To make fuel cells more economical, engineers want a fast and efficient iron-based molecule that splits hydrogen gas to make electricity.
Online Feb. 17 at Nature Chemistry, researchers report such a catalyst. It is the first iron-based catalyst that converts hydrogen directly to electricity. The result moves chemists and engineers one step closer to widely affordable fuel cells.
"A drawback with today's fuel cells is that the platinum they use is more than a thousand times more expensive than iron," said chemist R. Morris Bullock, who leads the research at the Department of Energy's Pacific Northwest National Laboratory.
His team at the Center for Molecular Electrocatalysis has been developing catalysts that use cheaper metals such as nickel and iron. The one they report here can split hydrogen as fast as two molecules per second with an efficiency approaching those of commercial catalysts. The center is one of 46 Energy Frontier Research Centers established by the DOE Office of Science across the nation in 2009 to accelerate basic research in energy.
Fuel cells generate electricity out of a chemical fuel, usually hydrogen. The bond within a hydrogen molecule stores electricity, where two electrons connect two hydrogen atoms like a barbell.
Fuel cells use a platinum catalyst -- essentially a chunk of metal -- to crack a hydrogen molecule open like an egg: The electron whites run out and form a current that is electricity. Because platinum's chemical nature gives it the ability to do this, chemists can't simply replace the expensive metal with the cheaper iron or nickel. However, a molecule that exists in nature called a hydrogenase (high-dra-jin-ace) uses iron to split hydrogen.
Bullock and his PNNL colleagues, chemists Tianbiao "Leo" Liu and Dan DuBois, have taken inspiration for their iron-wielding catalyst from a hydrogenase. First Liu created several potential molecules for the team to test. Then, with the best-working molecule up to that point, they determined and tweaked the shape and the internal electronic forces to make additional improvements.
One of the tricks they needed the catalyst to do was to split hydrogen atoms into all of their parts. If a hydrogen atom is an egg, the positively charged proton that serves as the nucleus of the atom would be the yolk. And the electron, which orbits around the proton in a cloud, would be the white. The catalyst moves both the proton-yolks and electron-whites around in a controlled series of steps, sending the protons in one direction and the electrons to an electrode, where the electricity can be used to power things.
To do this, they need to split hydrogen molecules unevenly in an early step of the process. One hydrogen molecule is made up of two protons and two electrons, but the team needed the catalyst to tug away one proton first and send it away, where it is caught by a kind of molecule called a proton acceptor. In a real fuel cell, the acceptor would be oxygen.
Once the first proton with its electron-wooing force is gone, the electrode easily plucks off the first electron. Then another proton and electron are similarly removed, with both of the electrons being shuttled off to the electrode.
The team determined the shape and size of the catalyst and also tested different proton acceptors. With the iron in the middle, arms hanging like pendants around the edges draw out the protons. The best acceptors stole these drawn-off protons away quickly.
With their design down, the team measured how fast the catalyst split molecular hydrogen. It peaked at about two molecules per second, thousands of times faster than the closest, non-electricity making iron-based competitor. In addition, they determined its overpotential, which is a measure of how efficient the catalyst is. Coming in at 160 to 220 millivolts, the catalyst revealed itself to be similar in efficiency to most commercially available catalysts.
Now the team is figuring out the slow steps so they can make them faster, as well as determining the best conditions under which this catalyst performs.
This work was supported by the Department of Energy, Office of Science.
Reference: Tianbiao Liu, Daniel L. DuBois and R. Morris Bullock. An iron complex with pendent amines as a molecular electrocatalyst for oxidation of hydrogen, Nature Chemistry, Month Day, 2013, doi:10.1038/NCHEM.1571.
Interdisciplinary teams at Pacific Northwest National Laboratory address many of America's most pressing issues in energy, the environment and national security through advances in basic and applied science. PNNL employs 4,500 staff, has an annual budget of nearly $1 billion, and has been managed for the U.S. Department of Energy by Ohio-based Battelle since the laboratory's inception in 1965. For more, visit the PNNL's News Center, or follow PNNL on Facebook, LinkedIn and Twitter.
DOE's Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit the Office of Science website at science.energy.gov.
Mary Beckman | EurekAlert!
Colorectal cancer risk factors decrypted
13.07.2018 | Max-Planck-Institut für Stoffwechselforschung
Algae Have Land Genes
13.07.2018 | Julius-Maximilians-Universität Würzburg
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
13.07.2018 | Event News
13.07.2018 | Materials Sciences
13.07.2018 | Life Sciences