Phosphoric acid fuel cells development

Advanced Water-Cooled Phosphoric Acid Fuel Cell Development, Final Report," Report No. DE/MC/24221-3130, International Fuel Cells Corporation for U.S. DOE under Contract DE-AC21-88MC24221, South Windsor, CT, September 1992. 

Fig. 13.18. Sandwich configuration of phosphoric acid fuel cells developed by United Technologies. (Reprinted from J. O M. Bock-ris and S. Srinivasan, Fuel Cells, p. 179, copyright 1993, McGraw-Hill. Reproduced with permission of The McGraw-Hill Companies.)...

Electrochemical corrosion of carbon supports was widely studied in the context of phosphoric acid fuel cell development (Antonucci et al. 1988 Kinoshita 1988), but recently also the low-temperature fuel cell community paid more attention to this process (Kangasniemi et al. 2004 Roen et al. 2004). Carbon corrosion in fuel cell cathodes in the form of surface oxidation leads to functionalization of the carbon surface (e.g., quinones, lactones, carboxylic acids, etc.), with a concomitant change in the surface properties, which clearly results in changes of the hydrophobicity of the catalyst layer. Additionally, and even more severe, total oxidation of the carbon with the overall reaction... 

Phosphoric Acid Fuel Cell This type of fuel cell was developed in response to the industiy s desire to expand the natural-gas market. The electrolyte is 93 to 98 percent phosphoric acid contained in a matrix of silicon carbide. The electrodes consist of finely divided platinum or platinum alloys supported on carbon black and bonded with PTFE latex. The latter provides enough hydrophobicity to the electrodes to prevent flooding of the structure by the electrolyte. The carbon support of the air elec trode is specially formulated for oxidation resistance at 473 K (392°F) in air and positive potentials. 

Because of this extreme sensitivity, attention shifted to an acidic system, the phosphoric acid fuel cell (PAFC), for other applications. Although it is tolerant to CO, the need for liquid water to be present to facilitate proton migration adds complexity to the system. It is now a relatively mature technology, having been developed extensively for stationary power usage, and 200 kW units (designed for co-generation) are currently for sale and have demonstrated 40,000 hours of operation. An 11 MW model has also been tested. 

Stonehart P. 1990. Development of advanced noble metal-aUoy electrocatalysts for phosphoric-acid fuel cells (PAFC). Ber Bunsenges Phys Chem 94 913-921. 

This survey focuses on recent developments in catalysts for phosphoric acid fuel cells (PAFC), proton-exchange membrane fuel cells (PEMFC), and the direct methanol fuel cell (DMFC). In PAFC, operating at 160-220°C, orthophosphoric acid is used as the electrolyte, the anode catalyst is Pt and the cathode can be a bimetallic system like Pt/Cr/Co. For this purpose, a bimetallic colloidal precursor of the composition Pt50Co30Cr20 (size 3.8 nm) was prepared by the co-reduction of the corresponding metal salts [184-186], From XRD analysis, the bimetallic particles were found alloyed in an ordered fct-structure. The elecbocatalytic performance in a standard half-cell was compared with an industrial standard catalyst (bimetallic crystallites of 5.7 nm size) manufactured by co-precipitation and subsequent annealing to 900°C. The advantage of the bimetallic colloid catalysts lies in its improved durability, which is essential for PAFC applicabons. After 22 h it was found that the potential had decayed by less than 10 mV [187],... 

A. Kaufman, "Phosphoric Acid Fuel Cell Bus Development," Proceedings of the Annual Automotive Technology Development Contractors Coordination Meeting, Dearborn, MI, October 24-27, 1994, SAE Proceedings Volume P-289, pp. 289-293, 1995. 

M. Aoki, Y. Ueki, H. Enomoto, K. Harashima, "Some Approaches to Improve the Life Performance of Phosphoric Acid Fuel Cell," paper provided to the authors by Fuji Electric Corporate Research and Development, 1992, date of preparation unknown. 

F.S. Kemp, IFC, "Status of Development of Water - Cooled Phosphoric Acid Fuel Cells," in Proceedings of the Second Annual Fuel Cell Contractors Review Meeting, U.S. DOE/METC, 1990. 

A. Kaufman, Phosphoric Acid Fuel Cell Bus Development, Proceedings of the Annual... 

Operators of the Tokyo demonstration plant have concluded that phosphoric acid fuel cell technology is ready for commercialization. The project demonstrated that (I) fuel cells can be sited in urban areas which are regulated by strict environmental constraints (2) performance and operational characteristics were very close to design goals and (3) utility personnel can efficiently operate and maintain fuel cell plant equipment with minimal additional training. As a consequence of the demonstration plant success, a new 11 -MW power plant will be developed and marketed. A comparison of the new 1 C 23 Unit with the 4,5 MW demonstration plant is given in Table 4. 

In the area of fuel cells, reliability and availability have much improved. Recent U.S. military experience with phosphoric acid fuel cells found that the mean time between failure (MTBF) was almost 1,800 h and the availability was 67%. This is comparable with the MTBF service intervals for diesel generators. These fuel cells also favorably compare with the service interval needed for a typical gas turbine generation set. Still, much more development is required to obtain a commercially viable product. Today, the typical fuel cell system still requires servicing every 3-4 days to replace its scrubber packs. 

Phosphoric Acid Fuel Cell. This cell demonstrates the possibilities of using very concentrated phosphoric acid to allow the temperature of the solution to be raised to about 200-205 °C without the need for high-pressure equipment. The higher temperature makes it possible to produce large amounts of free steam for the re-forming of natural gas to the hydrogen upon which most development has been based. 

Several types of fuel cells have been developed and are classified according to the electrolytes used alkaline fuel cells, molten carbonate fuel cells, phosphoric acid fuel cells (PAFCs), PEMFCs, and solid oxide fuel cells (SOFCs). As shown in Figure 1.3, the optimum operation temperatures of these fuel cells are different, and each type has different advantages and disadvantages. 

This review identifies the progress that has occurred over many years for developing the electrocatalyst and matrix technology towards commercial realization of phosphoric acid fuel-cells. 

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