Cheaper Hydrogen Fuel Cells: Utility of Non-Precious-Metal Catalysts Documented

Cheaper Hydrogen Fuel Cells: Utility of Non-Precious-Metal Catalysts Documented

  9:21:00 AM    Science Lover

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Los Alamos National Laboratory scientists have developed a way to avoid the use of expensive platinum in hydrogen fuel cells, the environmentally friendly devices that might replace current power sources in everything from personal data devices to automobiles.

Los Alamos National Laboratory scientists have 
developed a way to avoid the use of expensive 
platinum in hydrogen fuel cells, the environmentally 
friendly devices that might replace current power 
sources in everything from personal data devices 
to automobiles. (Credit: Image courtesy of DOE/Los 
Alamos National Laboratory)

In a paper published April 21 in Science, Los Alamos researchers Gang Wu, Christina Johnston, and Piotr Zelenay, joined by researcher Karren More of Oak Ridge National Laboratory, describe the use of a platinum-free catalyst in the cathode of a hydrogen fuel cell. Eliminating platinum -- a precious metal more expensive than gold -- would solve a significant economic challenge that has thwarted widespread use of large-scale hydrogen fuel cell systems.

Polymer-electrolyte hydrogen fuel cells convert hydrogen and oxygen into electricity. The cells can be enlarged and combined in series for high-power applications, including automobiles. Under optimal conditions, the hydrogen fuel cell produces water as a "waste" product and does not emit greenhouse gasses. However, because the use of platinum in catalysts is necessary to facilitate the reactions that produce electricity within a fuel cell, widespread use of fuel cells in common applications has been cost prohibitive. An increase in the demand for platinum-based catalysts could drive up the cost of platinum even higher than its current value of nearly $1,800 an ounce.

The Los Alamos researchers developed non-precious-metal catalysts for the part of the fuel cell that reacts with oxygen. The catalysts -- which use carbon (partially derived from polyaniline in a high-temperature process), and inexpensive iron and cobalt instead of platinum -- yielded high power output, good efficiency, and promising longevity. The researchers found that fuel cells containing the carbon-iron-cobalt catalyst synthesized by Wu not only generated currents comparable to the output of precious-metal-catalyst fuel cells, but held up favorably when cycled on and off -- a condition that can damage inferior catalysts relatively quickly.

Moreover, the carbon-iron-cobalt catalyst fuel cells effectively completed the conversion of hydrogen and oxygen into water, rather than producing large amounts of undesirable hydrogen peroxide. Inefficient conversion of the fuels, which generates hydrogen peroxide, can reduce power output by up to 50 percent, and also has the potential to destroy fuel cell membranes. Fortunately, the carbon- iron-cobalt catalysts synthesized at Los Alamos create extremely small amounts of hydrogen peroxide, even when compared with state-of-the-art platinum-based oxygen-reduction catalysts.

Because of the successful performance of the new catalyst, the Los Alamos researchers have filed a patent for it.

"The encouraging point is that we have found a catalyst with a good durability and life cycle relative to platinum-based catalysts," said Zelenay, corresponding author for the paper. "For all intents and purposes, this is a zero-cost catalyst in comparison to platinum, so it directly addresses one of the main barriers to hydrogen fuel cells."

The next step in the team's research will be to better understand the mechanism underlying the carbon-iron-cobalt catalyst. Micrographic images of portions of the catalyst by researcher More have provided some insight into how it functions, but further work must be done to confirm theories by the research team. Such an understanding could lead to improvements in non-precious-metal catalysts, further increasing their efficiency and lifespan.

Project funding for the Los Alamos research came from the U.S. Department of Energy's Energy Efficiency and Renewable Energy (EERE) Office as well as from Los Alamos National Laboratory's Laboratory-Directed Research and Development program. Microscopy research was done at Oak Ridge National Laboratory's SHaRE user facility with support from the DOE's Office of Basic Energy Sciences.

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Novel Nanowires Boost Fuel Cell Efficiency

Novel Nanowires Boost Fuel Cell Efficiency

  12:26:00 AM    Science Lover

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Fuel cells have been touted as a cleaner solution to tomorrow's energy needs, with potential applications in everything from cars to computers.

Taylor and Schroers engineered nanowires out of a novel material called bulk metallic glass in order to make fuel cell catalyst systems more durable and efficient. (Credit: Golden Kumar and Miriam Schroers)

But one reason fuel cells aren't already more widespread is their lack of endurance. Over time, the catalysts used even in today's state-of-the-art fuels cells break down, inhibiting the chemical reaction that converts fuel into electricity. In addition, current technology relies on small particles coated with the catalyst; however, the particles' limited surface area means only a fraction of the catalyst is available at any given time.

Now a team of engineers at the Yale School of Engineering & Applied Science has created a new fuel cell catalyst system using nanowires made of a novel material that boosts long-term performance by 2.4 times compared to today's technology. Their findings appear on the cover of the April issue of ACS Nano.

Yale engineers Jan Schroers and André Taylor have developed miniscule nanowires made of an innovative metal alloy known as a bulk metallic glass (BMG) that have high surface areas, thereby exposing more of the catalyst. They also maintain their activity longer than traditional fuel cell catalyst systems.

Current fuel cell technology uses carbon black, an inexpensive and electrically conductive carbon material, as a support for platinum particles. The carbon transports electricity, while the platinum is the catalyst that drives the production of electricity. The more platinum particles the fuel is exposed to, the more electricity is produced. Yet carbon black is porous, so the platinum inside the inner pores may not be exposed. Carbon black also tends to corrode over time.

"In order to produce more efficient fuel cells, you want to increase the active surface area of the catalyst, and you want your catalyst to last," Taylor said.

At 13 nanometers in scale (about 1/10,000 the width of a human hair), the BMG nanowires that Schroers and Taylor developed are about three times smaller than carbon black particles. The nanowires' long, thin shape gives them much more active surface area per mass compared to carbon black. In addition, rather than sticking platinum particles onto a support material, the Yale team incorporated the platinum into the nanowire alloy itself, ensuring that it continues to react with the fuel over time.

It's the nanowires' unique chemical composition that makes it possible to shape them into such small rods using a hot-press method, said Schroers, who has developed other BMG alloys that can also be blow molded into complicated shapes. The BMG nanowires also conduct electricity better than carbon black and carbon nanotubes, and are less expensive to process.

So far Taylor has tested their catalyst system for alcohol-based fuel cells (including those that use ethanol and methanol as fuel sources), but they say the system could be used in other types of fuel cells and could one day be used in portable electronic devices such as laptop computers and cell phones as well as in remote sensors.

"This is the introduction of a new class of materials that can be used as electrocatalysts," Taylor said. "It's a real step toward making fuel cells commercially viable and, ultimately, supplementing or replacing batteries in electronic devices."

Other authors of the paper include Marcelo Carmo, Ryan C. Sekol, Shiyan Ding and Golden Kumar (all of Yale University).

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200-Fold Boost in Fuel Cell Efficiency Advances 'Personalized Energy Systems'

200-Fold Boost in Fuel Cell Efficiency Advances 'Personalized Energy Systems'

  7:32:00 AM    Science Lover

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The era of personalized energy systems -- in which individual homes and small businesses produce their own energy for heating, cooling and powering cars -- took another step toward reality today as scientists reported discovery of a powerful new catalyst that is a key element in such a system.

A new catalyst could help speed development of inexpensive home-brewed solar energy systems for powering homes and plug-in cars during the day (left) and for producing electricity from a fuel cell at night (right). (Credit: Patrick Gillooly/MIT)

They described the advance, which could help free homes and businesses from dependence on the electric company and the corner gasoline station, at the 240th National Meeting of the American Chemical Society, being held in Boston.

"Our goal is to make each home its own power station," said study leader Daniel Nocera, Ph.D. "We're working toward development of 'personalized' energy units that can be manufactured, distributed and installed inexpensively. There certainly are major obstacles to be overcome -- existing fuel cells and solar cells must be improved, for instance. Nevertheless, one can envision villages in India and Africa not long from now purchasing an affordable basic system."

Such a system would consist of rooftop solar energy panels to produce electricity for heating, cooking, lighting, and to charge the batteries on the homeowners' electric cars. Surplus electricity would go to an "electrolyzer," a device that breaks down ordinary water into its two components, hydrogen and oxygen. Both would be stored in tanks. In the dark of night, when the solar panels cease production, the system would shift gears, feeding the stored hydrogen and oxygen into a fuel cell that produces electricity (and clean drinking water as a byproduct). Such a system would produce clean electricity 24 hours a day, seven days a week -- even when the sun isn't shining.

Nocera's report focused on the electrolyzer, which needs catalysts -- materials that jumpstart chemical reactions like the ones that break water up into hydrogen and oxygen. He is with the Massachusetts Institute of Technology in Cambridge, Mass. Good catalysts already are available for the part of the electrolyzer that produces hydrogen. Lacking, however, have been inexpensive, long-lasting catalysts for the production of oxygen. The new catalyst fills that gap and boosts oxygen production by 200-fold. It eliminates the need for expensive platinum catalysts and potentially toxic chemicals used in making them.

The new catalyst has been licensed to Sun Catalytix, which envisions developing safe, super-efficient versions of the electrolyzer, suitable for homes and small businesses, within two years.

The National Science Foundation and the Chesonis Family Foundation provided funding for this study. Nocera did the research with post-doctoral researcher Mircea Dinca and doctoral candidate Yogesh Surendranath. The U.S. Department of Energy's Advanced Research Projects Agency has recently awarded the team with a grant, which it plans to use to search for related compounds that can further increase the efficiency of its electrolyzer technology. The team hopes that nickel-borate belongs to a family of compounds that can be optimized for super-efficient, long-term energy storage technologies.

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Hydrogen Storage Gets New Hope

Hydrogen Storage Gets New Hope

  9:28:00 PM    Science Lover

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A new method for “recycling” hydrogen-containing fuel materials could open the door to economically viable hydrogen-based vehicles.

Ammonia borane (AB) is a potential hydrogen releasing fuel. In this Los Alamos National Laboratory graphic, the AB would be used on-board the vehicle to run a fuel cell. Once hydrogen is released, the AB could then be regenerated and reused. In the scheme shown,
the recycle of dehydrogenated fuel back into AB would take place off-board the vehicle.
(Credit: Image courtesy of DOE/Los Alamos National Laboratory)

In an article appearing in Angewandte Chemie, Los Alamos National Laboratory and University of Alabama researchers working within the U.S. Department of Energy’s Chemical Hydrogen Storage Center of Excellence describe a significant advance in hydrogen storage science.

Hydrogen is in many ways an ideal fuel for transportation. It is abundant and can be used to run a fuel cell, which is much more efficient than internal combustion engines. Its use in a fuel cell also eliminates the formation of gaseous byproducts that are detrimental to the environment.

For use in transportation, a fuel ideally should be lightweight to maintain overall fuel efficiency and pack a high energy content into a small volume. Unfortunately, under normal conditions, pure hydrogen has a low energy density per unit volume, presenting technical challenges for its use in vehicles capable of travelling 300 miles or more on a single fuel tank—a benchmark target set by DOE.

Consequently, until now, the universe’s lightest element has been considered by some as a lightweight in terms of being a viable transportation fuel.

In order to overcome some of the energy density issues associated with pure hydrogen, work within the Chemical Hydrogen Storage Center of Excellence has focused on using a class of materials known as chemical hydrides. Hydrogen can be released from these materials and potentially used to run a fuel cell. These compounds can be thought of as “chemical fuel tanks” because of their hydrogen storage capacity.

Ammonia borane is an attractive example of a chemical hydride because its hydrogen storage capacity approaches a whopping 20 percent by weight. The chief drawback of ammonia borane, however, has been the lack of energy-efficient methods to reintroduce hydrogen back into the spent fuel once it has been released. In other words, until recently, after hydrogen release, ammonia borane couldn’t be adequately recycled.

Los Alamos researchers have been working with University of Alabama colleagues on developing methods for the efficient recycling of ammonia borane. The research team made a breakthrough when it discovered that a specific form of dehydrogenated fuel, called polyborazylene, could be recycled with relative ease using modest energy input. This development is a significant step toward using ammonia borane as a possible energy carrier for transportation purposes.

“This research represents a breakthrough in the field of hydrogen storage and has significant practical applications,” said Dr. Gene Peterson, leader of the Chemistry Division at Los Alamos. “The chemistry is new and innovative, and the research team is to be commended on this excellent achievement.”

The Chemical Hydrogen Storage Center of Excellence is one of three Center efforts funded by DOE. The other two focus on hydrogen sorption technologies and storage in metal hydrides. The Center of Excellence is a collaboration between Los Alamos, Pacific Northwest National Laboratory, and academic and industrial partners.

Referring to the work described in the Angewandte Chemie article, Los Alamos researcher John Gordon, corresponding author for the paper, stated, “Collaboration encouraged by our Center model was responsible for this breakthrough. At the outset there were myriad potential reagents with which to attempt this chemistry.”

“The predictive calculations carried out by University of Alabama professor Dave Dixon’s group were crucial in guiding the experimental work of Los Alamos postdoctoral researcher Ben Davis,” Gordon added. “The excellent synergy between these two groups clearly enabled this advance.”

The research team currently is working with colleagues at The Dow Chemical Company, another Center partner, to improve overall chemical efficiencies and move toward large-scale implementation of hydrogen-based fuels within the transportation sector.

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