How a fuel cell works?

A fuel cell is an electrochemical energy converter. It consists of an anode and a cathode which are separated by an electrolyte (e.g. a Polymer Exchange Membrane). The anode is supplied with hydrogen and the cathode is supplied with oxygen. At the anode the hydrogen molecules are split in electrons and protons.

If anode and cathode get electrically connected, the protons move trough the electrolyte to the cathode, whereas the electrons run via an external electrical connection to the cathode while driving an electrical load. At the cathode protons and electrons react to water with the supplied oxygen (e.g. from air).