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Researchers Develop More Reactive Form of Platinum That Could Result in Less Expensive, More Efficient Fuel Cells

Researchers at the Department of Energy’s SLAC National Accelerator Laboratory and the University of Houston have tuned the catalytic activity of dealloyed bimetallic nanoparticles to produce a more reactive form of platinum that could be used to make less expensive, more efficient fuel cells. Their work is described in a paper published online 25 April in the journal Nature Chemistry.

By tweaking platinum’s reactivity, the researchers were able to curtail the amount of platinum required by 80%, and hope to soon reduce it by another 10%, greatly trimming away at the overall cost of fuel cells.

This is a significant advance. Fuel cells were invented more than 100 years ago. They haven’t made a leap over to being a big technology yet, in part because of this difficulty with platinum. I think with a factor of ten, we’ll have a home run

—Anders Nilsson, Stanford Institute for Materials and Energy Sciences, a joint institute between SLAC and Stanford University

Fuel cells use hydrogen and oxygen to drive their energy-producing reactions; when oxygen enters the metal cathode, it is broken down into individual atoms before it forms water with hydrogen. The choice of metal for the cathode is extremely important, as some metals cannot break apart the oxygen atoms while others try to bind too strongly to the oxygen atoms, taking them away from the key reaction.

Scientists seek the balance point at which the number of oxygen bonds broken is maximized and the oxygen atoms bind more weakly to the catalyst. They achieved the balance with platinum, which is strong enough to break the oxygen bonds but does not bind to the free oxygen atoms too strongly. Unfortunately, it also costs enough to make platinum-electrode fuel cells untenably expensive.

In 2005, University of Houston researcher Peter Strasser started looking for ways to crack the platinum problem not by replacing platinum outright, as other researchers sought to do, but by making platinum more reactive.

“The distance between two neighboring atoms affects their electronic structure. By changing the interatomic distance, we can manipulate how strongly they form bonds.”
—Peter Strasser, lead author

To do this, Strasser and colleagues used a process called dealloying. First, they combined platinum with varying amounts of copper to create a copper-platinum alloy. Then they removed the copper from the surface region of the alloy. When they tested the binding properties of the dealloyed platinum-copper catalyst, they found it was much more reactive than it would be otherwise.

To find out why, Strasser, Nilsson and colleagues Mike Toney and Hirohito Ogasawara put dealloyed samples under the X-ray beam at the Stanford Synchrotron Radiation Lightsource. By studying how X-rays scattered from the dealloyed samples, they were able to create detailed pictures of the metal’s internal structure, revealing that the increased reactivity was caused by lattice strain—a phenomenon in which the arrangement of platinum atoms is modified.

By compressing the surface platinum atoms closer together, the process causes platinum atoms to bind a little more weakly to oxygen atoms and inch closer to the balance point between molecule dissociation and catalytic binding.

...we show how lattice strain can be used experimentally to tune the catalytic activity of dealloyed bimetallic nanoparticles for the oxygen-reduction reaction, a key barrier to the application of fuel cells and metal–air batteries. We demonstrate the core–shell structure of the catalyst and clarify the mechanistic origin of its activity. The platinum-rich shell exhibits compressive strain, which results in a shift of the electronic band structure of platinum and weakening chemisorption of oxygenated species. We combine synthesis, measurements and an understanding of strain from theory to generate a reactivity–strain relationship that provides guidelines for tuning electrocatalytic activity.

—Strasser et al.

The next step for the researchers will be to use the SSRL beam to get a closer look at the reactions between oxygen and platinum, and to determine what can be done to make the process even more efficient. The ultimate goal is to create a potential replacement not only for gasoline engines but also for the batteries found in small electronic devices.

The majority of this research is supported by the US Department of Energy Office of Science through its programs at the Stanford Synchrotron Radiation Lightsource and the Stanford Institute for Materials and Energy Sciences at SLAC National Accelerator Laboratory and Stanford University. Collaborating institutions also include Argonne National Laboratory, Oak Ridge National Laboratory, Technical University Berlin and the University of Houston.

Resources

  • Peter Strasser, Shirlaine Koh, Toyli Anniyev, Jeff Greeley, Karren More, Chengfei Yu, Zengcai Liu, Sarp Kaya, Dennis Nordlund, Hirohito Ogasawara, Michael F. Toney, & Anders Nilsson (2010) Lattice-strain control of the activity in dealloyed core–shell fuel cell catalysts. Nature Chemistry doi: 10.1038/nchem.623

Comments

HarveyD

This may be great to reduce the initial cost of fuel cells but hydrogen production, handling and distribution infrastructure cost remain to be fully and adequately addressed before fuel cell vehicles become a reality. By that time, lower cost, safer EVs will be in common used worldwide.

Donough Shanahan

Quite general; the phrase 'a little more weakly' is interesting. They have added an extra complex step or two (adding and then removing copper) for what, a supposed 80% reduction in platinum. Of course as we use so little platinum in the fuel cell, it is only one of a number of significant costs.
An HD is correct the real costs are that of infrastructure.

Allen

...the researchers were able to curtail the amount of platinum required by 80%, and hope to soon reduce it by another 10%

There is a big difference between another 10% and another 10 percentage points. From the context, it is clear the researchers hope to achieve a total reduction of 90%. That sentence therefore needs to be written as either "hope to soon reduce it by another 10 percentage points", or "hope to soon reduce it by another 50%", or "hope to soon achieve 90%", all of which say the same thing, in contrast to "by another 10%", which means that the total reduction would only be ~82%.

wintermane2000

Generaly hydrogen can be made rather cheaply it was transporting it that was spendy as hell and that is being fixed rather quickly. At any rate the companies involved manage to SELL h2 at around the same price as gasoline and as that gives you 3x the range per unit thats more then cheap enough.

Davemart

I get a little tired of very good progress in technology being rather belittled by pointing to other remaining obstacles often in rather different fields.
It is nearly as bad as the converse, which simply assumes that all obstacles will be overcome.
It's clear that both in reducing the expense of fuel cells and in developing storage we are doing fairly well.

Mannstein

The importance of this work is not whether the cost of fuel cells can be reduced or if they can beat out batteries for traction applications.

What's remarkable is that lattice strain can be used to tune electro catalyisis. This understanding is imortant to a host of other chemical processes. It is the first step to designer catalyists.

Mannstein

I can't agree with Davemart more.

Ole Grampa

At Mannstein: and I agree too. It became fashionable to criticize the whole hydrogen effort, especially after Bush signed on to it. Thousands of companies are pursuing it for good reason, all over the world. They know better than you, Harvey D.

Roger Pham

A platinum-conserving development means that there will be platinum available to build a much larger fleet of FCV's. The high cost of platinum means that it will also be recycled again and again, ensuring the availability of this noble metal far into the future. This will secure the future for FCV's, which will soon be available commercially around 2015, according to not just one, but several car companies.

Henry Gibson

Hydrogen can be produced more cheaply than gasoline sells for because producers have also become speculators and have developed a system to keep the price of of oil far above production costs and to limit the supply. These oil speculators invest in a lot of lobbying to prevent alternative fuel factories from being built. The main lobby point is that more CO2 would be produced if gasoline were made from coal than from crude oil. The fact that is being ignored is that coal costs ten times or more less than oil per unit energy. Also the CO2 cost of oil from different nations is not known, and CO2 from the factories can be captured and used.

Diesel engines can get as high an efficiency as fuel cells, especially when operated in a series hybrid mode.

Hydraulic hybrids with the NOAX free piston engine could be far cheaper to build and have lower operating costs than fuel cell electric hybrids.

You may remember that the developers of fuel cells killed the product ready electric car production.

ZEBRA batteries for long distance and long life and lithium batteries for acceleration and a small range extender engine for rare long distance travel represents a very useful combination that can absorb all of the windpower and solar power that the US should ever produce since most cars are mostly stationary all the time near the grid.

The main promotor of fuel cells in Europe abandoned hydrogen years ago as being impractical. Ammonia will give the same results but can be used for longer distances. It is also too expensive to produce compared to electricity for battery cars. ..HG..

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