ELECTROCHEMICAL REDUCTION OF 2,6-DIPHENYLPYRYLIUM CATIONS BY SPIN-POLARIZED ELECTRONS - THE HEDVALL EFFECT

The influence of transition from ferromagnetism to paramagnetism on th e activity of metal catalysts (the Hedvall effect) is explained on the basis of induced spin-polarization of adsorbed radicals. This assumpt ion was verified using the electrochemical reduction of 2,6-diphenylpy rylium cations as a model. This reduction leads to formation of unchar ged radicals that undergo fast dimerization in the bulk of the solutio n. Cations were reduced by spin-polarized electrons that have been gen erated in the conduction band of a p-GaAs photocathode, illuminated un der conditions of optical orientation. When electron spin-polarization was ''switched on'' an inhibition of the reduction rate was observed.