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

电化学能源科学与技术 2022-06-30

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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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