50 Multiple steady states in electrochemical reactors

Abstract

The uniqueness of the isothermal steady state operation of electrochemical reactors is examined for electrocatalytic reactions with simultaneous mass transport limitations. Analysis includes planar as well as porous, flow-by and packed-bed electrodes, used for electrochemical processing and energy generation. More than one steady state can exist with complex reaction kinetics in certain potential regimes, dependent also on the convective or diffusive transport conditions. From these states, at least one is unstable and it can result in potential or current (rate) oscillations, as indicated by reported experimental observations. In channel-flow electrochemical reactors instabilities can develop at some point within the reactor due to concentration and possibly potential changes. In order to determine conditions and regions of non-uniqueness, the non-linear kinetic and transport equations are solved by polynomial expansion and orthogonal collocation in the interior of the porous electrodes. While a first-order collocation is sufficient here to demonstrate multiplicity, higher order polynomial approximations are necessary to determine the exact potential and concentration regimes for the existence of multiple steady states.