Contribution of an Electro-Vortex Flow to Primary, Secondary, and Tertiary Electric Current Distribution in an Electrolyte

journal article in Web of Science

en

Three different approaches, known as primary, secondary, and tertiary current distributions, are employed to calculate the electric current distribution throughout an electrochemical system. Ohm's law is used for the primary and secondary, whereas Nernst-Planck equations for the tertiary. The electromagnetic field is calculated in the entire system (CaF2-based electrolyte, air, electrode, and graphite crucible), while the electro-vortex flow and concentration fields of ions are solved only in the electrolyte. The model accounts for the faradaic reaction of the formation of Fe2+ at the anode and the discharge of Fe2+ and Ca2+ at the cathodic crucible. The electric double layer (EDL) is modeled considering the generalized Frumkin-Butler-Volmer (gFBV) formula. The dissimilarity in the calculated concentration of Fe2+ between secondary and tertiary current distributions decreases with the increase of the applied voltage. A strong stirring of the electrolyte by (exclusive) Lorentz force cannot guarantee uniform concentration for all ions. As the applied voltage increases the migration may locally surpass the advection flux, leading to accumulation of ions near the anode/cathode. All current distributions (primary, secondary and tertiary) predict equal bulk electrical resistance in the absence of diffusive electric current, equal diffusion coefficients for all ions, despite the non-uniform distribution of electrical conductivity in the tertiary current distribution. The modeling results enabled us to elucidate the origin of an experimentally observed phenomenon, i.e., the formation of a thick layer of FeO under the tip of electrode. (C) 2018 The Electrochemical Society.

Three different approaches, known as primary, secondary, and tertiary current distributions, are employed to calculate the electric current distribution throughout an electrochemical system. Ohm's law is used for the primary and secondary, whereas Nernst-Planck equations for the tertiary. The electromagnetic field is calculated in the entire system (CaF2-based electrolyte, air, electrode, and graphite crucible), while the electro-vortex flow and concentration fields of ions are solved only in the electrolyte. The model accounts for the faradaic reaction of the formation of Fe2+ at the anode and the discharge of Fe2+ and Ca2+ at the cathodic crucible. The electric double layer (EDL) is modeled considering the generalized Frumkin-Butler-Volmer (gFBV) formula. The dissimilarity in the calculated concentration of Fe2+ between secondary and tertiary current distributions decreases with the increase of the applied voltage. A strong stirring of the electrolyte by (exclusive) Lorentz force cannot guarantee uniform concentration for all ions. As the applied voltage increases the migration may locally surpass the advection flux, leading to accumulation of ions near the anode/cathode. All current distributions (primary, secondary and tertiary) predict equal bulk electrical resistance in the absence of diffusive electric current, equal diffusion coefficients for all ions, despite the non-uniform distribution of electrical conductivity in the tertiary current distribution. The modeling results enabled us to elucidate the origin of an experimentally observed phenomenon, i.e., the formation of a thick layer of FeO under the tip of electrode. (C) 2018 The Electrochemical Society.

MODEL; SIMULATIONS; TRANSPORT; CATHODE

01.09.2018

ELECTROCHEMICAL SOC INC

PENNINGTON

0013-4651

165

11

E604–E615

12