By using solar energy to reversibly attach and detach hydrogen atoms on a 6-carbon ring called benzene, scientists have developed a simple and efficient method to store, transport, and release hydrogen potentially on a large scale. The hydrogen storage problem is currently one of the biggest challenges facing the development of hydrogen as a widespread energy carrier, and the researchers hope that the new strategy may lead to a safe and inexpensive solution to this problem.
As the researchers explain, hydrogen has a very high mass energy density but a very low volumetric energy density. The high mass energy density, which is at least three times higher than that of other chemical fuels, is what makes hydrogen such an attractive energy carrier. However, its low volumetric energy density under ambient conditions makes it difficult to store large amounts of hydrogen in small spaces. To overcome this problem, hydrogen is often stored at high pressures or low temperatures, but these storage methods present their own challenges.
The hydrogen storage system demonstrated in the new paper works under ambient conditions and stores the hydrogen in abundant, lightweight, and inexpensive molecules called hydrocarbons. The researchers demonstrated that six hydrogen atoms can be added to benzene (C6H6) in a "hydrogenation" process that forms cyclohexane (C6H12), which serves as the hydrogen carrier. In the reverse process, cyclohexane is "dehydrogenated" as the six carbons are removed and available for use in energy storage devices and other applications.
This method of storing hydrogen atoms in hydrocarbons is not new, but because the dehydrogenation process requires a large amount of energy to proceed, current versions always require high temperatures to release the hydrogen.
Since performing the reaction at high temperatures is not suitable for practical applications, here the researchers demonstrated that solar energy can be used to drive the dehydrogenation reaction at ambient temperatures. This process involves using platinum-based nanoparticles as photocatalysts. After absorbing incoming photons, the platinum nanoparticles temporarily donate their photoexcited electrons to the cyclohexane molecules, breaking the carbon-hydrogen bonds and releasing the hydrogen atoms without the need for elevated temperatures.
As the researchers explain, hydrogen has a very high mass energy density but a very low volumetric energy density. The high mass energy density, which is at least three times higher than that of other chemical fuels, is what makes hydrogen such an attractive energy carrier. However, its low volumetric energy density under ambient conditions makes it difficult to store large amounts of hydrogen in small spaces. To overcome this problem, hydrogen is often stored at high pressures or low temperatures, but these storage methods present their own challenges.
The hydrogen storage system demonstrated in the new paper works under ambient conditions and stores the hydrogen in abundant, lightweight, and inexpensive molecules called hydrocarbons. The researchers demonstrated that six hydrogen atoms can be added to benzene (C6H6) in a "hydrogenation" process that forms cyclohexane (C6H12), which serves as the hydrogen carrier. In the reverse process, cyclohexane is "dehydrogenated" as the six carbons are removed and available for use in energy storage devices and other applications.
This method of storing hydrogen atoms in hydrocarbons is not new, but because the dehydrogenation process requires a large amount of energy to proceed, current versions always require high temperatures to release the hydrogen.
Since performing the reaction at high temperatures is not suitable for practical applications, here the researchers demonstrated that solar energy can be used to drive the dehydrogenation reaction at ambient temperatures. This process involves using platinum-based nanoparticles as photocatalysts. After absorbing incoming photons, the platinum nanoparticles temporarily donate their photoexcited electrons to the cyclohexane molecules, breaking the carbon-hydrogen bonds and releasing the hydrogen atoms without the need for elevated temperatures.
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