i) the most cathodic potential where oxidation current starts to flow, and (ii) the largest current density. Next, by employing a single cell with an anode catalyst of the same Pt-Ru composition, the I-V properties of 0.5 mol dm⁻³ fuel concentration exhibited similar trend as observed in CVs. However, methanol exceeds 2-propanol at high power operation. The inversion phenomenon is proven to be an accumulation of acetone, which is the only oxidation product of 2-propanol around the anode surface. Interestingly, by using a concentrated fuel of 5 mol dm⁻³, direct 2-propanol fuel cell exceeded direct methanol fuel cell even at high power operation. This demonstrates that 2-propanol could advantageously substitute for methanol as a high-power fuel in a fuel cell at room temperature operation.

We have developed a porous micro-ring electrode, which conventionally represents a part of membrane electrode assembly (MEA) of proton exchange membrane (PEM) fuel cell. The porous micro-ring electrode has a PEM/electrocatalyst layered structure at a tip of a glass capillary. This electrode has proven to exhibit electrocatalytic properties. Moreover, the methanol oxidation reaction at the PEM/electrocatalyst could be measured and evaluated.

A small direct methanol fuel cell (DMFC) pack with a series connection of eight cells for portable applications was designed and fabricated. The maximum output power achieved with a 10% methanol fuel and air breathing was 2 W. This DMFC pack was tested as the electrical power source of a portable phone. Using a buffer capacitor greatly reduced the voltage change during talktime to 0.2 V, making it possible to make calls by using the phone with the DMFC pack.

Bismuth ruthenium oxide with the pyrochlore structure was examined for the cathode of SOFC. The power generating characteristics of the SOFC was examined for the single cell of the SOFC constructed with the pyrochlore cathode with a composition, Bi₂Ru₂O₇, and the yttria stabilized zirconia as the electrolyte. The characteristics of the cell was examined at various temperatures; the pyrochlores showed high cathode performance and high power density even at low temperatures below 800°C. The pyrochlore is an attractive electrode for SOFC of low-temperature operating system.

Small size DMFC power units for driving portable electrical devices were constructed by improving power density and making compact system. In order to reduce methanol crossover, membrane modification by EB irradiation was performed. It was confirmed that PDAs can be driven using our compact fuel feeding system.

Direct methanol fuel cell (DMFC) is expected as a candidate for portable power supplies because it is able to constitute a miniature fuel cell without a reformer. In this study, a new type of DMFC is reported which is composed of tubular type polymer electrolytes. As the anode catalyst layer, Pt-Ru catalyst-supported carbon fibers were examined by cyclic voltammetry in order to select suitable one. Also, the optimization of Pt-plated electrode was pursued for the cathode catalyst layer. By selecting the carbon fiber and optimizing the Pt-plating, the output power 0.9 mW/cm² of the tubular-type micro DMFC was attained.

Direct alcohol fuel cells were studied by using OH form anion-exchange membrane. The performance of the cell fueled with ethylene glycol was higher than that fueled with methanol, due to smaller polarization for electro-oxidation of ethylene glycol than that of methanol. Hence, ethylene glycol is superior to methanol in direct alcohol fuel cells employing anion-exchange membrane as electrolyte.

Direct type polymer electrolyte fuel cell (PEFC) using methoxy fuels such as methanol, dimethyl ether (DME), dimethoxy methan (DMM) and trimethoxy methan (TMM) were investigated. The performances of the direct DMM fuel cell and the direct TMM fuel cell were almost equal to that of the direct methanol fuel cell (DMFC). The performance of the direct DME fuel cell using Pt-Ru catalyst on the anode was lower than that of the other methoxy fuel cells. Decomposition species from the DMM and TMM fuel cells contained large quantities of methanol. The former also contained formaldehyde, while the latter contained formic acid, as expected from hydrolysis of the fuels. Decomposition species from the DME fuel cell did not contain methanol and formaldehyde but contain formic acid, the quantity of which increased with current.

Supported PtRu electrocatalysts on carbon black were prepared using three different combinations of Pt and Ru complexes in order to investigate the precursor effects on the methanol oxidation activities at room temperature. The CO adsorbed on the electrode surface was oxidized at an extremely lower potential using the catalysts prepared from (1,5-cyclooctadiene) dimethylplatinum (II) (Pt(C₈H₁₂)(CH₃)₂) and RuNO(NO₃)_x or Pt(NH₃)₂(NO₂)₂ and RuNO(NO₃)_x than that from H₂PtCl₆ and RuCl₃. The catalyst obtained from the combination of Pt(C₈H₁₂)(CH₃)₂ and RuNO(NO₃)_x showed higher current densities for the methanol oxidation for all metal loadings than the other catalysts.

In order to realize an electrolyte membrane for DMFC having low methanol permeability, suppression of methanol permeability of Nation by introducing polyaniline (PAn) was attempted. The membrane obtained by the electropolymerization of aniline at Nafion-coated Pt electrode had bi-layered morphology, and it showed lower ionic conductivity and lower methanol permeability compared with those of Nafion, compared to PAn introduced Nafion membrane by the chemical oxidative polymerization of aniline in Nafion. The PAn introduced Nafion by chemical oxidative polymerization showed superior characteristics to Nafion from the viewpoint of conductivity and methanol permeability.

In order to realize an electrolyte membrane for DMFC having low methanol permeability, addition of ionic conductivity by the introduction of polypyrrole into engineering polymers was attempted. By the chemical oxidation of pyrrole monomer inside the polymer matrix, the composite films of polypyrrole (PPy) and engineering plastics were prepared. By the PPy introduction to poly(ethyleneterephthalate) (PET) the ionic conductivity across the film was increased. Methanol permeability was also examined to assess the performance of the film as the DMFC electrolyte. The composite film of PPy/PET, which was formed by pyrrole oxidation, showed better performance of high ionic conductivity and low methanol permeability.

Proton conductive inorganic-organic hybrid membranes were prepared from 3-glycidoxypropyltrimethoxysilane, tetramethoxysilane and orthophosphoric acid by the sol-gel method. The ionic conductivity of the hybrid membranes increased with an increase in the content of orthophosphoric acid in the membranes, and was about 1 × 10⁻² S cm⁻¹ at 30°C under relative humidity of 80%, for the membranes with a molar ratio of P/Si = 1.5. Test cells were fabricated using the hybrid membranes with composite electrodes prepared from the precursor sol of the hybrid membranes and Pt black powders, and these cells were confirmed to work as a fuel cell.