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Over the past one decade, several cell component materials and their combinations have been attempted to match with the appropriate requirements of solid oxide fuel cells (SOFCs). A large number of cell component materials with superior properties have been developed. The general observation is that most of the technological challenges associated with the development of SOFCs are related to materials science. For example, development of superior oxide-ion conductor electrolyte as well as cost-effective fabrication processes involves tremendous materials challenges. The improvements of the materials properties mostly include electrical conductivity, catalytic activity, stability and thermal expansion coefficient. Of late, significant improvements have also been made in the area of fast oxide-ion conductors. These oxide-ion conductors show extraordinarily high electrical conductivity compared to traditional zirconia-electrolyte. This helps SOFC not only to operate at lower temperature but also minimizes the polarization losses which is the key factor for a high performance cell (high power density or power per unit area). The differences between the operating cell voltage and the expected reversible voltage is termed as polarization or overpotential. More clear understanding of the fundamentals of these materials has been published by several groups through numerous articles (Steele 1993, 2000, Mogensen et al. 2000, Goodenough 2003, Singhal et al. 2003, Stöver et al. 2003, Kilner 2005). Reduction of electrolyte thickness also has tremendous advantages particularly from the technological point of view. Lower the electrolyte thickness lower is the internal resistance of the electrolyte, which in turn helps the cell to operate at a considerably lower temperature. The current research trend undoubtedly is more focused towards the development of high performance SOFC at low temperature (650°C and below). For making such high performance cell, inter facial contacts between two adjacent cell components is very critical. Therefore, an excellent compatibility (connectivity) between electrolyte and electrodes, and also with the interconnect (while stacking) is absolutely necessary. [ABSTRACT FROM AUTHOR]

Future development and implementation of fuel cell technology would depend on upward trend in global oil price, depletion of oil wells, fall in oil well discovery and the improvement of hydrogen energy infrastructure. The concern for environmental pollution and damage from the emission of automobile, thermal power plant, petroleum-crude refinery would catalyse the process of development unless financial benefits in terms of lowering of pollution damage cost are perceived by users and the manufacturers. Infrastructure development of the hydrogen energy encompasses production, distribution, dispensing and safety regulations of fuels (e.g., hydrogen, alcohol, esters and natural gases, naphtha and synthesis gases), which is directly fed to the fuel cells or to the fuel processor. Out of these hydrogen and alcohols can be generated from renewable sources (wind, solar power in water electrolysis, biomass gasification and fermentation) and others including hydrogen and alcohol can also be generated from fossil fuel. In the former case, green house gas emission is much lower and almost negligible. One can dream of zero emission of air pollutant and green house gases from automobiles and stationary power plants except for the case of biomass gasification. In the latter case, the air pollutant will be generated in a centralized location and cities will be free of pollution, which is otherwise generated from automobile using internal combustion engine. It should be noted that the hydrogen fuel cell vehicle (H2FCV) and H2FCV-hybrid electric vehicle offers least environmental damage among all the advanced options. When fuelled with hydrogen derived from natural gas, pollution damage costs are 1/8 as large as for today's gasoline internal combustion engine vehicles without CO2 sequestration and 1/15 as large with CO2 sequestration (Ogden et al. 2004). Although economics does not work out at present for PEMFC (Proton Exchange Membrane Fuel Cell) based automobile or SOFC (Solid Oxide Fuel cell) based stationary power plant with present inadequate hydrogen infrastructure but it is hoped that with the increase in crude price, no new crude or gas reserve findings, increase in fuel cell stack efficiency and decrease in cost of the fuel cell and improvement of hydrogen energy infrastructure facility, the Fuel Cell Vehicle (FCV) and distributed power generation from fuel cell will become more profitable leaving aside the cost benefits due to less environmental pollution. [ABSTRACT FROM AUTHOR]

Currently, USA is the largest consumer of energy in the world with projected consumption of 5207 billion kWhs in 2025 (http://www.eia.doe.gov/), with the actual and forecast demand for electrical energy is growing in all the end-use sectors. The highest annual growth rates are projected for the commercial, industrial, and residential sectors at about 2.2, 1.6 and 1.4%, respectively, as shown in Fig. l(a). From 2000 to 2003, 69 GWs of peaking capacity was added and 112 GWs of combined-cycle capacity, which is efficient in both baseload and cycling applications, was installed. To meet increasing base and peak power demands, the demand for energy resources is rapidly increasing and unfortunately, as Fig. l(b) shows, progressively depleting resources, such as natural gas and coal, which cause environmental pollution, still account for more than 50% of the total energy-generation resources (http://www.eia.doe.gov/). Furthermore, as the demand for natural gas continues to rise, domestic production dwindles and world-wide demand and supply scenario for oil and gas approach a delicate balance, we are forced with greater reliance on importation (which incidentally, is still insufficient to meet the demand) and economic vulnerability. Clearly, there is an urgent need for alternative sources of energy. [ABSTRACT FROM AUTHOR]

A solid oxide fuel cell (SOFC) is composed of two porous ceramic electrodes and a solid state electrolyte, made of solid metal oxides. For this reason, the SOFC is also referred to as ‘ceramic fuel cell'. The idea of using a stabilized zirconia material as an electrolyte is derived from the experiments conducted by Nernst in 1899. Further studies, including those of Bauer and Preis (1937), showed that the so-called "Nernst Mass" (85% zirconia and 15% yttria), and other zirconia-based materials, at high temperature (600-1000°C), present an ionic conduction that meets the SOFC requirements. The ‘typical modern' SOFC is composed of an electrolyte made of yttria-stabilized zirconia (YSZ), a porous anode made of nickel and ytrria stabilized zirconia (Ni/YSZ) cermet and a porous cathode composed of doped LaMnO3 (LSM). In order to obtain acceptable ionic conductivity, YSZ needs to operate at a relatively high temperature, typically above 700°C. Historically, the first SOFC operated at 1000°C. At this temperature, the protonic conductivity of the YSZ is negligible, while the ionic conductivity is about 15 S/m (Bossel). Due to the poor mechanical characteristics of the electrodes manufactured until the late 90s, SOFC had to be electrolyte supported. This is the main factor that constrained the operating temperature at typically 1000°C. Because of the minimum required thickness of the supporting structure (electrolyte), in fact, a lower temperature would lead to unacceptable ohmic resistance. Alternative configurations, like for example the previous design of the tubular Westinghouse cell (Bessette and Wepfer 1996) were based on an external (porous) support. However, this solution limits the mass transport through the cell and makes the manufacturing process more complex. By the end of the 90s and the early 2000s, the good mechanical characteristics, mostly due to the development of nano-powders for the manufacturing process, enabled the realization of electrode supported cells. Although some developers, like for example Siemens-Westinghouse, based their design on a cathode supported structure (Minh and Takahashi, 1995) many SOFC developers are now focusing on anode supported cells (Patel et al. 2004, Minh et al. 2004, Patel-Maru et al. 2004, Minh, Amaha et al. 2004). [ABSTRACT FROM AUTHOR]

A long-held dream of early energy science and technology has been a fuel cell that would directly convert coal char (if not raw coal) into electric power—bypassing the emission problems of combustion and the efficiency limitations of thermal cycles. Such a fuel cell would generate electric power from an electrochemical reaction similar to the combustion reaction of carbon: 1$$ C + O_2 = CO_2 (\Delta H^0 _{298 K} = - 94.05 kcal/mole, E^0 = 1.02 {\text{V at }}750^\circ {\text{C}}) $$ As an example, the fuel cell (Fig. 1) might use carbon plates or particulates wetted with a molten alkali carbonate electrolyte, a melt saturated porous ceramic separator, and an air electrode catalyzed by lithiated NiO, such as used in the molten carbonate hydrogen fuel cell (Cherepy et al, 2005; Vutetakis, 1985; Weaver et al, 1979). [ABSTRACT FROM AUTHOR]

In recent years, carbonate fuel cell technology has enjoyed a steady improvement both in cost reduction and performance. Large-scale manufacturing combined with a multitude of power plant installations has resulted in the establishment of the carbonate fuel cell technology as a leading candidate for efficient and reliable distributed generation. [ABSTRACT FROM AUTHOR]

Of the hydrogen-oxygen fuel cell systems the most mature is the phosphoric acid fuel cell (PAFC). It operates at 150-190°C and pressure ranging from ambient to 5 atm. PAFC systems use primarily Pt as catalyst both for hydrogen and oxygen electrodes. The operating temperature range of PAFC allows it to take up hydrogen directly from hydrogen sources like reformer gases. Less than one percent of CO present in the reformer gases are not adsorbed on Pt sites owing to high operating temperature. The other components used in PAFC are mainly made of graphite and carbon. All these factors make PAFC a versatile member of the hydrogen-oxygen fuel cell family. [ABSTRACT FROM AUTHOR]

The alkaline fuel cell (AFC) was the first fuel cell technology used in many practical services like Apollo space mission and running an automobile (Kordesch et al. 1999, Carrette et al. 2001). It is a low temperature fuel cell technology, which uses hydrogen as a fuel, oxygen or air as oxidant and alkaline solution as electrolyte. The development of AFC technology has reached its peak in the beginning of 1980s (Schulze et al. 2004) but its further development is stopped due to many technical, commercial and safety issues. The research and development on fuel cell is gaining momentum as a new way power generation technology, which is environmental friendly. The main focus of technology development of fuel cells is to increase the power output per unit area of electrode at low cost. The interest in AFC increased again due to more favorable oxygen reduction (Burchardt et al. 2002, Yu et al. 2004) and fuel oxidation reactions (Wang et al. 2003, Rahim et al. 2004) in alkaline condition. Apart from these, the cost, simplicity, efficiency and the possibility to use the non-noble metal catalyst (Schulze et al. 2004, Cifrain et al. 2003a) compared to other low temperature fuel cell technology have given an impetus to the AFC research. A detailed comparison of AFC with polymer electrolyte membrane fuel cell (PEMFC) is given by McLean et al. (2002). [ABSTRACT FROM AUTHOR]

The advent of microelectromechanical systems (MEMS), micromachines, microsystems, integrated passive components and low power electronics for various types of functionalities has resulted in a surge of research in the development of power sources of matching configuration to meet the device requirements (Chan et al., 2005; Yen et al., 2003). The increasing demand for a wide variety of commercial, portable, electronic appliances such as cellular phones, laptop computers, personal organizers, digital cameras, portable radios, notebook computers, personal digital assistants, embedded monitors, military devices and specialised devices such as autonomous sensors, clinical and diagnostic test devices, micro-analytical systems, global positioning systems etc., has spurred the development of micro power sources (Lu et al., 2004; Choban et al., 2004). Since energy is stored in a fuel cell as a reservoir of fuel rather than as an integral part of the power source, fuel cells are expected to provide higher total energy for a given size or weight than batteries, calculated as Watt-hours per liter (Wh/1) or Watt-hours per kilogram (Wh/kg) due to the high amount of energy that can be stored in fuels such as hydrogen, sodium borohydride, methanol, ethanol, hydrocarbon. A second advantage of fuel cells is that once the fuel is consumed, it can be replenished instantly and the system continues to provide power. In fact, a fuel cell will continue to supply power indefinitely as long as fuel and air (O2) are supplied. As a result along with the evolution of various electronic devices, the miniature fuel cells have emerged as a possible power source through the endless pursuit of ever-higher levels of performance, density and functionality. [ABSTRACT FROM AUTHOR]

Anew generator performing highly-efficient with low (or no) pollutant emission is necessary to resolve the problem of exhaustion of fissile fuel and spreading environmental pollution. Fuel cell has been expected as one candidate of the generator. Among several types of fuel cells polymer electrolyte membrane fuel cell (PEMFC), can operate at low temperature (below 100°C) and generate specific power and a power density higher than any other fuel cell with relatively simple constitution. These benefits make us enthusiastic to apply PEMFC to the power source of transportation, portable and resident (Larminie et al., 2003). [ABSTRACT FROM AUTHOR]

The main components of a proton exchange membrane (PEM) fuel cell are the gas diffusion layer, membrane and catalyst. Gas diffusion layers (GDLs) are commercially available in various forms such as carbon paper or woven carbon fabrics. These are placed on either side of the membrane in a fuel cell. A GDL should allow the flow of reactant gases H2, air/oxygen and product gases to pass through it. The water formed in a cell should not choke the pores of this paper or fabric and so they are pre-coated with polytetrafluoroethylene (PTFE), which changes the GDL material from hydrophilic to hydrophobic. PTFE is also commonly called Teflon. The platinum catalysts for both the anode and cathode side can be coated on the surface of a GDL. The hydrogen or oxygen reacts in three phases: interface-gas phase (hydrogen or oxygen), liquid phase (water) and solid phase (catalyst). The carbon paper or fabric serves as a structural support for the electrocatalyst layer as well as current collector. Some of the GDLs available on the market are not coated with PTFE and are thinner in size. In such cases, the user has to coat the GDL with PTFE. [ABSTRACT FROM AUTHOR]

The polymer electrolyte membrane fuel cell (PEMFC) also known as proton exchange membrane fuel cell, polymer electrolyte fuel cell (PEFC) and solid polymer fuel cell (SPFC) was first developed by General Electric in the USA in the 1960's for use by NASA in their initial space applications. The electrolyte is an ion conducting polymer membrane, described in more details in Section 2.2. Anode and cathode are bonded to either side of the membrane. This assembly is normally called membrane electrode assembly (MEA) or EMA which is placed between the two flow field plates (bipolar plates) (Section 2.5) to form what is known as "stack". The basic operation of the PEMFC is the same as that of an acid electrolyte cell as the mobile ions in the polymer are H+ or proton. [ABSTRACT FROM AUTHOR]

Fuel cells are electrochemical devices, which convert chemical energy of the fuel to electrical energy and heat energy. In a combustion engine, fuel is mixed with air in appropriate stoichiometric ratios to initiate a combustion reaction that further creates work. In a combustion reaction, the gas species are not spatially separated, but in proton exchange membrane fuel cell (PEMFC), these combustion reactions are split into two half-cell reactions, namely, fuel oxidation and oxygen reduction, that occurs in two separate chambers called anode and cathode, respectively. If all of the chemical energy can be converted into electrical energy, then we start with the following transfer function: ΔG = Electrical work (1) where ΔG (Gibbs free energy) determines the maximum useful work that can be extracted from the system of interest. For a fuel cell reaction with hydrogen as fuel at temperature 25°C, the overall exothermic chemical reaction is given as 1$$ \Delta G = Electrical work $$ [ABSTRACT FROM AUTHOR]

A fuel cell is an electrochemical device (a galvanic cell) which converts free energy of a chemical reaction into electrical energy (electricity); byproducts are heat and water/steam if hydrogen and air are the reactants; in some fuel cell types, the additional byproducts may be carbon dioxide and leftover lower forms of hydrocarbons depending on the fossil fuels used. There is no combustion in this process and hence no NOx are generated. Sulfur is poison to all fuel cells so it must be removed from any fuel before feeding to any fuel cell type; hence, no SOx are generated. A fuel cell produces electricity on demand continuously as long as the fuel and oxidant are supplied. For reference, primary cell or battery is also an electrochemical energy producing device (one-way chemical reaction producing electricity) and needs to throw away once the battery is discharged. A rechargeable or secondary battery is an electrochemical energy storage device having reversible chemical reaction producing or using electricity, but it also has a limited life. [ABSTRACT FROM AUTHOR]