Determination of energy efficiency for a direct methanol fuel cell stack by a fuel circulation method

A method of fuel circulation with a fixed amount of fuel was employed to investigate a direct methanol fuel cell (DMFC) stack that was built with metal foam flow fields for the air and fuel flows. The stack power output increases significantly with environmental temperature from 20 to 40 °C. The average peak power per cell at 40 °C is 26 mW cm−2 per cell. The average discharge voltage per cell at peak power does not change with temperature but remains at 0.3 V. The energy output of the stack was determined at constant current or constant voltage with a fixed amount of methanol to feed the anode of the stack until the fuel was consumed. The results by constant current discharge show that at higher temperature the stack has remarkably higher energy output; while at the same temperature only a suitable magnitude of discharge current can achieve the highest energy output. The results by constant voltage discharge show that the Faradic efficiency is 86%, and the energy efficiency is 17% at 30 °C.