A photocatalyst developed by researchers at Oregon State University could provide a more efficient route to hydrogen production.
Publishing their research in the journal Angewandte Chemie, the researchers say that their photocatalyst is based on a metal organic framework (MOF). The MOF was used to develop a metal oxide heterojunction – a combination of two materials with complementary properties – to make a catalyst that, when exposed to sunlight, could quickly and efficiently split hydrogen from water.
The heterojunction features MOF-derived ruthenium oxide and titanium oxide doped with sulphur and nitrogen. The researchers tested a number of heterojunctions, which they call RTTA, with different amounts of the oxides and found that the lowest ruthenium oxide content exhibited the fastest rate of hydrogen production.
In just one hour, a gram of RTTA-1 was able to produce more than 10,700 micromoles of hydrogen. The team said the process utilized photons—light particles—at an “impressive” rate of 10%, so that for every 100 photons that struck RTTA-1, 10 contributed to hydrogen production.
The researchers said the photocatalyst could enables the high-speed, high-efficiency production of hydrogen, used in fuel cells for cars as well as in the manufacture of many chemicals including ammonia, in the refining of metals and in making plastics.
"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," said Kyriakous Stylianou, assistant professor in the Department of Chemistry at Oregon State University College of Science.
"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," Stylianou added.
Current catalytic processes for producing hydrogen from water involve electrocatalysis. The sustainability of this route depends on using renewable energy, and to be competitive in the market, the energy must be inexpensive. Producing hydrogen by splitting water through a catalytic process is cleaner than the conventional method of deriving hydrogen from natural gas via a carbon-dioxide-producing process known as methane-steam reforming.
Techniques that can bring down the cost of producing hydrogen by splitting water are therefore welcome.
Presently, methane-steam reforming produces hydrogen at a cost of about $1.50 per kilogram, compared to about $5 a kilogram for green hydrogen.
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."
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