#photocatalysts

Photocatalysis using particles in water is a promising technology for generating fuels from sunlight. One major obstacle to producing these solar fuels cheaply and abundantly, though, is that it requires semiconductors that are efficient but prone to corrosion.

In a breakthrough that overcomes this challenge, the lab of Shu Hu, assistant professor of Chemical & Environmental Engineering, has found a solution with a first-of-its-kind coating. The results are published in the Proceedings of the National Academy of Sciences.

Water-splitting systems—which break water down to hydrogen and oxygen—need semiconductor materials with narrow bandgaps (a property allowing for absorbing more sunlight), which efficiently converts solar energy to chemical energy. While these materials can easily capture sunlight, they all corrode under illumination via self-reduction or self-oxidation. It’s a challenge that researchers have spent more than a half-century trying to solve. Strategies to protect these materials tend to limit their abilities to separate the charges of negative electrons and positive holes, a process that is essential to photocatalysis but harder to achieve than it is for other systems, such as solar cells. Typically, layers designed to guard these systems protect only one of the system’s two electrodes, namely the cathode or anode, limiting it to allow for the transport of either electron or hole—but not both.

Hydrogen gas, an important synthetic feedstock, is poised to play a key role in renewable energy technology; however, its credentials are undermined because most is currently sourced from fossil fuels, such as natural gas. A KAUST team has now found a more sustainable route to hydrogen fuel production using chaotic, light-trapping materials that mimic natural photosynthetic water splitting.

The complex enzymes inside plants are impractical to manufacture, so researchers have developed photocatalysts that employ high-energy, hot electrons to cleave water molecules into hydrogen and oxygen gas. Recently, nanostructured metals that convert solar electrons into intense, wave-like plasmon resonances have attracted interest for hydrogen production. The high-speed metal plasmons help transfer carriers to catalytic sites before they relax and reduce catalytic efficiency.

Getting metal nanoparticles to respond to the entire broadband spectrum of visible light is challenging. “Plasmonic systems have specific geometries that trap light only at characteristic frequencies,” explains Andrea Fratalocchi, who led the research. “Some approaches try to combine multiple nanostructures to soak up more colors, but these absorptions take place at different spatial locations so the sun’s energy is not harvested very efficiently.”

A research team led by Professor Su-Il In from Department of Energy Science and Engineering had succeeded in developing photo catalysts that can convert carbon dioxide into usable energy such as methane or ethane.

As carbon dioxide emissions increase, the Earth’s temperature rises and interest in reducing carbon dioxide, the main culprit of global warming, has been increasing. In addition, the shift to reusable fuel for existing resources due to energy depletion is also drawing attention. In order to solve trans-national environmental problems, research on photocatalysts, which are essential in converting carbon dioxide and water into hydrocarbon fuels, is gaining attention.

Although many semiconductor materials with large band gaps are often used in photocatalyst studies, they are limited in absorbing solar energy in various areas. Thus, photocatalyst studies focusing on improving the photocatalyst structure and surface to increase solar energy absorption areas or utilizing two-dimensional materials with excellent electron transmission are under way.

Professor In’s research team developed a high-efficiency photocatalyst that can convert carbon dioxide into methane (CH₄) or ethane (C₂H₆) by placing graphene on reduced titanium dioxide in a stable and efficient way.

Study: Pointed tips on aluminum ‘octopods’ increase catalytic reactivity.

Points matter when designing nanoparticles that drive important chemical reactions using the power of light.

Researchers at Rice University’s Laboratory for Nanophotonics (LANP) have long known that a nanoparticle’s shape affects how it interacts with light, and their latest study shows how shape affects a particle’s ability to use light to catalyze important chemical reactions.

In a comparative study, LANP graduate students Lin Yuan and Minhan Lou and their colleagues studied aluminum nanoparticles with identical optical properties but different shapes. The most rounded had 14 sides and 24 blunt points. Another was cube-shaped, with six sides and eight 90-degree corners. The third, which the team dubbed “octopod,” also had six sides, but each of its eight corners ended in a pointed tip.