Proton exchange membrane fuel cells (PEMFC) were invented by General Electric for use in NASA's 'Gemini' manned space vehicles . 224 Also known as solid polymer electrolyte membrane fuel cells, They use a solid, acidic polymer membrane that conducts hydrogen cations through its structure when saturated with water. Most commercial cells use a perfluorosulfonic acid ionomer membrane from the Nafion family developed by DuPont. 225 A primary advantage of PEM cells is low weight in comparison to liquid electrolytes, making it the main fuel cell candidates to power electric vehicles as well as more portable power applications, although stationary applications are also possible. The disadvantage is that the membrane must be hydrated to conduct protons, which means the membrane must be kept at around 80°C below the boiling point of water (though high temperature versions above 200°C have been studied) and water management in general can be an issue . PEM fuel cells also require very pure hydrogen with minimal or no CO, which poisons the expensive platinum catalysts at low temperatures, but this becomes mostly a non-issue if the hydrogen is produced via greener methods like water electrolysis instead of steam reforming. PEMFC fuel cells have the same operating principles shown in Figure and Eq. 5-8.