Catalytic Electrochemical Reduction of Perchlorate over Rh-Cu/SS and Rh-Ru/SS Electrodes in Dilute Aqueous Solution

Mono metallic (Mo, Ru, Rh, Cu, and Pd) and bimetallic (Rh-Cu and Rh-Ru) catalysts supported on stainless steel (SS) were prepared for perchlorate reduction. Results showed that perchlorate reduction followed a decreasing order: Rh/SS>Cu/SS>Ru/SS>Mo/SS>Pd/SS>SS. Bimetallic catalyst SS-supported electrodes exhibited significant perchlorate reduction; perchlorate reduction over Rh-Cu/SS (78% reduction) was greater than that on Rh-Ru/SS (60% reduction). Chloride production was high at 95%. The imbalance in the chlorine mass could be attributed to the adsorption of perchlorate on the electrode and chlorine formation. Metal oxides and elemental metal dominated the catalyst surface based on X-ray photoelectron spectroscopy (XPS) analysis. X-ray diffraction (XRD) spectra showed the presence of both crystalline and amorphous metallic catalysts. The free energy of perchlorate adsorption on the Rh-Cu/SS was around 25 kJ/mol. The activation energy (Ea) of perchlorate reduction on the Rh-Cu/SS electrode was 19.5±1.3 and 110.9±0.8 kJ/mol in the temperature range of 303–343 K and 283–298 K, respectively. A proposed perchlorate reduction pathway was developed and successfully used to predict the reaction kinetics. No other oxyanions of chlorine, such as ClO3−, ClO2−, or ClO−, were detected as intermediates during perchlorate reduction.