Abstract
Proton exchange membranes (PEMs) suffer performance degradation under certain conditions—temperatures greater than 80 °C, relative humidity less than 50%, and water retention less than 22%. Novel materials are needed that have improved water retention, stability at higher temperatures, flexibility, conductivity, and the ability to function at low humidity. This work focuses on polyimide-poly(ethylene glycol) (PI-PEG) segmented block copolymer (SBC) membranes with high conductivity and mechanical strength. Membranes were prepared with one of two ionic liquids (ILs), either ethylammonium nitrate (EAN) or propylammonium nitrate (PAN), incorporated within the membrane structure to enhance the proton exchange capability. Ionic liquid uptake capacities were compared for two different temperatures, 25 and 60 °C. Then, conductivities were measured for a series of combinations of undoped or doped unannealed and undoped or doped annealed membranes. Stress and strain tests were performed for unannealed and thermally annealed undoped membranes. Later, these experiments were repeated for doped unannealed and thermally annealed. Mechanical and conductivity data were interpreted in the context of prior small angle X-ray scattering (SAXS) studies on similar materials. We have shown that varying the compositions of polyimide-poly(ethylene glycol) (PI-PEG) SBCs allowed the morphology in the system to be tuned. Since polyimides (PI) are made from the condensation of dianhydrides and diamines, this was accomplished using components having different functional groups. Dianhydrides having either fluorinated or oxygenated functional groups and diamines having either fluorinated or oxygenated diamines were used as well as mixtures of these species. Changing the morphology by creating macrophase separation elevated the IL uptake capacities, and in turn, increased their conductivities by a factor of three or more compared to Nafion 115. The stiffness of the membranes synthesized in this work was comparable to Nafion 115 and, thus, sufficient for practical applications.
Highlights
Nafion is a widely used state-of-the-art proton exchange membrane (PEM)
When looking at Proton Exchange Membrane_1 (PEM_1) to Proton Exchange Membrane_5 (PEM_5), ionic liquids (ILs)-doped membranes at two temperatures, it is observed that the IL uptake and water uptake (WU) uptake values increase with increasing temperature
It has been shown that the morphology was strongly influenced by thermal annealing, which led to increases in IL uptake (ILU) and conductivities
Summary
Nafion is a widely used state-of-the-art proton exchange membrane (PEM). there are other PEMs for fuel cell applications based on perfluorosulfonic acid (PFSA) derived from Nafion membrane such as Nafion 115, Nafion 117, etc. [1,2,3,4,5]. Deligöz et al developed a highly conductive and thermomechanically stable complex membrane based on sulfonated polyimide/ionic liquids (IL), for which the dynamic mechanical analysis indicated only a slight decrease in the mechanical strength until the temperature reached 350 ◦C [55]. These studies clearly show that material characteristics such as structural order, intermolecular interactions, and free volume play critical roles in the design of membranes with desirable properties. The information gained should serve to elucidate the effect of the changes in the transport properties of membranes as a function of ILU and the changes in the mechanical properties induced by thermal annealing
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
