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Researchers Design Semiconductor Coating

Tuesday, February 23, 2021

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Earlier this month, researchers from the Yale School of Engineering and Applied Science announced the development of a new coating strategy for semiconductors that provides corrosion protection, improves efficiency, and could even lower the cost of solar fuel production.

The research group was led by Shu Hu, assistant professor of chemical and environmental engineering.

Semiconductor Coatings

According to Yale News, solar fuels are produced when semiconductors are illuminated so that specific materials can allow for the splitting of water into hydrogen and oxygen. The energy produced from the process is referred to as photocatalytic water splitting.

However, the university notes that the illumination process is prone to corrosion and can lead to the frequent replacement of materials only after a few hours of use. In the past, researchers have attempted to protect the semiconductors by interfering with the separation of charged particles within the semiconductor—a crucial part in the device’s function.

In applying a new method that both allows for separation and prevents corrosion, Hu’s group developed a protective titanium dioxide coating.

Yale University

Earlier this month, researchers from the Yale School of Engineering and Applied Science announced the development of a new coating strategy for semiconductors that provides corrosion protection, improves efficiency, and could even lower the cost of solar fuel production.

“With this new coating, we not only improve the stability of the photocatalyst from a few hours to more than 150 hours, but it also improves the solar-hydrogen conversion efficiency above 1.7%,” said Tianshuo Zhao, postdoctoral associate and lead author of the study.

Zhao further notes that the 1.7% efficiency was a record high for solar-to-hydrogen conversion and believe that future optimization could lead to more increases.

“If we even get to 10%, then the way that we produce solar fuel will completely change,” Hu said. “You see a pathway where the cost of fuels from sunlight is starting to be comparable to the gasoline price or natural gas price. That’s where the tipping point is.”

Currently, Rito Yanagi GRD ’24, an author of the paper and Yale graduate student reported that solar-hydrogen production is dominated by materials such as oxides and nitrides, as opposed to semi-conductive materials, and are not efficient enough to be practical.

Should solar fuels see generation at a large scale, the process would require using a material that is both efficient and stable, which lead Hu’s group to work on the improvement of the hydrogen half-reaction of the water-splitting reaction. Although, future studies plan to address the oxygen half-reaction.

In terms of cheaper production through the utilization of photocatalysts, Jaehong Kim, senior professor and chair of chemical and environmental engineering at the School of Engineering and Applied Science said, “The cost reduction promised by using these photocatalysts is particularly noteworthy. We now see a trajectory to achieve less than $2 per kilogram [of hydrogen], which is comparable to the gasoline price when you use [hydrogen] to run a fuel cell car.”

Echoing the benefits of the study, Gary Brudvig, professor of molecular biophysics and biochemistry and Director of the Yale Energy Sciences Institute said that the paper was a significant advance for the field of renewable energy production.

Brudvig and Hu’s research groups are currently working together to explore how water-oxidation catalysts could improve the efficiency of the reactions.

A paper on the study has since been published in the Proceedings of the National Academy of Sciences of the United States of America.

TiO2 Studies, Classifications

Earlier this month, engineers from Purdue University reported that they had discovered a way to make concrete more sustainable—by adding small amounts of nanoscale titanium dioxide to the cement.

Mirian Velay-Lizancos, an assistant professor of civil engineering at Purdue, along with her team, published a study in the journal Construction and Building Materials about the mixture, which the researchers say nearly doubles concrete’s absorption of greenhouse gas.

Initially, Velay-Lizancos and two of her doctoral students, Carlos Moro and Vito Francioso, were studying how TiO2 might interact with cement to make concrete stronger and how curing temperature might affect those interactions.

However, during their experiments, they noticed that some of the concrete samples that included nano-titanium dioxide absorbed carbon dioxide from the surrounding air faster than other samples.

The photocatalytic effect in concrete is when the ultraviolet light from the sun interacts with the concrete to help oxidize nitrogen oxide gases into nitrate. Velay-Lizancos’ research indicates that including the small amount of TiO2 could make the concrete double the amount of carbon dioxide that it naturally sequesters over time.

Her research on the sustainability and durability of concrete is ongoing.

TiO2, a white inorganic substance, occurs naturally in several kinds of rock and mineral sands and has been used in many products for decades. It can be manufactured for use as a pigment or as a nanomaterial.

A controversial material, in July of last year, Titanium Dioxide Manufacturers Association and its member companies, as part of a wider group of TiO2 producers, submitted an action to the General Court of the European Union seeking an annulment of its recent classification of TiO2, which finalized TiO2’s classification as a suspected cause of cancer via inhalation, under Category 2.

The RAC originally made this announcement in June 2017 and was followed by a France dossier that recommended cancer labeling for TiO2. At the time, French regulators argued that the substance was likely a Category 1B carcinogen, meaning it is known to cause cancer in humans. The French regulatory body ANSES sought “harmonized classification” for the substance across the entire EU.

In the coatings industry, TiO2 is most notably used as a white pigment, in industrial and protective coatings as well as architectural paints. The ACA has repeatedly expressed concerns that all paint products containing the substance could be labeled as carcinogens under the EU’s classification system.

The REACH Committee of the European Commission met several times to discuss the matter in 2019, without coming to a majority decision, which put the assessment in the hands of the Commission now in the fall.

That September, the Commission said after an expert hearing that it would likely follow through with the classification, despite the objections.

On Oct. 4, the Commission decided to move forward with the classification, and, in February, the decision was solidified.

With the new regulation, titanium dioxide products that are in powder form containing 1% or more of the substance with aerodynamic diameter of 10μm or less are required to carry a cancer warning on the label.

In the TDMA’s July announcement of the action, the group said that it worked to find “a practical and defensible interpretation of the classification to enable meaningful and consistent compliance.”

The classification is slated to take effect September 2021. Meanwhile, a decision from the General Court is expected to take up to three years—beyond the 2021 date.

   

Tagged categories: Asia Pacific; Coating Materials; Coatings Technology; Colleges and Universities; EMEA (Europe, Middle East and Africa); Latin America; North America; Protective Coatings; Research; Research and development; Solar; Solar energy; Titanium dioxide; Z-Continents

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