[oneat]

I need carbon fiber as the material for electrolysis.
I heard that it's conductive and very thin.

Do you know where can I buy it from Poland and what are the prices?

[Enthalpy]

You get carbon fibres at a model-maker shop. Used to make model aeroplanes.

A good electric contact between copper and carbon fibres is difficult to obtain. Try to spread the fibres and press a lot.

These fibres are thin, but if your electrolysis produces bubbles, they will limit the contact with the electrolyte.