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A five-cell 150 W air-feed direct methanol fuel cell (DMFC) stack was demonstrated. The DMFC cells employed Nafion 117® as a solid polymer electrolyte membrane and high surface area carbon supported Pt-Ru and Pt catalysts for methanol electrooxidation and oxygen reduction, respectively. Stainless steel-based stack housing and bipolar plates were utilized. Electrodes with a 225 cm2 geometrical area were manufactured by a doctor-blade technique. An average power density of about 140 mW cm−2 was obtained at 110 °C in the presence of 1 M methanol and 3 atm air feed. A small area graphite single cell (5 cm2) based on the same membrane electrode assembly (MEA) gave a power density of 180 mW cm−2 under similar operating conditions. This difference is ascribed to the larger internal resistance of the stack and to non-homogeneous reactant distribution. A small loss of performance was observed at high current densities after one month of discontinuous stack operation.

Serpentine (SFF) and interdigitated (IFF) flow fields were investigated with regard to their use in a direct methanol fuel cell (DMFC). The DMFC equipped with SFFs showed lower methanol cross-over, higher fuel utilisation and slightly larger voltage efficiency at low current densities. IFFs enhanced mass transport and membrane humidification allowing to achieve high power densities of 450 and 290 mW cm−2 in the presence of oxygen and air feed, respectively, at 130°C. A fuel efficiency of 90% was obtained with the IFFs in the presence of 1 M methanol feed at 130°C and a current load of 500 mA cm−2.

The structure, chemistry and morphology of commercial unsupported Pt–RuOx and in-house prepared Pt–Ru catalysts were analysed. The catalytic activity of these materials towards electro-oxidation of methanol in solid-polymer-electrolyte direct methanol fuel cells have been investigated at 130°C. The in-house prepared unsupported Pt–Ru catalyst showed higher performance with lower activation control and mass polarisation losses in relation to the Pt–RuOx catalyst. An enhancement of mass-transport properties was obtained in the presence of interdigitated flow-fields. Maximum power densities of about 0.45 and 0.29 W cm−2 in the presence of oxygen and air-feed, respectively, were obtained at 130°C. Methanol cross-over rates and fuel efficiency were determined under various conditions.

Operation of a liquid-fed Direct Methanol Fuel Cell (DMFC) working at 145°C was demonstrated by using a composite membrane made of Nafion ® ionomer and silica. The enhanced humidification conditions of the membrane–electrode (ME the measured methanol cross-over rate was 4×10 −6 moles min −1 cm −2 . A physico-chemical characterization of the cell components is also reported.

A physico-chemical investigation of catalyst–Nafion® electrolyte interface of a direct methanol fuel cell (DMFC), based on a Pt–Ru/C anode catalyst, was carried out by XRD, SEM-EDAX and TEM. No interaction between catalyst and electrolyte was detected and no significant interconnected network of Nafion micelles inside the composite catalyst layer was observed. The influence of some operating parameters on the performance of the DMFC was investigated. Optimal conditions were 2 M methanol, 5 atm cathode pressure and 2–3 atm anode pressure. Power densities of 110 and 160 mW cm −2 were obtained for operation with air and oxygen, respectively, at temperatures of 95–100°C and with 1 mg cm −2 Pt loading.

Conventional and 'paste process' methods were investigated to fabricate the membrane/electrode assembly (M&E) for application in a vapour-feed direct methanol fuel cell. A quaternary Pt-Ru-Sn-W/C and a Pt/C catalysts were employed for methanol oxidation and oxygen reduction, respectively. The structure and chemical composition of the catalysts were investigated by transmission electron microscopy (TEM) and X-ray powder diffraction (XRD). A crystalline Pt f.c.c. phase was found to prevail in both catalysts. Agglomeration and twinned particles were frequently observed in the Pt-Ru-Sn-W/C catalyst. Electrochemical investigations were performed by a.c.-impedance spectroscopy and galvanostatic polarization. The 'paste process' based assembly showed a significantly lower uncompensated resistance and an approximately two-fold power density increase with respect to the conventional assembly. According to the scanning electron microscopy analysis the observed results were attributed to improved bonding between catalysts and perfluorosulfonic membrane and to a larger extension of the three-phase reaction zone in the 'paste process' based assembly. © 1996 Chapman & Hall.

Transmission and scanning electron microscopy techniques were used in conjunction with X-ray microchemical analysis to investigate the structure, morphology and composition of direct methanol fuel cells components. Two different preparation methods were adopted for fabrication of membrane—electrode assembly. The first was based on a conventional method involving ionomer spreading on electrodes, the second method concerned the direct mixing of catalyst and ionomer. The latter method allowed improved electrochemical activity and conductivity characteristics to be obtained. According to electron microscopy and X-ray microchemical analyses, the observed results were attributed to an improved bonding between catalyst and ionomer and to a larger extension of the three-phase reaction zone at the electrode—electrolyte interface.