Analysis of a Passive Tubular Direct Methanol Fuel Cell

In this work, it is shown that a novel tubular-shaped, passive Direct Methanol Fuel Cell (DMFC) can produce up to 2 times the instantaneous volumetric power density of a planar DMFC. First a numerical model was developed to determine the benefits of a tubular geometry and design characteristics for a passive tubular-shaped DMFC. Secondly, a tubular-shaped DMFC frame was designed, built, and tested to improve upon existing tubular DMFC literature and compare against an identical planar-shaped DMFC. From the numerical model, it was determined that increasing the ambient temperature from 20 to 40 °C increases the peak power density produced by the fuel cell during operation with 1 and 2 M methanol solutions. During operation with 3 M methanol the increased methanol crossover and oxygen depletion along the Cathode Transport Layer (CTL) reduce the power from the tubular DMFC. It was also determined that the thickness of the CTL must be greater than 1 mm for 1 M operation, greater than 5 mm for 2 M operation, and greater than 10 mm for 3 M methanol operation to prevent oxygen limitations along the CTL. From the experimental work, a tubular-shaped DMFC was built that presented an 870% improvement in power density from the previous best, passive, tubular-shaped DMFC found in the literature. The tubular DMFC produced 24.9 mW cm⁻² while the planar DMFC produced 23.0 mW cm⁻² with a Nafion® 115 membrane and 3 M methanol. The tubular DMFC experienced slightly higher methanol crossover than the planar DMFC, potentially due to a higher static fluid pressure in the Anode Fuel Reservoir (AFR), which is caused by the vertical orientation of the tubular fuel reservoir.