It is well known that the electrode structure of a PEMFC has a huge influence on the water management and thereby on the cell performance. In this work, two MEAs – one prepared by an airbrushing technique and the other by a novel fast spray coating technique (multilayered MEA) – were analysed with respect to porosity, pore size distribution, tortuosity and their electrochemical performance. FIB nanotomography with following 3D reconstruction, SEM investigation on ultramicrotomic thin‐sections, and single cell tests were performed on these MEAs. The results show a higher porosity and lower pore size for the multilayered MEA. The multilayered MEA reaches a Pt utilisation of 1,962 mW mg–1 and a peak power density of 210 mW cm–2, whereas the airbrushed MEA only provides a Pt utilisation of 879 mW mg–1 and a peak power density of 218 mW cm–2. The Pt utilisation calculations showed in combination with the structural characterisations that a homogeneous pore structure and Pt distribution provide an advantage with regard to performance and efficiency of the PEMFC. Furthermore, the multilayered MEA may offer an advantage over the airbrushed MEA in its long term stability, which was observed in preliminary tests.

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Membrane electrode assemblies (MEA) for fuel cells require optimization of their nanoscale organization to reach performance parameters, which include enhanced power density, increased catalyst utilization and reduced cost. We applied sprayed layer-by-layer assembly to produce a high activity MEA for H(2)/O(2) fuel cells from polyaniline fibers (PANI-F). This technique produces "fast-prepared" membranes with nanoscale structure, which allows to adequately address specific tuning of their porosity, platinum loading, electronic conductivity, and proton conductivity. Pt nanoparticles were attached to the PANI-F in a reaction of selective heterogeneous nucleation. After functionalization, Pt/PANI-F were assembled with Nafion. Microscopic investigation revealed that functionalized polyaniline fibers formed a highly porous yet tight network of interpenetrating conductors connected to the catalytic Pt particles. The Pt/PANI-F LBL ultrathin MEA demonstrated a power densitiy of 63 mW cm(-2) and yielded a Pt utilization of 437.5 W g(-1) Pt which is comparable to the traditional fuel cell using carbon black as Pt support. Moreover, the amount of Pt used in this work is almost 2 times lower than for usual carbon-supported Pt catalysts.

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The performance of a low temperature fuel cell is strongly correlated with parameters like the platinum particle size, platinum dispersion on the carbon support, and electronic and protonic conductivity in the catalyst layer as well as its porosity. These parameters can be controlled by a rational choice of the appropriate catalyst synthesis and carbon support. Only recently, particular attention has been given to the support morphology, as it plays an important role for the formation of the electrode structure. Due to their significantly different structure, mesoporous carbon microbeads (MCMBs) and multiwalled carbon nanotubes (MWCNTs) were used as supports and compared. Pt nanoparticles were decorated on these supports using the polyol method. Their size was varied by different heating times during the synthesis, and XRD, TEM, SEM, CV, and single cell tests used in their detailed characterization. A membrane-electrode assembly prepared with the MCMB did not show any activity in the fuel cell test, although the catalyst's electrochemical activity was almost similar to the MWCNT. This is assumed to be due to the very dense electrode structure formed by this support material, which does not allow for sufficient mass transport.

One major issue still impeding the rapid market introduction of low-temperature polymer electrolyte membrane fuel cells (PEMFC) is the catalyst's poor long-term stability. In particular in the harsh conditions at the cathode side corrosion of the standard carbon support takes place, and high platinum loadings even speed up this process. Recent research focuses on novel, non-carbon support materials, using either electron-conductive oxides or conductive polymers. In this paper the synthesis and characterization of TiO2-supported Pt, niobium-doped TiO2-supported Pt, Sb-doped tin oxide as well as polyaniline-supported Pt as novel cathode catalysts for PEMFC are presented.

Pt utilization are comparable to a standard Pt/carbon black electrode possessing the same Pt loading in the electrode. Beside this, it is shown for the fi rst time that ITO serves as support material under real fuel cell conditions. 570 www.MaterialsViews.com www.advenergymat.de

The use of alternative support materials and special MEA preparation techniques allow a replacing of Nafion® within the electrode layer. A possible candidate for the replacement is the electron/proton conductive polymer polyaniline (PANI). This material has proven its suitability and stability as support in a fuel cell environment. The incorporation of Pt/single-walled carbon nanotubes (SWCNT) between the PANI layers can improve the electron conductivity of the system. The assembly is fabricated by the newly introduced spray coating technique, in which alternating layers of Pt/PANI or Ru/PANI, and Pt/SWCNT are sprayed directly onto a Nafion® membrane. 3D electrodes are obtained with an expected high porosity and enhanced noble metal utilization. The assembled multilayered electrodes were used at the anode side with a commercial Pt/CB-Nafion® catalyst layer at the cathode side in a real fuel cell test. The MEAs showed high Pt utilization values with an adequate power density.