质子交换膜燃料电池催化层化学稳定性研究

Chemical Stability Investigations of Catalyst Layer in PEMFC

本文采用Fenton试剂离线加速衰减测试考察质子交换膜燃料电池(PEMFC)催化层的化学稳定性.在经100 h Fenton试剂处理后,氟离子流失测试和傅里叶红外光谱表征(ATR-FTIR)证明催化层中全氟磺酸离聚物(Nafion)发生了化学降解;通过透射电镜(TEM)观察到催化层中发生了明显的Pt颗粒团聚和炭载体腐蚀,与TEM表征相一致,循环伏安测试(CV)表明电化学活性面积(ECSA)降低了58%,并伴随着双电层区域的明显减少;FTIR测试进一步表征了炭载体的表面状态,并没有观察到明显的含氧官能团的产生,减少的炭载体可能以CO_2的形式释放出去.全电池测试表明,自由基攻击对催化层组成和结构造成了明显损坏,显著增加了催化层中的质子传导阻力和局部气体传输阻力,导致全电池性能大幅降低.

This work was intended to study the effect of free radicals on the chemical stability of catalyst layer via ex situ accelerated stress test（AST）. Fenton reagent was used as the free radical provider in this research. Apart from the decomposition of Nafion in catalyst layer, the agglomerated Pt nanoparticles and the corroded carbon support were also observed after being treated in Fenton reagent for 100 h. Firstly, the existence of fluoride（F） ions evidenced the chemical decomposation of Nafion after being attacked by trace radical species, which was supported by the intensity decrease in the C-F stretching and vibration peak（1250 cm^-1）observed in attenuated total reflection Fourier transform infrared（ATR-FTIR） spectrum. The transmission electron microscopic（TEM） studies showed that the severe Pt nanoparticles agglomeration and carbon support corrosion happened. To gain more insight,the cyclic voltammetry（CV）, ATR-FTIR and single cell performance measurements were conducted. A large loss（58%） of the electrochemical active surface area（ECSA） was observed. Another meaningful finding was the reduced double layer region, which demonstrated the reduction of carbon support. Notably, further ATR-FTIR analysis revealed the disappearance in the spectra at1719 cm^-1 ～ 1578 cm^-1 which were assigned to the hydroquinone-quinine（HQ-Q） redox couple on the oxidized carbon surface. On the bases of these results, it could be concluded that carbon support might be decayed by releasing CO2 instead of forming oxides on its surface. Finally, the single cell performance data indicated an obvious performance loss in high current density range, due to the proton and local gas transport limitations in the decayed electrodes.