This work presents two strategies on how the disintegration of FeN4 sites by iron carbide formation can be avoided.

Ruthenium catalysts modified by selenium are of interest as a methanol insensitive oxygen reduction catalyst in a polymer electrolyte membrane fuel cell for mobile application. To elucidate the structural and chemical features of unsupported and carbon supported ruthenium nanoparticles prepared by thermolysis of Ru 3 (CO) 12 in an organic solvent with and without the presence of dissolved selenium, different bulk and surface sensitive methods such as transmission electron microscopy, X-ray diffractometry, thermogravimetry coupled with mass spectrometry, X-ray photoelectron spectroscopy, and extended X-ray absorption fine structure analysis were performed. It was found that the as-grown catalytic particles prepared without Se and handled under ambient conditions are distinguished by a ruthenium core of 4 nm size, the surface of which is covered by an amorphous ruthenium oxide/hydroxide and metal organic residues from the process of synthesis. In the presence of Se, Ru-Se and Se-O bondings have additionally been found at the surface. After heat treatment at 900 °C under vacuum, organic residues and ruthenium oxides could be removed. The particles have grown to a size of about 10 nm, the surfaces of which are covered by Ru-Se and Ru-SeO 3 units. The as-grown and heat-treated catalysts were characterized electrochemically by cyclovoltammetry, rotating disk electrode with and without methanol in the electrolyte, and rotating ring disk electrode measurements to quantify H 2 O 2 production. As expected from structural analysis, best results have been obtained with heat-treated, Se-modified ruthenium catalysts. It is proposed that in the heat-treated samples an interaction between Se 2-, [Se 2 ] 2-, and SeO 3 2decorating the surface of the ruthenium particles is responsible for the improved oxygen reduction process.

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We present transmission electron microscope (TEM) tomography investigations of ruthenium-based fuel cell catalyst materials as employed in direct methanol fuel cells (DMFC). The digital three-dimensional representation of the samples not only enables detailed studies on number, size, and shape but also on the local orientation of the ruthenium particles to their support and their freely accessible surface area. The shape analysis shows the ruthenium particles deviate significantly from spherical symmetry which increases their surface to volume ratio. The morphological studies help to understand the structure formation mechanisms during the fabrication as well as the high effectiveness of these catalysts in the oxygen reduction reaction at the cathode side of fuel cells.

Pyrolysis of chloroiron-tetramethoxyphenyl-porphyrin (FeTMPP-Cl) in the presence of iron oxalate ({plus minus} sulphur) leads to the formation of higly porous and active catalysts for the oxygen reduction reaction (ORR). In order to clarify the influence of sulphur the pyrolysis process is analyzed by thermogravimetry (TG) and by high-temperature X-ray diffraction (HT-XRD). In the absence of sulphur iron carbide (FexC) is formed which catalyses the proceeding graphitisation of the pyrolysis products. As a result catalytic active centres are decomposed by this reaction. This can be avoided by the addition of sulphur because iron monosulphide (FeS; troilite) is formed instead of FexC. Furthermore, FeS can easily be removed in a successive etching step so that nearly all inactive by-products can be removed. The results are in accordance with the higher electrochemical performance of the sulphur containing catalysts.

Carbon supported Ru x Se y O z catalysts were prepared from Ru 3 (CO) 12 and RuCl 3 Á xH 2 O as ruthenium precursors and H 2 SeO 3 and SeCl 4 as the selenium sources. Highly active catalysts for the oxygen reduction reaction (ORR) in direct methanol fuel cells (DMFC) were obtained via a multi-step preparation procedure consisting of a CO 2 -activation of the carbon support prior to the preparation of a highly disperse Ru particles catalyst powder that is subsequently modified by Se. Ultimately, an excess of Se was removed during a final thermal annealing step at 800°C under forming gas atmosphere. The morphology of the catalysts was analyzed by transmission electron microscopy (TEM) and X-ray diffraction (XRD), which shows that the catalysts consist of crystalline Ru-particles with sizes ranging from 2 to 4 nm exhibiting a good dispersion over the carbonaceous support. The corresponding catalytic activity in the process of oxygen reduction was analyzed by cyclic voltammetry (CV) and rotating disk electrode (RDE) measurements. The nature of the carbon support used for the preparation of RuSe cathode catalysts is of significant importance for the activity of the final materials. Catalysts supported on CO 2 -activated Black Pearls 2000 gave the highest ORR-activity. Se stabilizes the Ru-particles against bulk oxidation and actively contributes to the catalytic activity. An exceptional property of the carbon supported Ru-particles modified with Se is their resistance to coalescence up to temperatures of 800°C under inert or reducing conditions. Additional effects of Se-modification are the enhanced stability towards electrochemical oxidation of Ru and a lowering of the H 2 O 2 formation in the ORR.

WO 3 -modified carbon-supported bi-component ruthenium-selenium, RuSe x (Ru, 20; Se, 1 wt%), nanoparticles were dispersed in the form of Nafion-containing inks on glassy carbon electrodes to produce electrocatalytic interfaces reactive towards electroreduction of dioxygen in acid medium (0.5 mol dm -3 H 2 SO 4 ). It was apparent from the rotating disk voltammetric experiments that the reduction of oxygen proceeded at WO 3 -modified electrocatalyst at more than 100 mV more positive potential when compared to bare (WO 3 -free) RuSe x system (that had been prepared under analogous conditions and deposited at the same loading of 156 lg cm -2 ). The ring-disk rotating voltammetric measurements show that, while the production of hydrogen peroxide intermediate was significantly lower, the kinetic parameter (heterogeneous rate constant) for the oxygen reduction was higher for WO 3 -modified RuSe x (relative to bare RuSe x ). Comparison was also made to highly-efficient Vulcan-supported Pt or Pt/Co nanoparticles: while the half-wave potential for the oxygen reduction at WO 3 -modified carbon-supported RuSe x was still more negative relative to the potentials characteristic of Pt-based electrocatalysts, the oxygen reduction rotating disk voltammetric current densities (measured at 1600 rpm) were almost identical.

An improved method for the preparation of porous silica xerogels is described. Tetraethoxysilane (TEOS) as the starting alkoxide is modified by transesterification with 2-methylpentane-2,4-diol (MPD) prior to hydrolysis. The specific surface area and the pore size distribution of the calcined gels can be easily controlled by variation of the preparation parameters. Thus, a xerogel exhibiting a specific surface area of 11 08 m2 g -' was obtained after calcination at 450 "C for 4 h. The species formed by the transesterification of tetramethoxysilane (TMOS) with MPD were studied by 29Si NMR spectroscopy and chemical ionisation mass spectroscopy (CI MS).