Passive Direct Methanol Fuel Cell System with Adaptive Fuel Concentration Control based on Liquid Surface Tension

The direct methanol fuel cell (DMFC) is considered as a potential power source candidate for portable electronics due to its high power density, efficient and environmental friendly operation. However, the fixed concentration fuel supply in existing DMFC systems relies on either the diluted methanol solution carrying or the active delivery driven by attached pump. Both approaches limit the power density or degrade the overall efficiency of the DMFC system significantly. Such disadvantages become more severe in small-scale DMFCs which require high conversion efficiency and small physical space suitable for portable electronics. In this paper, a passive fuel delivery component based on surface tension driving mechanism was designed and integrated in a laboratory-made prototype to achieve consumption depending fuel concentration control and power-free fuel delivery. The unidirectional methanol-to-water smooth flow is achieved through the capillaries of the Teflon PolyTetraFluoroEthylene (PTFE) membrane based on the difference in their properties of liquid surface tension. The prototype was demonstrated to exhibit a better polarization performance compared to the conventional DMFCs. Its high efficiency and load regulation performance was also proved in contrast with active DMFC fed with constant concentration fuel. The passive fuel delivery effect demonstrated here is believed to be more applicable for the future small scale DMFC development.