In order to take full advantage of the high energy density available in methanol fuel, one must use high concentration methanol in direct methanol fuel cells (DMFCs). However, this causes severe methanol crossover and leads to low power density and fuel efficiency. In this work, a tubular shape is adopted to generate higher volumetric power density; porous polytetrafluoroethylen (PTFE) membranes at the anode are used to control methanol transport with a high concentration fuel. A novel passive tubular-shaped DMFC is improved to achieve stable operation with methanol concentrations up to 20 M. It is observed that a balance between fuel transport resistance, power density, energy density, and fuel efficiency exists. Increased resistance enhances fuel efficiency, hence, energy density, but limits the fuel supply and causes low power density. With the improved anode structure and higher concentration fuel (1 M to 15 M), the energy output of the tubular DMFC increases 591%, from 0.094 Wh to 0.65 Wh with 2 ml fuel. The power densitymaintains the same level as 16 mW/cm2. For different fuel concentrations, there exists an optimum structure to generate the highest power density, which is a result of minimizing the methanol crossover while also providing sufficient fuel. The discharge characteristic at constant voltage and its effect on fuel efficiency are also discussed.

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