A novel crosslinking strategy for preparing poly(vinyl alcohol)-based proton-conducting membranes with high sulfonation

Abstract

This study synthesizes poly(vinyl alcohol) (PVA)-based polymer electrolyte membranes by a two-step crosslinking process involving esterization and acetal ring formation reactions. This work also uses sulfosuccinic acid (SSA) as the first crosslinking agent to form an inter-crosslinked structure and a promoting sulfonating agent. Glutaraldehyde (GA) as the second crosslinking agent, reacts with the spare OH group of PVA and forms, not only a dense structure at the outer membrane surface, but also a hydrophobic protective layer. Compared with membranes prepared by a traditional one-step crosslinking process, membranes prepared by the two-step crosslinking process exhibit excellent dissolution resistance in water. The membranes become water-insoluble even at a molar ratio of SO 3H/PVA–OH as high as 0.45. Moreover, the synthesized membranes also exhibit high proton conductivities and high methanol permeability resistance. The current study measures highest proton conductivity of 5.3 × 10 −2 S cm −1 at room temperature from one of the synthesized membranes, higher than that of the Nafion ® membrane. Methanol permeability of the synthesized membranes measures about 1 × 10 −7 cm 2 S −1, about one order of magnitude lower than that of the Nafion ® membrane.