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New family of non-precious metal catalysts outperform platinum for oxygen-reduction reaction in fuel cells at 10% the production cost

Srep02715-f3
ORR polarisation curves of Pt/C and FeCo-OMPC catalysts before and after 10,000 potential cycles in O2-saturated 0.1 M HClO4. Potential cycling was carried out from 0.6 to 1.0 V vs. RHE at 50 mV s−1. Cheon et al. Click to enlarge.

Researchers from Ulsan National Institute of Science and Technology (UNIST), Korea Institute of Energy Research (KIER), and Brookhaven National Laboratory have discovered a new family of non-precious metal catalysts based on ordered mesoporous porphyrinic carbons (M-OMPC) with high surface areas and tunable pore structures. Porphyrins are any of a class of heterocyclic compounds containing four pyrrole rings arranged in a square.

These catalysts exhibit better performance than platinum in the oxygen-reduction reaction (ORR) important for fuel cells at 10% of the production cost of a platinum catalyst, the team said. The finding, described in an open access paper in Nature’s Scientific Reports, is potentially a step towards reducing the cost of fuel cell technology—one of the impediments to widespread commercialization.

Owing to their high energy conversion efficiency and environmental benignity as well as their applicability for small electronic devices, residential power generation, and automobile transportation, polymer electrolyte fuel cells (PEFCs) have long been considered promising energy conversion devices. As electrocatalysts of PEFCs, carbon-supported platinum-based nanoparticles have been used predominantly in anode as well as cathode electrodes. However, even Pt-based electrocatalysts exhibit sluggish kinetics for the oxygen reduction reaction (ORR) at the cathodes of PEFCs. Moreover, they tend to sinter or agglomerate into larger particles during long-term fuel cell operation, resulting in a marked loss of activity. The prohibitively high cost and scarcity of Pt have also been bottlenecks that further impede the widespread use of PEFCs. Therefore, the high cost along with the low durability of Pt-based catalysts triggered the quest for low-cost, high-performance non-precious metal catalysts.

...Here we report on a simple approach to scalable and highly reproducible synthesis of a new family of non-precious metal catalysts—self-supported, transition metal-doped ordered mesoporous porphyrinic carbons (M-OMPCs)—which exhibit Pt-like catalytic activity for the ORR. The M-OMPC catalysts were prepared by nanocasting ordered mesoporous silica (OMS) templates with metalloporphyrin precursors, and were constructed with three-dimensional networks of porphyrinic carbon frameworks. Our synthetic strategy for the non-precious metal catalysts included a multitude of advantages that would be favorable to PEFC applications.

—Cheon et al.

Such advantages include:

  • The synthetic route is amenable to simple and mild experimental conditions.

  • The pore size and connectivity of the M-OMPC catalysts were tunable by utilizing OMS templates with different pore sizes and structures.

  • The synthesis of the M-OMPC catalysts could be readily scaled up, with the preservation of structural integrity, to a few tens of grams in a single batch.

  • The well-developed, hierarchical micro-mesoporosity would be advantageous for efficient transport of fuels and by-products.

  • The M-OMPC catalysts showed very high surface areas, which could significantly increase the density of the catalytically active sites accessible to reactants.

Among the family of M-OMPC catalysts, the Fe and Co co-doped OMPC (FeCo-OMPC) showed an extremely high electrocatalytic activity for ORR in acidic media. To our knowledge, its ORR activity is one of the best among the non-precious metal catalysts reported in the literature, and even higher than the state-of-the-art Pt/C catalyst by 80% at 0.9 V (vs. RHE). In addition, the FeCo-OMPC showed superior long-term durability and methanol-tolerance in ORR, compared to the Pt/C...We attribute the high ORR activity of the FeCo-OMPC to its relatively weak interaction with oxygen as well as the high surface area design of catalyst.

—Cheon et al.

The materials developed by the UNIST research team were prepared by nanocasting ordered mesoporous silica (OMS) templates with metalloporphyrin precursors. In addition they were constructed with three dimensional networks of porphyrinic carbon frameworks.

Cheon2
Comparison of kinetic currents of Pt/C and FeCo-OMPC catalysts before and after 10,000 potential cycles. Cheon et al. Click to enlarge.

To investigate the durability of the FeCo-OMPC catalysts, the team cycled the catalysts 10,000 times between 0.6 and 1.0 V (vs. RHE) at a scan rate of 50 mV s−1, following the accelerated durability test protocol of the US Department of Energy (DOE).

They found that, based on the changes in half-wave potentials as well as kinetic current densities between the cycling tests, the FeCo-OMPC catalyst exhibited superior durability over the Pt/C catalyst. (See diagram at right.)

The M-OMPC catalysts also showed enhanced poison-tolerance compared to the Pt/C catalysts.

The research was led by Sang Hoon Joo, professor of the School of Nano-Bioscience and Chemical Engineering at South Korea’s UNIST. Fellow authors include: Jae Yeong Cheon from UNIST; Gu-Gon Park from the Korea Institute of Energy Research (KIER); and Radoslav R. Adzic from the Chemistry Department of the Brookhaven National Laboratory.

Recent years have witnessed a rapid progress in the development of electrocatalysts for ORR. For instance, nanoparticles composed of a Pt monolayer on PdAu core, intermetallic Pt-Co nanoparticles, and mesostructured PtNi thin films have demonstrated significantly improved ORR activity and durability in acidic media. We believe that, along with these new catalysts, the M-OMPCs could emerge as highly promising ORR catalysts. Furthermore, the design concept towards enhanced electrocatalytic performances presented in this work could be extended to other electrocatalytic reactions in energy devices, such as metal-air batteries and electrolyzers.

—Cheon et al.

This research was supported by the Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Education, the support from Korea Institute of Energy Research, National Junior Research Fellowship, and Global Ph.D. Fellowship.

Resources

  • Jae Yeong Cheon, Taeyoung Kim, YongMan Choi, Hu Young Jeong, Min Gyu Kim, Young Jin Sa, Jaesik Kim, Zonghoon Lee, Tae-Hyun Yang, Kyungjung Kwon, Osamu Terasaki, Gu-Gon Park, Radoslav R. Adzic & Sang Hoon Joo (2013) Ordered mesoporous porphyrinic carbons with very high electrocatalytic activity for the oxygen reduction reaction. Scientific Reports 3, Article number: 2715 doi: 10.1038/srep02715

Comments

Davemart

To someone like me who is in no way an industrial chemist, this still sounds like one of the most hopeful catalysts yet.
Cheap and durable, and not using precious metals.
Happy days!

Engineer-Poet

How much of the system cost does the ORR catalyst represent?

Davemart

@EP:
Platinum runs at around $30/gram and a modern stack uses around 30 grams:
http://green.autoblog.com/2010/10/26/gm-director-fuel-cell-vehicles-will-be-cost-competitive-with-hy/

So call it around $1000, not a big proportion of the total cost.

However, the cost of the platinum is quite 'sticky' as a lot of the rest of the total stack cost will reduce heavily with volume production, which is tough to get whilst you are laying out $1k just on the platinum.

On top of that, if hydrogen is supplied using electrolysis, the cost of the electrolyser will be reduced by this catalyst, so cost is taken out throughout the fuel cell system.

yoatmon

Electrolysis is not really the most efficient method to produce quality hydrogen. Several photosynthesis methods have been discovered that exceed electrolysis.
The most recent and promising one is described in:

http://www.greencarcongress.com/2013/09/20130919-mit.html

Developing such a method to top performance and scaling it to an industrial level would be a sound answer to existing problems confronting FC technology.

Davemart

@EP:
Perhaps you could throw some light on the third point here:

'"First, our synthetic method is amenable to simple and mild experimental conditions. Second, the synthesis of the M-OMPC catalysts could be readily scaled up to a few tens of grams in a single batch. Third, well-developed, hierarchical micro-mesoporosity would be advantageous for efficient transport of fuels and by-products. Finally, the M-OMPC catalysts showed very high surface areas, which could significantly increase the density of the catalytically active sites accessible to reactants."'

http://www.sciencedaily.com/releases/2013/09/130923143630.htm

How's it going to help fuel transport?
Colour me baffled.

Davemart

@yoatman:
Longer term, sure, if that pans out.

Shorter term though, especially for low volume stations, they are looking at electrolysers, as the only connection needed is a plug, and they have periodic surpluses of wind and solar in places like Germany.

It makes no real sense to take an intermittent source and use an electrolyser part-time to convert surplus power, but if you are going to do it cheaper electrolysers certainly reduce the cost.

Engineer-Poet

The "hierarchical, micro-mesoporosity" would appear to improve transport by having larger holes for more rapid diffusion to the active sites.

Davemart

@EP:
Ah! A light dawns! WITHIN the fuel stack!
I was thinking the meant mass transportation of hydrogen etc, and so was flummoxed.
Many thanks.

Smeeg

Platinum cost?
At the $47 cost per KW from 2012, $20 is stack cost and about $9.42 was the Catalyst Ink & Application (NSTF). So 47% of the stack cost and 20% of the cost per kW. So if the new process is 10% of the $9.42 lets say that makes cost of the stack now $11.52 and the cost per KW $38.52.

Davemart

@smeeg:
That is not stack costs in 2012, but projected stack costs at, from memory, a production level of 500,000 per year.

For a 100kw stack the ~$10kw for the catalyst comes out to around the ~$1,000 I gave, so we are in close agreement.

Alain

How would Pt price evolve if a bilion fuelcells & a bilion electrolizers were built?

Davemart

@Alain:
The price of platinum would not evolve at all if they used this technology, as it doesn't use it.

Even catalysts which continue to use platinum are rapidly dropping the amount used, and they look as though they can get it to levels comparable to the amount used in ICE vehicle's catalytic converter (GM).

Engineer-Poet

The price of platinum might fall, as some existing uses could be replaced.

gryf

The ORR catalyst requires roughly 80% of the platinum in a PEM fuel cell. Others like ACAL Energy ("FlowCath") are using flow battery technology to replace the ORR platinum catalyst.

Dave Murphy

Run NH3 made from natural gas in the that's bulk power cheap and clean! No NOX or CO2.

Ben Redfield

We've been doing Fe,CO and Zeolite doping on our metal catalytic converter solutions and have been working to eliminate platinum from our products as much as possible. This is fascinating stuff. . .

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