Barnes Austin M, Liu Brendan, Buratto Steven K
Department of Chemistry and Biochemistry , University of California, Santa Barbara , Santa Barbara , California 93106-9510 , United States.
Langmuir. 2019 Nov 5;35(44):14188-14193. doi: 10.1021/acs.langmuir.9b02160. Epub 2019 Oct 22.
Anion exchange membrane (AEM) fuel cells (AEMFCs) are a promising cost-effective alternative energy conversion technology because of the potential implementation of earth-abundant catalysts, obviating the need for precious metals. AEMs, however, have low conductivity and suffer from poor stability. The conductivity of the AEM is inherently tied to the complex phase-separated morphology, as its dependence on the hydration level is not well understood. In this report, we employ phase-contrast tapping mode and conductive-probe atomic force microscopy (cp-AFM) to study the nanoscale surface morphology and hydroxide conductance of a commercially available quaternary ammonium (QA) AEM by FuMA-Tech GmbH (Fumapem FAA-3). The chemical structure of FAA-3 consists of a poly(phenylene oxide) backbone with QA functionality. The morphology of FAA-3 was observed in the bromide (FAA-3-Br) and hydroxide form (FAA-3-OH) in dehydrated and hydrated conditions. Under dehydrated conditions, both membranes showed no phase contrast, indicating the absence of phase-separated hydrophilic domains at the surface. At hydrated conditions, FAA-3-Br shows randomly dispersed isolated clusters, while FAA-3-OH shows elongated fibrillar structures extending microns in length. cp-AFM of hydrated FAA-3-OH showed that these elongated regions were insulating. These results provide morphological evidence for the conduction of hydroxide at the surface and its dependence on the hydration level.
阴离子交换膜（AEM）燃料电池（AEMFCs）是一种很有前景的具有成本效益的替代能源转换技术，因为有可能采用地球上储量丰富的催化剂，从而无需使用贵金属。然而，AEM的电导率较低且稳定性较差。AEM的电导率与复杂的相分离形态本质上相关，因为其对水合水平的依赖性尚未得到很好的理解。在本报告中，我们采用相衬轻敲模式和导电探针原子力显微镜（cp-AFM）来研究由德国富马科技有限公司（Fumapem FAA-3）提供的市售季铵（QA）AEM的纳米级表面形态和氢氧化物电导率。FAA-3的化学结构由具有QA官能团的聚氧化苯撑主链组成。在脱水和水合条件下，观察了FAA-3在溴化物（FAA-3-Br）和氢氧化物形式（FAA-3-OH）下的形态。在脱水条件下，两种膜均未显示相衬，表明表面不存在相分离的亲水域。在水合条件下，FAA-3-Br显示出随机分散的孤立簇，而FAA-3-OH显示出长度延伸达微米的细长纤维状结构。水合FAA-3-OH的cp-AFM表明这些细长区域是绝缘的。这些结果为氢氧化物在表面的传导及其对水合水平的依赖性提供了形态学证据。
