PEM fuel cells are popular in automotive applications due to their relatively low operating temperature and their ability to start up quickly even in below-freezing conditions. As of March 2019 there were 6,558 fuel cell vehicles on the road in the United States, with the Toyota Mirai being the most popular model. California leads the United States in hydrogen refueling stations with 43, with the California Energy Commission having access to $20 million per year in funding until 2023 to expand coverage. PEM fuel cells have seen successful implementation in other forms of heavy machinery as well, with Ballard Power Systems supplying forklifts based on the technology. The primary challenge facing automotive PEM technology is the safe and efficient storage of hydrogen, currently an area of high research activity. Polymer electrolyte membrane electrolysis is a technique by which proton-exchange membranes are used to decompose water into hydrogen and oxygen gas. The proton-exchange membrane allows for the separation of produced hydrogen from oxygen, allowing either product to be exploited as needed. This process has been used variously to generate hydrogen fuel and oxygen for life-support systems in vessels such as US and Royal Navy submarines. A recent example is the construction of a 20 MW Air Liquide PEM electrolyzer plant in Québec. Similar PEM-based devices are available for the industrial production of ozone. See also Alkali anion exchange membrane Artificial membrane Dry electrolyte Dynamic mechanical analysis Electrolysis of water Electroosmotic pump Gas diffusion electrode Isotope electrochemistry Membrane electrode assembly Polymer electrolyte membrane electrolysis Roll-to-roll References External links Dry solid polymer electrolyte battery EC-supported STREP program on high pressure PEM water electrolysis Fuel cells Electrochemistry Polymers Hydrogen technologies Membrane technology Proton