A new strategy for designing high-performance sulfonated poly(ether ether ketone) polymer electrolyte membranes using inorganic proton conductor-functionalized carbon nanotubes

Abstract

Abstract Remarkable progress has been made on the use of polymer electrolyte membranes (PEMs) for renewable-energy-related research. In particular, carbon nanotubes (CNTs) have emerged as versatile nanomaterials to modify PEMs. However, the inert ionic conduction ability and possible short-circuiting risk are the two major obstacles to their further development. In this work, CNTs are firstly functionalized with an inorganic proton conductor, boron phosphate (BPO 4 ), using a facile polydopamine-assisted sol-gel method to yield BPO 4 @CNTs. This new additive is then used to modify sulfonated poly(ether ether ketone) (SPEEK). Polydopamine coating layer can act as an extraordinary glue to homogeneously adhere BPO 4 nanoparticles on CNTs, thereby not only reducing the risk of short-circuiting, but also fabricating new proton-conducting pathways in the composite membranes. A comprehensive characterization reveals that the thermal stability, tensile properties, and dimensional stability of PEMs are significantly improved. Compared with pure SPEEK, the proton conductivity of SPEEK/BPO 4 @CNTs-2 is improved by 45% and 150% at 20 °C and at 80 °C, respectively. Furthermore, the H 2 /O 2 cell performance of SPEEK/BPO 4 @CNTs-2 membrane exhibits a peak power density of 340.7 mW cm −2 at 70 °C, which is significantly better than that of pure SPEEK (254.2 mW cm −2 ), demonstrating the great potential of proton conductors-functionalized CNTs in PEMs.