Fuel Cells Using Nanotechnology

ScienceDaily (Nov. 10, 2010) — Stop-and-go driving can wear on your nerves, but it really does a number on the precious platinum that drives reactions in automotive fuel cells. Before large fleets of fuel-cell-powered vehicles can hit the road, scientists will have to find a way to protect the platinum, the most expensive component of fuel-cell technology, and to reduce the amount needed to make catalytically active electrodes.


Now, scientists at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory have developed a new electrocatalyst that uses a single layer of platinum and minimizes its wear and tear while maintaining high levels of reactivity during tests that mimic stop-and-go driving. The research -- described online in Angewandte Chemie, International Edition -- may greatly enhance the practicality of fuel-cell vehicles and may also be applicable for improving the performance of other metallic catalysts.

The newly designed catalysts are composed of a single layer of platinum over a palladium (or palladium-gold alloy) nanoparticle core. Their structural characterization was performed at Brookhaven's Center for Functional Nanomaterials and the National Synchrotron Light Source.

"Our studies of the structure and activity of this catalyst -- and comparisons with platinum-carbon catalysts currently in use -- illustrate that the palladium core 'protects' the fine layer of platinum surrounding the particles, enabling it to maintain reactivity for a much longer period of time," explained Brookhaven Lab chemist Radoslav Adzic, who leads the research team.

In conventional fuel-cell catalysts, the oxidation and reduction cycling -- triggered by changes in voltage that occur during stop-and-go driving -- damages the platinum. Over time, the platinum dissolves, causing irreversible damage to the fuel cell.

In the new catalyst, palladium from the core is more reactive than platinum in these oxidation and reduction reactions. Stability tests simulating fuel cell voltage cycling revealed that, after 100,000 potential cycles, a significant amount of palladium had been oxidized, dissolved, and migrated away from the cathode. In the membrane between the cathode and anode, the dissolved palladium ions were reduced by hydrogen diffusing from the anode to form a "band," or dots.

In contrast, platinum was almost unaffected, except for a small contraction of the platinum monolayer. "This contraction of the platinum lattice makes the catalyst more active and the stability of the particles increases," Adzic said.

Reactivity of the platinum monolayer/palladium core catalyst also remained extremely high. It was reduced by merely 37 percent after 100,000 cycles.

Building on earlier work that illustrated how small amounts of gold can enhance catalytic activity, the scientists also developed a form of the platinum monolayer catalyst with a palladium-gold alloy core. The addition of gold further increased the stability of the electrocatalyst, which retained nearly 70 percent of reactivity after 200,000 cycles of testing.

"This indicates the excellent durability of this electrocatalyst, especially when compared with simpler platinum-carbon catalysts, which lose nearly 70 percent of their reactivity after much shorter cycling times. This level of activity and stability indicates that this is a practical catalyst. It exceeds the goal set by DOE for 2010-2015 and it can be used for automotive applications," Adzic said.

He noted that fuel cells made using the new catalyst would require only about 10 grams of platinum per car -- and less than 20 grams of palladium. Currently, in catalytic convertors used to treat exhaust gases, 5 to 10 grams of platinum is used. Since fuel-cell-powered cars would emit no exhaust gases, there would be no need for such catalytic converters, and therefore no net increase in the amount of platinum used.

"In addition to developing electrocatalysts for automotive fuel cell applications, these findings indicate the broad applicability of platinum monolayer catalysts and the possibility of extending this concept to catalysts based on other noble metals," Adzic said.

The fundamental science leading to the development of the new electrocatalyst and early scale-up work was funded by the DOE Office of Science. Additional funding came from the Toyota Motor Corporation.

FTA And BTI Working With CTE To Make Better Buses

WASHINGTON--(BUSINESS WIRE)--Fuel cell buses have operated successfully in public transit fleets around the world, according to a new report written for the Federal Transit Administration (FTA) by the Breakthrough Technologies Institute (BTI) and the Center for Transportation and the Environment (CTE).

The report examined hydrogen bus demonstrations in 19 cities in North America, Europe, Asia and Australia. Among other things, the report found that the vast majority of buses performed better than expected and were very popular among passengers. The buses also were popular with drivers, many of whom reported being less tired at the end of their shifts, primarily because fuel cell buses make significantly less noise than their internal combustion counterparts.

“Fuel cell buses were more reliable, better performing, and easier to integrate into public transportation fleets than many had expected,” said William Vincent, a lead author of the report. “With additional research and development, they hold real promise to reduce pollution, greenhouse gas emissions, and petroleum dependence in public transportation fleets.”

The fuel cell buses typically were operated daily in 16-hour duty cycles. Collectively, they covered more than 1.6 million miles and served more than seven million passengers. The fuel cells were much more reliable than many transit agencies had expected and the operating life was increased significantly over previous generations of fuel cell technology. For example, fuel cells in the European demonstrations averaged over 3,000 hours operating life, with a maximum of 5,000 hours. Moreover, the hydrogen fueling stations proved to be very safe. The buses were refueled more than 11,000 times without any major incident.

Based upon this success, most transit agencies that demonstrated fuel cell buses are eager to deploy larger fleets in the future. In fact, AC Transit in California recently purchased four additional fuel cell buses and BC Transit in British Columbia purchased a fleet of 20 fuel cell buses. Many transit agencies also called for enhanced government support for fuel cell buses, thus enabling more buses to be deployed in a shorter timeframe.

The report, “A Report on Worldwide Hydrogen Bus Demonstrations, 2002-2007,” can be downloaded free from the FTA’s website: http://www.fta.dot.gov/documents/ReportOnWorldwideHydrogenBusDemonstrations_2002to2007.pdf.
Contacts
Breakthrough Technologies Institute (BTI)
Jennifer Gangi, 202-785-4222, Ext. 17

Harvesting Hydrogen From Wood

ScienceDaily (Feb. 17, 2009) — Tomorrow's fuel-cell vehicles may be powered by enzymes that consume cellulose from woodchips or grass and exhale hydrogen. Researchers at Virginia Tech, Oak Ridge National Laboratory (ORNL), and the University of Georgia have produced hydrogen gas pure enough to power a fuel cell by mixing 14 enzymes, one coenzyme, cellulosic materials from nonfood sources, and water heated to about 90 degrees (32 degrees Celsius).

The group announced three advances from their "one pot" process: 1) a novel combination of enzymes, 2) an increased hydrogen generation rate -- to as fast as natural hydrogen fermentation, and 3) a chemical energy output greater than the chemical energy stored in sugars – the highest hydrogen yield reported from cellulosic materials. "In addition to converting the chemical energy from the sugar, the process also converts the low-temperature thermal energy into high-quality hydrogen energy – like Prometheus stealing fire," said Percival Zhang, assistant professor of biological systems engineering in the College of Agriculture and Life Sciences at Virginia Tech.

"It is exciting because using cellulose instead of starch expands the renewable resource for producing hydrogen to include biomass," said Jonathan Mielenz, leader of the Bioconversion Science and Technology Group at ORNL.

The researchers used cellulosic materials isolated from wood chips, but crop waste or switchgrass could also be used. "If a small fraction – 2 or 3 percent – of yearly biomass production were used for sugar-to-hydrogen fuel cells for transportation, we could reach transportation fuel independence," Zhang said. (He added that the 3 percent figure is for global transportation needs. The U.S. would actually need to convert about 10 percent of biomass – which would be 1.3 billion tons of usable biomass).

The research is supported by the Air Force Office of Scientific Research; Zhang's DuPont Young Professor Award, and the U.S. Department of Energy

Fuel Cells Made From Hydrogen May Be A Solution 21st Century Energy Challenges

Using hydrogen as an energy vector and in fuel cells may provide solutions to the specific energy challenges of the 21st century. Hydrogen production is currently based on the catalytic properties of “noble” metals such as platinum. For the first time, researchers at the joint Laboratoire de chimie et biologie des métaux (metal chemistry and biology, CEA-CNRS-Université Joseph Fourier, CEA's Grenoble site) have succeeded in producing hydrogen with a molecular system that doesn't require a noble metal catalyst. This outcome has important implications for the financial future of hydrogen energy.

Research to improve hydrogen production is based largely on chemical reactions observed during photosynthesis in plants. More specifically, certain micro-organisms produce hydrogen from water with the help of light. To reproduce and adapt these processes, researchers have developed molecular systems capable of both photosensitisation, which captures light energy, and catalysis, which uses the energy collected to liberate hydrogen from water.

To date, all the technological systems developed to produce or use hydrogen rely on noble metals such as...