The hanging meniscus contact: geometry induced diffusional overpotential. The reduction of oxygen in dimethylsulphoxide at Au(111)

Mass transport in the hanging meniscus configuration has been studied. The effects of this geometry on an electrochemical reaction of a gas phase species with a high solubility in the electrolyte phase have been investigated, both numerically and experimentally. The steady-state process is modelled in cylindrical polar coordinates using a fully implicit finite-difference numerical method and solved with a preconditioned Krylov subspace method. The numerical method incorporates an expanding mesh technique to optimise electrode flux error-cancelling. The nature of the meniscus boundary such as to permit the ingress of electroactive material mentioned, but not the egress of electrode reaction products is shown to result in a diffusional overpotential in the steady-state voltammogram. This observation has been examined experimentally by using the reduction of O2 in dimethylsulphoxide solution on a Au(111) single crystal electrode.