Rhodium deposits on pyrolytic graphite substrate:: Physico-chemical properties and electrocatalytic activity towards nitrate reduction in neutral medium

The electrodeposition of metallic rhodium on pyrolytic graphite from 10 mM Na3RhCl6 + 0.5 M NaCl aqueous solution was studied by potentiostatic method with the use of a double-pulse technique involving nucleation and growth pulses. Physico-chemical properties of Rh deposits were investigated by electrochemical methods and scanning electron microscopy. The activity of Rh-modified graphite electrodes towards nitrate reduction in neutral medium was demonstrated, the activation energy of nitrate reduction and NO3 Langmuir adsorption constant on Rh deposits were determined. The use of double-pulse technique resulted in enhanced surface coverage in comparison with usual potentiostatic deposition and in decreasing the mean particle size down to 30 nm, while the specific catalyst surface area attains 32 m(2) g(-1). The increase in the nucleation pulse duration from 20 to 100 ms enhances the mass catalytic activity towards NO3- reduction, which reaches 175 A g-1 for the best samples. Irrespectively of electrodeposition parameters, only NH3 and NO2- were detected as nitrate reduction products. The rate of NO3 destruction was equal to 5.4 mol g(Rh)(-1) h(-1) which is much higher than that of most of Pd/Cu-based nitrate hydrogenation systems and Ag/TiO2 photocatalysts. (c) 2005 Elsevier B.V. All rights reserved.