Impact of hydroxylation and ion structure on conductivity and stability of short-chain alkylammonium-based protic ionic liquids
摘要
This study explores alkylammonium-based protic ionic liquids (PILs) with varied alkyl chain lengths and hydroxyl group inclusions, focusing on their viability in high-temperature proton exchange membrane fuel cells (PEMFCs). Operating above 100 °C offers potential benefits such as reduced carbon monoxide catalyst poisoning, improved reaction kinetics, and enhanced heat management, leading to greater system efficiency and durability. Conductivity and viscosity measurements from 30 °C to 120 °C show that PILs containing hydroxylated cations like 2-hydroxyethylammonium ([2HEA]+) and 2-methyl-2-hydroxyethylammonium ([m-2HEA]+) demonstrate superior performance. Conductivities exceeded 10− 3 S/cm at 60 °C and 10− 2 S/cm at 90 °C. Higher acidity PILs, such as 2-hydroxyethylammonium acetate ([2HEA][Ac]), exhibited enhanced conductivity due to improved proton transfer mechanisms. Thermal decomposition analysis indicated most PILs decompose above 100 °C, with exceptions like diethylammonium acetate ([DEA][Ac]), which showed anodic and cathodic peaks at higher temperatures due to by-product formation, limiting its applicability at high temperatures. With increasing temperature, a transition from viscosity-dominated to proton hopping mechanisms, like the Grotthuss mechanism, was observed. Hydroxyl groups in cations enhance proton transfer, significantly increasing conductivity at elevated temperatures, while intensified hydrogen-bond networks amplify temperature effects. These findings underscore the potential of hydroxylated PILs in advanced fuel cell technologies, emphasizing the need for balanced viscosity, conductivity, and thermal stability for optimal performance.