Science for our
Nation's
Energy Future

Energy Frontier Research Center

Community Website
Frontiers in
Energy Research
Newsletter
May 2013

Creating the Next Generation of Porous Materials

“Bare” nanocrystals are templated with polymers to produce highly functional porous architectures

Gyu Leem

Scanning electron microscopy images of various templated nanocrystal-based mesoporous films: (a) ITO, (b) Mn3O4, (c) (Mn,Fe)2O3, and (d) CdSe. The center figure is a general schematic representation of a nanocrystal mesoporous film.

The proliferation of battery-powered electronic devices, the growth of solar power and the development of renewable catalytic processes have set the stage for new energy storage devices. These devices will require the development of new materials, and mesoporous materials are an exciting option for many of these applications. Mesoporous materials, defined as synthetic materials with a pore diameter of about 2 to 50 nanometers, represent an interesting class of materials for building electrical charge storage devices. Researchers with the Molecularly Engineered Energy Materials, or MEEM, have designed nanocrystal-based mesoporous materials, which are synthesized by templating “bare” nanocrystals with amphiphilic (polar and nonpolar functional groups) polymers. These materials exhibit a unique combination of features such as high surface area, good pore accessibility and homogeneous open pore structures.

The ability to control the structure of nanomaterials is crucial for electrical energy storage because storage mechanisms rely on chemical reactions between molecules in solution and chemical sites on the structure. To date, they have been prepared using several synthetic routes including sol-gel chemistry. In those sol-gel-based methods, amphiphilic polymer species are used as a scaffold for molecular precursors to form an organic/inorganic mesostructured composite that, upon thermal treatment, results in a film with a pore-solid architecture. However, fully crystallizing the inorganic network, while retaining the porosity and high crystallinity, remains a major challenge.

To address such challenges, MEEM researchers started with fully crystalline nanocrystals, where the capping organic molecule on the nanocrystal surface had been removed and replaced by inorganic anions to produce “bare” nanocrystal building blocks. These bare nanocrystals were then co-assembled with large polymer templates to produce mesostructured composites. Thermal treatment of the polymer template resulted in materials that exhibited mesopores (arising from the polymer template), and micropores (which form between the nanocrystals comprising the pore walls).

"This process thus opens the door to the production of a very wide range of nanoporous materials with applications for both electrochemical energy storage and solar energy harvesting,” says Sarah H. Tolbert, a professor at University of California at Los Angeles, who led the team of researchers at MEEM.  

Their recent articles in ACS Nano and Advanced Materials demonstrated that nanocrystal-based mesoporous materials (made from materials such as ITO, Mn3O4, (MnFe)2O3 and CdSe) exhibit uniform mesoporosity with highly crystalline pore walls, high surface areas and an open interconnected porosity, leading to enhanced electrochemical performance. This novel synthetic route provides a new path to develop charge storage materials.

Tolbert remarks, “In this work, we show that the templating and formation of porosity can be decoupled from the basic inorganic synthesis so that nanocrystals can be made under highly reactive conditions and then assembly can take place under mild conditions."

With this information, scientists can optimize mesoporous materials through these types of solution-based chemistries, not only to produce interesting architectures, but to design electrodes that should lead to enhanced electrochemical energy storage performance.

More Information

Rauda IE, R Buonsanti, LC Saldarriaga-Lopez, K Benjauthrit, LT Schelhas, M Stefik, V Augustyn, J Ko, B Dunn, U Wiesner, DJ Milliron, and SH Tolbert. 2012. “General Method for the Synthesis of Hierarchical Nanocrystal-Based Mesoporous Materials.” ACS Nano 6(7):6386-6399. DOI: 10.1021/nn302789r

Rauda IE, LC Saldarriaga-Lopez, BA Helms, LT Schelhas, D Membreno, DJ Milliron, and SH Tolbert. 2013. “Nanoporous Semiconductors Synthesized Through Polymer Templating of Ligand-Stripped CdSe Nanocrystals.” Advanced Materials 25(9):1315-1322. DOI: 10.1002/adma.201203309

Acknowledgments

This work was primarily supported by Molecularly Engineered Energy Materials, an Energy Frontier Research Center, funded by the Department of Energy, Office of Science, Office of Basic Energy Sciences.

About the author(s):

  • Gyu Leem is a postdoctoral research associate in Kirk Schanze’s group at the University of Florida and a member of the Center for Solar Fuels, an Energy Frontier Research Center. He received his Ph.D. in chemistry from the University of Houston in 2008. Before joining Schanze’s research group in 2012, he worked in the division of petrochemical and polymer at LG Chem. Currently, his research interests are in designing and synthesizing polymer assemblies for potential use as light-harvesting antenna.

New Synthesis Method Creates Materials with Interesting Features for Energy Storage

More surface area and accessible, regular pores could, one day, appear in batteries

Mesoporous materials (schematic shown here), which are synthetic materials with a pore diameter of about 2 to 50 nanometers, represent an interesting class of materials for building electrical charge storage devices for solar farms and other applications. 

Conventional batteries cannot store solar energy and provide it when needed. New energy storage devices mean new materials with open, uniform and interconnected pores that enhance specific energy storage reactions. Current synthesis methods leave behind carbon-based molecular strings or ligands. The ligands prevent clumping, but interfere with the material’s porosity. Researchers devised a bare synthesis method that avoids the ligands altogether. The resulting material does not clump and has the desired pore structure and a high surface area, meaning a small amount of the material contains a significant number of pores. This method is not limited to oxides, as are many conventional synthesis processes. The process could lead to more effective energy storage and solar cell materials. Scientists at the Molecularly Engineered Energy Materials, led by the University of California, Los Angeles, did the research.

More Information

Rauda IE, R Buonsanti, LC Saldarriaga-Lopez, K Benjauthrit, LT Schelhas, M Stefik, V Augustyn, J Ko, B Dunn, U Wiesner, DJ Milliron, and SH Tolbert. 2012. “General Method for the Synthesis of Hierarchical Nanocrystal-Based Mesoporous Materials.” ACS Nano 6(7):6386-6399. DOI: 10.1021/nn302789r

Rauda IE, LC Saldarriaga-Lopez, BA Helms, LT Schelhas, D Membreno, DJ Milliron, and SH Tolbert. 2013. “Nanoporous Semiconductors Synthesized Through Polymer Templating of Ligand-Stripped CdSe Nanocrystals.” Advanced Materials 25(9):1315-1322. DOI: 10.1002/adma.201203309

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.