C. Diaphragms used to be manufactured from asbestos but the material has been rejected due to health issues. Nowadays membranes are made of composites based on porous ceramic materials. Concerning main advantages of alkaline electrolysis, these are: maturity, experience and spread of the technology, possibility of construction of big cell modules even up to megawatts scale (5-25 MW) – scalability, very high durability and stability, commercialization of the technology. The most significant drawbacks are: necessity of frequent electrolyte replacement, low current density (100-300mAcm-1), poor efficiency (50-60%), use of noble metals as catalysts, liquid and corrosive electrolyte, narrow margin of dynamic load change, bad purity of generated gases.
2.2 Proton exchange membrane electrolysis (PEM)