New material enables high-speed, high-efficiency production of green hydrogen

Oregon State University researchers have made a groundbreaking discovery in the field of clean energy. Led by Kyriakos Stylianou, the team has developed a photocatalyst that efficiently converts sunlight and water into hydrogen. This hydrogen can be used in fuel cells for cars, as well as in the production of various chemicals, refining of metals, and manufacturing of plastics.

This innovative material has the potential to significantly reduce greenhouse gas emissions and combat climate change. Stylianou’s focus on metal-organic frameworks has led to this remarkable advancement in sustainable energy production.

MOFs consist of metal ions carrying a positive charge and surrounded by organic “linker” molecules, possessing nanosized pores and adjustable structural properties. They can be tailored using various components to define their properties.

In this research, a MOF was employed to produce a metal oxide heterojunction – a fusion of two materials with complementary traits – to create a catalyst that efficiently and rapidly divides water into hydrogen when exposed to sunlight.

The heterojunction, known as RTTA, contains ruthenium oxide and titanium oxide derived from MOFs, both doped with sulfur and nitrogen. Multiple RTTAs with varying amounts of the oxides were tested, leading to the identification of a prominent performer.

“Among various RTTA materials, RTTA-1, with the lowest ruthenium oxide content, exhibited the fastest hydrogen production rate and a high quantum yield,” Stylianou said.

He observed that within a single hour, a gram of RTTA-1 could generate more than 10,700 micromoles of hydrogen. This mechanism made use of photons, or light particles, at an impressive efficiency of 10%, indicating that out of every 100 photons hitting RTTA-1, 10 took part in the production of hydrogen.

Image depicting how the photocatalyst splits water into hydrogen and oxygen. Credit: Oregon State University

“The remarkable activity of RTTA-1 is because of the synergistic effects of the metal oxides’ properties and surface properties from the parent MOF that enhance electron transfer,” Stylianou said. “This study highlights the potential of MOF-derived metal oxide heterojunctions as photocatalysts for practical hydrogen production, contributing to the development of sustainable and efficient energy solutions.”

When it comes to producing hydrogen, using a catalytic process to split water is a much cleaner alternative to the traditional method of deriving hydrogen from natural gas. The current process utilizes electrocatalysis, which involves running electricity through the catalyst. For this method to be truly sustainable, it’s crucial to rely on renewable energy sources. Additionally, to compete in the market, the cost of energy needs to be affordable.

At present, producing hydrogen through methane-steam reforming costs about $1.50 per kilogram, whereas green hydrogen production comes in at around $5 per kilogram.

“Water is an abundant source of hydrogen, and photocatalysis offers a method to harness the Earth’s abundant solar energy for hydrogen production,” Stylianou said. “Ruthenium oxide is not cheap, but the amount used in our photocatalyst is minimal. For industrial applications, if a catalyst shows good stability and reproducibility, the cost of this small amount of ruthenium oxide becomes less important.”

Journal reference:

Emmanuel N. Musa, Ankit K. Yadav, Kyle T. Smith, Min Soo Jung, William F. Stickle, Peter Eschbach, Xiulei Ji, Kyriakos Stylianou. Boosting Photocatalytic Hydrogen Production by MOF-derived Metal Oxide Heterojunctions with a 10.0% Apparent Quantum Yield. Angewandte Chemie, 2024; DOI: 10.1002/anie.202405681

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