Proton conductive nano-channel membranes based on polyaniline with phosphonic acid moieties for low relative humidity

Most sulfonic acid based-membranes come to the limit because of high cost and low performance at low relative humidity (RH). Therefore, we synthesized phosphonic acid functionalized polyaniline (PA-PANI). PANI was used as polymer back bone because of excellent chemical mechanical stability and easy synthesis from relatively cheap monomer, and phosphonic acid presents the relatively high proton conducting in nano-channel without water because of its self dissociation nature. PA-PANI was synthesized by bonding chemically with phosphonic acid groups using 3-bromopropylamine as a reagent. PA-PANI nano-channel membrane showed high and stable conductivities (approximately 0.035 S/cm at 80 to approximately 180 degrees C) under low RH. And PA-PANI nano-channel membranes compared with Nafion (10(-4) S/cm at < 30% RH), have higher proton conductivities. This fact showed phosphonic acid groups were more effective at low RH than sulfonic acid groups. Because the proton conductivity of Nafion decreases considerably at elevated temperature due to dehydration, our low cost membranes using phosphonic acid moiety may be expected to substitute sulfonic acid based-membranes such as Nafion.