Synthesis And Properties Of Sulfonated Polybenzothiazoles (Polybenzimidazoles) As Proton Exchange Membranes

The proton exchange membrane(PEM)is one of the vital components of proton exchange membrane fuel cells and largely affects the performance of the cells.At present,commercial PEMs are perfluorinated sulfonic acid membranes(Nafion),but there are still some defects,such as harsh use conditions,high permeability of methanol,and high cost.Therefore,the exploration of new sulfonated aromatic polymer membranes has become the focus of PEM research.In this paper,the main chain structure of the polymer was designed and regulated.Different series of sulfonated polybenzothiazole(imidazole)polymers were prepared by direct polycondensation combined with the doping,block,and crosslinking modification method,and the comprehensive performance of sulfonated polybenzothiazole(imidazole)as PEM was characterized in detail.The contents of each chapter are described below.In Chapter 2,a novel sulfonated polybenzothiazoles(s PBT-E)containing flexible ether bonds and sulfonated biphenyl units were prepared by the direct polycondensation method.Meanwhile,the composite membranes(s PBT-E62.5/SGO)were also prepared by doping with sulfonated graphene oxide(SGO).The results showed that both s PBT-E and s PBT-E62.5/SGO membranes exhibited good thermal stability,oxidation stability,and mechanical properties.Compared with the s PBT-E series,the s PBT-E62.5/SGO series showed higher water uptake and lower swelling ratio,and remained in the range of 54.4-60.2%and 10.3-13.6%at 80℃.In addition,under the condition of 80℃and 100%RH,the proton conductivity of s PBT-E62.5/SGO3 membrane was up to 0.139 S/cm,the activation energy was as low as 7.01 k J/mol,the current density and power density were 1.73 A/cm~2 and 519.9m W/cm~2,respectively.These are superior to commercial Nafion 117 membranes.In Chapter 3,3,3’-disulfonate-2,2-bis(4-carboxyphenyl)hexafluoropropane(SCFA)monomer was synthesized,and then a series of sulfonated polybenzothiazoles polymers(s PBT-F)containing hexafluoroisopropyl were synthesized by direct polymerization.With the introduction of hydrophobic flexible hexafluoroisopropyl,s PBT-F membranes could be prepared by solution casting.The results showed that s PBT-F series membranes had good thermal stability,oxidation stability and mechanical properties,but also show excellent water uptake,and dimensional stability.At 80℃,the water uptake and swelling ratio remained in the range of 30-46%and 7.8-14.2%,respectively.Under the condition of 80℃and 100%RH,the proton conductivity of s PBT-F82.5 membrane was up to 0.143 S/cm,the required activation energy was only 4.38 k J/mol,the power density,and current density were 344.33m W/cm~2 and 0.99 A/cm~2,respectively.Meanwhile,after a 20 h durability test,s PBT-F82.5membrane could still maintain a stable voltage of 0.6V.In Chapter 4,the relative properties of the PEM were improved by controlling the aggregation structure of the hydrophilic and hydrophobic phases.First,a series of sulfonated polybenzimidazole-polybenzimidazole block copolymers(s PBTx-PBI)were synthesized by coupling reaction.Then,s PBTx-PBI block copolymer membranes were prepared by solution casting method,and a series of membranes with different crosslinking degrees were obtained by high-temperature crosslinking.The results showed that s PBT12-PBI membrane had the best comprehensive properties among the block copolymer membranes.Its water uptake,swelling ratio,and proton conductivity at 80℃were 40.5%,14.8%,and 0.124 S/cm,respectively.After crosslinking treatment,the swelling ratio of s PBT12-PBI-20%crosslinking membrane was 14.2%,and the dissolution time of s PBT12-PBI-20%in the Fenton reagent increased to 7.3 h.Under the condition of 80℃and 100%RH,the proton conductivity of s PBT12-PBI-20%membrane could reach 0.115 S/cm,and the power density of 384.00 m W/cm~2 and the current density of 1.37 A/cm~2 were shown.It is better than a commercial Nafion 117 membrane under the same conditions.