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PEM

"Proton Exchange Membrane Fuel Cell" or "Polymer Electrolyte Membrane Fuel Cell"

PEM stands for Proton Exchange Membrane, or sometimes Polymer Electrolyte Membrane. The membrane is a permeable polymer sheet, which allows protons (hydrogen ions) to pass through it, but keeps electrons and whole atoms from passing through. The membrane is considered an electrolyte, just like the fluid in a battery.

A platinum catalyst is used on both sides of the membrane to speed the reaction. Hydrogen atoms are stripped of their electrons, or "ionized," at the anode, and the positively charged protons diffuse through one side of the membrane and migrate toward the cathode. The electrons pass from the anode to the cathode through an exterior circuit and provide electric power along the way. At the cathode, the electrons, hydrogen protons and oxygen (from the air) combine to form water.

PEM fuel cells’ operate at relatively low temperatures (under 200°F/93°C), have high power density, and can vary their output quickly to meet shifts in power demand. PEM fuel cells’ relatively small size, low material cost, high performance and high-volume manufacturability make them ideal for transportation, stationary and portable applications.

PEM Fuel Cell History

While fuel cells were invented in 1839, PEM technology wasn’t developed until the early 1960s. The PEM fuel cell was developed for the U.S. Navy and Army. This first unit was fueled by hydrogen generated by mixing water and lithium hydride. This fuel mixture was contained in disposable canisters that could be easily supplied to personnel in the field. The cell was compact and portable, but it was expensive.

The next development in PEM technology was for NASA's Project Gemini in the early days of the U.S. piloted space program. Batteries had provided power for earlier missions, but future missions would be longer, requiring a different power source. PEM cells were selected, but encountered repeated technical difficulties, including internal cell contamination and membrane leakage. So, Gemini’s 1 through 4 flew with batteries instead. A redesigned PEM cell served adequately for the remaining Gemini flights.

By the mid-1970s, PEM cells were developed for underwater life support, leading to the US Navy Oxygen Generating Plant. The British Royal Navy adopted this technology in early 1980s for their submarine fleet. Other groups also began looking at PEM cells. In the late 1980s and early 1990s, Los Alamos National Lab and Texas A&M University experimented with ways to reduce the amount of platinum required for PEM cells. Recently the weatherproofing material Gore-Tex was added to PEM cells to strengthen the electrolyte.


PEM Fuel Cell Applications

PEM cells started in space, but they have applications that are more down-to-earth. PEM fuel cells can provide both stationary and portable power for many applications including lighting, communications, navigation, computation and entertainment. Vehicular applications include busses, long-distance aircraft and cars.

Vehicular PEM Applications

In 1995, PEM cells were tested in buses in Vancouver and Chicago and later in experimental vehicles. PEM cells have also supplied power to unmanned blimps called aerostats and to sonobuoys, which are nautical buoys that generate and receive sonar signals.

Automotive research has taken off, as air quality regulations grow steadily stricter, particularly in California. Car manufacturers are spending billions annually on development of PEM fuel cell stacks for hybrid and electric cars. Mass-produced fuel cell cars should be available in 2004 or before. Fuel cell cars will be at least 50% more economical in operation than internal combustion cars.

Stationary Power PEM Applications

Since the mid-1980s, stationary power PEM development has included some of the following applications. In 1989, a 5 kW hydrogen and air PEM stack was introduced. Two years later, a 250 kW PEM fuel cell plant at Crane Naval Air Station in Indiana began operating. In 1998, a 5 kW PEM unit began powering a home in Albany, New York, as a demonstration project. In 2000, Bonneville Power Administration tested 6 PEM Alpha units.

Portable Power PEM Applications

PEM and direct methanol fuel cells may someday replace the batteries that power cellular phones, laptop computers and other portable electronic devices. In 2000, a portable fuel cell prototype produced 0.24 watts and 0.9 volts. A fuel cell stack made up of eight of these 1x1x3/8-inch modules could power a cell phone. The goal is to power a cell phone for up to 40 days on standby and 20 hours of talk time. Also, several PEM fuel cells have been developed for notebook PC’s.

Renewable Energy PEM Applications

Early in 2000, PEM technology was selected to provide nighttime power for the solar-powered Helios, a long-duration aircraft. The goal was to make the unpiloted aircraft fly continuously for up to six months. Photovoltaic panels during the day ran electric motors and electrolyzed water. At night, the fuel cell ran the motors by converting the hydrogen and oxygen back into water.


External of Interest

The Schatz solar/PEM fuel cell project has been aerating the aquarium at Humboldt State University since 1994. It uses energy from the sun to generate and produce hydrogen that will be used in a PEM fuel cell when the sun is not available. The result is that the fish have enjoyed solar and fuel cell powered air bubbles twenty-four hours a day for over 7 years. To learn more about this project, go to http://www.humboldt.edu/~serc/trinidad.html.

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