Convection caused by three-phase boundary reactions

When a ferrocene (Fc)-included nitrobenzene droplet was set on an electrode immersed in an aqueous solution, the electrochemical oxidation of Fc at the interface of nitrobenzene vertical bar water vertical bar electrode gave rise to the convection, which flowed from the top of the hemispherical nitrobenzene droplet on the electrode to the three-phase boundary both in the nitrobenzene and aqueous phases. The flow velocity was determined by tracing the dispersed carbon powders with a video microscope. The convection was ascribed to two asymmetries of the flow: the dragging force on nitrobenzene by the diffusing species (Fc) toward the three-phase boundary without any counter diffusion of the product (Fc(+)), and the difference in the frictional force near the oil vertical bar electrode boundary and the oil vertical bar water boundary. The convective diffusion equation was combined with Navier-Stokes' equation associated with the diffusion force of Fc in the oil phase. The combined equations were solved semi-quantitatively on the assumptions of the one-dimensional stream model. The solution explained the potential dependence of the flow velocity. (c) 2006 Elsevier B.V. All rights reserved.