Is hydrogen the solution?
Partial Oxidation Reforming Reaction: CH 4 + 0.5H 2 O → CO + 2H 2 Water-gas Shift Reaction: CO + H 2 O → CO 2 + H 2
Another method in separating hydrogen that shows great promise, is called water splitting, which is a series of chemical reactions involving water to produce hydrogen. An example of a water-splitting cycle is a thermochemical water-splitting cycle process involving cerium (IV) oxide and cerium (III) oxide for the production of hydrogen, which requires temperatures of roughly 500°C and 2000°C 8 to start both chemical reactions. Although this method produces near-zero greenhouse emissions and only uses water and sunlight, solar thermochemical systems such as this one have complications such as: the price of concentrating mirror systems us too costly to be made commercial; the efficiency and durability of reactant material in the cycle needs to be improved and reactor designs need to be modified to handle the high temperatures and heat cycling needed to drive this process.
Reduction: 2Ce(IV) O 2 → Ce(III) 2 O 3 + 0.5O 2 Oxidation: Ce(III) 2 O 3 + H 2 O → 2Ce(IV) O 2 + H 2 Net Reaction: H 2 O → 0.5O 2 + H 2
There exist many different types of water-splitting processes to extract hydrogen from water, but one of the most promising water-splitting methods makes use of silicon nanoparticles, where the reaction does not require light, heat or additional energy to drive the reaction.
Silicon Oxidation: Si +2 H 2 O → SiO 2 + 2H 2
In a study by Mark Swihart, professor of chemical and biological engineering at the University of Buffalo, it has been revealed that ‘ 10-nm of silicon nanoparticles can generate hydrogen 150 times faster than 100-nm silicon nanoparticles, and 1,000 times faster than bulk silicon ’ . 9 Although silicon- water oxidation is relatively slower compared to other water-splitting techniques, silicon demonstrates most promise with the following theoretical benefits: it is abundant, easy to transport and has a high energy density. However, the main disadvantage of silicon oxidation is the inputted energy required to make the silicon nanoparticles exceeds the energy created from the hydrogen produced, which would be a problem in large-scale applications. One of the ways researchers are dealing with this issue is the use of metal hydrides in a mixture of silicon nanoparticles to increase overall hydrogen generation capacity from silicon oxidation. Swihart states: compounds like lithium hydride and sodium hydride react with water to produce the base (LiOH or NaOH) that is needed to catalyse the silicon oxidation. However, they can react too fast with water(explosively) . . . Mixing them with silicon nanoparticles or coating them with silicon nanoparticles may serve to both temper their reactivity and increase the hydrogen
8 https://www.energy.gov/eere/fuelcells/hydrogen-production-thermochemical-water- splitting#:~:text=Thermochemical%20water%20splitting%20processes%20use,and%20produces%20hydrogen %20and%20oxygen. 9 Lisa Zyga: https://phys.org/news/2013-01-nanosilicon-rapidly-electricity.html.
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