Development of energy storage systems that can be used to study principles of supercapacitors, fuel cells,
and batteries. Pupils can assemble the energy source and use it to drive a model car, for example.

A homemade aluminum-air battery
A nice scientific experiment, maybe it is the future energy source of all vehicles.
2 carbon cathodes 14 Eur

Consist of nanoporous carbon press-glued onto a special alloy metal mesh. 4.4 x 7 cm active area (fits into a large Tic-Tac box). Suitable for a DIY aluminum-air battery experiment with NaCl or 10% NaOH electrolyte (sewage cleaning liquid).
Shipping cost (up to 5 packs) to USA: Letter (6-8 days) ~9 Eur, Courier (2-3 days) ~100 Eur
to Europe: Letter (2-7 days) ~8 Eur
anywhere else: Letter (5-30 days) ~9 Eur
contact: (specify product, nr of items, and delivery address)

A homemade microbial fuel cell
Free energy from wastewater. Power is a few mW, but fuel is something you pay to get rid of.
Great scientific project at home or school.
Also ask for the whole kit including vessel.

Two electrodes for a microbial fuel cell 17 Eur.

Anode and cathode having diameter of 7.6 cm and 8 cm, respectively. Suitable for a DIY microbial fuel cell, just find a vessel and some fuel (wastewater, mud, waste food). Anode is packed airtightly, oxygen removed. Instructions are here.

A homemade supercapacitor
A full kit containing everything to make a supercapacitor at home is under development. Scientific project at home or school to study electric energy storage.
Supercapacitor kit

Electrochemical characteristics with KOH electrolyte is shown here.