Insight toward the Electrochemical Properties of Sulfonated Poly(2,6-dimethyl-1,4-phenylene oxide) via Impregnating Functionalized Boron Nitride: Alternate Composite Polymer Electrolyte for Direct Methanol Fuel Cell

A series of polymer electrolytes of sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (sPPO) in combination with two-dimensional sulfonated boron nitride (s-BN) has been synthesized to form composite polymer electrolytes for direct methanol fuel cell (DMFC). The sulfonation of boron nitride (BN) has been confirmed by XPS, FT-IR, and elemental analysis. The composite membranes have been characterized for their water content, ion transport phenomenon, and thermo-mechanical stabilities along with methanol crossover resistance. Further, s-BN shows good dispersion in sPPO composite membranes by forming amplified long-range ionic clusters via hydrophilic or hydrogen bonding interaction between the s-BN and sPPO matrix. The optimized s-BN/sPPO (5 wt %) composite membrane reveals 67% higher proton conductivity and one-third methanol permeability compared to pristine sPPO membrane. The s-BN/sPPO (5 wt %) composite membrane presents a DMFC peak power density of 122 mW/cm2, which is higher than the peak power densities of 88 and 60 mW/cm2 for Nafion 117 and pristine sPPO, respectively. The preferential increase in electrochemical selectivity of composite membranes suggests their potential in DMFCs.