Highly Effective Proton-Conductive Matrix-Mixed Membrane Based on a -SO 3 H-Functionalized Polyphosphazene.

A polyphosphazene with in-built -SO 3 H moieties ( PP-PhSO 3 H ) was facilely synthesized by the polymeric combination of hexachlorocyclotriphosphazene (HCCP) and sulfonate p -phenylenediamine. Characterization reveals that it is a highly stable amorphous polymer. Proton conductivity investigations showed that the synthesized PP-PhSO 3 H exhibits a proton conductivity of up to 6.64 × 10 -2 S cm -1 at 353 K and 98% relative humidity (RH). This value is almost 2 orders of magnitude higher than the corresponding value for its -SO 3 H-free analogue, PP-Ph , which is 1.72 × 10 -4 S cm -1 when measured under the same condition. Consequently, matrix-mixed membranes (labeled PP-PhSO 3 H-PAN) were further prepared by mixing PP-PhSO 3 H with polyacrylonitrile (PAN) in different ratios to test its potential application in the proton-exchange membrane (PEM) fuel cell. The analysis results indicate that when the weight ratio of PP-PhSO 3 H / PAN is 3:1 [named PP-PhSO 3 H-PAN (3:1) ], its proton conductivity can reach up to 5.05 × 10 -2 S cm -1 at 353 K and 98% RH, which is even comparable with those of proton-conductive electrolytes currently used in PEM fuel cells. Furthermore, the continuous test demonstrates that the PP-PhSO 3 H-PAN (3:1) has long-life reusability. This research reveals that by using phosphazene and sulfonated multiple-amine modules as precursors, organic polymers with excellent proton conductivity for the assembly of matrix-mixed membranes in PEM fuel cells can be easily synthesized by a simple polymeric process.