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This study is focused on development of membrane electrode assembly (MEA) for direct formic acid fuel cell (DFAFC). The effects of the backing layer, the loading of the gas diffusion layer (GDL), the carbon structures and the electrolyte membrane types, and fuel concentrations on the DFAFC's performance are investigated. Two types of backing layer are used in either a carbon paper (CP) or carbon cloth (CC) form, and three different types of carbon structures, carbon black (CB), carbon nanofiber (CNF) and carbon nanotube (CNT), are studied. A single cell DFAFC is tested to obtain the performance of the MEA, including the open circuit potential (OCP), current density, and power density. From the results, carbon paper indicates a much better performance than carbon cloth and gas diffusion layer (GDL) with 1 mg cm-2 loading shows a uniform surface morphology under scanning electron microscopy (SEM) and records a higher power density than 2.5 mg cm-2. Moreover, it is found that the power density increases with increase of the formic acid concentration up to an optimum concentration. However, the optimum fuel concentrations are different for each type of carbon structure. The highest power density is obtained using a combination of CNT and electrolyte membrane of Nafion 117 at 18.36 mW cm-2 using 10 M fuel concentration.

An air-breathing stack for a direct formic acid fuel cell (DFAFC) was designed, fabricated and evaluated. The DFAFC stack consisted of six cells arranged in a hexagonal arrangement and each single cell contained a pair of stainless steel current collectors, a membrane electrode assembly (MEA) and a cathode end-plate. A fuel reservoir was located at the center which supplied formic acid supply to the anode of each cell. The effects of fuel concentration, palladium (Pd) loading at the anode and activation on DFAFC performance and long term operation were evaluated. DFAFC stack performance increased with increasing fuel concentration and a stable power up to 200 mW at 2.4 V was achieved for passive and ambient conditions at a 7 M fuel concentration. Catalyst loading had a slight effect on DFAFC performance, where 4 mg cm -2 Pd loading was best for 7 M fuel operation. During long-term operation, the DFAFC stack could be operated for 27 hours without adding more fuel and less than a 20 % reduction in performance during operation. MEA reactivation with deionized water technique was required for immediate recovery of stack performance.Keywords: stack, activation, passive direct formic acid fuel cell, membrane electrode assembly Abstrak Tindanan pasif udara bagi sel bahan api asid formik langsung (DFAFC) direka bentuk, difabrikasi dan diuji. Tindanan DFAFC mengandungi enam sel yang dibentuk secara susunan heksagon. Setiap sel mempunyai sepasang pengumpul arus, himpunan membran elektrod (MEA) dan plat penghujung katod. Takungan bahan api ditempatkan di tengah yang mana akan membekalkan asid formik ke setiap sel. Kesan kepekatan bahan api, kandungan palladium (Pd) di anod dan pengaktifan terhadap prestasi dan jangka masa panjang DFAFC dikaji. Prestasi tindanan DFAFC meningkat dengan peningkatan kepekatan bahan api dan kuasa yang stabil sehingga 200 mW dicapai pada 2.4 V dan 7 M kepekatan bahan api dalam keadaan pasif dan persekitaran. Kandungan mangkin mempunyai kesan minimum terhadap prestasi DFAFC yang mana kandungan Pd 4 mg cm -2 merupakan kandungan terbaik bagi pengoperasian 7 M kepekatan asid formik. Sepanjang pengoperasian jangka masa panjang, tindanan DFAFC boleh beroperasi selama 27 jam tanpa menambah bahan api di dalam takungan dan kurang daripada 20 % pengurangan prestasi tindanan. Pengaktifan MEA menggunakan teknik nyahion air diperlukan bagi pemulihan segera prestasi tindanan DFAFC.Kata kunci: tindanan, pengaktifan, sel bahan api asid formik langsung pasif, himpunan membran elektrod ISSN -2506 Mohd Shahbudin et al: EFFECTS OF FUEL CONCENTRATIONS, CATALYST LOADINGS AND ACTIVATION ON THE PERFORMANCE OF DIRECT FORMIC ACID FUEL CELL (DFAFC) STACK 878Introduction With respect to direct liquid fuel cells (DLFCs), a direct formic acid fuel cell (DFAFC) is a promising alternative to direct methanol fuel cell (DMFC) and direct ethanol fuel cell (DEFC) cells. The main advantages of DFAFC are a relatively high electro-catalytic oxidation rate [1,2] and low crossover rate for the fuel [3 -5] and has the potential...

In order to prepare high Pd containing Pd/SECNF (SiO2 containing carbon nanofiber) catalyst, which showed high formic acid oxidation reaction activity, the effect of the time and frequency on the ultrasonication before the chemical reduction process was investigated. It was found that 45 kHz and 45 min was the optimum condition. Based on this condition, Pd/SECNF containing 80 wt% of Pd was successfully prepared. Using this catalyst for the DFAFC anode, power generation characteristics was investigated. It was found that the performance was similar to the conventional DFAFC using Pd/C for anode catalyst although the catalytic activity of Pd/SECNF was higher than that of Pd/C. This is due to the high anode mass transport resistance in the anode catalyst layer in the case of Pd/SECNF.

In this study, we developed a carbon black (CB)-embedded carbon nanofiber (CNF) as a Pd support, which showed a high level of formic acid oxidation reaction (FAOR) activity. For the support preparation, heat treatment involving calcination at 1000 °C in a nitrogen atmosphere (carbonization) followed by calcination at 850 °C in water vapor (steam activation) was conducted to form a CB, which contained carbon nanofibers made from a polyacrolynitrile (PAN) fiber prepared by electrospinning. This catalyst showed a high level of FAOR activity. In this situation, the CB was also heat-treated, therefore, it was unclear whether the origin of the high FAOR activity of the CB-embedded CNF was caused by the CNF itself or the heat treatment of the CB. In order to establish the cause of the high FAOR activity of the CB-embedded CNF, the CBs underwent several heat treatments; i.e., stabilization, carbonization, and steam activation. Two types of carbon black with different pore structures, i.e., Ketjen black and Vulcan XC-72, were used to investigate the FAOR activity. The appropriate heat treatment of the CB promotes the improved FAOR activity; however, excessive heat treatment caused a deterioration in the FAOR activity, especially for Ketjen due to the presence of numerous micropores. However, by embedding the CB into the CNF, the FAOR activity improved, especially in the case of Ketjen, even though the embedded CB underwent several heat treatments. The optimum ratio of CB/PAN in the CB-embedded CNF was also investigated. The highest FAOR activity was observed at 0.25 CB/PAN for both the Vulcan and Ketjen. The electronic state of Pd3d in which the binding energy of the metallic Pd shifted to a lower binding energy suggested that the metal–support interaction is strong at the CB/PAN ratio of 0.25. On the basis of these results, it was found that heat treatment of the CB by embedding it in the CNF is a promising way to achieve a metal–support interaction without destroying its structure.