Two polyvinyl chloride (PVC) composites were synthesized and tested for their performance in an electrochemical ethanol sensor device. A PVC-Nafion composite was synthesized by imbuing a porous freestanding PVC membrane with a Nafion solution and allowing the Nafion to cast within the PVC. A PVC-sulfonated silica composited was also synthesized by first allowing a solgel reaction to take place between tetraethylorthosilicate (TEOS) and 3-(trihydroxysilyl)-1-propanesulfonic acid (TPS). A PVC membrane was then imbued with this solution and the sol-gel reaction was allowed to finish within the PVC membrane. The membranes were characterized with FTIR and TGA to confirm the presence of the additives to the PVC membrane. The PVC-Nafion composite was found to show extremely poor performance in a sensor role, due to the Nafion blocking the pores to allow for adequate ionic transport within the PVC film. The PVC-sulfonated silica showed comparable performance to the freestanding PVC, but using 75% less water to achieve the similar results. This has the advantage of being less prone to leaching and flooding, which has significant advantages in a sensor application role. Polyvinyl chloride (PVC) is widely used in industry, and has found a use as a proton exchange membrane (PEM) for fuel cell devices.
1,2Specifically, PVC is used as the membrane of choice for fuel cell breathalyzers, or breath alcohol sensors (BrAS). PVC is used for its durability, chemical robustness, cost and stiffness.3 The PVC used in these devices are of a porous free standing nature with 10 μm spheres and pores of the same diameter. While the PVC itself does not produce the ionic conductivity required for proton conduction, the porous film is usually filled with ca. 4 M H 2 SO 4 to impart ionic conductivity to the membrane.2 This creates a material that has superior ionic conductivity and water-uptake to the more commonly used Nafion membrane for power generating PEM fuel cells. A more detailed analysis of the PVC used in BrASs can be found in our previous studies.
1,2Our previous studies have highlighted that the hydration state of the membrane electrode assembly (MEA) can greatly affect the performance of these BrASs. 1,4 The hydration state of the MEA is mainly influenced by the relative humidity (RH) of the environment in which it is operated. Higher humidity conditions will reduce ionic resistance within the MEA, while lower RH conditions will increase ionic resistance.5 If the device is not calibrated for the humidity conditions it will operate in, the reliability and accuracy of the device will be greatly reduced.Improving water management and retention within the BrAS should reduce the performance variation caused by variable RH. We have recently demonstrated that chemical modification of the porous PVC will not only increase ionic conductivity, but also improve the overall uptake of water within the membrane.2 With a greater content of water within the membrane, performance in lower humidity is expected to increase.We have synthesized composi...