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Hydrogen fuel cell system components

2023-02-16


In order to maintain the normal operation of the reactor, the hydrogen fuel cell system also needs the cooperation of the hydrogen supply system, water management system, air system and other external auxiliary subsystems. The corresponding system components include hydrogen circulating pump, hydrogen bottle, humidifier and air compressor. Fuel cells produce a lot of water when they are in operation. Too low a water content will produce a phenomenon called "dry film", which prevents proton transmission. Excessive water content can result in "waterlogging", which hinders the diffusion of gas in the porous medium, resulting in low reactor output voltage. The accumulation of impurity gas (N2) penetrating from the cathode side to the anode obstructs the contact between hydrogen and the catalyst layer, resulting in local "hydrogen starvation" and chemical corrosion. Therefore, the balance of water is of great significance to the reactor life of PEM hydrogen fuel cells. The solution is to introduce hydrogen circulation equipment (circulation pump, injector) into the reactor to achieve gas purging, hydrogen reuse, hydrogen humidification and other functions.


The hydrogen circulating pump can control the hydrogen flow in real time according to the working conditions and improve the hydrogen utilization efficiency. However, "hydrogen embrittlement" is easy to occur in the environment involving hydrogen and wading. The freezing phenomenon at low temperature may cause the system to fail to work normally. Therefore, hydrogen circulating pump needs to have strong water resistance, stable output pressure and oil-free performance, which is difficult to prepare and expensive to manufacture. Therefore, the schemes of single ejector and double ejector have been developed. The former is not easy to maintain the stability of workflow under high/low load, system start-stop, system variable load and other working conditions, while the latter can adapt to different working conditions but has complex structure and difficult control [18]. There are also some ejector and hydrogen circulating pump in parallel, ejector plus bypass hydrogen circulating pump scheme, also has distinct advantages and disadvantages. In 2010, the American technology consulting company proposed a design of hydrogen cycle system, which uses the returned exhaust gas to humidize the injected hydrogen (without anode humidifier), which represents the development direction of the future hydrogen cycle equipment.


The air compressor in the hydrogen fuel cell system can provide the oxidizer (air) that matches the power density of the reactor. It has the advantages of high pressure ratio, small volume, low noise, large power, no oil and compact structure. The common on-board fuel cell air compressor has the types of centrifugal, screw, scroll and so on. At present, screw air compressors are widely used, but centrifugal air compressors have more application prospects because of their good airtightness, compact structure, small vibration and high energy conversion efficiency. In the key components of air compressor, bearing, motor is the bottleneck technology, low cost, friction resistance coating material is also the focus of development. General Electric, United Technologies, Prager Energy, Xcellsis of Germany, Ballard Power Systems of Canada and Toyota Motor Corporation of Japan all have commercial air compressor product lines.


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