Solid acid fuel cells

Boysen, D., Uda, T., Chisholm, C., Haile, S. (2004). High-performance solid acid fuel cells through humidity stabilization. Science 303,68-70. 

Matsuo, Y., Saito, K., Kawashima, H., Ikehata, S. (2004). Novel solid acid fuel cell based on a superprotonic conductor Tl3H(S04)2- Solid State Comm. 130,411-414. 

Sasaki, K.A., Varga, A., Giapis, K.P., and Haile, S.M. (2009) From laboratory breakthrough to technological realiTa-tion the development path for solid acid fuel cells. Electrochem. Soc. Interface, 18, 53. 

Uda T, Haile SM. Thin membrane solid acid fuel cell. Electrochem Solid-State Lett... 

Uda T and Haile S M (2005) Thin-Membrane Solid-Acid Fuel Cell, Electrochemical and Solid-State Letters, 8, A245-A246. 

In a simple version of a fuel cell, a fuel such as hydrogen gas is passed over a platinum electrode, oxygen is passed over the other, similar electrode, and the electrolyte is aqueous potassium hydroxide. A porous membrane separates the two electrode compartments. Many varieties of fuel cells are possible, and in some the electrolyte is a solid polymer membrane or a ceramic (see Section 14.22). Three of the most promising fuel cells are the alkali fuel cell, the phosphoric acid fuel cell, and the methanol fuel cell. 

There are six different types of fuel cells (Table 1.6) (1) alkaline fuel cell (AFC), (2) direct methanol fuel cell (DMFC), (3) molten carbonate fuel cell (MCFC), (4) phosphoric acid fuel cell (PAFC), (5) proton exchange membrane fuel cell (PEMFC), and (6) the solid oxide fuel cell (SOFC). They all differ in applications, operating temperatures, cost, and efficiency. 

Solid polymer fuel cells use sulfonic acid group in polymer as an electrolyte and have an OT of 50 to 80°C. 

Close to a thousand systems that produce over 10 kilowatts each have been installed worldwide. Most of these are fueled by natural gas. Phosphoric acid fuel cells (PAFCs) have typically been used for large-scale applications, but molten carbonate and solid oxide units also compete with PAFCs. 

Progress continues in fuel cell technology since the previous edition of the Fuel Cell Handbook was published in November 1998. Uppermost, polymer electrolyte fuel cells, molten carbonate fuel cells, and solid oxide fuel cells have been demonstrated at commercial size in power plants. The previously demonstrated phosphoric acid fuel cells have entered the marketplace with more than 220 power plants delivered. Highlighting this commercial entry, the phosphoric acid power plant fleet has demonstrated 95+% availability and several units have passed 40,000 hours of operation. One unit has operated over 49,000 hours. 

Shah V.B. ASPEN Models for Solid Oxide Fuel Cell, Molten Carbonate Fuel Cell and Phosphoric Acid Fuel Cell Prepared by EG G Washington Analytical Services Center for the Morgantown Energy Technology Center under Contract No. DE-AC21-85MC21353, 1988. 

SOFC = solid oxide fuel cell MCFC = molten carbonate fuel cell PAFC = phosphoric acid fuel cell AFC = alkaline fuel cell PEMFC = proton exchange membrane fuel cell DMFC = direct methanol fuel cell SAMFC = Solid alkaline membrane fuel cell. 

Fuel cells can be broadly classified into two types high temperature fuel cells such as molten carbonate fuel cells (MCFCs) and solid oxide polymer fuel cells (SOFCs), which operate at temperatures above 923 K and low temperature fuel cells such as proton exchange membrane fuel cells (PEMs), alkaline fuel cells (AFCs) and phosphoric acid fuel cells (PAFCs), which operate at temperatures lower than 523 K. Because of their higher operating temperatures, MCFCs and SOFCs have a high tolerance for commonly encountered impurities such as CO and CO2 (CO c)- However, the high temperatures also impose problems in their maintenance and operation and thus, increase the difficulty in their effective utilization in vehicular and small-scale applications. Hence, a major part of the research has been directed towards low temperature fuel cells. The low temperature fuel cells unfortunately, have a very low tolerance for impurities such as CO , PAFCs can tolerate up to 2% CO, PEMs only a few ppm, whereas the AFCs have a stringent (ppm level) CO2 tolerance. 

C. G. Vayenas and R. D. Farr, Science 208, 593 (1980), describe a solid electrolyte fuel cell in which ammonia is the fuel and is catalyt-ically converted at 1000 K with oxygen (or air) to nitric oxide. The idea is that the energy released in this step in industrial nitric acid production (Section 9.4) could be recovered directly as electricity. 

Note PAFC phosphoric acid fuel cell PEMFC proton exchange membrane fuel cell/polymer electrolyte membrane fuel cell MBFC microbiological fuel cell DMFC direct methanol conversion fuel cell AFC alkaline fuel cell MCFC molten carbonate fuel cell SOFC solid oxide fuel cell ZAFC zinc air fuel cell. 

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