Due to the unique physico-chemical properties of hydrogen, this gas is the most attractive fuel for fuel cells. At the moment the main methods of producing hydrogen include steam reforming, partial oxidation and autothermal reforming of hydrocarbons, and conversion of biofuels. For PAMTA is the preferred technology highly selective oxidation of CO. For use with fuel cells, running on hydrogen, in transport and in mobile devices select the most optimal method of storage or a local hydrogen production.
There are several ways of storing hydrogen: production of liquid hydrogen, compressing hydrogen gas, metal hydrides, borohydride, carbon nanotubes, zeolites and metal organic frameworks. Most widely used is the storage of hydrogen in compressed form in the lung cylinders made of polymer and carbon fibers under pressure up to 700 bar. The direct use of liquid fuels in fuel cells is advantageous because of the greater density of stored energy compared to gaseous fuels. Liquid fuel, such as methyl and ethyl alcohols, relatively cheap, easy to handle, transport and store.However, it should be noted that the power density of TE liquid fuel is negligible compared to the power densities of fuel cells with gas under similar modes of operation, mainly due to the slow kinetics of the oxidation of relatively large molecules, involving up to 18 electrons and not excluding numerous adverse reactions.
Also, along with a higher density of stored energy, you need to take into account the possible environmental problems from the use of such fuels. Methanol, produced mainly by reforming of natural gas is very toxic and flammable. Best alternative for mobile devices due to a much smaller potential danger is ethanol, which can be synthesized from acetylene or obtained by alcoholic fermentation. Electrochemical oxidation of most liquid fuels is, unfortunately, mostly incomplete.For example, the main products of the electrooxidation of methanol – formaldehyde and formic acid. Formaldehyde is highly corrosive, toxic, carcinogen. In the case of ethanol the main obstacle lies in the strong C–C bonds; the products are acetaldehyde and acetic acid. Dimethyl ether can also be used as fuel because it is the simplest ether with no C–C bond and less toxic compared with methanol.However, the main products of direct dimethyl ether electrooxidation in fuel cells are all the same methanol and methylformate, and the proportion of methanol does not depend on the current, but increases with temperature. A further selection of possible fuels gives similar results.
Thus, the operation of fuel cells on liquid fuels is inevitably associated with the cleaning or processing of the reaction products.