Effect of Formic Acid on Fuel Cell Performance for Automobile Applications

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Introduction The allowable concentration of formic acid is defined as 0.2 ppm in Grade D of ISO 14687: 2019, which is the hydrogen quality specification for fuel cell vehicles. The effect of formic acid in hydrogen on polymer electrolyte fuel cell (PEFC) performance has been reported by some researchers [1-4], but the reaction mechanism of formic acid in the PEFC is not well understood. In this study, the reaction behavior of formic acid in the PEFC and its impact on voltage decrease were investigated. Experimental The effect of formic acid in hydrogen was evaluated using a single cell. A “JARI Cell 2” with a 25 cm2 electrode area and double serpentine flow channels was used in the experiment. The anode and cathode catalysts were Pt/C (TEC10E50E, Tanaka Kikinzoku Kogyo). The platinum loadings on the anode and cathode were 0.05 mg cm-2 and 0.30 mg cm-2, respectively. The electrolyte membrane was a fluorine-based material with a thickness of 12 μm. The 22BB (SGL Carbon) gas diffusion layers were used on both the anode and cathode.The single-cell tests were performed at a cell temperature of 60°C and without external humidification. This is because formic acid easily dissolves in water and is likely to be exhausted from the cell with water at high humidification, so no humidification is considered the most severe condition. Before formic acid addition, the preconditioning was conducted at 1.0 A cm-2 of current density using high-purity hydrogen as a fuel for more than 10 hours. Then, formic acid (15-300 ppm) was started to supply the anode. After a period of time, the supply of formic acid to the anode was stopped and the voltage recovery was evaluated. Results and discussion Figure 1 shows the voltage drop over time due to formic acid in hydrogen at a current density of 1.0 A cm-2 and cell temperature of 60˚C. The voltage dropped quickly after the start of the formic acid supply, but the amount was small even at high formic acid concentrations. The voltage drop due to formic acid was 14 mV after 25 hours at 60 ppm and 20 mV after 5 hours at 300 ppm. The voltage was recovered after stopping the formic acid addition.To understand the reaction behavior of formic acid during the fuel cell operation, the anode and cathode exhaust gas were analyzed by gas chromatograph-mass spectrometer. The result showed that no formic acid was detected from the anode or cathode while the fuel cell was operated at a current density of 1.0 A cm-2 with 15 ppm formic acid addition to the anode. Meanwhile, the amount of CO2 equivalent to that supplied to the anode as formic acid was detected from the cathode exhaust gas. The results suggest that formic acid supplied to the anode permeated through the electrolyte membrane as shown in Fig. 2 and was oxidized at the cathode. Acknowledgment This work is based on results obtained from a project, JPNP18011, commissioned by the New Energy and Industrial Technology Development Organization (NEDO).