Scanning transmission electron microscope image of a nickel-platinum composite material created at The Ohio State University. At left, the image is overlaid with false-color maps of elements in the material, including platinum (red), nickel (green) and oxygen (blue). Imaging by Isabel Boona, OSU Center for Electron Microscopy and Analysis; Left image prepared by Renee Ripley. (Courtesy of The Ohio State University)
The researchers who developed the use of a quantum mechanical effect to convert heat into electricity have developed a way to apply their technique into a form that can be used in industry.
Researchers from The Ohio State University developed a method using magnetism on a composite of nickel and platinum to amplify the voltage output 10 times or more by using a thicker piece of material that more closely resembles components for future electronic devices.
Previously, this process was only done using a thin piece of film and produced very small voltages but with the thicker piece of material more electricity was able to be produced.
Electrical and mechanical devices, including car engines, produce heat called waste heat as a byproduct of their normal operation and the research team was able to capture the waste heat inside specially designed materials to generate power and increase overall energy efficiency.
Stephen Boona, a postdoctoral researcher at Ohio State and co-author of the study, explained some of the stumbling blocks that has precluded this type of advancement in the past.
“Over half of the energy we use is wasted and enters the atmosphere as heat,” Boona said in a statement “Solid-state thermoelectrics can help us recover some of that energy.
“These devices have no moving parts, don’t wear out, are robust and require no maintenance,” he added. “Unfortunately, to date, they are also too expensive and not quite efficient enough to warrant widespread use. We’re working to change that.”
Researchers from Ohio State first demonstrated in 2012 that magnetic fields could boost a quantum mechanical effect called the spin Seebeck effect and in turn boost the voltage output of thin films made from exotic nanostructured materials from a few microvolts to a few millivolts.
The team built on that work by increasing the output for a composite of two very common metals—nickel with a sprinkling of platinum from a few nanovolts to tens or hundreds of nanovolts—a smaller voltage but in a simpler device that requires no nanofabrication and can be readily scaled up for industry.
Joseph Heremans, a professor of mechanical aerospace engineering and the Ohio Eminent Scholar in Nanotechnology, said that to some extent using the same technique in thicker pieces of material required they rethink the equations that govern thermodynamics and thermoelectricity, which were developed before scientists knew about quantum mechanics.
Heremans research focused on magnons—waves and particles of magnetism.
“Basically, classical thermodynamics covers steam engines that use steam as a working fluid, or jet engines or car engines that use air as a working fluid,” Heremans said in a statement. “Thermoelectrics use electrons as the working fluid.
“And in this work, we’re using quanta of magnetization, or ‘magnons,’ as a working fluid,” he added.
In 2012, his team described hitting electrons with magnons to push them through thermoelectric materials and in the most recent paper they showed that the same technique can be used in bulk pieces of composite materials to further improve waste heat recovery.
Rather than applying a thin film of platinum on top of a magnetic material as they have done in the past, the researchers distributed a very small amount of platinum nanoparticles randomly throughout a magnetic material like nickel. This produced enhanced voltage output due to the spin Seebeck effect, which means that for a given amount of heat, the composite material generated more electrical power than either material could on its own.
The entire piece of composite is electrically conducting, meaning other electrical components can draw the voltage from it with increased efficiency compared to a film.
Heremans said the next step will be to further the research for applications for common waste heat generators, including car and jet engines. He said the idea right now is general and can be applied to a variety of material combinations, enabling entirely new approaches that don’t require expensive metals like platinum or delicate processing procedures like thin-film growth.
The study was published in Nature Communications.
