Recently, researchers at the Center for Translational Atomaterials (CTAM) at Swinburne University of Technology in Melbourne, Australia have developed a new type of graphene film that can absorb more than 90% of sunlight , While eliminating most of the infrared thermal emission loss, this is the first report of this feat. This is a highly efficient solar heating metamaterial that can quickly heat to 83 degrees Celsius (181 degrees Fahrenheit) with minimal heat loss in an open environment. The proposed applications of the film include thermal energy collection and storage, solar thermal power generation and seawater desalination.
Professor Jia Baohua, founding director of CTAM, said that suppressing the heat radiation loss (also known as black body radiation) while absorbing sunlight is very important for efficient solar heat absorbers, but it is extremely difficult to achieve this goal. She explained: "This is because, according to the absorbed heat and the characteristics of the absorber, the emission temperature is different, resulting in a significant difference in its wavelength. But we have developed a three-dimensional structure of graphene metamaterials (structured graphenemeta materials, SGM), which has high absorption and can selectively filter out black body radiation. "
This three-dimensional graphene supermaterial consists of a 30-nm-thick alternating graphene film and a dielectric layer deposited on a trench-like nanostructure. The structure doubles as a copper substrate to enhance absorption. More importantly, the substrate is patterned in a matrix arrangement to allow flexible tunability of wavelength selective absorption.
The graphene film is designed to absorb light with wavelengths between 0.28 and 2.5 microns. The structure of the copper substrate allows it to be used as a selective band-pass filter to suppress the normal emission of black body energy generated inside. The heat retained in this way can further increase the temperature of the metamaterial. Therefore, SGM can be quickly heated to 83 degrees Celsius. If specific applications require different temperatures, new channel nanostructures can be prepared and tuned to match specific blackbody wavelengths. "In our previous work, we showed a 90-nanometer graphene endothermic material," Professor Jia said. Although it can be heated to 160 degrees Celsius, "but its structure is more complex, including four layers: substrate, silver layer, silicon oxide layer and graphene layer. Our new two-layer structure is simpler and does not require vacuum deposition. Manufacturing method Scalable and low cost. "
This new material also significantly reduces the film thickness to one-third and uses less graphene. Its thinness helps to transfer the absorbed heat to other media such as water more efficiently. In addition, the film is hydrophobic, which helps self-cleaning, and the graphene layer effectively protects the copper layer from corrosion, helping to extend the life of the metamaterial.
"Since the structural parameters of the metal substrate are the main factors controlling the overall absorption performance of the SGM, rather than its inherent characteristics, different metals can be used according to the application needs or cost," said Keng-Te Lin, who was recently published in "Nature Communication" (Nature Communications) is the lead author of a paper on metamaterials and a researcher at Swinburne University. He pointed out that aluminum foil can also be used to replace copper without affecting performance.
Keng-Te said: “We used prototype film to produce clean water and achieved an impressive solar-steam efficiency of 96.2%. This is very competitive for clean water power generation using renewable energy Powerful. "
He added that this metamaterial can also be used for energy harvesting and conversion applications, steam power generation, wastewater purification, seawater desalination, and solar thermal power generation.
But a challenge that still exists is to find a manufacturing method to make the substrate scalable.
"We are working with a private company, Innofocus Photonics Technology, which has commercialized a coating machine for laying graphene and dielectric layers," Professor Jia said. "We are satisfied with this. We are now looking for a method suitable for mass production of copper substrates." She added that one possible method is to use a roll-to-roll process.
At the same time, researchers are continuing to fine-tune the design of nanostructures to improve the stability and absorption efficiency of SGM. "As for commercialization," Professor Jia said, "we think this is possible within one to two years."