The Experimental Materials Science Group, within NREL's Energy Sciences directorate, performs research to provide a knowledge base in materials science for responding to long-range fundamental issues that impact photovoltaics, solid-state lighting, electrochromic ("smart") windows, hydrogen storage, fuel cells, and solid-state batteries. We focus on research and development to rationally design and fabricate new materials using unique state-of-the-art modeling, synthesis, and measurement capabilities.
Our research capabilities and facilities include the following:
- Precision analysis of adsorption thermodynamics of hydrogen, methane, and carbon dioxide
- Electron spin resonance and nuclear magnetic resonance
- X-ray diffraction
- Inductively coupled plasma analysis
- Temperature-programmed desorption, volumetric capacity, and thermal gravimetric analysis
- Ultrafast spectroscopy, high magnetic field spectroscopy, and submicron spatial resolution optical spectroscopy
- Chemical vapor deposition, atomic layer deposition, and molecular beam epitaxy
- Facilities for high-energy and reactive-species synthesis
- National test facility for commercial dynamic windows.
We discuss details of our research under the following topics:
- Electrochromic Windows
- Spectroscopy of Solid-State Materials
- Fuel Cells
- Carbon Nanoscience
- Materials Synthesis
- Hydrogen Storage.
Low-Cost Spray Coating. We develop simple, inexpensive spray-coating techniques that combine film deposition and glass manufacturing processes to provide a lower-cost production method while reducing energy use and greenhouse gas emissions.
Thin-Film Electrochromic Transition Metal Oxides. We are improving the relatively poor performance of the counter electrode in electrochromic devices. Specific goals are to improve visual appearance; reduce switching speed; increase device efficiency and durability; and improve the basic understanding of the counter electrode and tailor it for improved performance.
Dynamic Window Accelerated Aging Testing.Electrochromic windows are cycled up to 50,000 times, under light that can be greater than 1-sun of global terrestrial air-mass 1.5 spectrum, and at ambient temperatures of -5° to 60°C and humidity of 2% to 5%.
Spectroscopy of Solid-State Materials
We focus on realizing materials that transcend the present constraints of photovoltaic and solid-state lighting technologies. Through materials growth, characterization, and theoretical modeling, we seek to understand and control fundamental electronic and optical processes in semiconductors.
Alloy Statistics and Spontaneous Ordering. Spontaneous ordering is a self-organized symmetry transformation during growth of certain ternary alloy semiconductors that results in modifying the alloy's structural, electronic, and optical properties. We are learning how to control this phenomenon so that it may be used for tailoring desirable electronic and optical properties.
Conventional III-Phosphides for Solid-State Lighting. Very high efficiency solid-state lamps are limited by the inability to fabricate light-emitting diodes with strong emission at green and amber wavelengths. We are exploring high-bandgap III-phosphide alloys, such as AlInP, grown metamorphically on GaAs, as candidate materials with useful characteristics.
Isoelectronic Impurities and the Physics of Abnormal Alloys. Device designers have sought semiconductors that could yield a 1.0-eV-bandgap subcell for highly efficient multijunction solar cells while remaining nearly lattice-matched to GaAs. Dilute GaAs1-xNx was originally proposed, but exhibits problems. We have synthesized the novel dilute bismide alloy GaAs1-xBix to overcome typical problems. We are trying to understand the fundamental way that N and Bi affect the alloy's band structure and are exploring the physics of isoelectronic co-doping.
Collective Excitations in Photogenerated Plasmons. Exciting Bi-doped GaAs, even with a relatively low-powered continuous-wave laser, can build up a large electron density, as detected by our measurements of light scattering from its plasmon modes. This scattered signal represents a dynamically controllable frequency shift with possible photonic applications, and we are pursuing even higher densities in the mixed type-I/type-II quantum well (MTQW).
Ion-Beam Implantation. Using ion-beam implantation, we have nitrogen-doped a model catalyst system to investigate the effect on the durability of Pt–Ru nanoparticles, which are used as electro-oxidation catalysts for direct methanol fuel cells. Doping of powder materials is also possible through our development of a new modified ion-beam-assisted deposition (IBAD) system.
Core-Shell Catalyst Materials. We are studying the efficient use of platinum group metals (PGMs) for proton-exchange membrane (PEM) catalysts. Using atomic layer deposition, we are developing thin conformal PGM films to maximize electrochemical mass activity.
Next-Generation Metal Oxides. We are developing novel metal-oxide nanostructures as supports to enhance the performance of PEM cathode catalysts. Precise metallic deposition is achieved by atomic layer deposition.
Advanced Electrodes. Our researchers, working within the U.S. Department of Energy-sponsored project, Batteries for Advanced Transportation Technologies, are developing advanced electrodes for lithium-ion batteries suitable for energy storage applications. We have successfully used nanostructured materials to improve the rate capability of these batteries such that a vehicle could possibly be charged in about five minutes.
Ultra-Thin Coatings. We are developing ultra-thin coatings to improve the durability, voltage window, and capacity retention of next-generation materials. The coatings will improve safety and enable achieving higher power and energy densities.
Our researchers study the fundamental properties and applications of low-dimensional carbon—both graphene, where charge carriers move freely in two dimensions, and carbon nanotubes, where carrier transport occurs in one dimension.
The work includes synthesis and purification of graphene and single-walled carbon nanotubes, and characterization of the fundamental optical and electrical properties that determine how the materials will function in a device.
Graphene. We are focusing on the impact of grain size, grain boundaries, and local electronic structure on charge-carrier transport and interfacial charge transfer. Targeted applications include photovoltaics, hydrogen storage, fuel cells, solar fuels generation, and batteries.
Single-Walled Carbon Nanotubes. Our primary focus is to separate single-walled carbon nanotubes by diameter and electronic structure, which will help in understanding the impact of electronic structure on optical absorbance and emission, charge-carrier dynamics, carrier transport, and interfacial charge transfer.
Liquid Precursors for Photovoltaic Inks. We are developing precursors for atmospheric deposition of photovoltaic materials. Using our experience in synthesizing nanoparticles and organometallic materials precursors, we are solving materials problems related to solar cell fabrication using liquid precursors deposited and processed under atmospheric conditions. This work includes developing inks for inkjet printing of metals (e.g., Ag, Cu, Ni), metal oxides (e.g., ZnO, SnO2, (Ba,Sr)TiO3), and polymers, as well as developing precursors for depositing absorber layers (CdTe, CIGS, and CZTS) and layers that are barriers to water and oxygen.
Nanomaterials for Thermal Energy Storage. Our goal is to increase the heat capacity of thermal storage media by a factor of 2 to 4 by adding encapsulated nano-phase-change materials (nanoPCMs) to storage fluids including oils and molten salts. The nanoPCMs comprise core-shell nanostructures: the core is a metal, metal alloy, or salt nanoparticle that undergoes a phase change to store thermal energy; the shell is a metal oxide that encapsulates the PCM to protect it from the environment and contain the liquid phase. The nanoPCMs examined include metals (Al, Ag, Cu, Ag, Bi), alloys (Bi-Sn, Bi-Sb), and salts (KNO3, Cu(NO3)2, AgNO3, CsNO3), which were encapsulated in SiO2 or TiO2.
Our researchers design and develop nanostructured materials that efficiently store hydrogen. Some specific activities include the following:
- Making vehicular hydrogen storage systems smaller, lighter, and cheaper to enable U.S. energy independence with zero-emissions fuels. Hydrogen has a very high mass energy density; but its low volume density makes it difficult to store. Sorbent materials can be used to increase capacities.
- Developing low-cost materials with high capacities for on-vehicle refueling and storage. We have unique synthesis and characterization methods that enable us to design and develop novel materials.
- Designing materials with energy densities at ambient temperature and pressure higher than liquid hydrogen. One promising material is calcium graphite. We are leading efforts to develop weak chemisorption sorbents. We are continuing to develop materials that will meet the U.S. Department of Energy's 2015 and ultimate hydrogen storage targets.
For staff profiles, publications, and contact information, see the Chemical and Materials Science staff page.