New material turns sunlight, water into green hydrogen with increased efficiency

A new material that converts sunlight and water into clean energy has been developed by scientists.

The photocatalyst created by researchers at Oregon State University enables the high-speed, high-efficiency production of hydrogen.

The collaboration led by Kyriakos Stylianou of the OSU College of Science represented the potential new tool to use against greenhouse gas emissions and climate change. Stylianou’s research focuses on crystalline, porous materials known as metal organic frameworks, usually abbreviated as MOFs.

Researchers tested multiple RTTAs with different amounts of the oxides

In this study, researchers used an MOF to derive a metal oxide heterojunction – a combination of two materials with complementary properties – to make a catalyst that, when exposed to sunlight, quickly and efficiently splits water into hydrogen .

The heterojunction, which they refer to as RTTA, features MOF-derived ruthenium oxide and titanium oxide doped with sulfur and nitrogen. They tested multiple RTTAs with different amounts of the oxides and found a clear winner, according to Oregon State University

“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.

A gram of RTTA-1 was able to produce over 10,700 micromoles of hydrogen

In just one hour, he noted, a gram of RTTA-1 was able to produce over 10,700 micromoles of hydrogen. This process utilized photons—light particles—at an impressive rate of 10%, meaning that for every 100 photons that struck RTTA-1, 10 contributed to hydrogen production, according to the study.

“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.”

Hydrogen production by splitting water via a catalytic process is believed to be cleaner than the traditional method of deriving hydrogen from natural gas via a carbon-dioxide-producing process known as methane-steam reforming.

Currently, hydrogen production from water involves electrocatalysis – running electricity through the catalyst.

The sustainability of electrocatalysis depends on using renewable energy, and to be competitive in the market, the energy has to be inexpensive, according to the study .

“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.”

Currently, methane-steam reforming produces hydrogen at a cost of about $1.50 per kilogram, compared to about $5 a kilogram for green hydrogen.

Photocatalytic hydrogen production offers an alternative pathway to establish a sustainable energy economy. While numerous photoactive materials exhibit potential for generating hydrogen from water, the synergy achieved by combining two different materials with complementary properties in the form of heterojunctions can significantly boost their photocatalytic activity.

The study was published in Angewandte Chemie.