On the steady-state concentration and hydrodynamic fields close to a rotating hemispherical electrode with concentration dependent viscosity and diffusivity
Eletrochimica Acta
ABSTRACT:
This work addresses the steady-state boundary layer developed close to a rotating iron hemispherical electrode in an electrochemical cell. Dissolution of the electrode in the electrolyte directly related to the current passage gives rise to a concentration boundary layer, much thinner than the hydrodynamic one, due to a Schmidt number . This boundary layer, caused by the potential applied to the electrode, leads to an increase in the fluid viscosity close to the electrode, and to a decrease in the diffusion coefficient of the medium, coupling the hydrodynamic and chemical species fields. A phenomenological law is assumed, relating the fluid viscosity to the concentration of the chemical species. A parameter appearing in this law, previously evaluated on the basis of experimental electrochemical data (Mangiavacchi et al., 2007) is assumed. The steady-state solution of the governing equations is then obtained in terms of a power series of the polar angle. The radial velocity profiles are quantitatively close to the ones developed by constant viscosity electrolytes, except at a short distance from the electrode surface corresponding to the aforementioned boundary layer, thus modifying the torque, the mass flux, and therefore, the transport-limited current with respect to a constant properties solution.