Mechanism of the electroreduction of Ni (II) ions on mercury electrodes catalyzed by pyridine and its derivatives: Nicotinamide, N,N-diethylnicotinamide and nicotine: Concept of parallel heterogeneous catalytic reactions

The theory of the polarographic catalytic currents (mechanism CE) has been developed for the system: Ni²⁺-L-X^p- where L: pyridine (Py), nicotinamide (NA), N,N-diethylnicotinamide (DEN), nicotine (NC) and X ^p-: NO^- ₃, AcO^-, HPO^2- ₄ . The theory is based on the kinetic parallel heterogeneous catalytic reactions: equation presented with the use of Langmuir's adsorbed isotherm. The kinetic equations obtained for average and instantaneous currents allowed to determine the Langmuir's parameters (NA<DEN<NC), kinetic parameters and the contribution of reactions 1a and b to the summary catalytic currents. The k″_h value rises with the increase of the NiX ^2-p stability constant. The correlation k″ _h≤k″_h was explained by the additional effect of the field electrode through X^p-. These effects base the reaction 1b instead of accepted early alternative reaction of the ligand exchange. In spite of the fact that k″_h≤k″_h, the contribution of the reaction 1a in the summary catalytic current attained more than 60% (Py, DEN) due to the influence of the ψ₀ potential.