Johns Hopkins team plates Pt on cobalt to create low-cost, highly efficient fuel cell catalysts
11 January 2018
Researchers at Johns Hopkins University, with colleagues at Purdue and Oak Ridge National Laboratory (ORNL), have plated a one nanometer thick coating of platinum on a core of cobalt to create a cost-effective and highly efficient fuel cell catalyst. A paper on their work was published last year in the ACS journal Nano Letters.
The specific electrochemically active surface areas (ECSA) estimated are 54 m2/gPt for Co@Pt and 43 m2/gPt for Pt. Although the overall particle size of Co@Pt is significantly larger than Pt (~5 nm), the Co@Pt catalyst has a higher specific surface area owing to the presence of non-precious cobalt in the particle core, the researchers said.
The mass activity of Co@Pt achieved 1.21 A/mgPt—an improvement factor of 8.1 versus the commercial Pt catalyst. In addition to the high catalytic activity observed in the initial electrochemical studies, the researchers observed further activation of the Co@Pt catalysts after potential cycling in the ORR-relevant regime.
After 5,000 cycles between 0.6 and 1.0 V, the specific activity was raised to 3.02 mA/cm2, while negligible loss was observed in ECSA. As a result, the mass activity achieved 1.45 A/mgPt after the potential cycling, corresponding to an improvement factor of 9.7 versus Pt. The loss in catalytic activity after further potential cycling was found to be insignificant (e.g., up to 10,000 cycles).
—Wang et al.
The cobalt/platinum core/shell (denoted as Co@Pt) nanoparticles were synthesized via seed-mediated growth. The Co seeds were first synthesized by thermal decomposition of cobalt carbonyl, and the Pt shell was overgrown in situ by adding platinum acetylacetonate.
There’s a lot more cobalt out there than platinum. We’ve been able to significantly stretch the benefits of platinum by coating it over cobalt, and we even managed to enhance the activity of platinum at the same time.
—lead author Lei Wang
Earlier attempts to plate precious metals on non-precious materials were largely stymied by galvanic replacement reactions—oxidation of the non-precious metal. In this study, the team successfully suppressed such reactions by introducing carbon monoxide, a gas molecule that strongly binds to cobalt, protecting it from oxidation.
The researchers said the enhanced catalytic activity—almost 10x Pt alone—resulted from both the maximized exposure of platinum atoms on the surface and from interactions between the two metals.
The intimate contact between cobalt and platinum gives rise to compressive strain. It shortens the distance between platinum atoms and makes the chemical reactions more feasible on the surface.
—Lei Wang
Because platinum and other rare metals play key roles in many industrial applications, the implications of this work extend beyond fuel cells. Currently, the team is working on adapting their technique to other precious metals and non-precious substrates. New developments will target further applications of such materials in chemical conversions of hydrocarbons.
The research was supported by National Science Foundation grant DMR-1410175 and a Johns Hopkins University Catalyst Award. The researchers have obtained a provisional patent covering this technique through the Johns Hopkins Technology Ventures office.
Resources
Lei Wang, Zhenhua Zeng, Cheng Ma, Yifan Liu, Michael Giroux, Miaofang Chi, Jian Jin, Jeffrey Greeley, and Chao Wang (2017) “Plating Precious Metals on Nonprecious Metal Nanoparticles for Sustainable Electrocatalysts” Nano Letters 17 (6), 3391-3395 doi: 10.1021/acs.nanolett.7b00046
Hyundai tell us that the fuel cells in their Nexo car are good for comparable life to an ICE, having tested out to 100,000 miles and reckoning they are good for in the region of 150,000 miles or so.
This struck me as conservative, as the Ballard fuel cells in many buses have done 25,000 hours of service, equivalent to hundreds of thousands of miles in a car. Maybe there are differences in the fuel cells used in buses from cars, but if so I don't know what they are..
This latest would seem to open the prospect of not only reduced cost, but very high mileage indeed.
I don't really know what 10,000 cycles in a fuel cell implies, as I would have thought that they would be very fast cycling, but perhaps someone with a better technical background would explain.
In any case, it appears that they will be able to do way better than the already adequate figures for the Hyundai.
Posted by: Davemart | 11 January 2018 at 04:07 AM
Thinking about it a bit more, this presumably means a far more compact fuel stack, although the balance of plant would not change.
So they should be more easily able to produce more performance orientated FCEVs.
Posted by: Davemart | 11 January 2018 at 06:49 AM
The 10,000 cycle is about 30 year lifetime, lots of hours and miles during that period. It might depend on how pure the hydrogen is.
Posted by: SJC | 11 January 2018 at 10:39 AM
Hi SJC.
I thought you had to cycle fuel cells much faster than that, so that for a day you might have 100KW times 8 hours working day = 1,250 days = 3.5 years or so.
What have I missed?
Posted by: Davemart | 11 January 2018 at 11:37 AM
Cycling means up and down, you might do that once or twice per day, some days not at all because you are running on batteries.
Posted by: SJC | 12 January 2018 at 09:18 AM
SJC:
Thanks.
I had thought it referred to whatever the fuel cell equivalent of ignition events is, in which case it would be in the many millions, or even billions.
Posted by: Davemart | 13 January 2018 at 02:51 AM
Fuel cells stress when warming up and cooling down, PEMs not so much SOFCs a lot. The main factor is contamination of the membranes which can be due to bad hydrogen or polluted air.
Posted by: SJC | 13 January 2018 at 07:56 AM
This could become another way for much lower cost, higher performance, longer lasting FCs.
Coupled with lower cost ($2/Kg) H2, near future all weather extended range FCEVs, will quickly become competitive with BEVs counterpart.
Posted by: HarveyD | 14 January 2018 at 10:03 AM
Those buses likely never turn off, other than when they might have a yearly or quarterly inspection. If a manufacturer knows this, they could make it run all the time with some fuel loss, but incredible longevity.
This could be an advantage for robotaxis/buses, never shutting down. I know fuel cells ramp up and down, so would it be acceptable to run a small stack at 1-10% of its capacity at all times just to keep it alive longer? This could go backed to those 20kw range extenders mentioned in the past.
Posted by: CheeseEater88 | 17 January 2018 at 02:33 AM