A light-activated catalyst made using copper and iron has been used to produce gram-scale quantities of hydrogen gas from ammonia, according to a recently published paper in peer-reviewed journal Science.

The researchers say the discovery could pave the way for the replacement of precious metals in catalysts used to reconvert ammonia back to hydrogen. 

Ammonia has been suggested as a way to safely store and transport hydrogen using existing infrastructure. However, the process of converting hydrogen to ammonia and cracking it back again for end-use can result in energy loss of up to 22pc. Cracking to hydrogen is also an energy-intensive process, requiring high temperatures to speed up reactions and therefore necessitating fossil fuel combustion.

Thermocatalysts, which speed up the conversion of ammonia to hydrogen under intense heating, also present a significant cost for the chemical industry, as the most effective thermocatalysts are made using rare metals such as palladium, rhodium and ruthenium.

“This opens the door to entirely replace precious metals in plasmonic photocatalysis” Halas, Rice

The team behind the paper, which included researchers from private universities Rice and Princeton and startup Syzygy Plasmonics, has engineered a light-activated nanomaterial, or plasmonic photocatalyst, which splits ammonia into hydrogen and nitrogen. The catalyst was designed with copper and iron and its performance was compared with catalysts made with copper and ruthenium.

“This is the first report in the scientific literature to show that photocatalysis with LEDs can produce gram-scale quantities of hydrogen gas from ammonia,” says study co-author Naomi Halas, a professor at Rice University and co-founder of Syzygy Plasmonics. “This opens the door to entirely replace precious metals in plasmonic photocatalysis.”

Transition metals such as iron are typically poor thermocatalysts, but the team’s work shows they can be efficient plasmonic photocatalysts if exposed to light.

The study also “demonstrates that photocatalysis can be efficiently performed with inexpensive LED photon sources”, says Halas.

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Author: Polly Martin