Fuel Cell Technology

Electrochemical fuel cells convert the chemical energy of fuels directly into electrical energy to provide a clean and highly efficient source of electrical energy, potentially to power electric vehicles. Although fuel cell research dates back at least 30 years, nearly all large automakers recently have begun projects to develop and evaluate fuel cell-powered vehicles. Their goals are reduced costs, minimal pollution and high efficiency. Like a battery, a fuel cell consists of two electrodes separated by an electrolyte made of a thin polymeric membrane. But unlike a battery, a fuel cell doesn't need recharging. It will continue to produce electricity as long as fuel flows through it.

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 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.

SOURCE: Plug Power www.plugpower.com

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