Effect of zeolite content on proton conductivity and technical characteristics of the membranes based on crosslinked polyvinyl alcohol

Abstract

Polyvinyl alcohol (PVA)-based ion-exchange membranes are a promising group of materials for use in solid polymer fuel cells (SPFC) due to their high hydrophilicity, film forming ability, low cost, good mechanical properties and the possibility of crosslinking PVA with various chemicals. The compounds with a carboxyl or carbonyl functional group, such as polybasic acids and their anhydrides, were used as crosslinking agents resulting in the formation of a gel. Cross-linking reagents may contain ionic groups, for example, sulfonic, inducing the proton conductivity of PVA in membranes. Ceramic materials based on the oxides of aluminum, silicon, titanium, tin, zirconium, etc. serve as dopants in order to improve the technical characteristics of such membranes, such as to increase ionic conductivity, chemical and thermal stability, as well as the mechanical strength of the membranes. In this work, we report on the preparation of new biodegradable proton exchange membranes for SPFCs based on of polyvinyl alcohol crosslinked with sulfosuccinic acid and doped with beta zeolite particles. The content of zeolite in the composition of the membranes was varied from 1 to 25 %. The effect of the zeolite content on proton conductivity, ion-exchange capacity, moisture content, swelling coefficient, fuel (methanol) permeability and mechanical properties of membranes was studied. An increase in zeolite content from 1 to 25 % leads to an increase in the ion-exchange capacity of membranes from 1.5 to 2.9 mmol/g, a decrease in moisture content from 38 to 28 % and a methanol permeability from 2.27  10 -6 to 6.91  10 -7 cm 2 s -1 . The temperature dependence of the proton conductivity of composite membranes in the range from 30 to 80 oC at the relative humidity of 100 % was studied. The highest value of electrical conductivity was demonstrated by a membrane containing 25 % of BEA zeolite, whose proton conductivity was 23.2 mS·cm -1 .