Many scientists are conducting research to develop new energy conversion technologies to reduce the consumption and demand of traditional fossil fuels and protect the environment. Polymer electrolyte membrane fuel cells (PEMFCs) have attracted considerable attention for vehicular transportation and portable applications due to their low greenhouse gas emission and high energy conversion efficiency. As a key component of PEMFCs, proton exchange membranes (PEMs) support proton transfer, and their study is of great interest.
A new series of partially fluorinated and sulfonated poly(biphenylsulfone ketone) block copolymers as proton exchange membrane materials were directly prepared from hydrophilic and hydrophobic oligomers via a nucleophilic aromatic substitution reaction. The backbones of these block copolymers consisted of sulfonated poly(ether sulfone) and poly(ether ether ketone). The degrees of sulfonation (DS) of the block copolymers (10%, 30%, or 50%) were controlled by changing the molar ratio of the hydrophilic and hydrophobic parts. The copolymers were characterized by 1H NMR, FT-IR, gel permeation chromatography (GPC), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) thermograms. Proton NMR, FT-IR and GPC were used for DS determination and structural analysis. The membranes showed excellent thermal and oxidative stability; e.g., TGA and DSC demonstrated that all sulfonated block copolymers exhibited good thermal stability with an initial weight loss at temperatures above 200℃. Block copolymer-30 membranes showed low water uptake and acceptable ionic exchange capacity (IEC). The proton conductivity of the block copolymer-30 was 75 mS cm-1 at 90℃ and 100% relative humidity, while Nafion-117 had a value of 98 mS cm-1 under the same conditions. AFM analysis of the block copolymer-30 clearly showed that the morphology of the membranes separated the hydrophilic and hydrophobic domains which provided an effective proton-transport path way.