Fuel Cell Electrolytes of Polybenzimidazole Membranes Cross‐linked with Bis(chloromethyl) Arenes

Abstract

Cross‐linking of phosphoric acid doped polybenzimidazole membranes as fuel cell electrolytes represents an attractive approach to improving the mechanical robustness at a high acid loading. Numerous cross‐linking concepts have been reported in the literature, but a deeper understanding of how the cross‐linking chemistry affects the physicochemical properties of the membrane and its fuel cell performance and durability remains to be assessed. In this work, a series of cross‐linked membranes are prepared using cross‐linking agents of different regio‐chemistry and steric nature. It is shown, that the nature of the cross‐linking agent has a large impact on the effective degree of cross‐linking, which in turn determines the acid doping characteristics and ultimately the fuel cell performance and acid retention during long‐term operation.

From polybenzimidazoles to polybenzimidazoliums and polybenzimidazolides

“…Controlled crosslinking can be carried out by co-casting the polybenzimidazole from an organic solvent containing the bifunctional halomethyl electrophile and initiating the N-substitution in the solid state at elevated temperatures. The method has been utilized to produce crosslinked m-PBI with a wide range of crosslinking agents such as α,α´-dichloro-p-xylene (and derivatives thereof), 36,200 α,α´-dibromo-p-xylene, 201 1,12-diiodododecane, 202 1,3,5-tris(bromomethyl)benzene, 203,204 dichloromethyl phosphinic acid, 205 bismaleimide 35 and silanes. 206 Alternatively, m-PBI can be crosslinked in a heterogeneous process where the polymer film is immersed in a solution containing the crosslinking agent.…”

Polysulfone-polyvinylpyrrolidone blend membranes as electrolytes in alkaline water electrolysis

“…Density measurements were carried out to determine the concentrations by comparison with data in the literature [47]. Zirfon Perl UTP 500 was supplied by Agfa and the polybenzimidazole (poly(2,2´-(m-phenylene)-5,5´bibenzimidazole), m-PBI) membrane was prepared as reported elsewhere [48]. For electrode preparation, nickel foam (mean pore size/thickness: 800/2500 µm and 450/1600 µm) supplied by Alantum was used.…”

Performance degradation and mitigation of high temperature polybenzimidazole-based polymer electrolyte membrane fuel cells

“…Many PBI derivatives of widely different backbone structures have been designed and synthesized, and the structural scope has grown tremendously during the past two decades. 3 Crosslinking is one of the effective ways to increase membrane durability, and covalent crosslinking by N-coupling using bifunctional alkyl/aryl halides, [119][120][121] Michael acceptors, 122 or epoxides 123 is the most studied approach. Alternative routes of crosslinking have also been proposed e.g., via reactions between sulfonated polymers with electron-rich aromatic rings of the polymer backbone in a Friedel-Crafts sulfonylation.…”