The chemical reaction that occurs in fuel cells to produce energy is an electrochemical reaction. In a typical hydrogen fuel cell, hydrogen molecules react with oxygen molecules to produce water, electricity, and heat. This process occurs in two electrodes: the anode and the cathode. At the anode, hydrogen is oxidized, releasing electrons, while at the cathode, oxygen is reduced by accepting those electrons. The movement of electrons through an external circuit generates electricity. Fuel cells are considered a clean energy technology due to minimal emissions, primarily water vapor.