Effect of water vapor on the ion transport in polymer films of PVOH/LiH2PO4/H2O

Solid polymer ionic conductors have been prepared by chemical doping of poly(vinyl alcohol) (PVOH) with lithium dihydrogen-phosphate (LiH2PO4) and water. Transparent, strong and dry to the touch membranes are obtained if the ambient relative humidity (RH%) is lower than 50%. Samples with salt/polymer content of x≤0.2 exhibit a stable solid phase up to approximately 200 °C. The conductivity data of the membranes (their water content mass is about 10% of the sample's mass) show a sensitive variation with doping rate, reaching a value of the order of 10−3 S cm−1 at room temperature for the sample with the highest salt content (x=0.2). These conductivity data as a function of temperature are better modulated by a VTF equation. The latter depends very much on the presence of water. We have found that the equations valid for electrolytic solutions of completely dissociated salts fit the experimental data satisfactorily. In fact, a modified Onsager equation, valid for electrolytic solutions, seems to be suitable to describe the change in the film resistance as a function of relative humidity.