The kinetic parameters of the electrocatalytic reduction of the coordinated azide anions found from comparison of dc and ac measurements for the tristable Ni(II)–N3- system

The electroreduction of the azide complexes of nickel(II) is a source of tristable behavior due to the electrochemical mechanism of this process which involves the formation of the two regions of the negative differential resistances (NDR). One NDR region is due to N3--catalyzed reduction of Ni(II) to Ni(0) and the other one – due to the partial catalytic reduction of azide ligands in the presence of small excess of H+ ions. In the present paper we analyze the kinetics of the coordinated azide electroreduction for this system, using both dc and ac techniques. The following parameters of this electrode process were found from the fitting of the theoretical dc I–E   dependence, for the streaming electrode, to the experimental curve: formal potential Ef0=-1.113±0.004V, standard rate constant ks,2 = (3.51 ± 0.38) × 10−2  cm s−1, cathodic transfer coefficient αn = 0.513 ± 0.040. These results were confirmed by comparison of the experimental impedance spectra with the theoretical Nyquist diagrams, calculated according to our newly developed theory of spectra at the streaming electrodes. Based on the above kinetic data, the mechanism of the electroreduction of the protonated N3- ions, bound to Ni(II) central ion, was suggested.