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

Abstract

A series of novel segmented block copolymers of sulphonated polybenzimidazole (PBI) (s‐PBI) and p‐PBI were prepared with various polymer ratios (10–90 mol% s‐PBI; 90‐10 mol% p‐PBI). A two‐step synthesis of oligomeric species, followed by combination and further polymerisation was used via the polyphosphoric acid (PPA) process. The membranes showed improved high‐temperature proton conductivities and fuel cell performance over previous literature reports, with moderate incorporation of s‐PBI into the copolymer showing the best results. The non‐humidified fuel cell performance was extensively studied with various fuels and oxidants and showed excellent properties. Block copolymers that incorporated 40, 50 or 60 mol% s‐PBI and the corresponding 60, 50 or 40 mol% p‐PBI, at 0.2 A cm–2 and 160 °C, had hydrogen–air performances of 0.661–0.666 V, depending on composition. The performance was improved using hydrogen–oxygen, with voltages between 0.734 and 0.742 V at 0.2 A cm–2 and 160 °C. Fuel cells operating on a reformed hydrocarbon gas showed decreased performance (0.622–0.627 V, same conditions), especially at lower temperatures, but was significantly improved over previous literature reports of sulphonated PBI membranes operating at high temperatures.

Nanostructured poly(benzimidazole) membranes by N-alkylation

“…There are a few other attempts to achieve nanostructural control, which were reported recently, including (multi)block copolymer synthesis and generally, a positive effect on the conductivity was found but no detailed structural information (e.g. domain size) was provided so far [10][11][12]. Inspired by recent attempts to use graft copolymers to induce microphase-separated structures for organic-electronics applications [13], we aim to synthesize poly[2,2!-(m-phenylene)-5,5!bibenzimidazole] (PBI) based graft-copolymers that can undergo microphase separation.…”

Catalyst, Membrane, Free Electrolyte Challenges, and Pathways to Resolutions in High Temperature Polymer Electrolyte Membrane Fuel Cells

“…Another type, sulfonated PBI has a relatively high conductivity of 0.037 S/cm at 170 • C and zero hydration [58], and Mater and Benicewicz reported another new type of PBI with an impressive conductivity of 0.367 S/cm at 180 • C for a block copolymer consisting of sulfonated PBI segments [59,60]. The longest reported lifetime for a HT-PEM fuel cell is 18,000 h under steady-state conditions [61].…”

Recent advances in polybenzimidazole/phosphoric acid membranes for high‐temperature fuel cells

“…The group of Benicewicz has recently reported the fabrication of a series of PBI homopolymers as well as random and block copolymers . Comparison between homopolymers of m ‐ and p ‐phenyl bridged PBI and block and random copolymers of differing conformation provides insight into the importance of chemical structure to membrane conductivity and fuel cell performance.…”