Kinetics and mechanism pertaining to electroreduction of ammonia complexes of palladium(II) at the mercury electrode

Kinetics of electroreduction of ammonia complexes of palladium(II) at the dropping mercury electrode are studied in solutions containing 0.01-0.5 M NaF, 0.01-1.0 M NaClO4, and approximately 0.01-1.0 M NH3 at solution pH about 10.5-11.5. It is found that the limiting current is controlled by diffusion, and the electroreduction rate of the complexes depends on neither the concentration of ammonia molecules nor solution pH. Rate constants of the slow electrochemical stage are calculated on the basis of irreversible polarographic waves. The constants are shown to obey the Frumkin equation, which accounts for the influence exerted by the electrical double layer structure on the rate of the electrochemical stage. It is concluded that ammonia complexes of Pd(II) take part in the single-electron electrochemical stage and position themselves in the outer Helmholtz plane.