Micro fuel cell system
As the portable electronics market in recent years, the rapid development and create a huge battery market opportunities to both types of secondary batteries have certain restrictions, making micro fuel cell is high hopes. This article introduces the micro fuel cell the major trends, and the commercialization of technological bottlenecks and market considerations.
In recent years the rapid development of portable electronic products, including mobile phones, notebook computers, personal digital assistant (PDA), and even digital cameras and video camera, etc., creating a huge market and business opportunities; However, with product enhancements, the system for power higher demand, a small and light, continued longer battery power, would be consistent with the requirements of all consumers.
Micro fuel cell system development trends
Theoretically, the energy density of fuel cell lithium-ion batteries for five to ten times more (varies due to different systems), is technically up to three to five times; In addition, fuel cell without power charge, completely free from the burden of charging and limitations, fuel supply, instead of just a few seconds, providing great convenience for users. Therefore, micro fuel cells, the huge advantage of market incentives and features, is bound to greatly accelerate the development of relevant technologies mature.
Variety of fuel cells, micro portable system the most appropriate, including proton exchange membrane fuel cell (Proton Exchange Membrane Fuel Cell; PEMFC) and direct methanol fuel cells (Direct Methanol Fuel Cell; DMFC), always within this two room temperature operate with small size, light weight, convenient cell stack design and so on. Among them, the direct methanol fuel cell with liquid methanol as fuel, the volume energy density of about three to four times the liquid hydrogen, hydrogen storage and transportation of much convenience and security, and get easy, low cost, so more portable electronic products needs. In addition, the use of micro-reformer (Micro Reformer) to produce hydrogen fuel conversion of methanol, micro fuel cells are the possible direction of development; below will focus on direct methanol fuel cell (DMFC) for discussions.
DMFC technology development bottleneck
The working principle of DMFC with proton exchange membrane fuel cell is similar only in the anode part of the fuel entering the methanol and water, and methanol fuel produced through the catalytic role of protons, electrons and carbon dioxide, the cathode reaction is identical with the hydrogen system . Micro fuel cells to enter the commercialization stage, it still faces a number of technical bottleneck to be overcome, the key question is as follows.
1, methanol through
As the methanol transmission through, making the battery through the voltage (overpotential) increased potential can be used more in 0.4V below the battery efficiency and thus limited, but also result in fuel consumption. Methanol through the current issue of the DPRK to solve two directions: the development of proton exchange membrane materials, so that with high proton conductivity and lower methanol permeability; control the concentration of methanol fuel, to reduce the amount of methanol penetration.
Second, the water overflow (Waterflooding)
DMFC anode to generate 1 unit of protons will be pulling out of about 2.5 units of water or methanol Daoda cathode, while reaction Ye Hui Yin Ji generate Shui, Guoduo water Jiangzu Ai Jin Ru catalyst Cengerzaocheng oxygen cathode Xiaoneng substantial lowering of the water Cheng Wei overflow phenomenon. This problem has to take the initiative to increase circulation of air flow away from the excessive water-based, but which would consume a large power system, so MTI developed body of membrane electrode (MEA) design method of control.
Third, performance
DMFC anode current efficiency is low, so including the NEC and other companies tailor catalyst or catalyst support for the development, try to provide greater power density; nano technology will help to improve the catalyst performance is noteworthy development . In addition, the system operating temperature affect the DMFC performance of another important factor, but the application to 3C electronic products, the need for proper temperature control, so the system of thermal cycling or thermal management is also now actively addressed.
4, fuel and water treatment
As the methanol concentration control properly can reduce the penetration of methanol, together with portable electronic devices do not allow the cathode resulting in leakage of water generated by the case, so the actual system to go through a lot of control logic to achieve the overall methanol and water supply and The purpose of the concentration of control of balance.
Active vs. Passive response to the portable product applications, current DMFC system development is divided into active and passive, the following are illustrative.
First, the direct methanol fuel cell active
Schematic diagram of active DMFC systems are attached. Anode operating at the appropriate concentration of methanol (about 3 ~ 6% vol), the additional fuel tanks for storage of a high concentration of methanol solution; anode cycle consists of three channels: high concentrations of methanol, cathode recycling water, and repeat the cycle of fuel; in under normal operation the anode through the fuel pump drive cycle and exclude Pf generated carbon dioxide, the fuel concentration is too low or the stock too low, the pumps were Pm and Pw by the high concentration of methanol and water to the anode cathode recovery, to maintain the battery the system. On the other hand, cathode oxygen can be forced from the fan or compressor air circulation.
The advantage of active DMFC can improve the system by high energy density of methanol concentration and cell stack design by increasing output power; disadvantage to using a number of energy components, reducing system net power output, more complex and takes up space .
Second, passive direct methanol fuel cell
Passive DMFC cycle mainly by gravity, capillarity or natural diffusion method to fuel and air delivery to the electrode surface reaction, at room temperature operating conditions. Such systems the main body for the membrane electrode (MEA) and the structure of the material design, by pro-hydrophobic material characteristics and differences in the concentration of fuel and water, control the diffusion rate, and minimize the effects of methanol penetration to enhance the energy density . However, the drawback of passive DMFC system is unable to provide greater power density, while technological threshold is very high.
The popularization of future trends
In addition to these key technologies to break through, the micro and small fuel cells to enter the market still face the costs, regulations, and user habits. DMFC is still very high cost of the current need to develop catalysts and related materials breakthrough. The overall system size or the size of the external auxiliary components and cost depends on a more creative and discovery, can DMFC popularize.
In addition, the toxicity of methanol fuel, and application characteristics of the product, prior to entering the commercialization of the test criteria must be certified by the relevant laws and norms. Currently, the U.S., Japan and many European institutions have been actively involved in the work of regulation, development and integration, the future development of DMFC is expected to be increasingly diligent.
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