Sunday, December 04, 2022

Revolutionary photocatalyst for green hydrogen and ammonia

Very good news! This could be an fundamental breakthrough and game changer! Ammonia as storage for hydrogen. Photocatalytics could become a new powerful chemical method if it is able to scale up. Apparently, there is already a company trying to commercialize this kind of photocatalytics.

"A fundamental breakthrough in chemistry promises to unlock ammonia as a clean fuel, and it could help decarbonize the entire chemical industry in the process. Rice University researchers have created a small, LED-powered device that converts ammonia to hydrogen on the fly. It uses a light-driven catalyst that's as efficient as expensive thermal catalysts that need thousand-degree temperatures to operate, and it's made from cheap, abundant copper and iron. And it's only the beginning of a technology that could radically reduce costs and energy use in industrial chemistry.
Hydrogen is a very promising clean fuel that can be burned, or converted directly into electricity through a fuel cell. It's both expensive and difficult to handle, though, since it's a super-lightweight gas that needs to be compressed to 700 atmospheres, or else cryogenically cooled within sight of absolute zero to reach its liquid state.
Ammonia is famously a better hydrogen carrier than hydrogen gas itself; each of its nitrogen atoms binds three hydrogen atoms, and while it's caustic and extremely hazardous in high concentrations, it's a stable liquid at atmospheric temperatures and pressures, and its widespread use in many industries means people have plenty of experience handling it safely under a wide range of conditions. ...
It comes down to photocatalytics; this team has been working for more than 30 years to develop its "antenna-reactor" plasmonic photocatalysts. These are nanoparticles of a catalyst, dotted with little clumps of an "antenna" material designed to increase the catalyst's ability to absorb light. Properly tuned, these antenna-reactor particles take in energy from ambient light – be it sunlight, or light from low-energy LEDs – and kick out short-lived "hot electrons" with enough energy to start an efficient chemical reaction even at ambient temperatures.
This ammonia-splitting photocatalyst uses iron as its reactor, and copper as its light-collecting antenna – both cheap and abundant metals, as opposed to the typical copper-ruthenium thermal catalysts used today. ..."

"Harnessing iron for photocatalysis
Good catalysts bind substrates at intermediate strengths so that neither reactant binding nor product desorption limits the reaction. Platinum group metals often meet this criterion for many reactions and cannot be replaced with cheaper metals such as iron, which often oxidize under reaction conditions. Yuan et al. demonstrate ammonia decomposition to liberate hydrogen with a copper-iron photocatalyst in which plasmons excited in copper generate hot electrons that react with ammonia bound to iron. Iron is not a good thermal catalyst for this reaction, but photoinduced oxygen desorption makes it competitive with a similar copper–ruthenium photocatalyst and with ruthenium thermal catalysts. This reaction, which is driven with light-emitting diodes, may be competitive with thermal catalysts used in this hydrogen carrier system."

From the abstract:
"Catalysts based on platinum group metals have been a major focus of the chemical industry for decades. We show that plasmonic photocatalysis can transform a thermally unreactive, earth-abundant transition metal into a catalytically active site under illumination. Fe active sites in a Cu-Fe antenna-reactor complex achieve efficiencies very similar to Ru for the photocatalytic decomposition of ammonia under ultrafast pulsed illumination. When illuminated with light-emitting diodes rather than lasers, the photocatalytic efficiencies remain comparable, even when the scale of reaction increases by nearly three orders of magnitude. This result demonstrates the potential for highly efficient, electrically driven production of hydrogen from an ammonia carrier with earth-abundant transition metals."

Revolutionary photocatalyst is huge news for green hydrogen and ammonia

Rice’s ‘antenna-reactor’ catalysts offer best of both worlds (2016) In a find that could transform some of the world’s most energy-intensive manufacturing processes, researchers at Rice University’s Laboratory for Nanophotonics have unveiled a new method for uniting light-capturing photonic nanomaterials and high-efficiency metal catalysts.

Rice lab’s catalyst could be key for hydrogen economy Inexpensive catalyst uses energy from light to turn ammonia into hydrogen fuel


A reaction cell (left) and the photocatalytic platform (right) used on tests of copper-iron plasmonic photocatalysts for hydrogen production from ammonia at Syzygy Plasmonics in Houston. All reaction energy for the catalysis came from LEDs that produced light with a wavelength of 470 nanometers


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