Fuel Cells: The Next Evolution
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Fuel Cells: The
Next Evolution
Robert W. Lashway, Guest Editor Abstract The articles in this issue of MRS Bulletin highlight the enormous potential of fuel cells for generating electricity using multiple fuels and crossing a wide range of applications. Fuel cells convert chemical energy directly into electrical energy, and as a powergeneration module, they can be viewed as a continuously operating battery. They take in air (or pure oxygen, for aerospace or undersea applications) and hydrocarbon or hydrogen fuel to produce direct current at various outputs. The electrical output can be converted and then connected to motors to generate much cleaner and more fuelefficient power than is possible from internal combustion engines, even when combined with electrical generators in today’s hybrid engines. The commercialization of these fuel cell technologies is contingent upon additional advances in materials science that will suit the aggressive electrochemical environment of fuel cells (i.e., both reducing and oxidizing) and provide ionic and electrical conductance for thousands of hours of operation. Keywords: ceramics, electrochemistry, fuel cells, molten carbonates, polymer electrolyte membranes, solid-oxide membranes.
Introduction The invention of the solid-state transistor in the late 1940s led to a new age. The technological evolution of microprocessing, from simple watches and calculators to personal computing and wireless communications, has also been responsible for the progress in micro-manufacturing (e.g., microelectromechanical systems, cleanroom technology, and other advances in materials science). The solid-state fuel cell has the potential to generate another new age, in the areas of distributed energy, a cleaner environment, and more efficient use of the earth’s natural resources. The need for cleaner energy-producing equipment is becoming a commercial necessity and will continue to grow in importance as the demand for oil outpaces production capacity in the next decade.1 Advancements in materials science as well as in microprocessing will be needed to ensure the chemical and mechanical long-term reliability of the thin electrolyte membranes used in most fuel cell technologies.
What Is a Fuel Cell? A fuel cell is an electrochemical device, like a battery, that is continuously fueled (e.g., by fuel plus oxygen from the air). Each cell consists of an electrolyte (a conducting ionic membrane) with an inte-
MRS BULLETIN • VOLUME 30 • AUGUST 2005
grated porous anode and cathode. Hydrogen and/or hydrocarbon fuels react at the anode side, while oxygen (from air) reacts at the cathode side. The output is electrical energy in the form of direct current. When hydrogen is used as the fuel, the final exhaust product is simple water (i.e., zero oxides of sulfur and nitrogen, zero hydrocarbon soot, and zero carbon dioxide or monoxide). A fuel cell assembly is composed of multiple cells that are generally placed in stacks and electrically connected in series. The electrolyte conducts the ions, but must also retain
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