Potentiostat in a nutshell

  • Any (known to me) modern potentiostat is in fact a potentiostat/galvanostat. It is a potentiostat when you are doing an experiment in which you control the potential and measure the current. And it is a galvanostat when you control the current and measure the potential.   
  • In a texbook of physics we read that the potential (voltage) is measured by a voltmeter and the current is measured by an ampermeter. But in a potentiostat both the potential and the current are measured by electrometers. One electrometer measures votage by comparing it to a known internal reference voltage. The other electrometer also measures voltage. To be more exact, it measures the voltage drop on a resistor having a known value of resistance and calculates the corresponding current using Ohm's law. Why? Because this is a much more reliable, fast and stable  way of determining the current than directly measure it.
  • Each (known to me) modern potentiostat controls four electrodes (the fifth lead is ground, but it is less relevant here):
  1. WE (working electrode);
  2. RE (reference electrode);
  3. CE (counter electrode);
  4. SE (sense electrode).
  • Potential is measured in the circuit RE-SE, current is measured in the circuit WE-CE. However, the most frequently used setup is three-electrode rather than four-electrode. For the three-electrode setup WE=SE. It means that you should connect electrode leads of WE (usually, red) with that of SE (usually white).
  • Sometimes two-electrode configuration is used. This is convenient when you only want to measure the potential difference while the current is zero or unimportant. This is done, for example, when you need to calibrate one RE vs. another RE. When you use the two-electrode configuration, you should normally connect WE+SE and RE+CE. Please double check if this is the case for your potentiostat, because some manufacturers use other schemes.