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 k1 was increased in the second experiment from 30.1 × 10−3 min−1 to 39.0 × 10−3 min−1 but in the 6th experiment; the rate constant was decreased to 10.42 × 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.

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