Heat resistance in nanomaterials for electricity conversion

Breaking records for high-temperature stability, a new nanophotonic material could lead to more efficient power generation and a host of new opportunities for managing and converting thermal radiation.

Micrographs show no noticeable deterioration before and after heat treatment of the material. Image Credit: Andrej Lenert

This material is robust at temperatures up to 2,000 degrees in air and was created by a team of chemical and materials science engineers led by University of Michiganrepresents nearly a twofold advance over current methods.

Shorter wavelengths can pass through the material while infrared light is reflected using a process known as destructive interference. By reflecting infrared waves back into the system, this can significantly reduce heat waste in thermal cells, which convert heat into electricity but cannot use infrared energy.

Other applications of this material include photovoltaics, thermal imaging, environmental barrier coatings, sensing, and concealment from infrared monitoring equipment.

It’s similar to the way butterfly wings use interfering waves to get their color. Butterfly wings are made of colorless materials, but these materials are structured and textured in such a way that they absorb some wavelengths of white light but reflect others, resulting in the appearance of color.

Andrej Lenert, study co-author and assistant professor, Chemical Engineering, University of Michigan

Lennert added,This material does something similar to infrared energy. The hard part was preventing the collapse of that color-producing structure under high temperature.

The method represents a significant divergence from the current state of manufactured heat emitters, which typically use ceramics and foams to control infrared emissions.

Although they can withstand high temperatures, these materials have very little control over the wavelengths they allow to pass through. Although previous attempts have not been proven stable at high temperatures, melting or oxidizing processes (the process that forms rust on iron) can provide much greater control over nanophotons. Moreover, many nanophotonic materials can only remain stable in a vacuum.

By exceeding the previous mark of heat resistance among air-stable photonic crystals by more than 900 outdoors, the new material contributes to solving this problem. The material is also modifiable, allowing scientists to modify its energy for a wide range of potential applications.

According to the study team, adding these materials to existing TPVs will boost efficiency by 10%, and they expect future tuning will result in much higher efficiency gains.

By combining their knowledge of chemical engineering and materials science, the team created the solution. The first step Lennert’s chemical engineering team took was to identify materials that wouldn’t mix even if they started to dissolve.

The goal is to find materials that maintain nice, clear layers that reflect light the way we want them to, even when things get extremely hot. Therefore, we searched for materials with completely different crystal structures, as they tend not to mix‘,” Lennert said.

They hypothesized that a mixture of rock salt and the mineral perovskite, which consists of oxides of calcium and titanium, would work. Researchers from the universities of Michigan and Virginia ran supercomputer simulations to check the viability of the kit.

The materials were then precisely deposited using pulsed laser deposition to produce micro-layers with smooth interfaces by John Heron, co-author of the study and associate professor of materials science and engineering at UM, and Matthew Webb, a doctoral student in materials science and engineering.

Instead of using standard photovoltaic materials, they chose oxides because they can be layered more precisely and are less prone to breakdown at higher temperatures. This made the material more durable.

In the previous work, the conventional materials were oxidized under high heat, and they lost their orderly layered structure. But when you start with the oxides, this decomposition has already taken place. This results in increased stability of the final layered structure.

John Heron, study co-author and Assistant Professor, Materials Science and Engineering, University of Michigan

Sean McSherry, the study’s first author and a doctoral student in materials science and engineering at the University of Michigan, used computer modeling to find hundreds of other combinations of materials that would also likely function after testing demonstrated that the materials performed as intended.

The major discovery opens a new avenue for investigation of many other nanomaterials, which could help future researchers develop a range of new materials for a large number of purposes, even if commercial implementation of the material examined in the study is likely years away. .

The Defense Advanced Research Projects Agency, grant number HR00112190005, provided funding for the study.

magazine reference

McSherry, S.; et al. (2022) Nanophotonic control of thermal emission under air temperature extremes. Nature’s nanotechnology. doi: 10.1038/s41565-022-01205-1