Transient Distribution of Water in an Anion Exchange Membrane Fuel Cell Monitored by Operando Coherent Anti-Stokes Raman Scattering Spectroscopy (Supporting Information)

The hydration condition of an anion exchange membrane (AEM) in an operating fuel cell significantly affects its performance as well as its lifespan. In this paper, an in-house build coherent anti-Stokes Raman scattering (CARS) vibrational spectroscopy is used to establish the hydration of an AEM in an anion exchange membrane fuel cell (AEMFC) while it generates power. During steady-state operation, water on the anode side increased with current density. On the cathode side and at the center of the membrane, water initially decreased with current density and then started increasing at a slower pace than on the anode side. A deconvolution of the OH peak in the recorded CARS spectra into nine species revealed that only the H-bonded water species underwent variation. The rest of the species experienced a negligible change. A transient study revealed that maximum disturbance to the water distribution was achieved after 5 s of applying a current jump. The distribution of water became stable within 20 s after applying the current jump. The response to the current jump on the anode side was opposite to that on the cathode. These results open the way for a widespread dynamic study of water distribution in different AEMFCs. The technique could also be directly used to evaluate the dynamic degradation of AEMs.

在操作燃料电池中，阴离子交换膜（AEM）的水合状态对其性能及使用寿命具有显著影响。本研究中，我们利用自行构建的相干反斯托克斯拉曼散射（CARS）振动光谱技术，在阴离子交换膜燃料电池（AEMFC）发电过程中，对AEM的水合状态进行了深入研究。在稳态运行过程中，阳极侧的水含量随着电流密度的增加而上升。而在阴极侧及膜的中心区域，水含量在电流密度增加的初期有所降低，随后其增加速率较阳极侧缓慢。通过对记录的CARS光谱中OH峰的解卷积分析，识别出九种不同的物质，结果显示，仅有氢键结合的水分子种类发生了变化，其余物质变化微乎其微。瞬态研究表明，在施加电流跃变后5秒时，水分布的扰动达到最大。在施加电流跃变后20秒内，水的分布趋于稳定。在阳极侧对电流跃变的响应与阴极侧相反。这些研究结果为不同AEMFC中水分布的动态研究开辟了新的途径，该技术亦可直接用于评估AEM的动态退化。