Influence of Rh on electrocatalytic reduction of NO3- and NO2- over Pt and Pd films

Electrocatalytic reduction of NO3- and NO2- were performed using Rh-modified Pt and Pd electrodes supported on H+ conducting Nafion-117 polymer electrolyte. Cathodic electrolysis experiments showed that Pt-Rh and Pd-Rh cathodes could efficiently reduce nitrate and nitrite ions. The nitrate reduction followed first-order kinetics. The Value of constant k(1) was increased in the second experiment from 30.1 x 10(-3) min(-1) to 39.0 x 10(-3) min(-1) but in the 6th experiment; the rate constant was decreased to 10.42 x 10(-3) min(-1). The surface corrosion identified as the main reason of surface deactivation. The activity of the Pt-Rh surface was maximum at acidic pH (3.0), which was lost at basic pH (11.0). At potentials, negative than NO3- reduction peak potential, NO2- reduction currents, exceeded that of NO3- Currents. This feature eliminated the intermediate NO2- during cathodic electrolysis of NO3- at potentials negative than -1.2 V. The Pd-Rh assembly was proved to have better catalytic ability to reduce NO3- and NO2- over that of Pt-Rh assembly. (C) 2009 Elsevier B.V. All rights reserved.