Highly sulfonated carbon nano-onions as an excellent nanofiller for the fabrication of composite proton exchange membranes with enhanced water retention and durability

Abstract

Highly sulfonated carbon nano-onions (SP–CNOs) with large specific surface area are used as a new type of nanofiller in sulfonated poly(arylene ether sulfone) (SPAES) to construct and adjust the proton transfer channels efficiently. SP-CNOs are synthesized from nanometer diamonds via thermal annealing, phenylation and sulfonation, and characterized by XRD, XPS, BET, Raman and HRTEM. The obtained mesoporous SP-CNOs possess a large specific surface of 350 m2/g and an average pore size of 9.7 nm, which endow the nanoparticles with good dispersivity and hydrophilicity. A series of composite membranes based on SP-CNOs/SPAES are prepared through the solution casting approach and evaluated by FESEM, XRD, TGA, water uptake, proton conductivity, chemical stability and fuel cell performance. The results indicate that the composite membranes all show excellent mechanical toughness and greatly enhanced water-retention capacity, thermal, dimensional and oxidative stability due to the good interfacial compatibility and the formation of hydrogen-bond interaction between SP-CNOs and SPAES. The SPAES/SP-CNOs-1.5 membrane achieves the highest proton conductivity of 181.2 mS/cm at 90 °C, which is 45% higher than that of SPAES; H2/O2 fuel cell performance records a power density of 735 mW/cm2 at 80 °C, which is slightly better than that of Nafion® 112. In addition, the SPAES/SP-CNOs-1.5 membrane undergoes the CV decay of 0.38 mV/h after 168 h at 80 °C, which is comparable to Nafion® 112 (0.43 mV/h) but lower than that for the pristine SPAES membrane (0.54 mV/h). After the accelerated stress test, the SPAES/SP-CNOs-1.5 membrane exhibits superior cell performance and lower hydrogen crossover than the pristine SPAES membrane.