Synthesis and characterization of high molecular weight hexafluoroisopropylidene‐containing polybenzimidazole for high‐temperature polymer electrolyte membrane fuel cells

Abstract

A high molecular weight, thermally and chemical stable hexafluoroisopropylidene containing polybenzimidazole (6F‐PBI) was synthesized from 3,3′‐diaminobenzidine (TAB) and 2,2‐bis(4‐carboxyphenyl) hexafluoropropane (6F‐diacid) using polyphosphoric acid (PPA) as both the polycondensation agent and the polymerization solvent. Investigation of polymerization conditions to achieve high molecular weight polymers was explored via stepwise temperature control, monomer concentration in PPA, and final polymerization temperature. The polymer characterization included inherent viscosity (I.V.) measurement and GPC as a determination of polymer molecular weight, thermal and chemical stability assessment via thermo gravimetric analysis and Fenton test, respectively. The resulting high molecular weight polymer showed excellent thermal and chemical stability. Phosphoric acid doped 6F‐PBI membranes were prepared using the PPA process. The physiochemical properties of phosphoric acid doped membranes were characterized by measuring the phosphoric acid doping level, mechanical properties, and proton conductivity. These membranes showed higher phosphoric acid doping levels and higher proton conductivities than the membranes prepared by the conventional membrane fabrication processes. These membranes had sufficient mechanical properties to be easily fabricated into membrane electrode assemblies (MEA) and the prepared MEAs were tested in single cell fuel cells under various conditions, with a focus on the high temperature performance and fuel impurity tolerance. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4064–4073, 2009

Synthesis and Properties of Segmented Block Copolymers of Functionalised Polybenzimidazoles for High‐Temperature PEM Fuel Cells

“…Recently, a novel method of synthesising high-molecular weight PBI polymers and casting films was developed [32,33,[36][37][38][39][40][41]. This method, termed the PPA process, eliminates many of the problems associated with the conventional procedures.…”

“…Typically, the polymer backbone has a strong basic site such as an ether, alcohol, imine, amide or imide group and can react strongly with acids. Among the polymers investigated were poly(ethylene oxide) (PEO) [26], poly(vinyl acetate) (PVA) [27], polyacrylamide (PAAM) [28][29][30], poly(ethyleneimine) (PEI) [31] and polybenzimidazole (PBI) [32][33][34][35][36][37][38][39][40][41]. In these cases, phosphoric acid (PA) is typically used as the proton conductor due to its thermal stability and high-proton conductivity at high temperature.…”

Synthesis and Properties of Random Copolymers of Functionalised Polybenzimidazoles for High Temperature Fuel Cells

“…The polyphosphoric acid process (PPA process) can be used to synthesise a wide variety of PBI chemistries and removes the time intensive, multi-step process needed to produce conventional PA-doped PBI films. A number of homopolymers and copolymers have been investigated using the PPA process, including m-PBI, AB-PBI, p-PBI [32], pyridine-based PBIs [28], dihydroxy-PBI [29] and fluorinated PBIs [30,31].…”

Sulfonated Polybenzimidazoles for High Temperature PEM Fuel Cells

“…After approximately two hours, the solution was a uniform blue-green color and all polymer had dissolved. A 5 mL aliquot was removed at various time intervals (20,24,27,46,53, and 92 h) and quenched in ice water. Once quenched, the polymer was washed with ice water until a neutral pH was reached.…”

“…PBIs have been produced from 3,3 0 ,4,4 0 -tetraaminobiphenyl and various dicarboxylic acids. [23][24][25][26][27][28] After polymerization, PBI solutions are cast directly from PPA, a hygroscopic material, which then absorbs water from the atmosphere and is hydrolyzed to phosphoric acid (PA) in situ. PPA is a good solvent for many PBIs, whereas PA is not.…”