Ran into this on the element14 site and thought it was interesting. It’s technology I don’t really know that much about. Maybe you all do.

This video is of a Polymer Electrolyte Membrane (PEM) Hydrogen Fuel Cell (green color) powering a MP3 player. A PEM water electrolyser is show on the background (blue device) to generate pure hydrogen and oxygen gases on demand from distilled water.

PEM Fuel Cell powering a MP3 player