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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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.

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Pt-Ru electrocatalysts are commonly applied anode materials for low-temperature fuel cells, as the addition of ruthenium improves the CO tolerance of the otherwise CO-sensitive platinum catalysts, either by an electronic effect or by electro-oxidation via oxygen-containing adsorbates in the so-called bifunctional mechanism. However, since bulk ruthenium oxidation already takes place at potentials of less than 1.0V vs. RHE and hydrous ruthenium oxide is suggested to be the active species in the bifunctional mechanism, the amount and specific nature of ruthenium oxides play an important role in fuel cell catalysis. Two Pt-Ru catalyst systems with distinctly different Pt-Ru separation have been studied: a carbon-supported Pt-Ru alloy electrocatalyst (Pt-Ru) and a mixture of carbon-supported Pt and carbon-supported Ru (Pt/Ru). Controlled heat-treatment experiments were carried out in air atmosphere at 100°C and 500°C to study the effect of deliberate ruthenium oxidation on the catalyst structure and electrochemical performance. At a heat-treatment temperature of 100°C, the Pt-Ru alloy appears less sensitive towards oxidation than the Pt/Ru mixture, although its lattice parameter increases from about 3.880Å to 3.907Å indicating that part of the ruthenium is pulled out of the alloy phase to form a (amorphous) ruthenium oxide. After heat-treatment at 500°C in air, X-ray patterns of the Pt-Ru alloy and the Pt/Ru mixture look almost alike. However, transmission electron micrographs reveal a distinctly different separation between the Pt and the Ru oxide phase with the Pt-Ru alloy system having many more Pt/Ru neighbour sites available. Complementary XPS measurements show a higher share of electrocatalytically inactive ruthenium oxide in the Pt/Ru mixture catalyst heat-treated at 100°C. The onset of the methanol oxidation reaction (MOR) for the different catalysts increases in the order Pt-Ru < Pt/Ru < Pt independent of the treatment underlining the importance of Pt/Ru site distribution and ruthenium oxide content for the electrocatalytic activity.

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.

The structure of the interface between the gas diffusion layer (GDL) and the electrode is extremely important for the fuel cell's performance. However, although numerous methods exist for the analysis of either the GDL or the membrane-electrode assembly (MEA), not many techniques render themselves suitable for the simultaneous imaging of both components. Electron microscopy would be an option, but the preparation of cross-sections is extremely demanding due to the materials' different mechanical properties. This paper presents a sample preparation technique using the intrusion with low-melting Wood's metal, which stabilizes the porous GDL-electrode interface and enables its cutting into thin sections. Using this alternative approach, a considerable influence of the structure of the GDL on the electrode morphology could be demonstrated. In regions, where the fiber bundles from the backing recede from the membrane, delamination occurs more frequently. Furthermore, penetration of the MPL into the carbon fiber backing was observed.

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