250小时强化道路振动对燃料电池气密性、极化性能、OCV、均一性、阻抗状态的影响和失效位置规律
Effect of strengthened road vibration onperformance degradation of PEM fuel cell stack
Yongping Hou
Dong Hao
Jianping Shen
Ping Li
Tao Zhang
Hong Wang
Abstract
The vehicular fuel cell stack isunavoidably impacted by the vibration and shock in the real-world due to theroad unevenness. However, influences of vibration on fuel cell stack have yetto be investigated completely. In this paper, the performance of a fuel cellstack is experimentally studied in terms of gas-tightness, voltage degradation, AC impedance spectra, polarizationcurve and characteristic parameters in polarization curve through long-termstrengthened road vibration tests, in order to investigate the influences ofroad-induced vibration on performance degradation of fuel cell stack. Thevibration tests are carried out on a six-channel multi axial simulation tablewith the vibration excitation spectra originally derived from the strengthenedroad of the ground prove. During the vibration test, several kinds ofperformance test including gas-tightness test, AC impedance diagnosis andpolarization curve test are conducted at regular intervals. After the vibration test, the gas leakagerate of anode reaches 1.73 times of the initial value. The open circuit voltage and rated voltage decreases by 0.90% and 3.58%,respectively. Meanwhile, the performance of individual cell voltage uniformity becomes worse distinctly. With theincrease of vibration duration, theohmic resistance obtained from AC impedance diagnosis ascends approximatelylinearly and presents a growth of 5.36% ultimately. An improved empiricalfuel cell polarization curve model is adopted to fit the current–voltage dataand estimate the characteristic parameters which decide the shape ofpolarization curve. It is noted that the limitingcurrent density declines distinctly and the mass transfer loss increases mainly at the range of high currentdensities. The results indicate that the long-term strengthened roadvibration condition exerts a significant influence on the durability of fuelcell stack.
Fig. 2 e Schematic of the fuel cell stack: (a) Stack enclosure and rubber paddings; (b) Fuel cell stack; (c) Fuel cell stack components. ① Rubber paddings; ② Front endplate; ③ Rear endplate; ④ Bolts and nuts; ⑤ Current collector; ⑥ Bipolar plate; ⑦ Membrane electrode assembly; ⑧ Insulating plate; ⑨ Rubber cushion.
Table 1 e Material and density of each fuel cell stack component.
Fig. 3 e Flow diagram of the test procedure.
Fig. 4 e Vibration excitation spectra of FC stack in vibration test.
Table 2 e Schedule of performance test of FC stack.
Table 3 e Operational conditions of FC stack.
Fig. 5 e Gas-tightness degradation of anode during the vibration test.
Fig. 6 e Voltage degradation during the vibration test: (a) OCV; (b) Rated voltage.
Fig. 7 e Coefficient of variation curves during the vibration test.
Fig. 8 e Schematic of performance degradation of individual cells: (a) Rated voltages of cells before and after the vibration test; (b) Voltage drop rates of cells during vibration test.
对衰减位置特点的解释:
As a consequence, when the stack is subjected to vibration conditions, the force loads from front endplate are transferred to the adjacent bipolar plates directly without any vibration absorption measures, while the loads from rear endplate are damped by the rubber cushion between the rear endplate and the adjacent bipolar plates.
As a result, the non-uniform distribution of gas and water at the foreside of stack during operation should not be the primary reason for the faster degradation shown in the front part.
Fig. 9 e Nyquist plot of the FC stack impedance spectra. The inset displays enlarged view of impedance spectra (high frequency).
Fig. 10 e Equivalent circuit for EIS analysis of FC stack
Fig. 11 e Variation of ohmic resistance during the vibration test.
Fig. 12 e Variation of the polarization curves during the vibration test.
Fig. 13 e Variation of Tafel slope during the vibration test.
Fig. 14 e Variation of limiting current density during the vibration test.
Fig. 15 e Variation of mass transfer loss during the vibration test.
Conclusion
The effect of strengthened road vibration on performance degradation of PEM fuel cell stack is experimental investigated in this paper.
The gas-tightness of FC stack degrades dramatically under long-term strengthened road vibration.
Besides, the steady-state performance of FC stack is also significantly influenced by the strengthened road vibration. During the vibration test, fluctuant variations of polarization curves are detected. It is worth noting that the best performance of stack in this work appears before the beginning of the vibration test. The FC stack experience different degrees of performance degradation over the entire range of current densities and the voltage decay rates almost rise with the increase of current density. The rated voltage of stack decreases 3.58% with a decay rate of 77.60 mV/h.
At maximum current density, the coefficient of variation, which reflects the individual cell voltage uniformity during stack operation, increases to 8.81% from 3.47%. The steady-state performance of stack degrades apparently under long-term vibration environment.
During the vibration test, the ohmic resistance of FC stack obtained from AC impedance diagnosis presents rise approximately linearly and reaches a growth of 5.36%. Other key parameters that decide the shape of polarization curves vary as follows: a) the OCV decreases at the rate of 26.76 mV/h and ultimately declines by 0.90% of the origin value; b) the Tafel slope experience slight fluctuations; c) at high current densities, the mass transfer loss shows upward trends with the increase of vibration test duration. From the above, two main factors that lead to the performance degradation of FC stack are the increase of ohmic resistance and the rise of the mass transfer loss at high current densities.
From the experimental results, it can be concluded that strengthened road vibration has a significant influence on performance degradation of the FC stack. Hence, in the real-world, the influence of road-induced vibration on vehicular FC stack performance should be concerned and requires much further theoretical studies.
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