Direct methanol fuel cell performance comparison

Performance Comparison in Direct Methanol Fuel Cells... 

Fig. 1.74 Comparison of 1.0M and 3.0M methanol performance in a direct methanol fuel cell equipped with a PSSA-PVDF membrane (MEA- 2) at 80 C.

Fig. 1.79 Comparison of IR corrected plot of 1 x 1 size direct methanol fuel cell (USC-MEA 7) at 90 C and 20 psig with SOA Nafion 117 performance.

Fig. 1.100 Comparison of the performance of USC PSSA-PVDF membranes in direct methanol fuel cells (MEA 10 compared with MEA 13) at 90 C.

Rg. 1.82 Comparison of the performance of 1 x 1 -size direct methanol fuel cell (USC-MEA 8) containing PSSA-PVDF membrane with air and oxygen at 60 "C. 

PEEK with biphenyl pendant groups shows several advantages in comparison to commercial PEEK [71]. For example, the site of sutfonation and degree of sulfonation can be readily controlled. The use of such materials in direct methanol fuel cells showed an excellent performance. 

Electrode Catalysts for Direct Methanol Fuel Cells, Fig. 1 Comparison of cell performance of DMFC and PEFC... 

Figure 4.65. Performance comparison of DMFC equipped with extended reaction zone anode composed of pressed graphite felt with PtRu and PtRuMo, obtained by electrodeposition from a colloidal solution [86, 250], a) 333 K, b) 343, and 353 K. Anode catalyst characteristics are given in Table 4.4. Anolyte 1 M CH3OH - 0.5 M H2SO4, 5 mL min, ambient pressure. Cathode 4 mg cm Pt black, O2 flow rate 500 nil min at 2 atm (abs). [86]. (Reprinted from Journal of Power Sources, 167(2), Bauer A, Gyenge EL, Oloman CW, Direct methanol fuel cell with extended reaction zone anode PtRu and PtRuMo supported on graphite felt, 281-7, 2007, with permission from Elsevier.)...

Figure 10.5. Comparison of XRD patterns (A) shows that of (a) acid-treated CNT and (b) Pt-Ru/CNT (B) shows that of (a) Pt-Ru black and (b) Pt-Ru/CNT [51]. (Reproduced from Journal of Power Sources, 160(1), Jeng KT, Chien CC, Hsu NY, Yen SC, Chiou SD, Lin SH, et al. Performance of direct methanol fuel cell using carbon nanotube-supported Pt-Ru anode catalyst with controlled composition, 97-104, 2006, with permission from Elsevier.)...

Many research groups have reported the fuel cell performance of Pt nanoparticles supported on CNTs at the cathode of H2/O2 fuel cells or direct methanol fuel cells [63, 65, 66, 68, 69, 71, 81, 87, 188, 189, 191-193]. It has been shown that the performance of a CNT-based MEA is better than that of conventional Pt/C MEA [65, 71, 81, 189, 191-193]. For example, Matsumoto and coworkers [193] conducted the fuel cell tests of the MEA with CNTs used as a support for Pt catalysts at the cathode. The authors concluded that enhancements in PEM fuel cell performance are observed by using the CNT cathode in comparison to a conventional carbon cathode in a low current density region (Figure 14.27). The voltage drop above 400 mA/cm was ascribed to the proton diffusion. 

The preparation complexity of perfluorosulfonated membrane and the high cost have restricted PEMFC from commercialization. Many researchers are dedicated to the development of nonflnorinated PEM. The American company Dais has developed styrene/ethylene-bntylene/styrene triblock polymer [51]. This membrane is especially snitable for small power PEMFC working at room temperature. The lifetime of the membrane is up to 4000 h. Baglio did some experiments to test the performance comparison of portable direct methanol fuel cell mini-stacks between a low-cost nonfluorinated polymer electrolyte and Nafion membrane. He found that at room temperature, a single-cell nonfluorinated membrane can achieve maximum power density of about 18 mW/cm. As a comparison, the value was 31 mW/cm for Nafion 117 membrane. Despite the lower performance, the nonfluorinated membrane showed good characteristics for application in portable DMFCs especially regarded to the perspectives of significant cost reduction [52]. 

Baglio, V., Stassi, A., Modica, E., Antonucci, V., Arico, A.S., Caracino, R, BaUabio, O., Colombo, M., and Kopnin, E. Performance comparison of portable direct methanol fuel cell mini-stacks based on a low-cost fluoiine-free polymer electrolyte and Nafion membrane. Electrochimica Acta, 55(20), 6022-6027, 2010. 

Fig. 1.45 Comparison of the electrical performance of trimethoxymethane (0.5 M), dimethoxymethane (0.5 M), and methanol (1.0 M) in a liquid-feed direct oxidation fuel cell.

Matsuoka et al. [8] tested ADAFCs formed by Pt-Ru/C as anode catalyst, Pt/C or Ag/C as cathode catalyst, and the AHA membrane by Tokuyama Co. The cells operated at 50 °C and were fuelled with four polyhydric alcohols and methanol for comparison. These alcohols (1 M) were dissolved in 1 M KOH aqueous solution. The maximum power densities were in the order of ethylene glycol > glycerol > methanol > erythritol > xylitol. The direct ethylene glycol fuel cell showed the highest power density. AlkaUne direct alcohol fuel cells using silver as a cathode catalyst showed good performance however, the open-circuit voltage of a cell with... 

Fig. 1.60 Comparison of performance of 1.0 M trimethoxymethane and 1.0 M methanol in a direct oxidation 4" x 6"-size fuel cell at 100 C.

DMFCs have potential near-term applications mainly in the portable power source market, as they are smaller, lighter, simpler, and cleaner than conventional batteries. Liquid methanol is consumed directly in a DMFC, which implies a higher energy density of the fuel cell system. But the power densities achievable with state-of-the-art DMFCs are still very small in comparison to hydrogen-fuelled PEMFCs. One of the major problems lies in the use of liquid methanol solution on the anode of the DMFC, which, on the one hand, keeps the ionomeric membrane water saturated (and thus no humidification is needed) but, on the other hand, does not keep fuel (methanol or any other organic fuel, e.g., formic acid, ethanol) and water from permeating to the cathode side, since the basic PFSA membranes are permeable to both methanol and water. - The fuel and water crossover from anode to cathode hampers the performance of the air cathode. 

The kinetics of the formulas (2) and (3) is much slower than that of the HOR and ORR, which is a main reason for the inferior cell performance of the DMFCs. Although the cell performance of the DMFCs doesn t surpass that of the PEFCs due to the slow kinetics of the MOR, the direct electrooxidation of the methanol in the DMFCs is attractive from a perspective of generating electric power directly from the fuel without the reforming and PROX reactions. Furthermore, the methanol is much safer and easier to carry and store in comparison with the hydrogen. 

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