Open circuit voltage and methanol crossover in DMFCs

It is difficult to definitely measure the open circuit voltage (OCV) of a direct methanol fuel cell (DMFC). For example, after a cell is changed from a loaded state to a no load, open circuit state, the voltage increases quickly and reaches a peak value in seconds. Some might use this peak voltage as the OCV. However, the voltage starts to decline quite rapidly following the peak, and it takes several minutes to become stabilized at a lower value. This stabilized, lower voltage should be used as the OCV. Another unique and interesting phenomenon is the rapid cell voltage increase following an initial instant decline when a load is applied to a DMFC. This increase is believed to be due to diminishing of excess methanol that accumulates at the cathode side during the open circuit period. The effects of air flow rate, methanol concentration and cell temperature on the OCV, methanol crossover and cell performance were also studied.