An Iron-Based Generator That Uses Waste Heat to Power Small Electrical Devices

May 11, 2020 by Luke James

Researchers have discovered a way to convert heat energy into electricity by using a material mostly composed of iron.

A generator based on iron, which is cheap due to its abundance, could be used to power small devices such as remote sensors or wearables. And because the material is so thin, it can theoretically be shaped into various forms, too. 

This is according to researchers at the University of Tokyo, who published their research in the journal Nature on April 27.


Thermoelectric Generation Using the Anomalous Nernst Effect 

Thermoelectric generation using ANE is said to hold great promise for applications in energy harvesting technologies. This is because the transverse geometry of the Nernst effect should enable efficient, large-area, and flexible coverage of a heat source. If applications using ANE are to be viable and successfully power small devices, however, substantial improvements will be necessary for performance, safety, stability, and the cost of materials. 

"So far, all the study on thermoelectric generation has focused on the established but limited Seebeck effect," said the research team’s leader, Professor Satoru Nakatsuji. "In contrast, we focused on a relatively less familiar phenomenon called the anomalous Nernst effect (ANE)."


Simplifying Thermoelectric Generator Design 

ANE produces a voltage perpendicular to the direction of a temperature gradient across a material’s surface. If the right materials become more readily available, ANE could be utilized to simplify the design of thermoelectric generators and enhance their conversion efficiency.


Nodal web structure.

A diagram showing an illustration of the nodal web structure responsible for the anomalous Nernst effect developed by the University of Tokyo research team. Image used courtesy of Sakai et al



Boosting Ane via Doping

In their experiments, the team found that 25 percent doping of aluminum and gallium in alpha iron, an element that is naturally abundant, greatly enhances the ANE by around twentyfold, reaching around 4 and 6 microvolts per Kelvin at room temperature---close to the highest value reported so far. 

This is not the first time that the team as demonstrated ANE. However, previous experiments used materials that are less readily available and significantly more expensive than iron.


Molded to Suit the Application

The whole attraction of this device is that it is low cost and the materials are low cost and non-toxic. It can also be made in a thin film form so that it can be molded to suit various applications, ideal for small consumer electronics. 

"The thin and flexible structures we can now create could harvest energy more efficiently than generators based on the Seebeck effect," said Research Associate Akito Sakai. "I hope our discovery can lead to thermoelectric technologies to power wearable devices, remote sensors in inaccessible places where batteries are impractical, and more." It is thought that these thin structures, which exhibit a large ANE at zero fields, could also be used for designing low-cost, flexible, microelectronic thermoelectric generators. 


Reaching Proof of Concept Faster Through Calculations 

To realize their achievement, the team relied heavily on high-throughput computational methods for numerical calculations, reducing the time between the initial idea and proof of concept. This is a huge advantage in contrast to conventional developments in materials science, which typically require repeated iterations that are time-consuming. 

"Numerical calculations contributed greatly to our discovery; for example, high-speed automatic calculations helped us find suitable materials to test," said Nakatsuji. "And first-principles calculations based on quantum mechanics shortcut the process of analyzing electronic structures we call nodal webs which are crucial for our experiments."

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