The effect of electrode geometry on electrochemical properties measured in saline

The impedance, cyclic voltammetry, and charge-injection properties of rectangular, sputtered iridium oxide (SIROF) electrodes have been measured in buffered physiological saline over a range of geometric surface areas (GSA) and perimeter-to-area ratios (P/A). Electrodes with a higher P/A are expected to have a lower impedance and higher charge injection capacity (Q_inj), and both these effects were evident for SIROF electrodes with a GSA in the range 0.0023-0.0031 mm². However, the magnitude of the effect was modest. The increase in Q_inj for rectangular electrodes with a P/A ranging from 94 to 255 mm^-1 was 21-26% depending on pulse width. There was a corresponding decrease in impedance (0.1 to 10⁵ Hz) with increasing P/A and an increase in the SIROF charge storage capacity calculated from cyclic voltammetry. To assess the full usefulness of high P/A electrodes for increasing the reversible Q_inj of an electrode, measurements should now be extended to chronic in vivo preparations.