Abstract
A quaternized polybenzimidazole (PBI) membrane was synthesized by grafting a dimethylimidazolium end-capped side chain onto PBI. The organic–inorganic hybrid membrane of the quaternized PBI was prepared via a silane-induced crosslinking process with triethoxysilylpropyl dimethylimidazolium chloride. The chemical structure and membrane morphology were characterized using NMR, FTIR, TGA, SEM, EDX, AFM, SAXS, and XPS techniques. Compared with the pristine membrane of dimethylimidazolium-functionalized PBI, its hybrid membrane exhibited a lower swelling ratio, higher mechanical strength, and better oxidative stability. However, the morphology of hydrophilic/hydrophobic phase separation, which facilitates the ion transport along hydrophilic channels, only successfully developed in the pristine membrane. As a result, the hydroxide conductivity of the pristine membrane (5.02 × 10−2 S cm−1 at 80 °C) was measured higher than that of the hybrid membrane (2.22 × 10−2 S cm−1 at 80 °C). The hydroxide conductivity and tensile results suggested that both membranes had good alkaline stability in 2M KOH solution at 80 °C. Furthermore, the maximum power densities of the pristine and hybrid membranes of dimethylimidazolium-functionalized PBI reached 241 mW cm−2 and 152 mW cm−2 at 60 °C, respectively. The fuel cell performance result demonstrates that these two membranes are promising as AEMs for fuel cell applications.
Highlights
Polymer electrolyte membrane fuel cells are one type of fuel cell suitable for portable and transportation applications, which feature quick start-up, low operation temperature, low cost, high efficiency, and so on [1,2]
Depending on the polymer electrolyte membrane, this type of fuel cell can be further divided into proton exchange membrane fuel cell (PEMFC) [3,4] and anion exchange membrane fuel cell (AEMFC) [5,6]
AEMFC has been attracted considerable attention in the recent decade due to several advantages over PEMFC, including (1) faster oxygen reduction reaction (ORR) under the basic condition that allows the catalyst at the cathode to employ platinum-free metal or low-platinum catalysts [7,8,9], (2) negligible fuel crossover owing to the hydroxide transport direction opposite to the direction of liquid fuel’s crossover [10,11], as well as (3) minimized corrosion problems in alkaline environments [2,12]
Summary
Polymer electrolyte membrane fuel cells are one type of fuel cell suitable for portable and transportation applications, which feature quick start-up, low operation temperature, low cost, high efficiency, and so on [1,2]. Lin and Ding et al reported that the hydrophilic/hydrophobic micro-phase separation morphology can successfully form in the AEMs based on side chain type quaternized PBI containing dimethylimidazolium cations [24] Wu and He et al studied the influence of grafting strategies on the hydroxide conductivity and fuel cell performance for the AEMs based on side chain type quaternized PBI with quaternary ammounium end-capped groups [25]. Among these cations, dimethylimidazolium is expected to be more alkaline stable. The fuel cell performance tests were carried out to confirm that the pristine and organic–inorganic hybrid membranes of dimethylimidazolium-functionalized PBI promising as AEMs for AEMFC applications
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