New Nanomaterials Might Convert Waste Heat into Usable Electricity for Vehicles

Everyone has felt the heat emitted from a cell phone or computer, which is the energy dissipated from the device. When it comes to automobiles, it is calculated that 60% of fuel efficiency is lost because of waste heat. Can this energy be captured and converted into electricity?

According to scientists working in the field of thermoelectric power generation, this is absolutely possible. However, the question here is that if it can be done cost-effectively.

Currently, thermoelectric generators are used rarely, primarily in niche applications such as space probes, where there is no chance of refueling. Thermoelectricity is a dynamic field of research, mainly among automobile companies such as Audi and BMW. However, so far, the cost of transforming heat into electricity has been shown to be more expensive than the electricity itself.

Anveeksh Koneru, a senior lecturer in mechanical engineering at The University of Texas Permian Basin (UTPB), is investigating a new technique for collecting waste heat by utilizing the quantum mechanical motions of electrons in spin-polarized materials.

In particle physics, spin is an inherent form of angular momentum carried by composite particles (hadrons), elementary particles, and atomic nuclei. It has been demonstrated via a mechanism called the Spin Hall effect that a voltage can be produced by utilizing differences in spin populations on a metal contact mounted on a ferromagnetic material. The concept was first experimentally shown by Japanese scientists in 2008 and entered into materials science for some time but has not still found its optimal form.

Koneru assumes that, in cobalt oxide, he may have identified the appropriate material to exploit the effect for energy production. Cobalt oxide is an inorganic compound used in the ceramics industry to develop blue-colored glazes, as well as in water separation technologies. It has the exceptional potential to accept substitute transition metal cations, which enables them to be combined with copper, nickel, zinc, or manganese. These metals possess magnetic properties that can increase the separation between electrons spinning up and down and enhance the conversion of heat into electricity.

The material should be a good electrical conductor, but a bad thermal conductor. It should conduct electrons, but not phonons, which are heat. To study this experimentally, we'd have to fabricate thousands of different combinations of materials. Instead, we're trying to theoretically calculate what the optimal configuration of the material using substitutions is.

Anveeksh Koneru, Senior Lecturer, Mechanical Engineering, University of Texas Permian Basin

From the year 2018, Koneru has been employing supercomputers at the Texas Advanced Computing Center (TACC) to virtually test the energy profiles of a range of cobalt oxides with a variety of substitutions.

“Each calibration takes 30 to 40 hours of computing time, and we have to study at least a 1,000 to 1,500 different configurations,” he described. “It requires a huge computational facility and that's what TACC provides.”

Koneru, together with UTPB graduate students Gustavo Damis Resende, Nolan Hines, and a collaborator from West Virginia University, Terence Musho, demonstrated their first findings on the thermoelectric capacity of cobalt oxides at the Materials Research Society Spring Meeting in Phoenix, Arizona, on April 22^nd, 2019.

The scientists investigated 56-atom unit cells of three configurations of cobalt oxide, modified by substitutions of zinc and nickel, to achieve optimal thermoelectric performance. They employed a software package called Quantum ESPRESSO to estimate physical characteristics for each configuration. These include:

• the lattice parameters, which are the physical dimensions of cells in a crystal lattice
• the band gap, which is the minimum energy needed to excite an electron to a state where it conducts energy
• the spin polarization, which is the degree to which the spin is oriented with specified direction
• the effective mass of conduction electrons, which is the mass that a particle seems to have when responding to force

These basic properties were then used to carry out traditional charge and spin transport calculations, which inform the scientists how a configuration of the cobalt oxide can effectively convert heat into electricity.

According to the scientists, the technique created in this study can be applied to other remarkable thermoelectric materials with semiconducting and magnetic properties, rendering it widely useful for the materials science community.

Using the UT Research Cyberinfrastructure

Being a PhD student at West Virginia University, Koneru had access to large supercomputers to carry out his study. UTPB does not have such resources locally; however, he managed to get access to the advanced computing systems and services of TACC through the UT Research Cyberinfrastructure (UTRC) initiative, which, from the year 2007, has offered access to TACC’s resources, expertise, and training to scientists at any of the University of Texas System’s 14 institutions.

As part of the UTRC initiative, TACC faculties act as links, visiting UT System’s 14 campuses, providing consultation and training, and offering scientists the resources available to them. When TACC scientist Ari Kahn visited UTPB, he met Koneru and persuaded him to compute at TACC.

From that time onward, Koneru has been using Lonestar5—a system solely for UT System scientists—for his work. While they are still in their early phase, the outcomes until now have been promising.

“I’m excited because we could clearly see spin polarization when cobalt oxide spinels were substituted with nickel. That’s a good sign,” he stated. “We’re seeing that one particular configuration has a higher split in band-gap, something that’s surprising and we have to explore further. And all the calibrations are converging, which shows they’re reliable.”

Once he finds the right material for waste heat conversion, Koneru expects to create a paste that could be applied to the tailpipe of a vehicle, turning waste heat into electricity to power a car’s electrical systems. He approximates that such a device could cost below $500 per vehicle and could minimize greenhouse gas emissions by hundreds of millions of tons yearly.

“With the recent advances in nanofabrication, and computational calibrations for nanomaterials, spin-thermal materials can play a vital role in energy conversion in the future,” he stated.

TACC allows Koneru to investigate a large number of possible material configurations with great speed so that when it is time to test them experimentally, the number of candidates will be controllable.

TACC is such a highly useful system with personnel that can guide you if any problems arise. If faculty or students are interested in research that requires computational facilities, TACC is the right option to choose. It provides resources and expertise for free. It’s a great enabler for whatever you’re passionate about.

Anveeksh Koneru, Senior Lecturer, Mechanical Engineering, University of Texas Permian Basin

It’s our mission to encourage researchers all across the State to use TACC resources to make amazing discoveries that cannot be made in the lab or using local clusters. Dr. Koneru’s research is a great example of such a project that could have a major impact on air pollution and global warming.

Ari Khan, Scientist, TACC