Physico-Chemical nanomaterials science

Investigation and mathematical modeling of time-dependent and kinetic parameters of the electrode relaxation processes
Vyshnevska Yu.P.1, Brazhnyk I.V.2
1 National Technical University of Ukraine "Igor Sikorsky Kyiv Polytechnic Institute".
37K20, Peremohy Ave., Kyiv, 03056, Ukraine. 
E-mail: vishnevsk@ukr.net
2 Gimasi SA.
4, Piazzale Roncàa, Mendrisio, 6850, Switzerland.

Investigation of complex electrochemical systems that involve intermediate products or multistage redox reactions constitute a challenging topic. Available electroanalytical methods inextricably rely on the corresponding theoretical models for the correct interpretation of the experimental data. Moreover, the model limitations are found to be increasingly pronounced while shifting from well-studied systems with bulk materials toward novel heterogeneous and nanostructured materials. Experimental methods based on the analysis of the relaxation processes have a number of advantages when compared to traditional chronopotentiometry. For instance the potential vs. time charts does not suffer from the influence of the ohmic component. In addition, it is usually sufficient to apply relatively low polarization that does not shift the electrochemical system from the stationary condition to such an extent as in case of chronopotentiometry where much higher current densities should be applied to reliably identify the transition time.
Still, available theoretical models that describe relaxation processes are found to be mainly focused on the charge distribution within double layer for the determination of its capacitance, lacking adequate representation for the diffusion portion of the relaxation. In present study, a set of relations has been obtained analytically for the analysis of the potential vs. time relaxation curves - for the case of thin electrolyte layer and for semi-infinite diffusion. Proposed approach includes a solution of the diffusion problem using Fick’s second law as a theoretical basis implying assumption that after current cut off the charge does not pass through the electrode-electrolyte interface, and the reactants concentrations obeys the Sand equation (for the galvanostatic regime of polarization). The Nernst equation has been used for obtaining the potential vs. time relation on the basis of the surface concentration vs. time dependence. Obtained relations may be used for investigation of the kinetics of electrode processes in various cases like ion interca- lation, electrochemical alloy formation, anodic metal dissolution and beyond.