Heat Engines and the Carnot Cycle

A heat engine is defined by four requirements. It 1. Receives heat from a high-temperature source (e.g., coal furnace, nuclear reactor) 2. Converts part of this heat to work (e.g., by a turbine) 3. Rejects the remaining waste heat to a low-temperature sink (e.g., atmosphere, river) 4. Operates on a thermodynamic cycle The steam power plant fits most closely the definition of a heat engine, receiving heat from an external combustion chamber, extracting work by a turbine, and rejecting heat to a...

Humidifiers and Cooling Plates

A fuel cell stack may contain other components. The most prominent ones are cooling plates or other devices and techniques for removing reaction heat and, possibly, humidifiers. Cooling is vital to maintain the required point of operation for a given fuel cell stack. This may be an isothermal condition, or perhaps a temperature gradient may be deliberately superimposed in order to help water removal. Relatively simple calculations show that for very high power densities such as those FIGURE...

Kinetic Limitations

Considering only the thermodynamics of the DMFC, in principle methanol should be oxidized spontaneously when the potential of the anode is above 0.046 V with respect to the reversible hydrogen electrode (RHE) (see the discussion of electrochemical thermodynamics in Chapter 3). Similarly, oxygen should be reduced spontaneously when the cathode potential falls below 1.23 V vs. RHE. Hence, the DMFC would produce a cell voltage of 1.18 V at 100 voltage efficiency, independent of the current demand....

The Direct Methanol Fuel Cell

In the 1960s, the hope for a direct fuel cell emerged again, but instead of using coal, the fuel was methanol. Methanol, as opposed to coal, could be electrochemically oxidized at the electrodes. At the time, methanol was being used in fuel cells indirectly, undergoing steam reforming to produce hydrogen, but, if a fuel cell could use methanol directly to produce electricity, then the fuel reforming step could be circumvented, allowing for a simpler system. Before the major efforts of the...

General Design Features

Pemfc Air Cooling

The proton exchange membrane fuel cell, PEMFC, takes its name from the special plastic membrane used as the electrolyte. Robust cation exchange membranes were originally developed for the chlor-alkali industry by DuPont and have proved instrumental in combining all the key parts of a fuel cell, anode and cathode electrodes and the electrolyte, in a very compact unit. This membrane electrode assembly MEA , not thicker than a few hundred microns, is the heart of a PEMFC and, when supplied with...

Bipolar Plates

Mcfc Anode

Flow field plates in early fuel cell designs and still in use in the laboratory were usually made of graphite into which flow channels were conveniently machined. These plates have high electronic and good thermal conductivity and are stable in the chemical environment inside a fuel cell. Raw bulk graphite is made in a high-temperature sintering process that takes several weeks and leads to shape distortions and the introduction of some porosity in the plates. Hence, making flow field plates is...

Domestic Heat and Power Generation

Buderus Sofc

The majority of currently active fuel cell developers are focusing on the residential and small commercial power market in the range 1 to 20 kWel. These include traditional, leading fuel cell companies and startups that sometimes originate from a university laboratory or have some other technology base. A number of these companies have substantial financial backing from leading utilities see below . One of the attractions of this market lies in the belief that target cost, approximately 1000...

Voltage Efficiencyand PowerDensity

Theoretical Fuel Cell Voltage

Figure 4.3 shows a typical current voltage curve, broken down into the respective performance losses. The cell voltage at open circuit, the open circuit voltage OCV , usually does not reach the theoretical value of the reversible cathode potential at the given temperature and pressures as discussed in Chapter 3, for standard conditions, this would be 1.23 V . When no current is drawn from the cell, parasitic electrochemical processes show up next to the main two reactions, hydrogen oxidation...

Outlook

Buderus Sofc

Based on what has been said in this chapter, the following certainly subjective conclusions may be drawn. Large central power generation using fuel cell technology will only be viable when sufficiently high electric efficiencies particularly operating on coal gas can be obtained. Currently, only SOFC technology in combined cycle processes with gas turbines offers this potential, but cost reduction still has a long way to go. A number of developers are competing for the 100- to 100- kW...

Membranes and Ionomers

The strong interest in the PEM fuel cell stems from the advantages of using a solid polymer electrolyte. Solid polymer electrolytes form a thin but sound electronic insulator and gas barrier between the two electrodes while allowing rapid proton transport and high current densities. This, in turn, allows the high cell and stack power densities vital for automotive applications. Once put in place, the solid electrolyte does not redistribute, diffuse, or evaporate, making intermittent operation...

Reformer Technology

Fertiliser Reformer

Hydrogen is currently produced in large quantities primarily for two applications. Roughly 50 of the world hydrogen production is used for the hydroformulation of oil in refineries producing mainly automotive fuels. Approximately 40 is produced for subsequent reaction with nitrogen to ammonia, the only industrial process known to bind atmospheric nitrogen. Ammonia is used in a number of applications, especially fertilizer production. It is useful, however, to put the current industrial output...

Grubb and Niedrach at General Electric

Grubb and Niedrach 1960 developed a fuel cell with a solid ion-exchange membrane electrolyte in 1960. The ion-exchange membrane was a polymer sheet, 0.06 cm thick, made of cross-linked polystyrene with sulfonic acid HSO3 groups at the ends of the side chains and bound with an inert binder. According to Grubb 1959, in Grubb and Niedrach, 1960 , the membranes, in the hydrogen form, had a conductivity equivalent to that of a solution of 0.1 N Normal, 0.5 M sulfuric acid, H2SO4. But to maintain...

Maximum Thermal Efficiencies

The thermal efficiency of a heat engine is determined by the amount of work the engine can perform with the thermal energy supplied to the system. The heat, Qin, is released from the fuel when it is oxidized and is transferred to the working fluid in the case of an external combustion engine . The expansion of the working fluid the combustion gases themselves in an internal combustion engine is harnessed by machinery and converted to mechanical work, Wnet. Equation 3.34 is the general...

Prototypes and Examples

Fuel Tank Dmfc Design

The purpose of this section is not the in-depth discussion of business opportunities for new fuel cell start-ups. For each potential application, one is advised to do a thorough technical, market, and cost analysis that goes well beyond the scope of this book. It would appear that existing developers have not always done this. The intent here is merely to show typical examples within this rapidly developing set of fuel cell applications and name leading developers. The list of developers is far...

Technological Challenges Prior to DMFC Commercialization

Dmfc Reaction

Although the DMFC relies on thermodynamically favorable reactions, in practice both the anode and the cathode electrodes are kinetically limited due to the irreversible nature of the reactions. While this is also the case for the cathode reaction of the H2 PEMFC, which is identical to Eq. 7.2 , the anode reaction of the PEMFC is not performance limiting. In the DMFC, however, both anode and cathode suffer from similarly large overpotentials as shown in Fig. 7.4 later in this chapter. The key...

The PEMFC as a CHP System

Ballard is currently the only developer of PEMFC-based power systems in the 250-kW range. Ballard has developed these systems since the mid-1990s, and stationary power systems below 1 MW are now being developed by Ballard Generation Systems BGS , a partnership between Ballard Power Systems, GPU International, Alstom, and Ebara Corporation. GPU International is an international energy company based in New Jersey. Alstom is a world leader in the design and manufacture of equipment and systems for...

Metal Hydrides

Automated Filling Station

Most elements form ionic, metallic, covalent, or polymeric hydrides or mixtures thereof Greenwood and Earnshaw, 1984 . The ionic and metallic types are of particular interest because they allow reversible storage of hydrogen Sandrock, 1994 . FIGURE 5.3 The package study for MINI Cooper Hydrogen has a hydrogen tank that fits into the body of the MINI. Photograph coutesy of BMW. FIGURE 5.3 The package study for MINI Cooper Hydrogen has a hydrogen tank that fits into the body of the MINI....

Baur and Brunner

Cathode Tester Technology

Baur and Brunner 1935 returned to the problem of the direct coal air chain despite the problems associated with it high temperatures, ash formation, dilution of the fuel gases by carbon dioxide and water vapor , focusing their efforts on carbonate electrolytes. The electrolyte was a mixture of salts containing eight parts of K2CO3, seven parts of Na2CO3, and six parts of NaCl with some borates. With carbon as the anode electrode and platinum the cathode, they operated the cell at 500 to 600 C...

Pratt Whitney Aircraft Division and the Target Program

The culmination of the TARGET program Team to Advance Research for Gas Energy Transformation in 1975 was the demonstration in homes of phosphoric acid fuel cells operating on natural gas Appleby and Foulkes, 1989 . The program was initiated in 1967 by Pratt amp Whitney Aircraft Division of the United Technologies Corporation, responsible for developing the fuel cell, with sponsorship from 32 U.S. gas companies that wanted a share of the electricity market at a time when heating for homes was...

The MCFC as Small Scale CHP System and Large Central Power Plant

Micro Gas Turbine Chp

FuelCell Energy is based in Danbury, CT, and has a second facility in Torrington. The company was formed out of Energy Research Corporation founded in 1969 , which is probably best known for setting up the largest fuel cell power plant ever operated in the North America the Santa Clara Demonstration Project, with a nominal electric power output of 2.5 MW. Like other demonstration plants, it was based on 300-kW MCFC stack technology called Model 9000. Current plant sizes are 300 kW, 1.5 MW, and...

The Gaseous Voltaic Battery

Before it went by the name fuel cell Rideal and Evans, 1922 , it was first known as the gaseous voltaic battery Grove, 1842 . The gaseous voltaic battery of Grove used platinum electrodes and sulfuric acid electrolyte, with hydrogen and oxygen as reactants. At that time, platinum was already known to be a catalyst for the reaction between hydrogen and oxygen, and the first published experimental results of Grove were an important illustration of that principle Grove, 1839 . Schoenbein had...

Mond and Langer

Mond And Langer

The new form of gas battery described by Ludwig Mond and Carl Langer in 1889 was more than an improvement it was the prototype for the practical fuel cell. These researchers considered their main contribution as being a solution to the problem of electrode flooding, caused by a liquid electrolyte. The sulfuric acid could be held in place by using a matrix Grove , as well as later investigators, overlook one important point, viz., the necessity of maintaining the condensing power of the...

Liquid Fuel The Direct Methanol Fuel Cell

No doubt one of the most elegant solutions to the fueling problem would be to make fuel cells operate on a liquid fuel. This is particularly so for transportation and the portable sector. The direct methanol fuel cell DMFC , a liquid- or vapor-fed PEM fuel cell operating on a methanol water mix and air, therefore deserves careful consideration. The main technological challenges are the formulation of better anode catalysts to lower the anode overpotentials currently several hundred millivolts...

Fuel Cell Handbook Fifth Edition References

American Methanol Institute, www.methanol.org, 1999. Atkins, P.W., Physical Chemistry, 5th ed., Oxford University Press, Oxford, 1994. Bauman, J.W., Zawodzinski, T.A., Jr., and Gottesfeld, S., in Proceedings of the Second International Symposium on Proton Conducting Membrane Fuel Cells II, Gottesfeld, S. and Fuller, T.F., Eds., Electrochemical Society, Pennington, NJ, 1999. Bechtold, R.L., Alternative Fuels Guidebook, Society of Automotive Engineers, 1997. Biosaar GmbH, personal communication,...

Alder Wright and Thompson

Mond And Langer

One day after seeing the demonstration of Mond and Langer at a meeting of the Royal Society of London, Alder Wright and Thompson 1889 reintroduced a device that they had used in experiments performed in 1887, intending to prove that their work had been performed first. Their electrodes were called aeration FIGURE 2.5 In response to the demonstration of Mond and Langer's gas battery, Alder Wright and Thompson 1889 brought attention to their double aeration plate cells, which had been developed...

Biomass and Waste Biomassasa SourceofFuel CellPower

Biomass provides a possible solution to the fuel problem. 5.9 givesan overviewof thepotential routes from biomass to powering fuel cells. Biomass can of course be burned in order to generate steam for driving steam turbines or even steam engines to make electric power. More interesting in this context are the chemical routes, i.e., anaerobic digestion of soft biomass and thermal processing of hard biomass to make syngas, a mix of carbon monoxide and hydrogen. This latter, thermal 3 So-called...

Prospects of the Direct Methanol Fuel Cell

7.1 Operating Principle of the DMFC 7.2 Technological Challenges Prior to DMFC Commercialization Kinetic Limitations Electrode Kinetics of the Anode Reaction 7.3 Electrode Performance Martin Hogarth Half-Cell Data Single-Cell Data Johnson Matthey Technology Centre 7.4 Conclusions and Future Recommendations The direct methanol fuel cell DMFC is often considered to be the ideal fuel cell system since it operates on a liquid fuel, which for transportation applications can potentially be...

Characterization of Catalysts

Cyclic Voltammetry

As with conventional ceramic-supported catalysts, the whole range of routine ex situ physical characterization techniques can be applied to the study of fuel cell catalysts. A non-exhaustive summary is shown in Table 6.1. Figure 6.12 shows one example of a characterization technique a transmission electron micrograph of a carbon-supported Pt catalyst. The larger gray particles are the carbon support, and the smaller dark particles are the Pt. The particle size of the Pt is around 2 nm. Of...

Adiabatic Flame Temperature

For heat engines, the two reservoirs that provide the temperature gradients for heat addition and rejection have been simplified by assuming that they remain at constant temperature throughout the process. In actuality, the high temperature is generated by a combustion process that involves a chemical reaction between fuel and oxidant. The maximum efficiency of a heat engine, expressed in Eq. 3.24 , is a function of the temperature of the heat source, TH, and the greater the temperature, the...

The PAFC

The PAFC is an acid fuel cell using liquid concentrated phosphoric acid, H3PO4, as electrolyte. It is usually operated with hydrogen and air, and the electrode reactions are identical to those discussed in Chapter 4 for the PEMFC see Eqs. 4.1 and 4.2 . Electrodes, catalysts, and overall construction, including bipolar plates, are very similar to the PEMFC in fact, many of the present design features of PEMFCs, such as carbon-supported Pt catalysts, have been derived from PAFC technology compare...