Fuel cell is a power generation device, and it is not like general battery nor rechargeable battery. It's seen as a new energy for the reason that it only requires hydrogen to maintain the electricity. The operating principle is that the fuel cell contains cathode and anode filled with electrolyte, and there is a permeable membrane between the two electrodes.
Hydrogen enters from the anode, and oxygen (or air) enters from the cathode. Through the catalyst, the hydrogen are decomposed into two hydrogen protons and two electrons. The protons are attracted to the other side of the membrane, and the electrons reach the cathode after forming a current through the external circuit. After the action of the cathode catalyst, hydrogen protons, oxygen and electrons form H2O, so water can be the only emission of fuel cell. The "hydrogen" fuel used by the fuel cell can come from any hydrocarbon, such as natural gas, methanol, ethanol (alcohol), electrolysis of water, biogas, etc. Because the fuel cell generates current and water through the chemical reaction of hydrogen and oxygen, it is not only completely pollution-free, but also time-saving compared to traditional battery. It is currently the most promising new energy method. In vehicles and other highly polluting power generation tools, it will be able to significantly improve air pollution and the greenhouse effect.