The modification of fuel cell-based breath alcohol sensor materials to improve water retention of sensing performance

Abstract

Fuel cell based breath alcohol sensors (BrASs) are one of the most important tools used by law enforcement today. While these devices are used globally, they all suffer from a common deficiency: reliance on water. The ability of the fuel cell sensor to manage water content is one of the greatest fundamental challenges facing this technology today. A next-generation fuel cell was designed specifically for sensor testing along with a test station that allowed for rapid response and sensor characteristics of a given material. The in-house design was validated against a commercial cell to provide feedback on how materials in the in-house cell would behave in a commercial designed unit. The results showed that our cell with a commercial membrane electrode assembly (MEA) behaved identically to a commercial cell with the same MEA. Membranes were for their role in senor performance. Membranes for power generation, such as Nafion, were investigated and while they showed good performance in high humidity, performance suffered in low humidity. This is due to the thin characteristics of the material. Poly-vinyl chloride (PVC) membranes showed improved performance over Nafion, while composites of PVC and sulfonated silica showed performance that matched that of the commercial PVC, whilst using significantly less water. Finally, the catalyst layer and gas diffusion layer (GDL) were investigated. For the catalyst layer, platinum black and 20% platinum supported on carbon achieved similar results. The choice of catalyst was less of an issue than the choice of GDL. It was found that using carbon fiber paper GDLs lead to greater retention of water in the MEA compared to carbon cloth GDLs due to the lower air permeability. This came at a cost however in that with a lower air permeability, less ethanol vapour would reach the catalytic sites, reducing sensing performance.