1.4V高电位碳腐蚀和燃料电池加速衰减的关联,1.4V高电位腐蚀试验和1200小时AST失效结果的对比
Carbon corrosion induced fuel cellaccelerated degradation warning: From mechanism to diagnosis
Zunyan Hu
Liangfei Xu
Quanquan Gan
Xiaoli Du
Wei Dai
Qing Wang
Weibo Zheng
Yujie Ding
Jianqiu Li
Minggao Ouyang
Abstract
The degradation rate of fuel cellperformance changes from linear to nonlinear, which plays a role in the poordurability of fuel cells. Little research has been reported on the mechanismand diagnostic methods for the accelerated degradation of commercial fuelcells. An early warning method of fuel cell accelerated degradation based onthe high-potential holding test is studied in the present paper. Thedifference in decay rate between the electrochemical surface area andactivation resistance are used to provide early warning of fuel cell failure.In addition, a 1200 h accelerated stress test was used to validate themechanism of accelerated performance decay. Scanning electron microscopyobservations show that carbon corrosion makes the structure more fragile inthe region of linear degradation. When the fragile catalyst layer can nolonger withstand the packing force, structural collapse and electrolyte fillingcan result in a sudden decrease in performance. A three-stage degradationmechanism is proposed for analyzing the sudden decrease in performance in aproton exchange membrane fuel cell.
The widths of channel and land are 1.0/1.0 mm, and the depth of channel is 0.5 mm.
An AST test cycle was designed for analysis of the degradation mechanism. Each cycle comprised two parts. First, the fuel cell was maintained at 1.4 V@60 ◦C for 1 h to simulate corrosion of the carbon support. Next, a polarization curve test and EIS, CV, and LSV tests were conducted to analyze the performance degradation.
Fig. 2. (a) Polarization curves and (b) voltage–time curves showing the linear and nonlinear performance degradation of a fuel cell.
右图中的电压不稳定现象不完全是同一个原因。前两个似乎是供气的问题。
Table 1 Comparison of the electrochemical surface area and crossover current during three cycles of the investigated fuel cell
Fig. 3. Current–voltage curves obtained by (a) linear sweep and (b) cyclic voltammetry for three cycles of the investigated fuel cell.
Fig. 4. Polarization curves and high-frequency resistance as a function of current for the investigated fuel cell.
Fig. 5. EIS test results corresponding to (a) a low current density of 300 mA/cm 2 and (b) a high current density of 800 mA/cm 2 .
Fig. 6. DRT-based EIS reconstruction method
Fig. 7. DRT analysis results for EIS data obtained at a current density of 300 mA/cm 2 .
Fig. 8. DRT analysis: (a) DRT at 300 mA/cm 2 in detail and (b) DRT at 800 mA/cm 2 in detail.
Fig. 9. Fuel cell accelerated degradation warning indexes comparison.
没有太理解图9和图4中HFR的单位的对应关系。
Fig. 10. AST performance analysis: (a) rated point voltage drop; (b) a before-and-after AST test comparison.
图10、11和12是照搬文献的结果。不理解Because the AST experiment shows similar characteristics with the high-potential holding experiment, the analysis results of the AST test can help validate the assumed cause of the sudden performance degradation.如果具有相识性,为什么1.4V高电位后不进行同样的SEM表征进行对比,而借用文献中的AST实验后的SEM结果。
图10和图4的初始极化曲线、HFR的结果都差异很大。
AST实验前后HFR几乎不变,高电位腐蚀前后HFR显著增加。不理解为什么认为失效结果相同。
也不知道电池的结构是否是同一个。
Fig. 11. SEM analyses: (a) cross-section of a fresh MEA; (b) cross-section of a failed MEA (c) fresh MEA surface; (d) failed MEA surface
Fig. 12. A proposed three-stage fuel cell degradation process
Conclusion
The accelerated decay of a fuel cell due tocorrosion of the carbon support was studied. The high-potential holding testshowed that corrosion of the carbon support can lead to a sudden voltage drop,and a possible decay mechanism and process have been discussed. Neither theECSA nor the crossover current can be used to provide an early warning of asudden decrease in performance in the high-potential holding test.Distribution of relaxation times was used for EIS analysis. Analysis of thepeak characteristics show that the activation resistance increases is fasterthan the ECSA decreases. The corrosion of the carbon support in the linearregion was assumed to inefficient use of certain regions of the ECSA for oxygenreduction. On the basis of the results, the difference in the decay rateand the decrease in the carbon oxidation rate are used to provide an earlywarning of a nonlinear performance drop. In addition, the decaycharacteristics of fuel cells under operating conditions were analyzed. The SEMresults show that the CCL in the anode outlet region was destroyed.Combined with the results of the high-potential holding tests, a three-stagedegradation mechanism was proposed for the nonlinear performance drop resultingfrom carbon corrosion. In stage two, the linear drop region, carbon corrosionmakes micropores larger and the supporting structure becomes progressivelythinner; a reduction of the three-phase boundary is the direct reason forincreasing activation. When the fragile catalyst layer can no longer withstandthe packing force, structural collapse and electrolyte filling destroy thecatalyst-layer microstructure, resulting in a sudden performance drop. Inconclusion, we have studied early warning methods and the characteristics offuel cell accelerated decay, which plays an important role in fuel celldurability research. Because accelerated decay tests under operating conditionsare not straightforward, further verification is needed in future work.
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