Characteristics of exergy transport and energy utilization in direct methanol fuel cell

An exergy analysis model for direct methanol fuel cell (DMFC) was established. Taking methanol crossover and overpotential into account, an expression of exergy efficiency which revealed the effects of irreversiablity on exergy transport were deduced. Further more, the utilization rate of energy stored in methanol and investigated changes of electric efficiency and thermal efficiency under various methanol crossover rates, current densities, operating temperature, and cathode pressure were quantitatively calculated. Some suggestions on optimizing operating conditions of direct methanol fuel cell based on the findings were also conducted. It was found that the thermal energy generated in fuel cell covered a significant amount of exergy in total energy and should be sufficiently used to improve total efficiency in a DMFC. Based on the investigation, the high methanol crossover rate is the predominant cause of energy loss when the fuel cell operates under low current density and total exergy efficiency of a DMFC reaches peak value when operating current is near limited density.