REDUCTION OF PERCHLORATE ON RHODIUM AND ITS SPECIFICITY TO SURFACE CRYSTALLOGRAPHIC ORIENTATION

Catalytic properties of Rh(100), Rh(111) and polycrystalline rhodium electrodes in the process of perchlorate reduction in aqueous media have been studied. The reduction rates obtained under various conditions, as well as results of ultra-high vacuum (LEED, Auger) surface analyses of emersed Rh(100) surfaces, have provided evidence that surface chloride is the main reduction product. A temperature dependent chloride desorption has also been found via measurements of steady-state reduction currents and through chemical analysis of the electrolytic perchlorate solutions. The data demonstrate that under transient conditions, that is, when surface chloride formation determines the reaction rates, the reduction current decreases in the order: Rh(100) > Rh(poly) > Rh(111). Under steady-state conditions the rate order is: Rh(100) almost-equal-to Rh(poly) > Rh(111). The reduction process is pH dependent and, as a prerequisite, requires a contact adsorption of perchlorate on the metal sites. Prospects for using rhodium as a catalyst or catalytic additive in electrocatalysis of inorganic species are discussed.