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When measuring the dielectric properties of aqueous samples, the impedance of the electrode/sample interface can limit low frequency measurements. The electrode polarization problem can be reduced by increasing the effective surface area of the electrodes. In this work, impedance spectroscopy was used to characterize and compare three different electrode surfaces that can be used to mitigate this effect: platinum black, iridium oxide, and [polypyrrole/poly(styrenesulphonate)] (PPy/PSS) conducting polymer. All three materials were directly compared with a bright platinum electrode. Equivalent circuit models were used to extract the increase in the effective surface area of the electrodes: platinum black, iridium oxide and PPy/PSS increase the effective capacitance of the electrode by factors of approximately 240, 75, and 790, respectively. The practical aspects of all electrode materials are discussed. These results suggest that iridium oxide and PPy/PSS are good alternatives to the commonly used platinum black, which is prone to mechanical damage (scratches) and is potentially toxic to cells.

A pulsed-dc reactive sputtering technique was used for iridium oxide thin-film deposition. Pulsing frequency and oxygen flow were varied over several deposition cycles, regarding stimulation electrode applications. Surface and electrochemical analysis were performed for deposition evaluation. The results show the influence of the oxygen flow to the morphology and the electrochemical properties of the reactively sputtered films. Optimal surface structure and electrochemical properties for films deposited at 0.016 mbar working pressure, 100 kHz pulse frequency and 1 μs pulsewidth can be achieved at oxygen flows around 8 to 10 sccm.

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