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Improving the Performance of Platinum Electrocatalysts in Fuel Cells

12 January 2007

The journal Science and its online companion Science Express this week provide two reports from different research teams on efforts to improve the stability and performance of platinum electrocatalysts in PEM fuel cells.

Scientists at the US Department of Energy’s (DOE) Brookhaven National Laboratory have discovered that the addition of gold clusters to platinum electrocatalysts stabilizes them for use in fuel cells.

A PEM fuel cell converts hydrogen and oxygen into water and, as part of the process, produces electricity. Hydrogen is oxidized when electrons are released and hydrogen ions are formed; the released electrons supply current for an electric motor. Oxygen is reduced by gaining electrons, and in reaction with hydrogen ions, water, the only byproduct of a fuel cell reaction, is produced. Platinum electrocatalysts speed up these oxidation and reduction reactions (ORR).

In reactions during the stop-and-go driving of an electric car, however, the platinum dissolves, which reduces its efficiency as a catalyst—a major impediment for vehicle-application of fuel cells.

Under lab conditions that imitate the environment of a fuel cell, the Brookhaven researchers added gold clusters to the platinum electrocatalyst, which kept it intact during an accelerated stability test. This test is conducted under conditions similar to those encountered in stop-and-go driving in an electric car. The research is reported in the 12 January 2007 edition of the journal Science.

Fuel cells are expected to become a major source of clean energy, with particularly important applications in transportation. Despite many advances, however, existing fuel-cell technology still has drawbacks, including loss of platinum cathode electrocatalysts, which can be as much as 45 percent over five days, as shown in our accelerated stability test under potential cycling conditions. Using a new technique that we developed to deposit gold atoms on platinum, our team was able to show promise in helping to resolve this problem. The next step is to duplicate results in real fuel cells.

—Radoslav Adzic, co-author

In the unique method developed at Brookhaven, the researchers displaced a single layer of copper with gold on carbon-supported platinum nanoparticles. After being subjected to several sweeps of 1.2 volts, the gold monolayer transformed into three-dimensional clusters. Using x-rays as probes at Brookhaven’s National Synchrotron Light Source, a scanning transmission microscope at Brookhaven’s Center for Functional Nanomaterials, and electrochemical techniques in the laboratory, the scientists were able to verify the reduced oxidation of platinum and to determine the structure of the resulting platinum electrocatalyst with gold clusters, which helped them to gain an understanding of the effects of the gold clusters.

In the Brookhaven experiment, the platinum electrocatalyst remained stable with potential cycling between 0.6 and 1.1 volts in more than 30,000 oxidation-reduction cycles, imitating the conditions of stop-and-go driving.

The gold clusters protected the platinum from being oxidized. Our team’s research raises promising possibilities for synthesizing improved platinum-based catalysts and for stabilizing platinum and platinum-group metals under cycling oxidation/reduction conditions.

—Radoslav Adzic

This research is funded through the US Department of Energy’s Hydrogen Program.

In a separate study published online in Science Express, researchers enhanced the performance of platinum electrocatalysts in fuel cells. The slow rate of the oxygen reduction reaction (ORR) in PEM fuel cell is a major limiter for automotive applications.

The team from Argonne National laboratory, the University of Liverpool, Lawrence Berkeley National Laboratory and the University of South Carolina developed a Pt3Ni(111) catalyst that is 10-fold more active for the oxygen reduction reaction than the corresponding Pt(111) surface, and 90-fold more active than current state-of-the-art Pt/C catalysts.

The Pt3Ni(111) surface has an unusual electronic structure (d-band center position) and arrangement of surface atoms in the near-surface region. Under operating conditions relevant to fuel cells, its near-surface layer exhibits a highly structured compositional oscillation in the outermost and third layers are Pt rich and the second atomic layer is Ni rich. The weak interaction between the Pt surface atoms and non-reactive oxygenated species increases the number of active sites for O2 adsorption.

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Comments

I would assume that fuel cells would normally be used in HEVs/PHEVs and therefore the fuel cell would normally operate at a steady state and therefore not be subject to the stresses of stop and go driving.

I wonder if the first technique can be applied to the Pt3Ni? Could the 90 fold oxidation improvement of the Pt3Ni reduce the amount of Pt used in a fuel cell by an inverse amount (along with size and weight)?

Woops ... I meant ten fold (still fabulous)

Until recent annoucements by GM and Ford all car companies were describing the Fuel Cell to be used as the primary source of power for the electric motors and the smallish battery packs being used only for recapture of braking energy and a small boost to acceleration. The fuel cells were not designed to operate at a steady state like in a series hybrid.

The amount of money and brainpower being wasted on PEM fuel cells for transportation applications continues to amaze me. The operating temperature (~80 degC) of such a stack is so low you need a giant radiator to operate it in extremely hot weather (40-50 degC), regardless of how much gold and platinum you throw at the problem. It is extremely hard to fit such a large radiator under the hood of a car. Adding a heat pump would sharply reduce the overall energy efficiency.

The tenfold improvement in catalytic activity is noteworthy, though. Previously, each stack required as much platinum as was needed for the three-way catalysts of 10 cars.

Btw, VW has developed an intermediate temperature fuel cell based on phosphoric acid as the electrolyte. At coolant temperatures near 200 degC, the radiator surface area is no longer a serious packaging problem. The theoretical efficiency of this type of cell is only 40% or so, but that's still better than any small-scale ICE-based solution can manage in part load.

The Achilles heel of all fuel cells continues to be the production, distribution and on-board storage of the energy carrier, hydrogen. For mobile apps, nothing beats liquid hydrocarbons. According to Prof. Bargende of Stuttgart University, Choren Industries' BTL process yield would double if a ready source of external hydrogen were available.

Considering rapid development of battery I do not see a future for a fuel cell...

Although I am a BEV fan (I own one), I can still see some niche uses for fuel cells (forklifts, airport machinery, space craft). Although I would like to see more equitable government research spending on energy carriers, if private companies (car corps etc..) want to work on this stuff more power to em if they can make it fly. I wouldn't mind a PEM range extender for BEVs, they wouldn't have the same maintenance problems gasoline gensets have.

They are working on a higher temp PEM and if this could make it more immune to catalyst contamination that would be good.

For my money, a 20Kw SOFC with V2G in a battery dominant design is interesting. Copper/Ceria SOFCs are more immune to sulfur contamination and POX of diesel or gasoline to H2 and CO is possible for fuel.

To unfderstand the work on fuel cells you have to understand a concept thats rather smple but often overlooked.

Range of improvement.

In simple terms its how much you ecpect you can improve something and how fast you expect you can do it and WHEN you exopect it to happen.

Rgere are issues with lithium oin.. Not the least is lithium. HOW do they get enough of it to fit 1 billion cars with 200 kg of it each? Can they get that much and how long would it take to get it?

How good will lith ion get?

buofuels.. exactly how much and is it gona use? How clean is it realy? Do we REALY want a billion biofuel cars belching fumes and guzzling fuel madd from who knows where and at what ecological cost?

Fuel cells.. exactly how good can they get? When? How fast? In what ways? How many could we make? How could we fuel 1 villion fuel cell equiped cars? Jow would we make 1 billion fuel cells?

Can we make 1 billion of any of these things?

Can we make 330 million of each?.. BINGO the real question gets asked.

How many of ALL these things are we going to make? We sure as hell dont want to make all of just one or even 2.

We dont realy want to suck a trillion lb of lithium out of the oceans we dont realy want to farm en entire planet and ya I realy dont think we want wall to wall nuke plants either.

Does an internal combustion hydrogen engine require the use of platinum?

Brad,

Not that I know of. BNW has been working on running a 7 series on hydrogen and other than perhaps the catalytic converter to clean up some Nox, I don't think it uses platinum.

Ice h2 engines are in fact the same as normal ice engines so nope no platinum is needed. But the fuel econ is lower then a fuel cell and dont forget not all fuel cell designs currently use platinum.As with many other catalized reactions they are and will continue to improve materials that dont reaquite rare materials.

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