ELECTROCHEMICAL STUDY OF THE HETEROGENEOUSLY CATALYZED REACTION BETWEEN N,N-DIMETHYL-P-PHENYLENEDIAMINE AND CO(III)(NH3)5CL2+ AT MONOMETALLIC AND BIMETALLIC SURFACES OF SILVER AND GOLD

The mechanism of the heterogeneously catalysed reaction between N,N-di methyl-p-phenylenediamine and CoIII(NH3)5Cl2+ at silver, gold and silv er-on-gold (Ag/Au) discs has been studied by means of electrochemical methods. Both the mixed (or mixture) potentials and the mixture curren ts were determined by recording the current-potential curves of the re actants. Silver halide, formed during the reaction, was determined by subsequent galvanostatic reduction. The reaction at silver was strongl y inhibited by the formation of silver halide whereas the reaction at gold was inhibited by adsorption of the organic compounds as well as b y iodide. At Ag/Au discs almost no inhibition occurred. The explanatio n is that the reduction of the cobalt complex takes place predominantl y at the silver surface whereas the simultaneous oxidation of the p-ph enylenediamine occurs on the gold. In this way the formation of inhibi ting silver halide is suppressed as well as the inhibition caused by t he adsorption of p-phenylenediamine.