Transient analysis of passive direct methanol fuel cells with different operation and design parameters

• A transient multiphase model for passive DMFC is developed.
• Effects of current, voltage, MPL and methanol feeding condition are investigated.
• Voltage needs to be moderate to ensure energy efficiency and density.
• AMPL and CMPL can all reduce methanol crossover, but AMPL is more important.
• Fuel tank size has considerable effect on energy density, but not energy efficiency.

By developing a transient multiphase model for passive direct methanol fuel cell (DMFC), the effects of operating current density, voltage, micro-porous layer (MPL) and methanol feeding condition are comprehensively investigated for the whole operating processes (fuel tank from full to empty). It is found that for all the operating conditions, it is necessary to operate at moderate current density or voltage to limit the methanol crossover and ensure the energy conversion efficiency. The MPL in anode is needed to provide sufficient flow resistance at the MPL/gas diffusion layer (GDL) interface to improve the fuel efficiency. Although the cathode MPL can strengthen the convective transport of methanol from cathode to anode, its effect on reducing methanol crossover is less significant than the anode MPL. If the energy density is the most important factor, it is suggested to operate with sufficiently high methanol feeding concentration; and if the fuel and energy efficiencies have the priority, the methanol feeding concentration needs to be moderate. Increasing the size of fuel tank generally improves the energy density, but has negligible effect on the fuel and energy efficiencies.