Proton exchange membrane fuel cells
By analyzing the proton exchange membrane fuel cell migration patterns in the water, raised the need for fuel cell humidification, introduced the application is currently being studied techniques of self-humidifying Research, pointed out that technology is the future of self-humidifying proton exchange membrane fuel cell humidification technology development, with good prospects for the study.
Proton exchange membrane fuel cell (PEMFC) as an efficient, environmentally friendly power generation facilities, in recent years become a research hotspot. At present, the proton exchange membrane for PEMFC are needed in the water can be conducted in the presence of protons, and only state in the fully hydrated proton that has the best conductivity, so the proton exchange membrane must contain sufficient moisture, in a good state of hydration. On the other hand, the battery in the high water content will lead to the electrode catalyst in the flooded stains, loss of reactivity; will also result in the connected pores in the gas diffusion layers by water blocked, preventing the entry of the reaction gas contact with the catalyst or gas, so that air density decreases, a sharp decline in battery performance, so the battery in water management becomes very important in the humidifier is to solve the battery problem of effective water management methods.
In actual operation, on one hand with the current density increases, the reverse diffusion of water more than a positive electro-osmotic migration of water, which means that when the battery's cathode region has maintained a very good hydration conditions , the battery anode because of the migration of the water has reached the dry state, at high current density, the situation is particularly evident. On the other hand, when a large gas flow into the battery, air intake, especially at the cathode inlet of the proton exchange membrane to be dry, causing the battery's internal resistance increases, PEMFC sharp decline in performance, so the response must enter the cell gas humidification.
At present, people enter the battery pack for humidifying the reaction gas processing methods commonly used outside the humidifier and the humidification mode, the two methods are required to use the humidifier humidifiers auxiliary systems, proton exchange membranes to enter cells directly from water the reaction gas to control. Since humidification technology as a new technology, because it can remove a large, complex auxiliary humidification system as the focus of attention.
In the PEMFC operation, since the existence of cross-diffusion, a small amount of hydrogen will permeate through the proton exchange membrane produces the mixed potential of oxygen electrode, resulting in reduced efficiency, while a security risk. If the response to gas diffusion in the electrolyte membrane of the synthetic water, then not only can eliminate the adverse effects of the above, but also achieve real-time membrane humidification. New self-humidifying composite membranes is based on the concept.
Self-humidifying fuel cell operation is the use of the battery itself, the reaction of water to achieve the membrane humidification. Using self-humidifying technique that reduces production costs, simplify the battery to run the system, improve the fuel cell power volume ratio and power ratio.
Self-humidifying membrane electrode (MEA) is through the gas diffusion layer, catalyst and proton exchange membrane, and to optimize their combined or modified to enhance the electrochemical products of the anti-water diffusion to the anode, to achieve self-humidification purposes.
Zong-Qiang Mao, Yang Tao proposed structure of asymmetric membrane electrode is based on this idea, they were on the hydrogen electrode and oxygen electrode hydrophilic and hydrophobic, strengthening the cathode water back diffusion to the anode, the anode from the cathode to the net transfer water to make hydrogen electrode in the wet state, so that can maintain water balance in the film.
Based on the above electrode structure, Wang Cheng and other sol - gel process and SiO2 gel, dispersed in between the anode catalyst layer and the membrane, this SiO2 particles / Nafion polymer layer to further enhance the water to the anode cathode anti-proliferation effect.
Since humidification flow field mainly depends on the particular design of flow field plate to pass or keep part of the electrochemical products of water, the cell membrane electrode to create a relatively moist environment, ensure good proton channel.
Battery at the entrance to the reaction gas is very dry, the gas flow through the process, the water produced by wetting the battery, at the exit with a certain degree of humidity. F. N. Fuchi and other use of this feature, the use of countercurrent air intake means to achieve self-humidification function of the battery.
Wood, who designed a feature called "cross-finger flow" of the flow field structure, as shown in Figure (3) below. The flow chart like a maze without exit gas through forced convection mechanisms involved in cell reaction to reach the catalyst layer. The role of shear stress, the flow part of the water will flow out with the batteries, reducing the possibility of flooding the electrode; another part of the water will penetrate the membrane wetting dry.
Some researchers on the bipolar plate surface and the material studied. Shelekhinr raised on both sides of the bipolar plate flow lane paved section of hydrophilic, the hydrophilic material made from the inert hydrophilic, such as filter paper, glass fiber and other components; battery cathode side hydrophilic when the article to absorb and store excess water evenly, Article battery hydrophilic when water can be stored in water supply membrane electrode, in order to achieve self-humidifying membrane. S. H. Ge, etc. will be two polyvinyl alcohol sponges were placed in the cathode side of the water flow of the upper and lower part of the electrochemical reaction of absorbed water, to moisten the dry air inlet.
PEMFC humidification problems in recent years has become a research hotspot. Can be removed from the humidification technology because of its huge, complex external support system, simplify the battery system and reduce the battery manufacturing costs, so self-humidification of more practical significance, is considered the most promising application of fuel cell technology.
People in terms of comprehensive research results from the humidifier, I believe that the current focus of research since the humidifier is self-humidifying composite membrane design, if the self-humidifying composite membrane, self-humidifying membrane electrode, since the humidification flow field The design of the three organic combination, PEMFC technology of self-humidifying greater space for development.
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