hydrophobic structure prevents the electrolyte from leaking into the reactant gas flow channels and ensures diffusion of the gases to the reaction site. The two layers are then pressed onto a conducting metal mesh, and sintering completes the process. Further variations on the alkaline fuel cell include the metal hydride fuel cell and the direct borohydride fuel cell. Advantages over acidic fuel cells Alkaline fuel cells operate between ambient temperature and 90 °C with an electrical efficiency higher than fuel cells with acidic electrolyte, such as proton exchange membrane fuel cells (PEMFC), solid oxide fuel cells, and phosphoric acid fuel cells. Because of the alkaline chemistry, oxygen reduction reaction (ORR) kinetics at the cathode are much more facile than in acidic cells, allowing use of non-noble metals, such as iron, cobalt, or nickel, at the anode (where fuel is oxidized); and cheaper catalysts such as silver or iron phthalocyanines at the cathode, due to the low overpotentials associated with electrochemical reactions at high pH. An alkaline medium also accelerates oxidation of fuels like methanol, making them more attractive. This results in less pollution compared to acidic fuel cells. Commercial prospects AFCs are the cheapest of fuel cells to manufacture. The catalyst required for the electrodes can be any of a number of different chemicals that are inexpensive compared to those required for other types of fuel cells. The commercial prospects for AFCs lie largely with the recently developed bi-polar plate version of this technology, considerably superior in performance to earlier mono-plate versions. The world's first fuel-cell ship, the Hydra, used an AFC system with 5 kW net output. Another recent development is the solid-state alkaline fuel cell, utilizing a solid anion exchange membrane instead of a liquid electrolyte. This resolves the problem of poisoning and allows the development of alkaline fuel cells capable of running on safer hydrogen-rich carriers such as liquid urea solutions or metal amine complexes. See also Gas diffusion electrode Glossary of fuel cell terms Hydrazine Hydrogen technologies References External links Developers AFC Energy Independent Power Gencell Energy Fuel cells ja:燃料電池#アルカリ電解質形燃料電池 (AFC)