New technique could solve big problem for artificial photosynthesis

Artificial photosynthesis could be a promising future technology for absorbing carbon dioxide while generating oxygen and carbohydrates, but it has been held back by problems including the high price of precious metal catalysts.

Now, a team of researchers at the Korea Institute of Science and Technology (Kist) have developed a new technology to reduce the use of precious metals while improving efficiency and reducing costs.

Artificial photosynthesis recreates the natural process by which water, sunlight, and carbon dioxide (CO₂) are converted into sugar and oxygen. For it to be commercialised, the artificial catalyst – replacing the chlorophyll in plants – must be improved and costs reduced, the researchers said.

Of the effective electrochemical catalysts that have been studied so far, iridium-based catalysts are some of the most stable and high-performing, and are therefore widely known as some of the best oxygen-producing catalysts. Iridium is expensive however, and reserves and production volume are limited. A lot of research has been done on how to reduce the use of iridium and improve catalyst performance.

One of the most effective methods to reduce the use of iridium is to build a nanoscale iridium alloy catalyst using low-price metal, the researchers said. The team, which also involved researchers at Technical University Berlin, developed a core-shell nanocatalyst with an iridium oxide shell, by using iridium-cobalt alloy nanoparticles to reduce the use of iridium.

Using X-Ray absorption spectroscopy, Kist researchers found that the catalyst has high performance due to the short distance between the iridium and oxygen. Other analysis, carried our during catalyst reaction processes, also found high durability. When tested in water, it maintained a high level of performance for hundreds of hours.

The new catalyst reportedly uses 20% less iridium than existing catalysts and shows at least 31% higher performance. When it was applied to the CO₂ conversion system, the energy required was reduced by more than half. This resulted in more than twice the amount of compounds typically produced at the same voltage using other iridium oxide catalysts.

“I expect that this research will contribute greatly to the practicability of the electrochemical CO₂ conversion system, as it can be applied to water electrolysis systems for hydrogen production as well as various other electrolysis systems,” said Kist research leader Dr Oh Hyung-Suk.

The analysis results will inform the development of further catalysts.

The research was published in Applied Catalysis B-Environmental.