Thin Layer Semiconducting Cluster Electrocatalysts for Oxygen Reduction

Previous studies have demonstrated that, semicon-ducting mixed cluster Chevrel compounds (Mo4Ru2Ses) catalyze the reduction of molecular oxy-gen in acid medium (1). For cat-alyt ic purposes, it is interesting to produce this type of compound in thin layers. In order to achieve this, triruthenium dodecarbonyl and molybdenum hexacarbonyl were mixed with selenium powder in xylol under an argon atmosphere. This mixture reacted at ca. 140 ~ during 20 hours to produce thin layers of MOxRuySe z with a thickness of less than 1 I~m which deposited on different substrates (e.g., ITO, glassy carbon, glass, etc.). The product proved to be chemically stable (e.g., not attacked by aqua regia and electrochemically stable in laboratory exper iments). Different materials were ob-tained. When an element ratio Mo:Ru:Se of 4:2:8 was added moderate oxygen reduction ac-tivity was obtained as shown in the Tafel plot of figure 1 (curve a). After increasing the initial ruthenium concentration to an element ratio of 4:6:9 a clear improvement of the catalytic activity was obtained (curve b). A platinum electrode is also shown for comparison. The X-ray analysis of the material in powder form did not show significant diffraction peaks and suggested a largely amorphous st ructure or nanocrystall ine composition. High resolution transmission electron microscopical (TEM) studies turned out to be more instructive: figure 2(a) shows TEM images of the catalytic layer responsible for the char-acteristic Tafel curve (b) in fig