Performance of passive direct formate fuel cells with foamed metal anode

Direct formate fuel cells (DFFCs) are recently attracting more attention, primarily because of the use of the carbon-neutral fuel, the low-cost catalyst and membrane. For improving the passive DFFC cell performance, passive, anion-exchange membrane (AEM) DFFCs were developed in this study using Ni foam as anode diffusion layer (DL) on which the catalyst slurry was coated with three different techniques, including direct brushing (DB), dripping (DR) and dip coating (DC). The catalysts on cathode and anode of the AEM DFFCs were Pt and Pd, respectively, with identical loading of 2 mg/cm2. Nafion was used as anode binder with loading of 1.87 mg/cm2. Both V–I curves and electrochemical impedance spectroscopy (EIS) of those passive AEM DFFCs were measured and investigated with the mixture of potassium formate (HCOOK) and potassium hydroxide (KOH) as anolyte at room temperature. Besides, the micrographs of the catalyst-coated Ni foams were also presented to inspect the catalyst distribution on the DL. An additional cell using traditional carbon cloth as DL was also tested for comparison. The polarization curves and EIS showed that the mass transport to the catalyst layer was significantly enhanced for those cells using Ni foam as DL, compared to the carbon cloth-based passive, AEM DFFC. Besides, the performance of the Ni foam-based DFFC with anode catalyst coated by DC technique was the best among all, while the cell possessing carbon cloth-based anode yielded the lowest maximum power density, 22.5 mW/cm2. The maximum power density of the passive AEM DFFC in this study reached 37.7 mW/cm2 when the cell having Ni foam anode made by DC method was fed with the mixture of 3 M HCOOK in 3 M KOH as liquid fuel. The results suggested that not only the mass transport loss but the activation loss can be lowered with appropriate catalyst distribution over the skeleton of the Ni foam.