Experimental

The CoTPP catalysts were prepared and impregnated on carbons of 1:1 ratio of Vulcan XC-72 and Ketjenblack EC with a total surface area corresponding to 585 m2/g. Cobalt acetate was dissolved in methanol and homogenized with the carbon support, dried and then mixed again with meso-tetraphenylporphyrin in concentrated formic acid. Following the drying, mixing and homogenization steps, the catalyst material on support underwent pyrolysis at 700 "C under nitrogen atmosphere for 5 hours (1). The total surface area after the heat-treatment was found to be 202 m2/g. The support material for the preparation of the alloys was the same as for the CoTPP. Chloroplatinic acid dissolved in deionized water with 5% non-ionic surfactant was added under ultrasonic agitation to the cobalt acetate and carbon mixture. The atomic ratio of platinum to cobalt was 1:3. The mixture was finally heat-treated at 900 *C under a flow of 1:1 volume ratio of nitrogen and hydrogen gas mixtures for 2 hours. The BET-surface area of the catalyst and carbon mixtures was 540 m2/g.

PTFE-bonded gas diffusion electrodes were prepared by rolling the active (catalyst) layer and diffusion layer separately. The layers were then rolled together on a nickel screen (100 mesh) to obtain an electrode with a total thickness of 0.55-0.60 mm after compacting, drying and sintering. The carbon support on the diffusion layer was wet-proofed with a higher amount of PTFE than the catalyst layer. The electrodes were then assembled and tested galvanostatically at a constant load of 100 mA/cm2 in 6M KOH and at 80 *C. The deterioration or decay rate of the electrode was measured versus a Hg/HgO reference electrode and recorded over a period of time until the potential reached -200 mV.

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