| Abstract
| - Conventional theories of electrochemical kinetics, which are strictly applicable for two-dimensional surfaces,predict that the current (I) increases indefinitely with an increase in the reaction rate constant (kf), limitedonly by diffusion. By comparison, the I−t transients behave differently on electrodes with a rough and poroussurface (dimension, Df> 2) than on electrodes with a flat surface (Df = 2). The difference in the behavioris caused by the flux of the reactant toward the porous surface. The rate expression for the porous electrodeis obtained under the mass transfer conditions of partial diffusion in terms of Df, and kf, by extending thewell-known I−t behavior for the planar electrode. The expression predicts that for a porous electrode, thecurrents in I−t transients have higher values at higher kf, but only when t is close to zero. At longer times,however, the currents are higher at lower kf, where the rate is limited by partial diffusion, than at higher kf,where the rate is limited by total diffusion. The implications of long-term behavior of current and the associatedcharge (Q) are discussed in the context of electrochemical reactors such as fuel cells.
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