Carbonate Fuel Cell Technology and Materials
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Carbonate Fuel Cell Technology and Materials
M. Farooque, C.Yuh, and H.C. Maru Abstract High-temperature carbonate fuel cells are recognized as the cleanest and most efficient power generation option for commercial and industrial customers. The firstgeneration carbonate fuel cell plants have shown an electrical efficiency of 45–48%. The electrolyte in this fuel cell is a mixture of alkali carbonates, and it operates at a highenough temperature that the heat by-product can be used for cogeneration applications such as district heating, hot water, process steam, and absorption chilling for air conditioning. Alternatively, the heat by-product can be used with an unfired gas turbine for additional electrical generation. Depending on location, application, and load size, carbonate fuel cells are expected to achieve an overall energy efficiency of 65–80% in cogeneration and combined cycle applications. The cell hardware uses commonly available stainless steels. Electrode materials are nickel-based. Furthermore, standard, well-established manufacturing processes are employed. Therefore, carbonate fuel cells are well positioned to be cost-competitive with alternative technologies. Significant progress has been made in the development, manufacturing, product engineering, and field operation of carbonate fuel cell technology. Megawatt and submegawatt units are operating worldwide. A comprehensive review of carbonate fuel cell technology and materials are presented in this article. Keywords: carbonate fuel cells, direct fuel cells, high-temperature fuel cells, internal reforming fuel cells.
Carbonate Fuel Cells: Basic Concept The fuel cell produces direct-current electricity from electrochemical reactions of a fuel and an oxidant. An electrolyte is deployed to support the reactions by transporting charged ions between the electrodes. The fuel cell is commonly named by the electrolyte it uses, which also determines the operating temperature, electrochemical reactions, and cell construction hardware of the fuel cell. The carbonate fuel cell deploys a mixture of alkali carbonates as the electrolyte and operates at 550–650C. The basic electrochemistry of carbonate fuel cells involves the formation of carbonate (CO 32–) at the cathode by the combination of oxygen, carbon dioxide, and two electrons; transport of the carbonate ions to the anode through carbonate electrolyte; and finally, reaction of the carbonate ion with
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hydrogen at the anode, producing water, carbon dioxide, and two electrons: Cathode reaction: CO2 12 O2 2e– l CO32–
(1)
Anode reaction: H2 CO32– l H2O CO2 2e– Overall:
H2 12 O2 l H2O
(2) (3)
For each mole of hydrogen consumed in the anode compartment, one mole of carbon dioxide and one mole of water are produced. Hydrogen is made available to the anode in a carbonate fuel cell by extracting it from a common fuel (such as by steam-reforming natural gas). CO present
in the reformed fuel is also considered a fuel in this cell. Oxygen is supplied from air, and carbon dioxide is made availabl
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