I always liked to design/make things smaller than they originally are.
This is why I made this Water splitting cell, in a ear-drops container.

The cell consists of two stainless steel rods, pushed throught the side of the container,
with a screw terminal connected to them.
On the terminal, a pair of wires a soldered, making it easy to connect to a powersupply.

The coin is a danish 5DKK, it has a diameter of 28,4 MM (1.12 inches).

After adding the water and a couple of drops of NaOH, the cell was almost filled to the top.
Connecting power to the cell, at 12V it draws around 1.5Amps.

I haven’t got a build guide, but whenever my ears have a defect again, I’ll do another, to show you how it’s done.

A video to show that it’s real:

Always remember safety when you do things like this.

I’m not responsable for any damage to you or you equipment.