Novel oxygen reduction electrocatalysts are obtained by thermolysis of chelates such as cobalt- tetramethoxyphenylporphyrin (CoTMPP) in presence of the foaming agent FeC2O4. EXAFS spectra point to the presence of molecular Fe-N4 and Co N4 centres embedded in a graphite-like matrix. The foaming agent provokes the generation of a porous material (800 m2/g) exhibiting a high fraction of mesopores (5 to 30 nm). Adding elemental sulphur to the precursors CoTMPP and FeC2O4, the catalytic activity in ORR of the final catalyst significantly improves due to an increase of mesopores and the formation of extended graphene layers in a glassy carbon-type material. The added sulphur not only facilitates the removal of inorganic by-products formed in the process of pyrolysis, but also provides an appropriate environment for catalytic centres so that the formation of undesired H2O2 is significantly decreased. In RDE measurements a catalytic activity in ORR equal to commercial platinum catalysts has been achieved.
Ruthenium catalysts were prepared employing aqueous solutions of ruthenium salts as precursors to obtain 2 nm sized metal particles homogeneously dispersed on a CO2-activated carbon support after annealing in hydrogen at 200 {degree sign}C. Selenium treatment was performed pouring the reduced product into a H2SeO3 or a SeCl4 solution prior to reduction in hydrogen at 300 {degree sign}C and 800 {degree sign}C. RuSex clusters have been formed which convert into a RuSexOy cluster after exposure to air. The presence of selenium in the cluster surface leads to a significant stabilisa-tion against oxidation of the metallic core and enables a highly selective catalytic activity towards the oxygen reduction reaction. Varying metal loading, PTFE and NAFION content in the cathode layer of a DMFC-MEA structure, best results were obtained using a metal loading of 1 mg/cm2 obtaining power densities of 20 mW/cm2 at a cell voltage of 0.4 V in a single cell.
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