Basso Peressut Andrea, Di Virgilio Matteo, Bombino Antonella, Latorrata Saverio, Muurinen Esa, Keiski Riitta L, Dotelli Giovanni
Department of Chemistry, Materials and Chemical Engineering "Giulio Natta", Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy.
Environmental and Chemical Engineering Research Unit, Faculty of Technology, University of Oulu, Pentti Kaiteran katu 1, FI-90014 Oulu, Finland.
Molecules. 2022 Feb 23;27(5):1507. doi: 10.3390/molecules27051507.
This work deals with the development of graphene oxide (GO)-based self-assembling membranes as possible innovative proton conductors to be used in polymer electrolyte membrane fuel cells (PEMFCs). Nowadays, the most adopted electrolyte is Chemours' Nafion; however, it reveals significant deficiencies such as strong dehydration at high temperature and low humidity, which drastically reduces its proton conductivity. The presence of oxygenated moieties in the GO framework makes it suitable for functionalization, which is required to enhance the promising, but insufficient, proton-carrying features of GO. In this study, sulfonic acid groups (-SOH) that should favor proton transport were introduced in the membrane structure via a reaction between GO and concentrated sulfuric acid. Six acid-to-GO molar ratios were adopted in the synthesis procedure, giving rise to final products with different sulfonation degrees. All the prepared samples were characterized by means of TGA, ATR-FTIR and Raman spectroscopy, temperature-dependent XRD, SEM and EDX, which pointed out morphological and microstructural changes resulting from the functionalization stage, confirming its effectiveness. Regarding functional features, electrochemical impedance spectroscopy (EIS) as well as measurements of ion exchange capacity (IEC) were carried out to describe the behavior of the various samples, with pristine GO and commercial Nafion 212 used as reference. EIS tests were performed at five different temperatures (20, 40, 60, 80 and 100 °C) under high (95%) and medium (42%) relative humidity conditions. Compared to both GO and Nafion 212, the sulfonated specimens demonstrate an increase in the number of ion-carrying groups, as proved by both IEC and EIS tests, which reveal the enhanced proton conductivity of these novel membranes. Specifically, an acid-to-GO molar ratio of 10 produces a six-fold improvement of IEC (4.23 meq g) with respect to pure GO (0.76 meq g), while a maximum eight-fold improvement (5.72 meq g) is achieved in SGO-15.
本工作致力于开发基于氧化石墨烯（GO）的自组装膜，作为聚合物电解质膜燃料电池（PEMFC）中可能的创新型质子导体。如今，最常用的电解质是科慕公司的Nafion；然而，它存在显著缺陷，如在高温和低湿度下会严重脱水，这大大降低了其质子传导率。GO骨架中含氧部分的存在使其适合进行功能化，这是增强GO虽有前景但尚不充分的质子携带特性所必需的。在本研究中，通过GO与浓硫酸之间的反应，将有利于质子传输的磺酸基团（-SOH）引入膜结构中。在合成过程中采用了六种酸与GO的摩尔比，得到了具有不同磺化度的最终产物。所有制备的样品通过热重分析（TGA）、衰减全反射傅里叶变换红外光谱（ATR-FTIR）和拉曼光谱、变温X射线衍射（XRD）、扫描电子显微镜（SEM）和能谱分析（EDX）进行表征，这些表征指出了功能化阶段导致的形态和微观结构变化，证实了其有效性。关于功能特性，进行了电化学阻抗谱（EIS）以及离子交换容量（IEC）的测量，以描述各种样品的行为，以原始GO和商业Nafion 212作为参考。EIS测试在五个不同温度（20、40、60、80和100℃）下，在高（95%）和中（42%）相对湿度条件下进行。与GO和Nafion 212相比，磺化样品的离子携带基团数量增加，这通过IEC和EIS测试得到证明，这些测试揭示了这些新型膜增强的质子传导率。具体而言，酸与GO的摩尔比为10时，相对于纯GO（0.76 meq g），IEC提高了六倍（4.23 meq g），而在SGO-15中实现了最大八倍的提高（5.72 meq g）。
