Double channel electrodes and the measurement of heterogeneous reaction rates at the solid-liquid interface

The theory of collection efficiency measurements (under steady-state conditions) at double channel electrodes is extended to include the case where the species generated at the upstream electrode undergoes a heterogeneous reaction on the surface of the gap between the two electrodes. The problem is treated numerically using the Backwards Implicit method, which allows the collection efficiency to be related to the corresponding value of the rate constant for the heterogeneous process for chosen double electrode geometries and solution flow rates. The use of the technique is illustrated with experiments in which bromine, generated at the upstream electrode by the oxidation of bromide ions (in 0.5 M sulphuric acid), reacts with a cloth dyed with Direct Red 80, and is subsequently collected at the downstream electrode through transport-controlled reduction to bromide. Good agreement is found between theory and experiment.