KINETICS STUDIES OF OXYGEN REDUCTION IN ACID-MEDIUM ON NOVEL SEMICONDUCTING TRANSITION-METAL CHALCOGENIDES

The aim of this work was to investigate a Ru-cluster material with a l ow molybdenum concentration. This latter is considered to act as an ad sorption site for molecular oxygen. Transition metal chalcogenide mate rials based on Mo-Ru-Se for electrocatalytic reduction of molecular ox ygen in acid medium were chemically prepared by reacting the transitio n metal carbonyl compounds and selenium powder in xylene solvent (140 degrees C). The stoichiometry of the semiconducting electrocatalyst co rresponds to (Ru1-xMox)(y)SeOz where 0.02 < x < 0.04; 1 < y < 3 and z approximate to 2y. Kinetics parameters were obtained using steady stat e measurements with the rotating ring disk electrode (rrde) with elect rocatalyst deposited on glassy carbon disks or with the powder incorpo rated in a disk of carbon paste matrix. Oxygen reduction proceeds most ly via a four-electron transfer reaction (96%) to water as determined by the rotating ring disk electrode technique. The heterogeneous rate constants, k(1) (water formation from oxygen), k(2) (hydrogen peroxide formation) and k(3) (water production from generated H2O2) were evalu ated over the potential range of 0.70 to 0 V/nhe. Temperature dependen ce (296 K to 338 K) and kinetic parameters were evaluated It is conclu ded that minimising the molybdenum content leads to improved electroca talysis.