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

Abstract

Summary Development of anion exchange membranes (AEMs) with good performance, such as high conductivity, good alkaline stability and mechanical strength, has been a hot topic for the fuel cell application. Here, a novel kind of hyperbranched cross‐linker decorated with quaternary ammonium groups was introduced to polybenzimidazole (PBI) membranes and QOPBI‐x membranes (where x is the weight ratio of the hyperbranched cross‐linker). Compared with the linear OPBI membrane (0.091 S cm−1), QOPBI‐x membranes displayed an improved ionic conductivity (up to 0.122 S cm−1) at 60°C after they were doped in 6 M KOH for 7 days. The KOH‐doped QOPBI‐x membranes also exhibited a high tensile strength (54.5‐61.7 MPa) and superior alkaline stability. There is almost no decline in the ionic conductivity after being immersed in a 6 M KOH solution for 30 days. In addition, the alkaline direct methanol fuel cell (ADMFC) performance based on the KOH‐doped OPBI and QOPBI‐x membranes is described. The QOPBI‐15 membrane displayed good performance (75.6 mW cm−2), which is 33.3% higher than the OPBI membrane (56.7 mW cm−2).

Ionomer Significance in Alkaline Direct Methanol Fuel Cell to Achieve High Power with a Quarternized Poly(terphenylene) Membrane

“…Our group previously demonstrated a record-breaking power density of 160 mW/cm 2 for ADMFCs; however, the performance was obtained utilizing high catalyst loadings . Several developments were made thereafter in attempts to improve the performance, catalyst modification and changes in the AEM being the two most prominent areas of interest. ,,,,− However, it was not until recently with the use of a polybenzimidazole (PBI)-based membrane containing graphene oxide (GO) fillers that significant improvements to ADMFC performance were achieved. , Moreover, the researchers were able to decrease the loading of Pt–Ru by ∼75% compared to the ADMFC studied by our group, which is an important step toward reducing manufacturing costs. The improvements of cell performance were ascribed to properties of the membrane such as its high ionic conductivity and decrease in methanol permeability from the addition of the GO fillers.…”

Improvement the hydroxide conductivity and alkaline stability simultaneously of anion exchange membranes by changing quaternary ammonium and imidazole contents

“…Ion-exchange capacity (IEC) values of AEMs were measured by a typical reverse-titration method. [37][38][39] Sample of the membrane was dried at room temperature after soaking in 0.1 M HCl solutions for 48 hours. OH − in the sample membranes converted to Cl − .…”