Synthesis and properties of highly branched polybenzimidazoles as proton exchange membranes for high-temperature fuel cells

Abstract

Highly branched polymers applied as low-temperature proton exchange membranes (LTPEMs) have attracted attention from researchers because of their outstanding properties.

Branched Sulfonated Polyimide/Sulfonated Methylcellulose Composite Membranes with Remarkable Proton Conductivity and Selectivity for Vanadium Redox Flow Batteries

“…The WU s of all bSPI/s‐MC composite membranes are higher than that of Nafion 115 membrane. According to the molecular structure, the branched SPI membrane should have a treelike three‐dimensional spatial structure similarly as presented by H. X. Xie et al and J. P. Ni et al., because branched SPI polymer consists of branched monomer (TAPOB) with three reactive −NH 2 groups. Such a branching structure leads to a large free volume of most bSPI/s‐MC composite membranes compared with Nafion 115 membrane, causing the higher WU s of most bSPI/s‐MC composite membranes in contrast with Nafion 115 membrane.…”

Alkali‐doped hyperbranched cross‐linked polybenzimidazoles containing benzyltrimethyl ammoniums with improved ionic conductivity as alkaline direct methanol fuel cell membranes

“…[33][34][35][36] Most cross-linkers used in AEMs contained one or more quaternary ammoniums to connect the polymer chains to increase the concentration of OH − , thus improving the ionic conductivity; however, ammoniums are easy to be attacked by OH − , resulting in decreased mechanical properties and alkaline stability. We have focused on developing proton/anion exchange membranes several years, 32,[37][38][39][40][41][42][43][44][45][46][47][48][49] herein, to improve the ionic conductivity of alkali-doped PBIs without scarifying mechanical robust and alkali stability. This paper introduced a novel kind of hyperbranched cross-linkers to PBI membranes ( Figure 1).…”

Cross‐linked polymer electrolyte membrane based on a highly branched sulfonated polyimide with improved electrochemical properties for fuel cell applications

“…25,26 Cross-linking is based on the reactions between acridine groups and dibromoalkanes, 27 carboxylic and alkane diols, 28 maleimide and poly (ethylene glycol) diacrylates, 29 sulfonic acid groups and fluorenyl, 30 etc. 36,42,43 We believe that the branched structures in the molecular main chains improve the performance of a PEM in two ways: (a) the rigidity or distortion from the B 3 with long "arms" increases the interchain spaces of the PEM, which facilitates WU and proton conductivity; (b) the B 3 -linked molecular chains enhance the chemical stability. Generally, cross-linked membranes have shown lower water-uptake (WU) values and proton conductivities than the corresponding pristine membranes because molecular motion is depressed by the cross-linked structures.…”

“…41 In our previous work, highly branched polymer such as branched sulfonated polyether ether ketone, poly (arylene ether sulfone), and branched polybenzimidazole were synthesized and exhibited considerable proton conductivity, high oxidative stability, and good solubility. 36,42,43 We believe that the branched structures in the molecular main chains improve the performance of a PEM in two ways: (a) the rigidity or distortion from the B 3 with long "arms" increases the interchain spaces of the PEM, which facilitates WU and proton conductivity; (b) the B 3 -linked molecular chains enhance the chemical stability.…”