Fuel cells can be classified by the type of inner screen (electrolyte). For instance, phosphoric acid fuel cells are for low temperatures. It is used in cell phones and automobile power supplies that require high currents because it is much safer. Alkali fuel cells usually contain potassium hydroxide (KOH). Methanol fuel cells are used by reacting methanol electrochemically. This type of fuel cell is a better choice for simpler system. But methanol fuel cells have low output densities as its reacting rate is slow.