Capacitor consist of 2 oppositely charged conductive plates with dielectric layer between. It can reversibly store electric energy. Supercapacitor electrode is large surface-area porous carbon. Instead of dielectric, there is electrolyte, which consist of a salt and a solvent.
In this experiment, we are going to prepare a supercapacitor, using water cleaning filter’s active carbon that we will glue with epoxy onto an iron mesh (+ iron wire from a scouring pad). Electrolyte is sewer cleaning liquid – 10 % NaOH (5 M KOH gives better durability and power, but it might not be available in common stores). For avoiding short-circuit, shade cloth membrane (polypropylene) or paper towel is placed between the electrodes.
Electrodes and membrane are put into a Tic Tac case, plastic cover is welded with a soldering iron (case must be waterproof – check by squeezing inside water bath). Thereafter, a small hole is made into the lid and electrolyte solution is injected with the help of a plastic syringe. Now the hole is welded and the whole lid is covered with a quick epoxy glue.
NB! Sodium hydroxide is corrosive liquid and, therefore, just in case, hold such supercapacitor inside a closed vessel (not in your pocket).
Now we obtained a supercapacitor, which working potential is 1-1.2 V, capacitance 400-800 F, and short-circuit current up to 6 A. Total charging takes 0.5 to 2 h, discharging 10-30 min (1st charge takes overnight because of oxygen reduction). It may last years if is below 1.2 V and 50 0C.
Commercial supercapacitors have much higher power and higher voltage as well, but it is not possible to prepare these at home. Also, commercial supercapacitors are much more expensive per stored energy unit than this one.
There is a simple method for measuring capacitance:
1) Charge the capacitor up to 1.2 V.
2) Connect tester wires and resistor.
3) Measure the time while voltage drops to half of initial (0.6 V).
4) Calculate capacitance –> C = time / resistance.
Prepared supercapacitor can be used for powering a clock, radio or some electric motor. For higher voltage, several capacitors must be connected in series (still, it is wise to charge these connected in parallel because the capacitances may vary). You can use it as a battery for garden lamps with solar cells, to store electric energy produced by a wind generator, ignite car engine instead of a car battery …
We have calculated that the price of materials (bought from a local supermarket and a building store) needed to build one supercapacitor is 0.68 EUR (if Tic Tac case is available). So, if your mom won’t notice the missing kitchen table, then it is cheap.
Material used Amount Price / EUR
Large Tic Tac 0.96
Iron mesh 6⋅1.2 g 0.051
Scouring pad 0.058
Shade cloth 0.009
Hydroxide solution 27 mL 0.016
Active carbon (AC) 17 g 0.187
Epoxy glue 18% in AC 0.358
Total 77 g 1.64
(without Tic Tac 0.68)