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Currently the efficiency for hydrogen production by water electrolysis of electricity amounts to 75 to 85% [19] with potential up to 93% until 2030. [25] Efficiency for methanol synthesis of hydrogen and carbon dioxide currently is 79 to 80%. [19] Thus the efficiency for production of methanol from electricity and carbon dioxide is about 59 to 78%.
providing water along with methanol would make the fuel supply more cumbersome, so water has to be recycled in a loop; CO 2 has to be removed from the solution flow exiting the fuel cell; water in the anodic loop is slowly consumed by reaction and drag; it is necessary to recover water from the cathodic side to maintain steady operation.
The fuel cartridge stores the methanol fuel. Depending on the system design either 100% methanol (IMPCA industrial standard) or a mixture of methanol with up to 40 vol% water is usually used as fuel for the RMFC system. 100% methanol results in lower fuel consumption than water-methanol mixture (Premix) but goes along with higher fuel cell system complexity for condensing of cathode moisture.
A mixture of water and methanol with a molar concentration ratio (water:methanol) of 1.0 - 1.5 is pressurized to approximately 20 bar, vaporized and heated to a temperature of 250 - 360 °C. The hydrogen that is created is separated through the use of Pressure swing adsorption or a hydrogen-permeable membrane made of polymer or a palladium alloy.
The stored energy can be recovered by burning the methanol in a combustion engine, releasing carbon dioxide, water, and heat. Methane can be produced in a similar reaction. Special precautions against methane leaks are important since methane is nearly 100 times as potent as CO 2 , regarding the 20-year global warming potential .
The Allam-Fetvedt Cycle is a recuperated, high-pressure, Brayton cycle employing a transcritical CO 2 working fluid with an oxy-fuel combustion regime. This cycle begins by burning a gaseous fuel with oxygen and a hot, high-pressure, recycled supercritical CO 2 working fluid in a combustor.
In 2007 ethanol was priced at 3 to 4 dollars per gallon (0.8 to 1.05 dollars per liter) at the pump, while methanol made from natural gas remains at 47 cents per gallon (12.5 cents per liter) in bulk, not at the pump. Presently there are no operating gas stations in California supplying methanol in their pumps. Rep.
Water management is crucial to performance: if water is evaporated too slowly, it will flood the membrane and the accumulation of water inside of field flow plate will impede the flow of oxygen into the fuel cell, but if water evaporates too fast, the membrane will dry and the resistance across it increases.