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Membraneless Fuel Cells convert stored chemical energy into electrical energy without the use of a conducting membrane as with other types of fuel cells. In Laminar Flow Fuel Cells (LFFC) this is achieved by exploiting the phenomenon of non-mixing laminar flows where the interface between the two flows works as a proton/ion conductor. The interface allows for high diffusivity and eliminates the need for costly membranes. The operating principles of these cells mean that they can only be built to millimeter-scale sizes. The lack of a membrane means they are cheaper but the size limits their use to portable applications which require small amounts of power. Another type of membraneless fuel cell is a Mixed Reactant Fuel Cell (MRFC). Unlike LFFCs, MRFCs use a mixed fuel and electrolyte, and are thus not subject to the same limitations. Without a membrane, MRFCs depend on the characteristics of the electrodes to separate the oxidation and reduction reactions. By eliminating the membrane and delivering the reactants as a mixture, MRFCs can potentially be simpler and less costly than conventional fuel cell systems. The efficiency of these cells is generally much higher than modern electricity producing sources. For example, a fossil fuel power plant system can achieve a 40% electrical conversion efficiency while a nuclear power plant is slightly lower at 32%. Fuel cell systems are capable of reaching efficiencies in the range of 55%–70%. However, as with any process, fuel cells also experience inherent losses due to their design and manufacturing processes. == Overview == A fuel cell consists of an electrolyte which is placed in between two electrodes – the cathode and the anode. In the simplest case, hydrogen gas passes over the cathode, where it is decomposed into hydrogen protons and electrons. The protons pass through the electrolyte (often NAFION – manufactured by DuPont) across to the anode to the oxygen. Meanwhile, the free electrons travel around the cell to power a given load and then combine with the oxygen and hydrogen at the anode to form water. Two common types of electrolytes are a proton exchange membrane(PEM) (also known as Polymer Electrolyte Membrane) and a ceramic or solid oxide electrolyte (often used in Solid oxide fuel cells). Although hydrogen and oxygen are very common reactants, a plethora of other reactants exist and have been proven effective. Hydrogen for fuel cells can be produced in many ways. The most common method in the United States (95% of production) is via Gas reforming, specifically using methane,〔Ragheb, Magdi. "Steam Reforming." Lecture. Energy Storage Systems. University of Illinois, 3 Oct. 2010. Web. 12 Oct. 2010. However, since these methods of hydrogen production are often energy and space intensive, it is often more convenient to use the chemicals directly in the fuel cell. Direct Methanol Fuel Cells (DMFC's), for example, use methanol as the reactant instead of first using reformation to produce hydrogen. Although DMFC's are not very efficient (~25%),〔Kin, T., W. Shieh, C. Yang, and G. Yu. "Estimating the Methanol Crossover Rate of PEM and the Efficiency of DMFC via a Current Transient Analysis." Journal of Power Sources 161.2 (2006): 1183–186. Print.〕 they are energy dense which means that they are quite suitable for portable power applications. Another advantage over gaseous fuels, as in the H2-O2 cells, is that liquids are much easier to handle, transport, pump and often have higher specific energies allowing for greater power extraction. Generally gases need to be stored in high pressure containers or cryogenic liquid containers which is a significant disadvantage to liquid transport. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Membraneless Fuel Cells」の詳細全文を読む スポンサード リンク
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