Nanophotonic Material Can Convert Heat Into Electricity

Heat-Resistant Nanophotonic Material Could Help Convert Heat into Electricity   A new nanophotonic material is breaking records in high-temperature stability, paving the way for more efficient electricity generation and opening new possibilities in the control and conversion of thermal radiation. Developed by a team of chemistry and materials science engineers led by the University of Michigan, the material controls infrared radiation flow and remains stable at temperatures of 2,000 degrees Fahrenheit in air. This represents approximately a twofold improvement compared to current methods. The material uses a phenomenon called destructive interference to reflect infrared energy while allowing shorter wavelengths to pass through. This can potentially reduce heat waste in thermophotovoltaic cells that convert heat into electricity but cannot use infrared energy, by reflecting infrared waves back into the system. The material may also be useful in optical photovoltaics, thermal imaging, environmental barrier coatings, sensing, camouflage not detectable by infrared surveillance devices, and other applications. Andrej Lenert, Assistant Professor in the Department of Chemical Engineering at UM and co-author of the study in Nature Nanotechnology, explained: "The working principle of this material is similar to how butterfly wings use wave interference to produce color. Butterfly wings are made of colorless materials, but these materials are configured to absorb certain wavelengths of white light while reflecting others. "This material does something similar with infrared energy. The challenging part is preventing the color-producing structure from degrading under high heat." This approach represents a major departure from the current state of engineered thermal emitters, which typically use foam and ceramics to limit infrared emissions. These materials are stable at high temperatures but offer very limited control over which wavelengths they transmit. Nanophotonics can provide much more tunable control, but previous work has not been stable at high temperatures, usually resulting in melting or oxidation (the process that produces rust on iron). Additionally, many nanophotonic materials can only maintain their stability in a vacuum. The new material addresses this problem by breaking the previous record in heat resistance among air-stable photonic crystals, maintaining stability above 900 degrees Fahrenheit in open air. Furthermore, the material is tunable in nature, allowing researchers to fine-tune energy conversion for a wide range of potential applications. The research team predicted that applying this material to current TPVs would increase efficiency by 10 percent, and they believe that further optimization could yield even greater efficiency gains. The team developed a solution by combining expertise in chemical engineering and materials science. Lenert's chemical engineering team began by searching for materials that do not mix even when they start to melt. Lenert stated: "The goal is to find materials that will preserve beautiful, clean layers that reflect light the way we want, even when objects get very hot. That's why we looked for materials with quite different crystal structures, because these materials typically tend not to mix." The researchers hypothesized that a combination of rock salt and perovskite, a mineral composed of calcium and titanium oxides, would suit their purposes. Research partners at UM and the University of Virginia ran supercomputer simulations to confirm that this combination was a good choice. John Heron, co-author of the study and Assistant Professor of Materials Science and Engineering at UM, and Matthew Webb, a doctoral student in the same field, then carefully deposited the material using pulsed laser deposition to obtain precise layers with smooth interfaces. To make the material more durable, they used oxides instead of conventional photonic materials; oxides can be layered more precisely and are less likely to degrade under high heat. Heron noted: "In previous work, conventional materials oxidized under high heat and lost their regular layered structure. But when you start with oxides, this degradation has essentially already occurred. This provides greater stability in the final layered structure." After testing confirmed that the material worked as designed, Sean McSherry, first author of the study and a doctoral student in Materials Science and Engineering at UM, used computer modeling to identify hundreds of other potential material combinations. Although commercial application of the material tested in the study may occur years from now, the core discovery opens a new research avenue into various nanophotonic materials that could help future researchers develop a range of new materials for diverse applications.     Source More information: Sean McSherry et al, Nanophotonic control of thermal emission under extreme temperatures in air, Nature Nanotechnology (2022). DOI: 10.1038/s41565-022-01205-1 / Journal information: Nature Nanotechnology / Provided by University of Michigan https://phys.org/news/2022-09-heat-resistant-nanophotonic-material-electricity.html