Energy conversion devices, fuel cells

Fuel Cell Catalysts. Euel cells (qv) are electrochemical devices that convert the chemical energy of a fuel direcdy into electrical and thermal energy. The fuel cell, an environmentally clean method of power generation (qv), is more efficient than most other energy conversion systems. The main by-product is pure water. 

Chapter 1 by Joachim Maier continues the solid state electrochemistry discussion that he began in Volume 39 of the Modem Aspects of Electrochemistry. He begins by introducing the reader to the major electrochemical parameters needed for the treatment of electrochemical cells. In section 2 he discusses various sensors electrochemical (composition), bulk conductivity, surface conductivity, galvanic. He also discusses electrochemical energy storage and conversion devices such as fuel cells. 

Debra R. Rolison is head of Advanced Electrochemical Materials at the Naval Research Laboratory (NRL). She received a B.S. in chemistry from Florida Atlantic University in 1975 and a Ph.D. in chemistry from the University of North Carolina at Chapel Hill in 1980 under the direction of Royce W. Murray. Dr. Rolison joined the Naval Research Laboratory as a research chemist in 1980. Her research at NRL focuses on the influence of nanoscale domains on electron- and charge-transfer reactions, with special emphasis on the surface and materials science of aerogels, electrocatalysts, and zeolites. Her program creates new nano structured materials and composites for catalytic chemistries, energy storage and conversion (fuel cells, supercapacitors, batteries, thermoelectric devices), and sensors. 

Figure 3.3.2 Principle of a fuel cell as an electrochemical energy conversion device. Inside a fuel cell, fuel, e.g. hydrogen, and an oxidant, typically oxygen, combine electrochemically to form products, e.g. water, and electricity and some excess heat (not shown). Figure adapted from ref. [4]...

Solid State Electrochemistry, including the major electrochemical parameters needed for die treatment of electrochemical cells as well as the discussion of electrochemical energy storage and conversion devices such as fuel cells... 

Electrodes consisting of supported metal catalysts are used in electrosynthesis and electrochemical energy conversion devices (e.g., fuel cells). Nanometer-sized metal catalyst particles are typically impregnated into the porous structure of an sp -bonded carbon-support material. Typical carbon supports include chemically or physically activated carbon, carbon black, and graphitized carbons [186]. The primary role of the support is to provide a high surface area over which small metallic particles can be dispersed and stabilized. The porous support should also allow facile mass transport of reactants and products to and from the active sites [187]. Several properties of the support are critical porosity, pore size distribution, crush strength, surface chemistry, and microstructural and morphological stability [186]. 

The total number of molecules produced or consumed in the reaction is proportional to the surface area of the Pt/electrolyte interface. The plain interface shown in Figure 1.2 would give a very small current suitable for electrochemical studies, but would be of no practical interest for energy conversion devices. In practical fuel cells, the Pt/electrolyte interface should be as large as possible. This is achieved by mixing tiny carbon-supported catalyst particles with the polymer electrol3de and filling voids of carbon cloth or paper with this mixture. 

Ragone plots for electrochemical energy storage and conversion devices including batteries, fuel cells, and supercapacitors along with conversional capacitors. (Source Winter, M. 2004. 

CNTs, graphene and their compounds possess exceptional electrical properties for organic materials, and they have a huge potential in electrical and electronic applications, such as photovoltaics, sensors, semiconductor devices, display devices, conductors, smart textiles, and energy conversion devices (e.g., fuel cells, harvesters, and batteries). CNTs and graphene can greatly contribute to sustainable energy supplies and they are widely used in biomedicine. 

A fuel cell is equivalent to a generator it converts a fuel s chemical energy directly into electricity. The main difference between these energy conversion devices is that the fuel cell acccomplishes this directly, "without the two additional intermediate steps, heat release and mechanical motion. 

Proton Exchange Membrane Fuel Cells (PEMFCs) are being considered as a potential alternative energy conversion device for mobile power applications. Since the electrolyte of a PEM fuel cell can function at low temperatures (typically at 80 °C), PEMFCs are unique from the other commercially viable types of fuel cells. Moreover, the electrolyte membrane and other cell components can be manufactured very thin, allowing for high power production to be achieved within a small volume of space. Thus, the combination of small size and fast start-up makes PEMFCs an excellent candidate for use in mobile power applications, such as laptop computers, cell phones, and automobiles. 

For road transport, fuel cells are the most efficient conversion devices for using hydrogen. For the average drive cycle, which is dominated by a power demand that is only a fraction of the maximum available power, hybrid fuel cell systems offer a clear advantage over internal combustion engines, hybridized or not, when energy use, CO2 emissions and non-greenhouse pollutants are considered. 

S. M. Mitrovski, L. C. C. Elliott, and R. G. Nuzzo. Microfluidic devices for energy conversion Planar integration and performance of a passive, fully immersed H2-O2 fuel cell. Langmuir 20 (2004) 6974—6976. 

A fuel cell is an electrochemical conversion device. It produces electricity from fuel and an oxidant, which react in the presence of an electrolyte. The reactants flow into the cell, and the reaction products flow out of it, while the electrolyte remains within it. Fuel cells are different from electrochemical cell batteries in that they consume reactant, which must be replenished, whereas batteries store electrical energy chemically in a closed system. The chemical energy of the fuel is released in the form of an electrical energy instead of heat when the fuel is oxidized in an ideal electrochemical cell. Energy conversion by a fuel cell depends largely... 

Hydrogen may be the only link between physical energy from renewable sources and chemical energy. It is also the ideal fuel for modem clean energy conversion devices like fuel cells or even hydrogen engines. 

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