Strengthening Phosphoric Acid Doped Polybenzimidazole Membranes with Siloxane Networks for Using as High Temperature Proton Exchange Membranes

Abstract

Two silane compounds, i.e., ((chloromethyl)phenylethyl)trimethoxysilane (Ph‐Si) and 3‐chloropropyltriethoxysilane (Pr‐Si), are employed as covalent crosslinkers to fabricate high temperature proton exchange membranes based on polybenzimidazole (PBI) in order to better understand the correlation between the structure and the property of the crosslinked membranes. All the crosslinked PBI membranes display longer morphology durability over the neat PBI membrane toward the radical oxidation. The crosslinked membranes with the crosslinker containing a rigid group of phenylene (PBI‐Ph) show superior acid doping level, high conductivity, and excellent mechanical strength simultaneously, comparing to those with the crosslinker having a flexible alkyl chain (PBI‐Pr) and the pristine PBI based membrane. The technical feasibility for using as high temperature proton exchange membranes is demonstrated by the acid doped crosslinked PBI‐Ph membranes via fuel cell tests.

Fabrication and investigation of phosphoric acid doped imidazolium siloxane crosslinked poly(2,6‐dimethyl‐1,4‐phenylene oxide) for high temperature polymer electrolyte membranes

“…Therefore, the development of high temperature polymer electrolyte membranes (HT‐PEMs) for fuel cells has attracted much attention recently. The phosphoric acid (PA) doped polybenzimidazole (PBI) membrane has been considered as one of the most promising candidates for HT‐PEMs, as a result of high proton conductivities under low relative humidity and excellent thermal stability . However, several drawbacks still limit the further application of PBI/PA membranes in HT‐PEMFCs, including the poor solubility of PBI with high molecular weight in organic solvents and the toxicity of 3,3′,4,4′‐tetraaminobiphenyl monomer for PBI synthesis .…”

“…The redundant doped PA could increase the skeleton distance of the polymers, reduce intermolecular forces and thus decrease the mechanical strength and the lifetime of the fuel cell . This trade‐off between conductivity and mechanical strength can be expressed by chemical crosslinking, which has been regarded as an effective and widely used approach for the integration of superior properties of HT‐PEMs . For example, Na et al .…”

“…fabricated a dual crosslinked organic–inorganic hybrid membrane based on PAEK and (3‐aminopropyl)triethoxysilane to ensure the membrane had high mechanical properties . In previous work, we prepared PBI based HT‐PEMs using ((chloromethyl)phenylethyl)trimethoxysilane and 3‐chloropropyltriethoxysilane as crosslinkers, respectively . The crosslinked membranes obtained having acceptable mechanical strength retained higher acid doping contents and conductivities but a lower volume expansion than the pristine PBI membrane.…”

“…However, there are few reports on HT‐PEMs based on PPO derivatives . Inspired by previous work, we tried to design and prepare new HT‐PEMs based on imidazolium siloxane crosslinked PPO with excellent comprehensive performances. The imidazole groups in MeIm and SiIm reacted with the benzylbromide groups (–CH 2 Br) of BPPO in different mole ratios to obtain a series of imidazolium PPO membranes (PPO‐SiIm‐MeIm).…”

Effect of Surface-Sulfonated Silica on the Properties of Pyridine-Containing Polybenzimidazoles

“…Currently, the use of PBIs in HTPEFCs is less common mostly because of the deterioration of their mechanical strength at a high acid content and a significant decrease in conductivity caused by the leaching of acid in the presence of water formed during the operation of FCs [4]. The first of the problems can be solved by introducing inorganic particles capable of increasing the membrane rigidity or by chemical "crosslinking" of the polymer units [5,6]. To solve the second problem, new approaches to stabilizing the acid in the polymer matrix are being searched for.…”