Sun 10 Dec 2006
In a follow up to my previous potentiostat post, here is the three-electrode model. In situations where the electrolyte is sparse, the uncompensated solution resistance between the working electrode (WE) and counter electrode (CE) can unintentionally reduce the amount of current seen. For these situations, a third electrode called the reference electrode is introduced. The idea here is that you supply a potential on Vin and the potentiostat sets the working electrode potential to whatever it needs to be so that the potential difference between the working and reference electrode is equal to Vin. At the same time, the counter electrode is held at ground via current follower to track the required current to keep the working electrode at the desired potential. Below is a simple cyclic voltammagram of a iridium-oxide working electrode with a silver/silver-chloride reference and counter electrodes. The electrolytes are phosphate-buffered saline and saline. The scan waveform is triangular going from +0.6V to -0.6V with scan rate of 50mV/s. You may notice some strange lines crossing the plots, these are sampling artifacts. On a circuit design note, U1 and the peripheral resistor network can be replaced with an Analog Devices AMP03 so that there are less external components and the resistors are matched.
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