KINETICS AND MECHANISM OF ELECTROREDUCTION OF THE PD(II) GLYCINATE COMPLEXES AT THE PALLADIUM ELECTRODE

The electroreduction kinetics of Pd(gly)(2) and Pd(gly)(4)(2-) complex es is studied at a Pd rotating disk electrode in acidic and alkaline s olutions, respectively, in the presence of various supporting electrol ytes (NaF, NaClO4, Na2SO4). Electrodeposition of Pd occurs in the regi on of potentials where Pd starts to adsorb and absorb hydrogen, which affects especially noticeably cathodic currents in the region of the l imiting diffusion current of electroreduction of Pd(II) complexes. The slow two-electron electrochemical stage involves adsorbed Pd(II) glyc inate complexes that are parallel to the electrode surface. The compos ition of complexes that are involved in the electrochemical stage is i dentical to that of Pd(II) complexes in solution. Electroreduction mec hanisms of Pd(II) glycinate complexes at the Pd and dropping mercury e lectrodes are, on the whole, similar. However, electroreduction on Pd occurs at more negative potentials than on Hg. This is explained by a poorer adsorption of Pd(II) glycinate complexes at the Pd electrode su rface, which is due to a stronger adsorption of water molecules on Pd as compared with Hg.