Overpotential analysis of the Direct Formic Acid Fuel Cell

•The overpotential analysis of the DFAFC was conducted.•Anode mass transport overpotential increased with the increasing cell temperature.•Low anode MPL loading is appropriate for the DFAFC.•Improvement for the anode overpotential is required to obtain higher power desnsity. An overpotential analysis is carried out in the range of 298 K-353K to clarify the dominant overpotential factor above 333K of the direct formic acid fuel cell, DFAFC using 2mgcm−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 45mV to 196mV when the cell temperature increased from 298K to 353K 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 1–4mgcm−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 333K.