Application of a modified flow-type microcell to evaluate local mass transport coefficients

Abstract

In this work, an electrochemical modified microcell is proposed to obtain local mass transfer coefficients at microscopic electrode areas. Microcell modification includes the use of a small diameter plastic injector (inner radius <200 μm) placed inside a commercial plastic micropipette tip in a typical microcell arrangement. The flexible plastic micropipette tip facilitates the seal with the working electrode surface, without using a silicon gasket. The outflow emerging from the plastic injector impinges on the electrode surface and renews the solution inside the tip, which is convenient for corrosion and mass transfer studies. Cyclic voltammetry for the ferrocyanide/ferrycianide reversible couple under stagnant and flow conditions is reported. Polarization curves under stagnant conditions demonstrate a diffusion control response, while under flow conditions, a steady-state limiting current is observed. An empirical equation to predict mass transfer coefficients as a function of flow conditions and geometric microcell parameters is proposed. Mass transfer coefficients ranged from 4.5 × 10−6 to 2.5 × 10−5 m/s. A simulation of the velocity profile inside the plastic micropipette tip describes the outcoming flow inside the tip and the reverse flow.