Capacitors as energy storage devices don’t really work. As power capture/delivery devices, however, they are excellent. Especially if the capacitors are supercaps, which can store enough charge that their very high power capture and delivery capabilities can become functional in modern electronic devices (when paired with an appropriate energy storage/conversion device).
Impedance testing is also a challenge for these very low impedance devices. Supercapacitor—or ultracapacitor, or electrochemical double layer capacitor—researchers are striving to achieve two things: stability to higher voltages, and very high (accessible) surface area to mass ratios.
On the one side, these are achieved through improved electrolytes, and on the other through improved electrodes. While these are fundamentally materials questions, the performance is electronic and electrochemical, and therefore, the testing to determine the quality of a given electrolyte or electrode is electrochemical.
Since supercaps are rated for lifetimes in the hundreds of thousands to millions of cycles, more precision is necessary when performing cycling experiments than with batteries that are only rated to last a few hundred to a few thousand cycles.
Impedance testing is also a challenge for these very low impedance devices.
We have tested quite a few supercapacitors at Gamry and worked with supercap researchers. If you are new to the field, or to Gamry, you may want to read through our application notes. Along with our application notes on low impedance EIS, Gamry has several supercapacitor-specific application notes available.
A Gamry Reference 3000 operating with EIS300 (impedance) and PWR800 (CV and cycling) is ideal for most supercapacitor testing. For larger capacitors, additional current/power may be desired, and adding a Reference 30k Booster could be helpful.
For researchers on a tighter budget, or for those who want a multi channel system (MultEchem), the Series G 750 (or 300) can be used, though PHE200 will have to substitute out the PWR800 software. If being set up as a MultEchem, we would still advise one channel of Reference 3000 to go along with (1-8) channels of Series G.
Supercaps provide a challenge to normal potentiostatic testing in that their response to a voltage step produces theoretically infinite current. This causes most potentiostats to (however briefly) hit the current rail and stay there until the instrument comes into compliance. Capacitors in general are also problematic for digital instruments when running, e.g. cyclic voltammetry—an excellent tool for supercap researchers.
Gamry has tools to work through both problems. PWR800 potentiostatic experiments (other than CV) operate in a special mode that records all current data, ensuring no fraction of the capacity is lost due to potential steps. In cyclic voltammetry, Gamry’s surface mode preserves capacitance information (as well Faradaic current from bound species), allowing it to accurately measure supercaps.