For exemplo, if I have two screen-printed electrodes made from the same ink and deposited on the same substrate. In electrode A, the working electrode is larger than the counter electrode, while in electrode B, the working electrode is smaller than the counter electrode. What effects could this difference cause on the measurement/response of the electrode?"
It all depends what your question is, but generally it is always wise to have the CE much larger than the WE. The CE is to complete the current path, and the potentiostat simply provides whatever voltage is required at the CE to give the current. Provided this does not exceed the compliance voltage of the potentiostat this is OK.
However, it is really a kinetics question. What is the rate determining step in your electrochemical cell? We require this to be the electrode reaction at the working electrode. The electrode reaction at the CE is either the back reaction (rarely) or either oxidation or reduction of the solvent (depending whether the WE reaction is a reduction or oxidation respectively, or rarely the oxidation or reduction of the CE material itself. Solvent electrolysis reactions usually have relatively low exchange current densities (small K(0)). If the cell current is to be limited by the working electrode reaction, we need a large CE to ensure that the CE reaction is not limiting. The CE needs to be able to *instantly* supply whatever current the WE needs, and to do so without requiring voltages higher than the compliance voltage of the potentiostat. A further consideration is that since both water oxidation and reduction generate gaseous products, a small CE is more likely to lead to bubbles, as the rate of gas generation exceeds the solubility and rate of diffusion. Bubbles are usually undesirable and lead to noisy, messy signals.
If you're doing electroanalytical work, the response of your voltammograms is affected when the size of your working and counter electrodes is not consistent. Although it is generally preferable for the counter electrode to be larger than the working electrode, if your working electrode doesn't always have the same size, the area changes — and so does the signal. You'll never get truly reproducible experiments under those conditions. Likewise, the distance between electrodes will vary. Try to fix your variables: the size of your electrodes and the distance between them. Speaking from experience... Greetings from Ecuador.
- Badges
- Science topic