In a fuel cell, hydrogen gas from the fuel reacts electrochemically at one electrode and converts into protons and electrons. The protons move through the electrolyte to the other electrode, where they combine with oxygen from the air and with the electrons to form water, which is expelled from the cell as vapor. The involvement of hydrogen and oxygen in the two reactions - one releasing electrons and the other consuming them - yields electrical energy that is tapped across the electrodes for power, for example, to drive a motor.
Highly efficient fuel cells based on polymer electrolyte catalysts, known as proton-exchange membrane fuel cells, were developed by General Electric for the Gemini space program, but required large amounts of a costly platinum catalyst. The heart of the PEM fuel cell is a polymer membrane that has thin films of catalyst bonded on both its major surfaces, providing effective catalytic sites for the electrode processes. In the 1980s, Los Alamos National Laboratory scientists and others demonstrated how to achieve efficient energy conversion and power density in a PEM fuel cell with very low amounts of precious metal catalysts. Making fuel cells with minimal quantities of catalyst is crucial to achieving high performance and reliability at low cost. Los Alamos researchers came up with a breakthrough method of increasing the utilization of active catalyst, which allowed them to reduce the amount of platinum needed. This method reduced the amount of platinum needed by roughly 90 percent in some applications.
Los Alamos scientists also improved the structure and composition of the thin films of catalyst. They reduced the cost of materials, modified material properties for specific applications and identified new materials or material combinations for various fuel cell components. Los Alamos has tested advanced electrode technology in single cells for more than 3,000 hours, demonstrating negligible losses in performance; developed a way to avoid catalyst deactivation in the presence of trace impurities in the hydrogen fuel; and improved the properties of the membrane for effective water management.
Los Alamos and General Motors formed a major engineering development partnership in 1988 and worked together for nearly eight years to perfect a PEM fuel cell and improve fuel processing. Through the partnership, which also involved Dow Chemical Co. and Ballard Power Systems, Los Alamos developed diagnostic equipment for single fuel cells, stacks, combusters and other components. These high-quality measurements made possible further developments in PEM fuel cells, including operation of a 10 kilowatt demonstrator. Delphi Corp. currently is assembling a team of more than 150 to advance the GM-Los Alamos fuel cell concept.
Los Alamos has led in developing better ways to process the fuels needed to operate fuel cell-powered vehicles. The Department of Energy's Partnership for a New Generation Vehicle is funding current efforts at Los Alamos to improve on-board fuel delivery. One earlier achievement in this area was Los Alamos' solution of how to operate PEM fuel cells on impure hydrogen fuel. Traces of carbon monoxide in hydrogen fuel - which are generated in processing liquid fuels such as gasoline or methanol - hurt fuel cell performance. By bleeding low levels of air into the fuel feed stream, Los Alamos researchers removed the carbon monoxide catalytically within the cell, allowing fuel cells to run as well on contaminated hydrogen as on highly pure hydrogen. This development opened the way to practical use of PEM fuel cells with realistic hydrogen fuel feed streams derived from the processing of liquid fuels.
Los Alamos currently is involved in development of a multi-fuel reformer, which makes it possible for the same fuel cell to use hydrogen derived from gasoline, natural gas, methane or ethanol. Los Alamos also developed and is perfecting the preferential oxidizer, or PROX, an essential part of a fuel cell delivery system.
In the delivery system, fuel in whatever form is heated and mixed with warm air and steam. The partially burned fuel and other reaction products are channeled through a bed of catalysts, then to shift reactors that increase the amount of hydrogen in the mix.
The PROX then adds a small amount of air and preferentially burns carbon monoxide in the presence of hydrogen, converting the carbon monoxide to carbon dioxide while burning less than one percent of the hydrogen gas. The PROX is crucial, because carbon monoxide in amounts as small as 100 parts per million can poison the reaction at the electrode, decreasing voltage drastically.
The array of fuel cells, or stack, developed by Plug Power L.L.C. for the recent experiment at A.D. Little uses Los Alamos' technology for making effective, low-cost catalyzed membranes for fuel cells. The Plug Power fuel cells also incorporate Los Alamos' air bleed technique to remove effects of fuel impurities within the stack.
Los Alamos National Laboratory, a multidisciplinary research institution engaged in strategic science on behalf of national security, is operated by Los Alamos National Security, LLC, a team composed of Bechtel National, the University of California, The Babcock & Wilcox Company, and the Washington Division of URS for the Department of Energy's National Nuclear Security Administration.
Los Alamos enhances national security by ensuring the safety and reliability of the U.S. nuclear stockpile, developing technologies to reduce threats from weapons of mass destruction, and solving problems related to energy, environment, infrastructure, health, and global security concerns.