ELECTROREDUCTION OF NITRATE AND NITRITE ANIONS ON PLATINUM METALS - A MODEL PROCESS FOR ELUCIDATING THE NATURE OF THE PASSIVATION BY HYDROGEN ADSORPTION

A study of the dependence of the electroreduction of NO3- anions on a platinized platinum electrode on the solution pH, the concentration of NO3- ions and the adsorption of Cs+, La3+ and Cd2+ cations and Cu adatoms was performed with the aim of elucidating the mechanism of the process and, in particular, the nature of the extremal character of the rate dependence on potential. For comparison, the stationary and potentiodynamic polarization curves for the electroreduction of NO2- anions on platinum and NO3- anions on palladium and rhodium electrodeposits were measured. The behavior of NO3- and NO2- anions on platinum was similar, and an increase in the electroreduction rate of NO3- anions during the transition from Pt and Pd to Rh was observed. The latter behavior was explained by assuming that the metal-nitrogen bond was stronger in the case of rhodium. Possible reasons for the passivation of cathodic processes on platinum when complete hydrogen surface coverage is approached are discussed.