New semiconducting material works at temperatures low enough to improve fuel cell efficiency
Researchers have been trying to increase the efficiency of solid oxide fuel cells by lowering the temperatures at which they run. More efficient fuel cells might gain wider use in vehicles or as quiet, pollution-free, neighborhood electricity generating stations. A serendipitous finding has resulted in a semiconducting material that could enable fuel cells to operate at temperatures two-thirds lower than current technology, scientists reported August 18 in Nature Communications.
Routing: Oxygen can zigzag or take a circular route (red arrows) through this semiconducting crystal made of strontium (green), chromium (blue), and oxygen (red).
Image Courtesy of Nature Communications
In an attempt to create a metal oxide with the properties of metal, researchers at the Department of Energy's Pacific Northwest National Laboratory created a new form of the metal oxide. This particular strontium-chromium oxide performs as a semiconductor, or a material whose ability to conduct electricity can be turned on and off. It also allows oxygen to diffuse easily, a requirement for a solid oxide fuel cell. Best yet, it allows diffusion at a temperature that can lead to much more efficient fuel cells.
Nothing is Something
Energy researchers need improved materials to make fuel cells more widely used. Solid oxide fuel cells require oxides capable of absorbing and transmitting negatively charged oxygen atoms at low temperature. Current materials require temperatures around 800 degrees Celsius (for reference, car engines run at about 200 degrees Celsius and steel melts around 1500).
Researchers at PNNL were trying to make strontium chromium oxide in a kind of crystalline form called perovskite, which has many useful electronic properties. In this material, the strontium, chromium and oxygen atoms stack together in a cube. The metal atoms — strontium and chromium — bond completely to the oxygen atoms around them.
However, in the material that formed, the strontium chromium oxide packed into a rhombus-shaped crystal — think diamond — and many of the oxygen atoms were missing.
What's more, the holes where the oxygen atoms had been, also called oxygen vacancies, had come together to form well-defined planes within the new crystal structure. The researchers found that these planes act as channels that allow oxygen from outside the material to diffuse through the material at an exceptionally low temperature for these materials, about 250 degrees Celsius.
"At high enough concentrations, oxygen vacancies aggregate and form new mesoscale structures with novel properties that the original material doesn't have," said PNNL materials scientist Scott Chambers, who led the research. "In this case, the mesoscale crystalline structure transmits oxygen very efficiently."
Bad Angle Bonds
The scientists inadvertently generated the material by taking advantage of the natural tendency of chromium atoms to avoid certain bonding environments. They found that their attempts to make metallic SrCrO3 (strontium chromium oxide in a ratio of 1:1:3) lead instead to the formation of semiconducting SrCrO2.8 (with a ratio of 1:1:2.8).
Because chromium as an ion with a charge of +4 does not like to form 90o bonds with oxygen, as it must in SrCrO3, SrCrO2.8 forms instead with a completely different crystal structure. This material contains oxygen-deficient regions through which oxygen can diffuse very easily. Those regions might provide a way to take better advantage of the material's electronic properties.
"As an additional benefit, ordered arrays of oxygen vacancies might allow us to separate the material's electronic and thermal properties," said Chambers. "This would help us improve the performance of thermoelectrics, in either generating power from heat or for use in refrigeration."
The team made ultra-pure crystalline films of the new material and used instruments and expertise at EMSL, DOE's Environmental Molecular Sciences Laboratory, to understand the material's properties. A DOE Office of Science User Facility, EMSL scientists worked with Chambers to develop a new instrument called an oxygen-assisted molecular beam epitaxy deposition system that is specifically designed to make and study these kinds of crystalline films.
Towards Light and Electrons
In the future, the team plans to apply the understanding gained to other materials, such as the deposition, characterization, and understanding of epitaxial strontium-doped lanthanum chromite, which has potential importance in visible light harvesting.
In the long term, the team plans to exploit the observed phenomenon to carry out nanofabrication of novel heterogeneous catalytic structures by depositing submonolayer quantities of catalytically important metals on the surface of rhombus-shaped, semiconducting oxide, and using the intersection of the defect planes with the free surface to order the incoming metal atoms into nanowires.
This work was supported by the Department of Energy Office of Science, EMSL and PNNL.
Reference: Hong-Liang Zhang, Peter V. Sushko, RJ Colby, Yingge Du, Mark E. Bowden , and Scott A. Chambers. 2014. Reversible Nano-Structuring of SrCrO3-δ Through Oxidization and Reduction at Low Temperatures. Nature Communications, August 18, 2014. DOI: 10.1038/ncomms5669.
Mary Beckman | Eurek Alert!
From ancient fossils to future cars
21.10.2016 | University of California - Riverside
Study explains strength gap between graphene, carbon fiber
20.10.2016 | Rice University
Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.
"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...
In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.
A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...
By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.
"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...
COMPAMED has become the leading international marketplace for suppliers of medical manufacturing. The trade fair, which takes place every November and is co-located to MEDICA in Dusseldorf, has been steadily growing over the past years and shows that medical technology remains a rapidly growing market.
In 2016, the joint pavilion by the IVAM Microtechnology Network, the Product Market “High-tech for Medical Devices”, will be located in Hall 8a again and will...
'Ferroelectric' materials can switch between different states of electrical polarization in response to an external electric field. This flexibility means they show promise for many applications, for example in electronic devices and computer memory. Current ferroelectric materials are highly valued for their thermal and chemical stability and rapid electro-mechanical responses, but creating a material that is scalable down to the tiny sizes needed for technologies like silicon-based semiconductors (Si-based CMOS) has proven challenging.
Now, Hiroshi Funakubo and co-workers at the Tokyo Institute of Technology, in collaboration with researchers across Japan, have conducted experiments to...
14.10.2016 | Event News
14.10.2016 | Event News
12.10.2016 | Event News
21.10.2016 | Health and Medicine
21.10.2016 | Information Technology
21.10.2016 | Materials Sciences