New Si-based photocatalyst enables efficient solar-driven hydrogen production and biomass refinery
The study findings have been published in the July 2023 version of Advanced Materials
Peer-Reviewed PublicationIMAGE: PROFESSOR JUNGKI RYU AND HIS RESEARCHER YURI CHOI FROM THE SCHOOL OF ENERGY AND CHEMICAL ENGINEERING AT UNIST view more
CREDIT: UNIST
A team of researchers, led by Professor Jungki Ryu in the School of Energy and Chemical Engineering at UNIST and Professor Soojin Park from Pohang University of Science and Technology (POSTECH), have achieved a significant breakthrough in the development of a hybrid silicon photocatalyst. This innovative catalyst utilizes solar power to produce hydrogen and high-value compounds efficiently, marking a major step forward in green hydrogen production technology.
The newly developed photocatalyst is both non-toxic and eco-friendly, addressing the limitations associated with previous catalysts that were not sunlight-responsive or posed toxicity concerns. Silicon-based photocatalysts demonstrate excellent light absorption properties, making them highly efficient in utilizing solar energy. Moreover, these non-toxic materials do not emit harmful chemicals during their production process.
Previous research faced challenges in achieving continuous production of hydrogen alongside high-value compounds due to a lack of suitable catalysts. Toxic catalysts used under strong base conditions often led to environmental pollution issues. Additionally, as oxide layers formed on traditional silicon photocatalysts during reactions, it negatively impacted hydrogen production efficiency over time.
To overcome these obstacles, the research team developed a hybrid silicon photocatalyst by uniformly coating nickel-doped graphene quantum dots onto the surface of 2 to 3 nm thick silicon flakes. The modified surface enabled significantly higher hydrogen production efficiency compared to conventional silicon photocatalysts—achieving an impressive rate of 14.2 mmol gcat−1 h−1—a substantial improvement equating to approximately 28 times higher performance.
Furthermore, through oxidation reactions using biomass instead of water—an organic substance derived from biological sources—the hybrid silicon photocatalyst demonstrated its capability for producing high-value compounds alongside hydrogen production. The catalyst also maintained 98% of its original form, ensuring long-term stability.
Professor Ryu stated, “Previous research on hydrogen production has been limited to photocatalysts that absorb ultraviolet rays or involve toxic catalysts. Our non-toxic and cost-effective silicon photocatalyst is a significant advancement as it enables high-efficiency hydrogen production through superior solar absorption.”
Professor Park added, “The surface modification technique utilizing nickel-doped graphene quantum dots can be applied not only to silicon photocatalysts but also to various other types of photocatalysts, opening up new possibilities in energy applications.”
The study has been jointly participated by Yuri Choi (Research Assistant Professor, School of Energy and Chemical Engineering, UNIST) and Sungho Choi (Combined MS/Ph.D. Program of Advanced Materials Science, POSTECH). The findings of this study were published in Advanced Materials on July 27, 2023. This study has been supported by the grants through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT of Korea, as well as the Basic Science Research Program through the NRF funded by the Ministry of Education of Korea.
Journal Reference
Yuri Choi, Sungho Choi, Inhui Lee, Trang Vu Thien Nguyen, et al., “Solar Biomass Reforming and Hydrogen Production with Earth-Abundant Si-Based Photocatalysts,” Advanced Materials, (2023).
SCHEMATIC ILLUSTRATION OF THE SYNTHESIS AND APPLICATION OF SIF/NI-NGQDS FOR EFFICIENT BIOMASS REFORMING AND HYDROGEN PRODUCTION UNDER SOLAR IRRADIATION AND MILD CONDITIONS.
CREDIT
UNIST
JOURNAL
Advanced Materials
ARTICLE TITLE
Solar Biomass Reforming and Hydrogen Production with Earth-Abundant Si-Based Photocatalysts
KMOU researchers propose a novel liquid filter for enhanced solar energy utilization
The innovative emulsion filter improves the energy harvesting capabilities of de-coupled photovoltaic-thermal systems
IMAGE: THE PROPOSED FILTER BASED ON A MIXTURE OF WATER AND FISH OIL FACILITATES THE CONVERSION OF SUNLIGHT INTO ELECTRICITY AND THERMAL ENERGY AT A REMARKABLE 84.4% EFFICIENCY. view more
CREDIT: DR. JAE WON LEE FROM KOREA MARITIME & OCEAN UNIVERSITY (KMOU).
Photovoltaic (PV) modules are devices that convert sunlight into electrical energy. However, they suffer from a low conversion efficiency of around 20% because they can only convert near-infrared wavelengths into electricity, while other wavelengths simply heat up the PV module, reducing its efficiency. To counter this, scientists have developed photovoltaic-thermal (PVT) systems, in which the generated heat is carried away by a heat exchanger containing a coolant fluid (air or liquid). This, in turn, cools down the PV module, increasing its efficiency. Moreover, the captured heat can be utilized in the form of thermal energy.
To further enhance the cooling effect of PV modules and harvest thermal energy, de-coupled PVT systems equipped with liquid filters have been devised. These filters, placed over PV modules, capture specific wavelengths of sunlight that contribute minimally to electricity generation, including ultraviolet (UV), visible light, and near-infrared, facilitating their conversion into thermal energy for various applications. However, water, a popular liquid filter, cannot absorb UV rays.
Now, a team of researchers, led by Assistant Professor Jae Won Lee from Korea Maritime & Ocean University, has introduced an innovative emulsion (mixture) of fish oil and water as a liquid filter. It efficiently absorbs both infrared and UV light, increasing the energy harvesting potential of de-coupled PVT systems. Their work was made available online on April 28, 2023, and published in Volume 287 of the journal Energy Conversion and Management on July 1, 2023.
“Most liquid filters use either water or a mixture of water and solid nanoparticles to absorb the unused wavelengths of solar irradiance. However, water only absorbs the infrared portion of sunlight with wavelengths exceeding 1250 nm. Solid nanoparticles, on the other hand, tend to settle over time, which diminishes their efficiency,” points out Dr. Lee. In contrast, the proposed emulsion remains stable at high temperatures of up to 70 °C. Furthermore, the oil droplets within the emulsion are effective at absorbing UV light with wavelengths below 500 nm.
The presence of the emulsion filter significantly improved the conversion efficiency and lowered the operating temperature compared to systems with heat exchangers alone. The efficiency increased from 70.9% to 84.4%, while the temperature decreased from 46.7 °C to 33.1 °C. The researchers found that, under a standard solar irradiance of 1000 W/m², the de-coupled PVT system with emulsion filter produced electrical and thermal energies amounting to 72.2 Wh and 1176.7 Wh per day, respectively. This proved to be economically beneficial, with a lower cost payback time than both PVT systems and de-coupled PVT systems with water filter.
The proposed system can even be operated under specific requirements and environmental conditions. For example, during summer, the fluid in the liquid filter could be bypassed to maximize electricity production, while in winter, the liquid filter could capture thermal energy for heating applications. Its implementation is also expected to be straightforward. “Emulsion technology is already well established and finds applications in various industries, such as cosmetics and food,” explains Dr. Lee. “Therefore, emulsion filters can be easily applied to existing systems. Additionally, they hold immense potential for new applications, including selective separation of the solar wavelength spectrum.”
Let us hope that this technology will take us one step closer to realizing a carbon-neutral society!
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Reference
DOI: https://doi.org/10.1016/j.enconman.2023.117087
About National Korea Maritime & Ocean University
South Korea’s most prestigious university for maritime studies, transportation science and engineering, the National Korea Maritime & Ocean University is located on an island in Busan. The university was established in 1945 and since then has merged with other universities to currently being the only post-secondary institution that specializes in maritime sciences and engineering. It has four colleges that offer both undergraduate and graduate courses.
Website: http://www.kmou.ac.kr/english/main.do
About the author
Dr. Jae Won Lee is an Assistant Professor in the Division of Mechanical Engineering at Korea Maritime & Ocean University (KMOU). He received his PhD in Thermal Engineering from Korea University in 2017. His group conducts experimental and theoretical, fundamental, and applied research to improve the performance of a wide range of thermal engineering systems. Before coming to KMOU, he was a Research Professor at the Energy and Materials Circulation Laboratory and contributed to building energy reduction research.
JOURNAL
Energy Conversion and Management
METHOD OF RESEARCH
Experimental study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Development of solar radiation spectrum-controlled emulsion filter for a photovoltaic-thermal (PVT) system
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