Simulation of interdigitated array with counter electrode in shallow electrochemical cell

Interdigitated array of electrodes (IDAE) is a popular configuration for many sensors and transducers, including microfluidic electrochemical cells. Due to the difficulty of obtaining analytical equations for IDAEs in shallow electrochemical cells, numerical simulations are commonly performed. In particular, most of these simulations don’t include a counter electrode, since this is normally not the electrode of interest, or avoid to include it, because its potential and concentrations are unknown until the cell is experimentally potentiostated. In this research, the problem of unknown concentrations at the counter electrode is addressed by using a property of coplanar electrodes, which states that the average concentration at the plane of the electrodes does not change in time and equals the initial bulk concentration. This leads to obtain an additional boundary condition for the counter electrode, which allows the numerical calculation of collection efficiency (indicator of performance of the IDAE), and which is normally not possible when the counter electrode is not included in the simulation domain. Steady-state currents and collection efficiencies were computed for several cases of cell heights, showing that there is a compromise between sensitivity (current) and performance (collection efficiency) as the cell becomes shallower.