By some estimates, the amount of solar energy reaching the surface of the Earth in one year is greater than the sum of all the energy we could ever produce using non-renewable resources. The technology necessary to convert sunlight into electricity has developed rapidly, but inefficiencies in the storage and distribution of that power have remained a significant problem, making solar energy impractical on a large scale. However, a breakthrough by researchers from the University of Virginia’s (UVA’s) College and Graduate School of Arts & Sciences, the California Institute of Technology, and the U.S. Department of Energy’s Argonne National Laboratory, Lawrence Berkeley National Laboratory, and Brookhaven National Laboratory could eliminate a critical obstacle from the process, a discovery that represents a giant stride toward a clean-energy future. Their results were published in the journal Nature Catalysis.
One way to harness solar energy is by using solar electricity to split water molecules into oxygen and hydrogen. The hydrogen produced by the process is stored as fuel, in a form that can be transferred from one place to another and used to generate power upon demand. To split water molecules into their component parts, a catalyst is necessary, but the catalytic materials currently used in the process, also known as the oxygen evolution reaction, are not efficient enough to make the process practical.
Using an innovative chemical strategy developed at UVA, however, a team of researchers led by chemistry professors Sen Zhang and T. Brent Gunnoe have produced a new form of catalyst using the elements cobalt (Co) and titanium. The advantage of these elements is that they are much more abundant in nature than other commonly used catalytic materials containing precious metals such as iridium or ruthenium.
“The new process involves creating active catalytic sites at the atomic level on the surface of titanium oxide nanocrystals, a technique that produces a durable catalytic material and one that is better at triggering the oxygen evolution reaction.” Zhang said. “New approaches to efficient oxygen evolution reaction catalysts and enhanced fundamental understanding of them are key to enabling a possible transition to scaled-use of renewable solar energy. This work is a perfect example of how to optimize the catalyst efficiency for clean energy technology by tuning nanomaterials at the atomic scale.”
According to Gunnoe, “This innovation, centered on achievements from the Zhang lab, represents a new method to improve and understand catalytic materials with a resulting effort that involves the integration of advanced materials synthesis, atomic level characterization and quantum mechanics theory.”
“Several years ago, UVA joined the MAXNET Energy consortium, comprised of eight Max Planck Institutes [Germany], UVA, and Cardiff University [UK], which brought together international collaborative efforts focused on electrocatalytic water oxidation. MAXNET Energy was the seed for the current joint efforts between my group and the Zhang lab, which has been and continues to be a fruitful and productive collaboration,” Gunnoe said.
With the help of the Argonne and Lawrence Berkeley national laboratories and their state-of-the-art synchrotron x-ray absorption spectroscopy user facilities, which uses radiation to examine the structure of matter at the atomic level, the research team found that the catalyst has a well-defined surface structure that allows them to clearly see how the catalyst evolves in the meantime of the oxygen evolution reaction and allows them to accurately evaluate its performance.
“The work used x-ray beamlines from the Advanced Photon Source [APS] and the Advanced Light Source, including a portion of a ‘rapid-access’ program set aside for a quick feedback loop to explore emergent or pressing scientific ideas,” said Argonne x-ray physicist Hua Zhou, a co-author on the paper. “We’re very excited that both national scientific user facilities can substantially contribute to such clever and neat work on water splitting that will provide a leap forward for clean energy technologies.”
The studies at the Argonne Advanced Photon Source employed the X-ray Science Division (XSD) Spectroscopy Group’s 20-BM x-ray beamline to collect ex situ and in situ Co K-edge extended x-ray absorption fine structure spectra; and the XSD Structural Science Group’s 17-BM beamline, also at the APS, for in situ spatially resolved x-ray diffraction measurements on Co-TiO2 (Fig. 1). Soft x-ray x-ray absorption spectroscopy was performed at beamline 8.0.1 of the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory. The APS and ALS are Office of Science user facilities.
Additionally, researchers at Caltech, using newly developed quantum mechanics methods were able to accurately predict the rate of oxygen production caused by the catalyst, which provided the team with a detailed understanding of the reaction’s chemical mechanism.
“We have been developing new quantum mechanics techniques to understand the oxygen evolution reaction mechanism for more than five years, but in all previous studies, we could not be sure of the exact catalyst structure. Zhang’s catalyst has a well-defined atomic structure, and we find that our theoretical outputs are, essentially, in exact agreement with experimental observables,” said William A. Goddard III, a professor of chemistry, materials science, and applied physics at Caltech and one of the project’s principal investigators. “This provides the first strong experimental validation of our new theoretical methods, which we can now use to predict even better catalysts that can be synthesized and tested. This is a major milestone toward global clean energy.”
“This work is a great example of the team effort by UVA and other researchers to work towards clean energy and the exciting discoveries that come from these interdisciplinary collaborations,” said Jill Venton, chair of UVA’s Department of Chemistry.
See: Chang Liu1, Jin Qian2, Yifan Ye3, Hua Zhou 4, Cheng-Jun Sun4, Colton Sheehan1, Zhiyong Zhang1, Gang Wan4, Yi-Sheng Liu3, Jinghua Guo3, Shuang Li5, Hyeyoung Shin2‡, Sooyeon Hwang5, T. Brent Gunnoe1, William A. Goddard III2*, and Sen Zhang1**, “Oxygen evolution reaction over catalytic single-site Co in a well-defined brookite TiO2 nanorod surface,” Nat. Catal., published on line 14 December 2020. DOI: 10.1038/s41929-020-00550-5
Author affiliations: 1University of Virginia, 2California Institute of Technology, 3Lawrence Berkeley National Laboratory, 4Argonne National Laboratory, 5Brookhaven National Laboratory ‡Present address Chungnam National University (Republic of Korea)
This work was supported by the U.S. National Science Foundation (CBET-1805022, CBET-2004808 and CBET-2005250). This research used the resources of the Center for Functional Nanomaterials, which is a U.S. Department of Energy (DOE) Office of Science Facility at Brookhaven National Laboratory, under contract no. DE-SC0012704. This research used the resources of the Advanced Light Source, a U.S. DOE Office of Science User Facility, under contract no. DE-AC02-05CH11231. This research used the resources of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. DOE Office of Science by the Argonne National Laboratory under contract no. DE-AC02-06CH11357, and the Canadian Light Source and its funding partners.
The U.S. Department of Energy's APS is one of the world’s most productive x-ray light source facilities. Each year, the APS provides high-brightness x-ray beams to a diverse community of more than 5,000 researchers in materials science, chemistry, condensed matter physics, the life and environmental sciences, and applied research. Researchers using the APS produce over 2,000 publications each year detailing impactful discoveries, and solve more vital biological protein structures than users of any other x-ray light source research facility. APS x-rays are ideally suited for explorations of materials and biological structures; elemental distribution; chemical, magnetic, electronic states; and a wide range of technologically important engineering systems from batteries to fuel injector sprays, all of which are the foundations of our nation’s economic, technological, and physical well-being.
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