New bimetallic copper-titanium hydrogen evolution catalyst outperforms platinum by more than 2x
17 March 2015
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| Modeling study showing possible bimetallic sites on a Ti-modified Cu surface. The two Cu-Cu-Ti hollow sites exhibit HBE values close to that of Pt. The Cu-Ti-Ti hollow site binds hydrogen too strongly. Lu et al. Click to enlarge. |
A team from the University of Delaware and Columbia University, with colleagues at Lawrence Berkeley National Laboratory, reports that a new hierarchical nanoporous copper-titanium bimetallic electrocatalyst is able to produce hydrogen from water under a mild overpotential at more than twice the rate of state-of-the-art carbon-supported platinum catalyst. An open-access paper on their work is published in the journal Nature Communications.
Although copper and titanium are poor hydrogen evolution catalysts by themselves, the combination of the two creates unique copper-copper-titanium hollow sites which have a hydrogen-binding energy (HBE) very similar to that of platinum, resulting in an exceptional hydrogen evolution activity, the team found. In addition, the hierarchical porosity of the nanoporouscopper-titanium catalyst provides a large-surface area for electrocatalytic hydrogen evolution, and improves the mass transport properties. Further, the catalyst is self-supported, eliminating the overpotential associated with the catalyst/support interface.
It is widely believed that room temperature electrochemical reduction of water to molecular hydrogen offers a significant promise for supplying CO2-free hydrogen, which can be used directly as a fuel or as reactant to convert CO2 and to upgrade petroleum and biomass feedstocks to value-added chemicals and fuels through hydrotreating processes. All these applications require large-scale, commercial processes for water electrolysis, which in turn require breakthrough discoveries in at least two areas: (i) the availability of electricity derived from renewable energy sources, such as solar and wind, and (ii) the discovery of low-cost electrocatalysts to replace precious metals that are currently the state-of-the-art hydrogen evolution reaction (HER) catalysts.
HER in an acidic environment generally requires lower overpotentials than those in a basic environment. However, a hydrogen production system in a basic environment is still more promising, because of the possibility to consider non-precious-metal-based catalysts that cannot be used in acidic conditions, not only for HER at cathode, but also for oxygen evolution reaction at anode. Regardless of acidic or basic conditions, Pt, along with its alloys, is the benchmark electrocatalyst that requires very small overpotentials to drive the reaction, whereas the scarcity and high cost of Pt hinder its large-scale use for H2 production.
… In the present paper, DFT calculations show that Cu-Ti bimetallic materials have similar HBE values as Pt, and therefore are promising non-precious metal HER electrocatalysts. These predictions are experimentally verified on both bulk Cu-Ti alloys and highly porous catalysts.
—Lu et al.
The density functional theory (DFT) calculations showed that the Cu-Cu-Ti hollow site on a Cu-Ti bimetallic surface exhibits an optimal HBE for HER; the team identified three distinct adsorption sites. Two types of Cu-Cu-Ti hollow sites exhibit HBE values very close to that of Pt; however, the Cu-Ti-Ti hollow site containing two Ti atoms binds hydrogen too strongly.
To verify the DFT predictions, they team fabricated a series of Cu100−xTix (x=1, 3, 5, 7 and 9) alloys with homogeneously distributed atoms using an arc-melting technique followed by a melt-spinning process in order to retain their solid solution phase formed at high temperatures.
They found a significant increase in HER activity after modifying the Cu surface with as little as 1 at. % of Ti; maximum enhancement was for a bulk stoichiometry of Cu95Ti5. The surface Ti composition of Cu95Ti5 was 10.9 at. %—in good agreement with the optimal value predicted by DFT calculations of 1 Ti atom in a 3 × 3 cell (11.1 at. %). Greater Ti concentration leads to a decrease of HER activity.
To functionalize the material, they designed and synthesized a Cu-Ti bimetallic electrocatalyst with a highly hierarchical porous structure (denoted as np-CuTi) by making a multi-phase Al-Cu-Ti precursor, followed by a dealloying process. The atomic ratio of Ti to (Cu+Ti) was chosen to be the optimal value (5 at. %) from the bulk Cu-Ti studies.
The resulting nano-sized pores of the resulting np-CuTi are responsible for high surface areas, whereas the micrometer-sized pores served as gas diffusion channels to enhance mass transport properties. This catalyst is monolithic and self-supported, which enhances the electric transportation and eliminates the necessity of using a supporting conductive substrate.
They then compared electrocatalytic performances of np-CuTi with a commercial state-of-the-art Pt/C electrocatalyst. The activity of the np-CuTi catalyst exceeded Pt/C steadily with a more than twofold enhancement, most likely owing to its highly active surface, large surface area and enhanced mass transport properties, the team suggested.
An important area of future studies is to determine the surface valence state using in situ/operando surface-sensitive techniques. Also, a scale-up test of np-CuTi using practical electrolyzers, such as hydroxide exchange membrane-based electrolyzers, is highly desired for the implementation to commercial processes.
—Lu et al.
Resources
Qi Lu, Gregory S. Hutchings, Weiting Yu, Yang Zhou, Robert V. Forest, Runzhe Tao, Jonathan Rosen, Bryan T. Yonemoto, Zeyuan Cao, Haimei Zheng, John Q. Xiao, Feng Jiao & Jingguang G. Chen (2015) “Highly porous non-precious bimetallic electrocatalysts for efficient hydrogen evolution”, Nature Communications 6, Article number: 6567 doi: 10.1038/ncomms7567
Two approaches to producing hydrogen starting to bear fruit and reported on on the same day.
Remarkable.
Posted by: Davemart | 17 March 2015 at 01:10 PM
Using water and solar energy to produce unlimited amount of clean H2 could become very low cost in post 2020 era?
H2 could soon power our vehicles and our homes 24/7 without creating GHGs.
Existing NG pipelines and distribution system could be modified/upgraded to transport H2.
A low cost variable output home FC would replace existing furnaces.
Posted by: HarveyD | 17 March 2015 at 02:15 PM
Am I reading this right, that what they are announcing is "as efficient as platinum catalysts" so they will still instantly lose 30% of the energy they put in due to conversion losses? This is a cheaper catalyst material. That doesn't make it more efficient from well-to-wheels than BEV though.
Posted by: HealthyBreeze | 17 March 2015 at 03:02 PM
HB:
Exactly: But the only process that make any efficiency sense when producing the electron carrier called Hydrogen is direct solar used to split water. BTW, you still lose 40% in the fuel cell.
The most efficient form of transportation still appears to be Solar produced electrons stored in batteries and used in BEVs.
Having said all this you still must know that billions are being spent on research and PR to force the development of a U.S. hydrogen market by the auto companies, Oil and Gas, Washington and State politicians, etc. They seriously want "Gasoline 2," and will do what is necessary to get it.
Posted by: Lad | 17 March 2015 at 03:59 PM
Probably the only practical way to make hydrogen without generating CO2 is high temperature electrolysis using nuclear power and even then it is questionable. We will never have enough "renewable" electric power to waste on electrolysis. The power density is just not there. A good estimate for average electric capacity is 1 w/m2 for wind energy and about 25 w/m2 for solar photovoltaic for a reasonable sunny location. I did a calculation for the land area just to supply the current electric requirements for the US using 1.5 Mw wind turbines with the recommended spacing and ended up with twice the area of Wyoming.
Posted by: sd | 17 March 2015 at 04:33 PM
@Lad, HB, and sd,
It is practical to have PHEV's that can be charged at work, especially for those w/out home charging facility and for those with smaller battery packs (8-10 kWh). Quite simple to have rows of solar-PV-covered carports at work with charging receptacles dangling from above. Charge solely from DC solar power on sunny days. No charging on rainy days unless excess of wind power, in order to reduce investment cost on backup fossil fuel power plant. On rainy and calm days, simply use gasoline for ICE-PHEV or hydrogen for FC-PHEV. The cost of solar carport PV per kW installed is comparable with utility solar PV, much lower than residential PV panels.
It is very nice to be able to park under a carport at work to protect the car from UV and heat and rain damage. This feature alone is worth the monthly subscription fee...while the ability for low-cost solar charging will be a definite plus. No power meter would be necessary with a fixed monthly fee, nor DC to AC inverter necessary when car charging can be done DC to save on cost and efficiency loss from DC to AC and then DC conversion.
We should push hard for H2 fillup infrastructure and encourage ownership of FCEv's and FC-PHEV. The beauty of FC-PHEV is that, on weekends when no body is charging their PHEV's, the solar PV energy at work can be devoted to making H2, for use in FC-PHEV's in rainy days. You can't do that with ICE-PHEV.
As more and more non-dispatchable solar and wind electricity capacity will be installed, there will be increasing periods of excess Renewable Energy (RE) that can be used to make RE-H2. If there is no distributed demands for these H2, these excess RE will lower the revenues from RE investment and will impede high penetration of RE into the grid. However, being able to sell all the RE that nature will give us will increase return on investments of RE and will accelerate the growth of RE. It is so simple to me...is there any thing wrong with this picture?
Another example of excess RE would be in the future, when more and more solar energy will supply daytime business and industrial electricity demands for weekdays, while weekends-solar energy would be far in excess of demands, and can be used to make H2 .
Posted by: Roger Pham | 17 March 2015 at 07:07 PM
sd:
Interesting! So, we are left with creating H2 by reforming natural gas.
Posted by: Lad | 17 March 2015 at 07:28 PM
@sd said:
'Probably the only practical way to make hydrogen without generating CO2 is high temperature electrolysis using nuclear power and even then it is questionable. '
You have drawn your conclusion directly from your assumptions.
I agree that large scale wind to hydrogen does not make sense, although it can help at the margins.
There is though enormous progress being made on direct solar to hydrogen.
It is not necessary for any particular technology to provide a complete answer for all time either, and lower cost electrolysis sure helps.
As EP notes on these pages, if you are using nuclear you pretty much have the power when it is needed anyway, so there is no point incurring the losses of changing it into hydrogen and back.
If you want loads of electricity in the grid instead, then storage is needed, and hydrogen and its products are the only effective way of doing that in the quantities needed.
Posted by: Davemart | 19 March 2015 at 01:55 AM
@ Roger Pham,
So, your contention is that Fuel Cells will make energy sense when someone else pays for the electricity to reform the Hydrogen?
I mean, c'mon. Conversion from (Power Source X) to H2 (lose 30% of energy), then storage losses, then convert from H2 to electricity (lose 40% of what energy is left) is way too energy expensive. The motor ends up with less than 42% of the energy (from Power Source X) you started with.
Use good batteries and the motor will receive closer to 75% of the energy you started with. Batteries also seem to be improving faster than FC.
How can you, as an engineer, get fixated on FC in the face of such numbers?
FC only apparent advantages are refueling time (although not if you plug in the car and reform on board as you suggest), and potentially range depending on how store your H2. Partial recharge of batteries (from a pair of 220v chargers) is pretty quick now. Range on premium electrics is pretty good now, too so it comes down to price. How long before FC cost dramatically less than the battery pack that can produce similar peak power output?
Posted by: HealthyBreeze | 19 March 2015 at 08:44 PM
@HB,
The FC-PHEV will use battery for 80-90% of mileage, leaving only 10-20% of remaining driving on FC-H2.
FC-PHEV can be 900-1,000 lbs lighter than a comparable BEV having comparable range. For example, the Hyundai Tucson FCEV weighs about 4,000 lbs vs Tesla Model S 85-kWh weighing 4,600 lbs, or 600 lb different, both having comparable range. The Tucson is made out of steel, which can be lighten up by 500-600 lbs if made out of aluminum like the Model S. The Model S is 200-hp more powerful, that will add 300 lbs to its weight, that must be substracted from the weight difference.
This means that a FC-PHEV will consume less energy when running on battery power than an equivalent BEV, but more energy when running on H2, so overall, may be equivalent to or even slightly more efficient than a BEV.
For home use, H2-FC in the winter can take advantage of waste heat to attain nearly 100% efficiency.
During winter nights, the home FC can use the city-piping H2 to produce electricity to charge the FC-PHEV while using the heat to keep the house warm. The FC-PHEV in winters can turn on the FC for power whenever heating is necessary, while can run on battery power when the cabin is already warm and windshield already defrosted, or a combination of both.
Posted by: Roger Pham | 20 March 2015 at 02:47 PM
The reason no automaker is making these high AER FC-PHEV is because it would be doubly expensive and there is no infrastructure.
Packaging is also a very large problem.
Posted by: electric-car-insider.com | 20 March 2015 at 06:43 PM
@Roger Pham,
Let's add just one thing to your excellent concept. Place the hydrogen generator in the FC-PHEV so you have a reversible fuel cell. There should not be much more additional weight (< 100Kg) for the generator and water store. Then would it really be a BEV? You would not need an H2 infrastructure just use the current EV charging system.
Posted by: Account Deleted | 21 March 2015 at 07:36 AM