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Researchers devise Pt electrocatalysts with greatly increased activity; potential for significant cuts in fuel cell cost

Pt
Maximum achieved ORR activities for different Pt nanocluster samples. (a) SAs (specific activity) and (b) MAs (mass specific activity). The activities of two standard high-surface-area carbon-supported Pt catalysts (Pta and Ptb) are included as well. Source: Nesselberger et al. Click to enlarge.

Researchers in Denmark and Germany have found that size-selected platinum (Pt) nanoclusters can reach extraordinarily high ORR (oxygen reduction reaction—a key reaction in hydrogen fuel cells) activities, especially in terms of mass-normalized activity, if deposited at high coverage on a glassy carbon substrate.

When tested in the laboratory, the mass specific activity of commercial Pt fuel cell catalysts is around 1 A mg-1Pt. The researchers, led by associate professor of chemistry Matthias Arenz at the University of Copenhagen, found one of their catalysts delivered almost 8 A mg-1Pt. Their finding on the role of particle proximity in the efficiency of the Pt ORR activity might enable a significant reduction in the use of platinum in fuel cells for a given power output, resulting in less expensive fuel cells. A paper on their work is published in the journal Nature Materials.

One of the major hurdles for commercialization of the fuel cell technology is the sluggish cathodic ORR. Platinum has proven so far to be the most reliable and productive ORR electrocatalyst, but even so suffers from insufficient catalytic activity and stability—problems addressed by increasing the loading of the precious metal, and thus the cost of the fuel cell (e.g., earlier post, earlier post).

Substantial effort—experimental as well as computational modelling—has been devoted to gain an improved understanding of the structure–activity relationship of the ORR on Pt. In particular, an understanding of the underlying nature of the difference between bulk Pt and highly dispersed Pt nanoparticles and nanoclusters is still missing. As a consequence, no convincing strategy has been so far outlined of how to use the full potential of Pt catalysts for fuel cell technology. The importance of such a strategy is obvious, because most studies agree to the fact that when transferring Pt from a macroscopic material to a highly dispersed state—as necessary for applications in catalysis to maximize the number of reaction sites—Pt loses a factor of at least four in its surface-area-normalized specific activity (SA). Resolving this inhibition of highly dispersed Pt thus offers considerable possibilities for decreasing the cost of fuel cell catalysts, because it would be equivalent to at least a four-fold decrease in the required amount of Pt.

Most experimental studies concerning highly dispersed Pt nanoparticles are limited by the fact that they rely on the study of relatively poorly defined catalysts, that is, a distribution of Pt nanoparticle sizes synthesized on high-surface-area carbons. These studies indicate either that the SA is independent of size, or more often, that the SA decreases as the average size distribution of Pt nanoparticle decreases from 12 down to 1 nm. The authors, however, recently argued that although there is a considerable decrease in the SA going from bulk Pt, to 30 nm and ≤5 nm Pt nanoparticles, the activity of 1, 3 and 5 nm Pt nanoparticles remains constant. Another drawback of investigating high-surface-area carbon supported Pt nanoparticles is that by using conventional synthesis methods, such as incipient wetness or precipitation, the effect of the particle size (distribution) cannot be scrutinized independently from the nanoparticle coverage, and in turn, the interparticle distance.

In contrast to conventional methods, the size and coverage of clusters/particles can be independently controlled when using a cluster source to prepare them. This has been shown in recent studies in ultrahigh vacuum conditions using a laser ablation cluster source to deposit well-defined Pt nanoclusters and nanoparticles onto a planar, glassy carbon support. Here, we continue this approach on the basis of our previous efforts to study the influence of the nanocluster size as well as the nanocluster coverage on the ORR activity.

—Nesselberger et al.

The researchers investigated three different Pt nanocluster sizes: size-selected Pt20 (∅ = 0.6 nm); size-selected Pt46 (∅ = 0.8 nm); and Pt>46 (∅ = 2.3 nm).

Compared with two standard, state-of-the-art polymer electrolyte membrane fuel cell catalysts (Tanaka TKK), the Pt20 and Pt>46 showed significant enhancements in SA by a factor of 2 and 3.5, respectively, are achieved. Further, the mass specific activities (MAs) showed increases of more than 2 and 6, respectively.

They concluded that the Pt cluster coverage, and hence the interparticle distance, decisively influence the observed catalytic activity and that closely packed assemblies of Pt clusters approach the surface activity of bulk Pt.

...our results outline a new strategy for improving fuel cell electrocatalysts, thereby unfolding the full catalytic potential of Pt. The observed enhancement in activity can be discussed in terms of a more efficient reaction pathway or in terms of reduced OH coverage. We propose that the activity increase is related to a change in the EDL structure and its potential distribution. Our computational modelling indicates that the potential distribution in the EDL can be affected by an EDL overlapping effect, which alters the energetics of adsorbed blocking species, and thus leads to an overall increase in SA at a given potential.

—Nesselberger et al.

The next step will be to develop a chemical method to produce tightly packed catalysts on an industrial scale.

Resources

  • Nesselberger, Markus; Roefzaad, Melanie; Fayçal Hamou, R.; Ulrich Biedermann, P.; Schweinberger, Florian F.; Kunz, Sebastian; Schloegl, Katrin; Wiberg, Gustav K. H.; Ashton, Sean; Heiz, Ueli; Mayrhofer, Karl J. J.; Arenz, Matthias (2013) The effect of particle proximity on the oxygen reduction rate of size-selected platinum clusters. Nat Mater doi: 10.1038/nmat3712

Comments

Davemart

So another sucks, ya-bo! to the folks who don't like fuel cells!
Surrender now, we have you outnumbered and victory is inevitable!
For you, the war is over!

Davemart

'Five times more electricity for every gram of metal

When tested in the laboratory, catalysts bought on the market today will produce around one Ampere for every milligram of metal. The Arenz group developed a fuel cell catalyst that got a whopping eight Ampere per milligram of platinum. Their initial instinct was that they got a bigger power yield, because they had used smaller granules of platinum. But careful measurement revealed something much more surprising.

Unexpected effect discovered by chance

The key factor leading to platinum savings might never have been discovered by the group. They had produced a number of catalysts with varying sizes of platinum particles. By chance the particles were very tightly packed on a few of the sample catalysts and as it turned out, the packing of the particles was much more significant than the size. An effect, that the researchers have dubbed the "Particle Proximity Effect."

Next step will be to develop a chemical method to produce tightly packed catalysts on an industrial scale. Arenz has a few ideas for that as well, so he and his group have started applying for grants.'

http://www.sciencedaily.com/releases/2013/07/130721161749.htm

kelly

Fuel cell enthusiasm is nice, but not new..
http://www.rsc.org/chemistryworld/News/2005/August/02080501.asp electrolyte fuel cells (PEFCs)

http://www.groupes.polymtl.ca/jnmes/archives/2000_10/v03n04a01_p277-286.pdf

http://www.sciencedirect.com/science/article/pii/0013468694002723 Low platinum loading catalyst layers for polymer electrolyte fuel cells ..February 1995, Pages 355–363

Davemart

@kelly:
Do you want a list of the times batteries have overpromised and underdelivered?

However I will not join in your grey drizzle of negativity.

kelly

@Davemart, I've pointed out battery 'undelivered's, esp. Envia and the 2010 German http://green.autoblog.com/2011/04/05/dbm-energy-record-breaking-kolibri-battery-passes-government-tests/

I've also seen a fuel cell guy explain that platinum cost is MINOR, like the muffler platinum cost of a total new ICE car price.

Apparently, the REAL cost is the hundreds of stack elements, all keeping hydrogen gas sealed and operating without pollutant gradation, besides no infrastructure.

In any event, fuel cell vehicles(FCVs) need to pass the thousands of units of public sales, just as 1990's EV leases proved, but GM crushed.

Now it's too late for EV's to be put 'back in the bottle'.

IMHO, until FCV's are affordable, sold publicly, and have a year(s) of maintenance/resales - they are just a historical note(or R&D tax grant fraud) that began in 1839.

The exception being niche markets - like manned space and submarines - though Bloom may be changing this for stationary power use.

Davemart

@Kelly:
I suggest you read up again about how fuel cells work as you are seriously misinformed.

Davemart

More reasons why batteries alone aren't the answer everywhere:

'Kit Malthouse, London Deputy Mayor for Business and Enterprise and Chairman of the London Hydrogen Partnership, said: “The work of the London Hydrogen Partnership and other projects has really catapulted London towards the forefront of the move to a hydrogen future.

“Battery electric vehicles are a great technology but like the fax machine they are only temporary and there is a great deal of consumer resistance towards them for all manner of reasons, including range and the time it takes to recharge them.

“Even though we have around 1,300 charging points in the capital you cannot guarantee getting a space outside your house to charge overnight: London is just too densely populated.
For me, hydrogen cracks all those problems and it also solves other issues along the way such as making best use of wind energy, for example. We also produce a huge amount of waste and we are looking at schemes that convert biomass into hydrogen. So as well as producing a clean fuel we would be reducing the amount of waste we put into landfill."

http://fuelcellsworks.com/news/2013/07/22/worlds-first-full-production-fuel-cell-cars-to-arrive-in-the-uk/

Where it is difficult to plug in reliably, hydrogen can do the job.

kelly

If I'm mistaken about FCVs, they would have already been on the road for over twenty years.

Letstakeawalk

"I've also seen a fuel cell guy explain that platinum cost is MINOR, like the muffler platinum cost of a total new ICE car price.

Apparently, the REAL cost is the hundreds of stack elements, all keeping hydrogen gas sealed and operating without pollutant gradation..."

@Kelly

The cost of Pt is approximately 50% the cost of the whole stack. Reducing the amount of Pt is indeed a tremendous benefit, even when the amount of Pt involved is - as you put it - on par with a catalytic converter.

http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/merit03/103_tiax_eric_carlson.pdf

Stack costs are well illustrated in this report:

http://www.hydrogen.energy.gov/pdfs/12020_fuel_cell_system_cost_2012.pdf

Other major costs are the steel plates and the membranes within the stack, and those costs are also likely to come down as steel plates are replaced with less expensive materials and as better membranes are developed. So, we can see that fuel cell stack costs are being reduced on all fronts, from platinum loading to materials.

kelly

@ Letstakeawalk, here's a 'NO Platinum' fuel cell from seven years ago: http://ecst.ecsdl.org/content/3/1/453.abstract

Same difference - no FCVs on auto dealer show room floors, whenever..

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