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

In a paper published April 21 inScience, 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.

Source

Laser Sparks Revolution in Internal Combustion Engines

In the past, lasers strong enough to ignite an engine's air-fuel mixtures were too large to fit under an automobile's hood. At this year's Conference on Lasers and Electro Optics (CLEO: 2011), to be held in Baltimore May 1-6, researchers from Japan will describe the first multibeam laser system small enough to screw into an engine's cylinder head.

Equally significant, the new laser system is made from ceramics, and could be produced inexpensively in large volumes, according to one of the presentation's authors, Takunori Taira of Japan's National Institutes of Natural Sciences.

According to Taira, conventional spark plugs pose a barrier to improving fuel economy and reducing emissions of nitrogen oxides (NO_x), a key component of smog.

Spark plugs work by sending small, high-voltage electrical sparks across a gap between two metal electrodes. The spark ignites the air-fuel mixture in the engine's cylinder -- producing a controlled explosion that forces the piston down to the bottom of the cylinder, generating the horsepower needed to move the vehicle.

Engines make NO_xas a byproduct of combustion. If engines ran leaner -- burnt more air and less fuel -- they would produce significantly smaller NO_xemissions.

Spark plugs can ignite leaner fuel mixtures, but only by increasing spark energy. Unfortunately, these high voltages erode spark plug electrodes so fast, the solution is not economical. By contrast, lasers, which ignite the air-fuel mixture with concentrated optical energy, have no electrodes and are not affected.

Lasers also improve efficiency. Conventional spark plugs sit on top of the cylinder and only ignite the air-fuel mixture close to them. The relatively cold metal of nearby electrodes and cylinder walls absorbs heat from the explosion, quenching the flame front just as it starts to expand.

Lasers, Taira explains, can focus their beams directly into the center of the mixture. Without quenching, the flame front expands more symmetrically and up to three times faster than those produced by spark plugs.

Equally important, he says, lasers inject their energy within nanoseconds, compared with milliseconds for spark plugs."Timing -- quick combustion -- is very important. The more precise the timing, the more efficient the combustion and the better the fuel economy," he says.

Lasers promise less pollution and greater fuel efficiency, but making small, powerful lasers has, until now, proven hard. To ignite combustion, a laser must focus light to approximately 100 gigawatts per square centimeter with short pulses of more than 10 millijoules each.

"In the past, lasers that could meet those requirements were limited to basic research because they were big, inefficient, and unstable," Taira says. Nor could they be located away from the engine, because their powerful beams would destroy any optical fibers that delivered light to the cylinders.

Taira's research team overcame this problem by making composite lasers from ceramic powders. The team heats the powders to fuse them into optically transparent solids and embeds metal ions in them to tune their properties.

Ceramics are easier to tune optically than conventional crystals. They are also much stronger, more durable, and thermally conductive, so they can dissipate the heat from an engine without breaking down.

Taira's team built its laser from two yttrium-aluminum-gallium (YAG) segments, one doped with neodymium, the other with chromium. They bonded the two sections together to form a powerful laser only 9 millimeters in diameter and 11 millimeters long (a bit less than half an inch).

The composite generates two laser beams that can ignite fuel in two separate locations at the same time. This would produce a flame wall that grows faster and more uniformly than one lit by a single laser.

The laser is not strong enough to light the leanest fuel mixtures with a single pulse. By using several 800-picosecond-long pulses, however, they can inject enough energy to ignite the mixture completely.

A commercial automotive engine will require 60 Hz (or pulse trains per second), Taira says. He has already tested the new dual-beam laser at 100 Hz. The team is also at work on a three-beam laser that will enable even faster and more uniform combustion.

The laser-ignition system, although highly promising, is not yet being installed into actual automobiles made in a factory. Taira's team is, however, working with a large spark-plug company and with DENSO Corporation, a member of the Toyota Group.

This work is supported by the Japan Science and Technical Agency (JST).

Source

Chance Discovery May Revolutionize Hydrogen Production

The results of the research are published online inChemical Science. An international patent based on this discovery has just been filled.

Existing in large quantities on Earth, water is composed of hydrogen and oxygen. It can be broken down by applying an electrical current; this is the process known as electrolysis. To improve this particularly slow reaction, platinum is generally used as a catalyst. However, platinum is a particularly expensive material that has tripled in price over the last decade. Now EPFL scientists have shown that amorphous molybdenum sulphides, found abundantly, are efficient catalysts and hydrogen production cost can be significantly lowered.

Industrial prospects

The new catalysts exhibit many advantageous technical characteristics. They are stable and compatible with acidic, neutral or basic conditions in water. Also, the rate of the hydrogen production is faster than other catalysts of the same price. The discovery opens up some interesting possibilities for industrial applications such as in the area of solar energy storage.

It's only by chance that Daniel Merki, Stéphane Fierro, Heron Vrubel and Xile Hu made this discovery during an electrochemical experience."It's a perfect illustration of the famous serendipity principle in fundamental research," as Xile Hu emphasizes:"Thanks to this unexpected result, we've revealed a unique phenomenon," he explains."But we don't yet know exactly why the catalysts are so efficient."

The next stage is to create a prototype that can help to improve sunlight-driven hydrogen production. But a better understanding of the observed phenomenon is also required in order to optimize the catalysts.

Source

First Macro-Scale Thin-Film Solid-Oxide Fuel Cell: Strong, Nanostructured Membrane Enables Scaling for Clean-Energy Applications

While SOFCs have previously worked at the micro-scale, this is the first time any research group has overcome the structural challenges of scaling the technology up to a practical size with a proportionally higher power output.

Reported online April 3 inNature Nanotechnology, the demonstration of this fully functional SOFC indicates the potential of electrochemical fuel cells to be a viable source of clean energy.

"The breakthrough in this work is that we have demonstrated power density comparable to what you can get with tiny membranes, but with membranes that are a factor of a hundred or so larger, demonstrating that the technology is scalable," says principal investigator Shriram Ramanathan, Associate Professor of Materials Science at SEAS.

SOFCs create electrical energy via an electrochemical reaction that takes place across an ultra-thin membrane. This 100-nanometer membrane, comprising the electrolyte and electrodes, has to be thin enough to allow ions to pass through it at a relatively low temperature (which, for ceramic fuel cells, lies in the range of 300 to 500 degrees Celsius). These low temperatures allow for a quick start-up, a more compact design, and less use of rare-earth materials.

So far, however, thin films have been successfully implemented only in micro-SOFCs, where each chip in the fuel cell wafer is about 100 microns wide. For practical applications, such as use in compact power sources, SOFCs need to be about 50 times wider.

The electrochemical membranes are so thin that creating one on that scale is roughly equivalent to making a 16-foot-wide sheet of paper. Naturally, the structural issues are significant.

"If you make a conventional thin membrane on that scale without a support structure, you can't do anything -- it will just break," says co-author Bo-Kuai Lai, a postdoctoral fellow at SEAS."You make the membrane in the lab, but you can't even take it out. It will just shatter."

With lead author Masaru Tsuchiya (Ph.D. '09), a former member of Ramanathan's lab who is now at SiEnergy, Ramanathan and Lai fortified the thin film membrane using a metallic grid that looks like nanoscale chicken wire.

The tiny metal honeycomb provides the critical structural element for the large membrane while also serving as a current collector. Ramanathan's team was able to manufacture membrane chips that were 5 mm wide, combining hundreds of these chips into palm-sized SOFC wafers.

While other researchers' earlier attempts at implementing the metallic grid showed structural success, Ramanathan's team is the first to demonstrate a fully functional SOFC on this scale. Their fuel cell's power density of 155 milliwatts per square centimeter (at 510 degrees Celsius) is comparable to the power density of micro-SOFCs.

When multiplied by the much larger active area of this new fuel cell, that power density translates into an output high enough for relevance to portable power.

Previous work in Ramanathan's lab has developed micro-SOFCs that are all-ceramic or that use methane as the fuel source instead of hydrogen. The researchers hope that future work on SOFCs will incorporate these technologies into the large-scale fuel cells, improving their affordability.

In the coming months, they will explore the design of novel nanostructured anodes for hydrogen-alternative fuels that are operable at these low temperatures and work to enhance the microstructural stability of the electrodes.

The research was supported in part by the National Science Foundation (NSF) and performed in part at the Harvard University Center for Nanoscale Systems, a member of the NSF-funded National Nanotechnology Infrastructure Network.

Source