A polymer membrane is used as an electrolyte in this type of a fuel cell. The membrane must be conductive to hydrogen ions (protons). and must be moistened to function properly. Sulfonated fluoropolymers (Nafions) are most commonly used. Platinum is often used as a catalyst, applied in the form of a gas-diffusion layer, to create a gas-diffusion electrode with a fixed catalyst. Hydrogen or methanol is used as fuel and oxygen or air as an oxidizer. The operating temperature of this type of cell is up to 90 °C, making it the best option for powering vehicles.