Effect of deep eutectic solvents hydrogen bond acceptor on the anhydrous proton conductivity of Nafion membrane for fuel cell applications

This study intended to assess the role of halogens on proton conductivity of polymer electrolyte membranes (PEMs) for fuel cell applications. For this purpose, the halogens were used as hydrogen bond acceptors (HBA) to form deep eutectic solvents (DES) which were later used as electrolyte in Nafion membrane. The prepared DESs were initially characterized in terms of rheology, thermal behavior, and ionic conductivity. Then, Nafion/DES composite membranes were prepared and their electrochemical reactions, thermal stabilities and proton conductivities were characterized. Interestingly, the bromide containing DESs provided super proton conductivity in Nafion/DES composites so that a proton conductivity of 337 mS/cm was achieved at 100 degrees Cat anhydrous condition which was about 120% higher than the iodide based Nafion/DES membranes and about 1200 % higher than other Nafion/ionic liquid PEMs at anhydrous condition. An upper bound concept was introduced for the Nafion/DES composite membranes which was compared with those obtained for conventional Nafion/ionic liquid composite membranes at anhydrous conditions. Furthermore, fuel cell performance of Nafion/DES composite membrane showed that DESs can be considered as proper electrolytes for anhydrous PEMs, and their properties can be justified by halogen type.