Exergy Analysis of Polymer Electrolyte Fuel Cell Systems Using Methanol

An exergy (available energy) analysis has been conducted on a typical polymer electrolyte fuel cell (PEFC) system using methanol. The material balance and enthalpy balance were calculated for the PEFC system using methanol steam reforming, and the exergy flow was obtained. Based on these results, the exergy loss in each unit was obtained, and the difference between the enthalpy and exergy was discussed. The exergy loss in this system was calculated to be 178kJ/mole MeOH for the steam reforming process of methanol. Although the enthalpy efficiency approached unity as the recovery rate of the waste heat from the cell approached unity, the exergy efficiency remained around 0.45 since the cell’s operating temperature of 80°C is low. It was also found that the cell voltage should exceed 0.82V in order to obtain the exergy efficiency of 0.5 or higher. A direct methanol fuel cell (DMFC) was analyzed using the exergy and compared with the methanol reforming PEFC. In order to obtain the exergy efficiency higher than that of PEFC with steam reforming, the cell voltage of the DMFC should be 0.48V or greater at the current density of 600mA/cm².