(left) A single copper-doped tungstic acid nanocrystal; (right) Atomic resolution image of a nanocrystal. Credit: Melbert Jeem
Systematic copper doping increases all-solar utilization in tungsten acid nanocrystals.
Sunlight is an inexhaustible source of energy, and the use of sunlight to generate electricity is one of the cornerstones of renewable energy. More than 40% of the sunlight that hits the Earth is in the infrared, visible and ultraviolet spectrums; however, current solar technology uses primarily visible and ultraviolet rays. The technology for using the entire spectrum of solar radiation – the so-called full solar use – is still in its infancy.
Research results from Hokkaido University
A team of researchers from Hokkaido University, led by Assistant Professor Melbert Jeem and Professor Seiichi Watanabe in the Faculty of Engineering, synthesized copper-doped tungstic acid materials that showed full solar applications. Their findings were recently published in a journal Advanced materials.
“Currently, the near and mid-infrared spectrum of solar radiation, ranging from 800 nm to 2500 nm, is not used for power generation,” explains Jeem. “Tungstenic acid is a candidate for the development of nanomaterials that can potentially exploit this spectrum because it has a crystal structure with defects that absorb these wavelengths.”
Aggregate relative absorption of light by tungstic acid crystals in the range from ultraviolet to infrared light. 1, 5 and 10 are the copper concentrations that lead to the optocriticality of the nanocrystals. Credit: Melbert Jeem, et al. Advanced materials. July 29, 2023
Methodology and results
The researchers used a photofabrication technique they had previously developed, submerged crystallite photosynthesis, to synthesize tungsten acid nanocrystals doped with different concentrations of copper. The structures and light-absorbing properties of these nanocrystals were analyzed; their photothermal, photoassisted water evaporation and photoelectrochemical characteristics were measured.
Copper-doped tungsten oxide nanocrystals absorb light across the spectrum, from ultraviolet to visible to infrared; the amount of infrared light absorbed was greatest at 1% copper doping. 1% and 5% copper doped nanocrystals showed the highest temperature increase (photothermal characteristic); Crystals doped with 1% copper also showed the greatest water evaporation efficiency, approximately 1.0 kg per m2 per hour. Structural analysis of 1% copper-doped nanocrystals showed that copper ions can disrupt the crystal structure of tungsten oxide, leading to the observed characteristics when light is absorbed.
Final remarks
“Our discoveries represent a significant advance in the design of nanocrystallites capable of both synthesizing and harnessing solar energy,” concludes Watanabe. “We have shown that copper doping gives tungsten acid nanocrystals different properties through whole-solar applications. This provides a framework for further research in this area as well as for application development.”
Reference: “Defect Driven Opto-Critical Phases Tuned for All-Solar Utilization” by Melbert Jeem, Ayaka Hayano, Hiroto Miyashita, Mahiro Nishimura, Kohei Fukuroi, Hsueh-I Lin, Lihua Zhang and Seiichi Watanabe, 29 Jul 2023, Advanced materials.
DOI: 10.1002/adma.202305494
This work was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI (20H00295, 21K04823). This work was achieved in part by a supercomputer system at the Information Initiative Center at Hokkaido University. This work was carried out at Hokkaido University with the support of the Advanced Research Infrastructure for Materials and Nanotechnology in Japan (ARIM) of the Ministry of Education, Culture, Sports, Science and Technology (MEXT).
