Science for our
Nation's
Energy Future

Energy Frontier Research Center

Community Website
Frontiers in
Energy Research
Newsletter
Summer 2017

Better than Perfect: New Material to Turn Solar Energy into Clean Fuel

Material facilitates the production of hydrogen fuel from sunlight exceeding 100 percent efficiency

Zhanyong Li

A representation of the solar-powered device using quantum dots to produce clean fuel (hydrogen) from sunlight. The quantum dots are deposited on one of the electrode surfaces (right side). Upon being hit with sunlight, the hot electrons generated will be transferred in the form of electrical current to the other electrode where the platinum catalyst locates (left side). The electrons will combine with protons at the platinum catalyst surface to produce hydrogen fuel. Image courtesy of Nature Publishing Group

Are you thinking of getting a hydrogen-powered car that is environmentally friendly? Are you wondering where you’ll get the hydrogen fuel? How should it be produced with minimal environmental impact? Recently, researchers from the Center for Advanced Solar Photophysics (CASP), an Energy Frontier Research Center, developed a solar-powered fuel cell that can produce hydrogen exceeding 100 percent efficiency upon visible light irradiation.

Fossil fuels are used to make electricity and to run our cars. However, they have some serious issues, notably that they are finite. Clean and renewable energy sources are needed to remedy this problem. What is the most abundant and sustainable renewable energy source? The sunshine we see every day. One way to produce hydrogen fuel from sunlight uses a light-absorbing material submerged in water. Absorbing light excites an electron. This electron is delivered to the appropriate catalyst surface, generating electricity to facilitate the production of hydrogen. Sunlight might be free and abundant, but current catalysis technology is expensive and inefficient. One great challenge taken up by scientists at CASP is to develop low-cost and more efficient light-absorbing materials.

A new strategy to improve the efficiency, as the researchers used in the recent study, is to make a more efficient light absorber, taking advantage of quantum dots. What are quantum dots? Some of you might have not realized it, but it might already be used in the liquid crystal display (LCD) screens of your phone, tablet, TV or laptop. Quantum dots are semiconductors with unique optical properties that can make the LCD screen brighter and clearer. How so? Their small size. They are in the range of 2 to 10 nanometers (10−9 meters) in diameter. Based on their sizes, they emit different colors of light; for example, smaller particles appear blue, and slightly larger ones are red.

In traditional solar-to-fuel devices, the absorption of a bit of light, called a photon, usually generates one excited electron. But with quantum dots, multiple excited electrons may be produced from absorption of a single high-energy photon. The reason is, again, their unique small sizes. Assuming 100 percent efficiency occurs when all the “single electrons generated by one photon absorption” are used to produce hydrogen fuel, then the multiple electrons generated by quantum dots upon one photon absorption can make the efficiency higher than 100 percent possible. Researchers at the CASP have fabricated such a solar-powered hydrogen-producing fuel cell using electrodes coated with quantum dots. Researchers built this electrode in a layer-by-layer fashion, where lead sulfide quantum dots are deposited on the electrode surface. Upon being hit with light of sufficient energy, each quantum dot sends multiple electrons to the platinum electrode producing hydrogen fuel (see figure). The light-to-fuel production efficiencies exceed 100 percent at several tested wavelengths.

Generating solar fuels, such as hydrogen, using a low-cost material with high efficiency remains a great challenge. This study shows that quantum dots, with unique electron properties, could be a key ingredient necessary for widespread adoption of hydrogen fuel. Initial tests have shown great progress, but there is a long way to go still.

Acknowledgments

Y.Y. was supported by the startup fund at New Jersey Institute of Technology. Y.Y., R.W.C., B.D.C., G.F.P., A.R.M. and M.C.B. acknowledge support from the Center for Advanced Solar Photophysics (CASP), an Energy Frontier Research Center funded by the Department of Energy (DOE), Office of Science, Basic Energy Sciences. J.G. and J.A.T. acknowledge the solar photochemistry program within the Chemical Sciences, Geosciences and Biosciences division of the DOE, Office of Science, Basic Energy Sciences.

More Information

Yan Y, RW Crisp, J Gu, BD Chernomordik, GF Pach, AR Marshall, JA Turner and MC Beard. 2017. “Multiple Exciton Generation for Photoelectrochemical Hydrogen Evolution Reactions with Quantum Yields Exceeding 100%.” Nature Energy 2:17052. DOI: 10.1038/nenergy.2017.52

About the author(s):

  • Zhanyong Li is a postdoctoral researcher from the Hupp and Farha group in the chemistry department at Northwestern University and a member of the Inorganometallic Catalyst Design Center (ICDC). His research projects involve the development of new metal-organic framework derived materials for gas-phase catalysis.

From TVs to (Fuel) Tanks

Tiny material dots used in LCD screens have a big impact in using sunlight to produce fuel

While sunlight might be free and abundant, the catalysts involved in using sunlight to produce fuels are expensive and inefficient. Scientists are developing low-cost and more efficient options to create that fuel, using the same tiny dots found in LCD TV screens. Image courtesy of Nathan Johnson, Pacific Northwest National Laboratory

Hydrogen fuel offers a potential path away from fossil fuels for everyday transportation, but the current commercial production of hydrogen fuel often still relies heavily on fossil fuels. Researchers from the Center for Advanced Solar Photophysics (CASP), an Energy Frontier Research Center led by Los Alamos National Laboratory, are pioneering new ways to efficiently generate hydrogen fuels using the abundant sunlight. Using quantum dots as the light absorber, researchers have constructed a solar-powered hydrogen fuel cell with unprecedented efficiency, greater than 100 percent. The efficiency achieved in these cells is a potential breakthrough in generating solar fuels for widespread use. The center is funded by the Department of Energy.

Written by Robert Choens, Center for Frontiers of Subsurface Energy Security

More Information

Yan Y, RW Crisp, J Gu, BD Chernomordik, GF Pach, AR Marshall, JA Turner and MC Beard. 2017. “Multiple Exciton Generation for Photoelectrochemical Hydrogen Evolution Reactions with Quantum Yields Exceeding 100%.” Nature Energy 2:17052. DOI: 10.1038/nenergy.2017.52

Disclaimer: The opinions in this newsletter are those of the individual authors and do not represent the views or position of the Department of Energy.