In the Lab
A Commercially Viable Fuel Cell
University of California at Berkeley Lab researchers have developed a solid oxide fuel cell (SOFC) that promises to generate electricity as cheaply as the most efficient gas turbine.
Their innovation, which paves the way for pollution-free power generators that serve neighborhoods and industrial sites, lies in replacing ceramic electrodes with stainless-steel-supported electrodes that are stronger, easier to manufacture and, most importantly, cheaper. This latter advantage marks a turning point in the push to develop commercially viable fuel cells.
"We're closer to breaking the cost barrier than ever before," says Steve Visco, who developed the SOFC technology with fellow Materials Sciences Division researchers Craig Jacobson and Lutgard De Jonghe.
That barrier is $400 per kilowatt, a stringent bar set by the U.S. Department of Energy's Solid State Energy Conversion Alliance, a government, industry and scientific group tasked with developing affordable fuel cell-based power generators. The $400 target -- nearly one-tenth the cost of today's fuel cells -- is equivalent to the most efficient gas turbines and diesel generators, and is based on the premise that a fuel cell's success hinges on its competitiveness.
"Green is great for marketing, but people won't buy an environmentally friendly product if it's twice as expensive," says Visco.
Fuel cells work by converting chemical energy to electrical energy, capitalizing on hydrogen and oxygen's strong propensity to bond and form water. Unlike gas turbines, this process doesn't emit air pollutants, such as nitrous oxide and sulfur dioxide. And because fuel cells are more efficient than gas turbines, they emit far less carbon dioxide, a greenhouse gas.
An SOFC is composed of a gas-tight electrolyte layer sandwiched between porous cathode and anode layers. Oxygen from the air flows through the cathode, and a fuel gas containing hydrogen, such as methane, flows past the anode. Negatively charged oxygen ions migrate through the electrolyte membrane and react with the hydrogen to form water, which reacts with the methane fuel to form carbon dioxide and hydrogen. This electrochemical reaction generates electrons, which flow from the anode to an external load and back to the cathode, a final step that both completes the circuit and supplies electric power. To increase voltage output, several fuel cells are stacked together, a configuration called a fuel cell stack that forms the heart of a clean power generator.
Visco and colleagues' foray into affordable fuel cell design began several years ago when they developed a way to lower a fuel cell's operating temperature to 800 degrees Celsius without sacrificing efficiency. Until then, fuel cells worked most efficiently at 1,000 degrees Celsius, a high temperature that decreases the cell's life span and precludes the use of metal components.
They fabricated extremely thin ceramic electrodes that conduct ions at 800 degrees Celsius as readily as thicker electrodes do at 1,000 degrees Celsius. Lowering the temperature also allowed them to use metal components, instead of ceramic, to connect several ceramic cells into a stack. Their design didn't hit the $400 per kilowatt target, but it allowed them to reduce the cell's operating temperature without sacrificing performance.
"Craig Jacobson wondered if the electrode support itself could be made of metal, which is strong, cheap and readily available," Visco says.
With this in mind, they developed a fuel cell that features 10 to 15 microns of a zirconia-based electrolyte layered onto 10 to 20 microns of a nickel-based electrode. Together these are supported by and bonded to approximately two millimeters of porous high-strength commercial alloy.
But does the design meet the $400 per kilowatt target? First, there's more to a fuel-cell-based generator than fuel cells. Roughly speaking, one-third of a generator's cost lies in the actual fuel cell stack, the other two-thirds lies in external "plumbing" such as insulation and a DC-to-AC inverter. This means the fuel cell stack can't exceed $130 per kilowatt if the entire unit is to meet the $400 per kilowatt target. No problem there: the raw materials for the Berkeley Lab stainless steel-based fuel cell are only $37 per kilowatt.
For more information, visit www.lbl.gov.
Agricultural Science Helping Farmers Reduce Greenhouse Gas Emissions
With greenhouse gas (GHG) reduction on the public agenda, Agriculture and Agri-Food Canada (AAFC) researchers say agricultural science may be part of the solution.
Agriculture contributes 10 percent of Canada's GHG emissions. A team of researchers at AAFC is developing ways to reduce on-farm GHGs -- carbon dioxide (CO2), nitrous oxide (N20) and methane.
"Increases in the concentration of GHGs through human activities may cause changes to the earth's climate that we can't predict," said Dr. Ray Desjardins, AAFC atmospheric scientist. Unlike other industries which emit mostly CO2, agriculture emits N20 and methane.
"Methane accounts for about one-third of agriculture's emissions and comes largely from livestock," he added. "N20, which accounts for most of the rest, is emitted from farm soils, especially those that have received manures and fertilizers."
Dr. Henry Janzen, AAFC soil biochemist, noted that agriculture will be asked to help reduce these emissions and science can provide farmers with the tools to do it. One way is to store more carbon in soils. "Farmers are in the business of managing carbon, even from other industries," he said. "If we can help them to effectively store it longer in their fields, that means less greenhouse gas in the air we all breathe."
AAFC researchers have developed a virtual farm application to help farmers reduce these emissions. This computer based-application will allow farmers to examine a number of approaches on their farm to minimize GHG emissions while maintaining profitability. These factors include cultivation practices, fertilizer types and application techniques, cropping sequences, animal ration formulas and manure management.
GHG research is consistent with the goals of the Agricultural Policy Framework (APF).
On behalf of the agricultural sector, the government of Canada is building knowledge and awareness of environmental issues such as greenhouse gas produced on farms.
AAFC is committed to environmental research beyond the mitigation of greenhouse gas emissions. To ensure primary agriculture meets the needs of Canadians while remaining profitable and sustainable, AAFC research contributes to a suite of farm management practices to benefit soil, water, air and biodiversity.
This article originally appeared in the January/February 2003 issue of Environmental Protection, Vol. 14, No. 1, p. 12.
This article originally appeared in the 01/01/2003 issue of Environmental Protection.