Fuel cells are modern devices that can provide heat and electricity for buildings as well as electrical power for electronic devices and vehicles, such as aircraft. Similar to a battery, they convert the chemical energy of a fuel into electricity through electromechanical reactions. However, whereas a battery will run down and need to be recharged, fuel cells continually produce electricity and heat for as long as fuel is supplied. Typically, a fuel cell consists of a matching pair of electrodes (anode and cathode) that are separated by an electrolyte. The anode is the electrode at which oxidation, or loss of electrons, takes place, whereas the cathode is the electrode at which reduction, or the gain of electrons, occurs in a fuel cell. When a flow of fuel (e.g. hydrogen) and an oxidizer (typically oxygen) are delivered by the electrodes, it results in a chemical reaction that produces electricity, water, and a small amount of heat. This fuel can come in the form of hydrogen gas or be obtained from a hydrogen source such as liquid methanol (wood alcohol), which is renewable and can be transported more easily than hydrogen gas.