Overpotential analysis of the Direct Formic Acid Fuel Cell

An overpotential analysis is carried out in the range of 298 K-353 K to clarify the dominant overpotential factor above 333 K of the direct formic acid fuel cell, DFAFC using 2 mg cm−2 of Pd-black catalyst for the anode. It is found that the mass transport overpotential at the anode which is estimated at a specific current density showing the maximum current density increases from 45 mV to 196 mV when the cell temperature increased from 298 K to 353 K although the formic acid crossover flux through the membrane also increases. Moreover, the effect of the loading of microporous layer, MPL, in the range of 1-4 mg cm−2 at the anode fabricated using Nafion as a binder, which affects the mass transport, on the overpotential behavior is also investigated. It is found that the lower MPL loading is appropriate for the DFAFC operation due to the poor mass transport of the formic acid although the higher MPL loading is appropriate for the hydrogen-oxygen, PEFC, operation. Based on the comparisons of the overpotential distributions between the DFAFC and the PEFC, it is suggested that both the poor mass transport in the anode and the formic acid crossover should be simultaneously improved in order to obtain the higher power density of the DFAFC above 333 K.