By Zbigniew Stojek (auth.), Prof. Dr. Fritz Scholz (eds.)
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Extra info for Electroanalytical Methods: Guide to Experiments and Applications
4l) Substituting Eq. 41) into Eq. 47) If R e,t ~ Rd,e + R d,a' we speak of concentration polarization, while if R e,t ~ Rd,e + Rd,a' activation polarization prevails. This is meant to express that the overpotential is related either to the diffusion or the activation processes. , chemical reaction, crystallization or high resistance of a surface layer), thus there are also reaction, crystallization and resistance overpotentials. 2 Migration In a bulk electrolyte solution the current is related to the motion of ions under the influence of the electric field (potential gradient); the diffusion plays a minor role, if any, because the concentration gradient is generally small in the bulk phase.
It follows that the kinetic parameters ks and a can be determined if jK values are measured at different overpotentials. RDEs and RRDEs are powerful tools to study the kinetics of complex electrode processes (e. , multistep charge transfer reactions, coupled chemical and charge transfer reactions). General treatments of hydrodynamic problems in electrochemistry [1, 2], and details of the application of RDEs and RRDEs can be found in the literature [6-10]. 4 Reversibility, Quasi-Reversibility, Irreversibility These concepts are used in several ways.
This is possible if the initial (values at t =0) and boundary conditions (values at certain location x) are known, i. , if we have some idea (model) concerning the diffusion process. 32) Boundary conditions depend on the model of the diffusion. The most important cases are as follows. 34) X~~ lim CR(X, t) = where x ---7 00 means a large distance from the electrode where the concentration does not change during the experiment. 35) where T is the duration of the experiment. 36) This situation exists in well-stirred solutions when, beyond a given distance (6), called the diffusion layer thickness, the concentration is constant and the reservoir is infinite for the reactants.