How to extract hydrogen?

The most well-known method of producing hydrogen artificially is by electrolyzing water. However, this traditional method is not economical. To produce hydrogen equivalent to one liter of gasoline requires at least 45 kWh of electricity, which is already in short supply. The key to producing clean hydrogen energy lies in finding a non-polluting, less energy-intensive way to extract hydrogen molecules from water, the most abundant source of hydrogen.

Over the past few decades, researchers have searched for unique catalysts that use the sun's energy to extract hydrogen from water. Those catalysts first draw on photon energy from the sun and then use that energy to speed up the rate at which the hydrogen and oxygen atoms in the water molecule are cleaved, which in turn make up the water molecule still slowly, so that eventually there is hydrogen and oxygen bubbling out of the water. Such catalysts are usually prepared from inorganic semiconductor materials, such as silicon, which is used in computer chips. But semiconductor catalysts work very inefficiently and still consume too much energy to enter the realm of production and life.

Now, researchers are trying to find catalysts that can draw on the sun's energy more efficiently, making them more capable of transporting electrons between atoms more powerfully and more quickly. Now, such a catalyst has been found, but instead of a semiconductor-type inorganic substance, it's a super biomolecule, or giant molecular complex. This giant molecular complex is made up of two main parts -- called the molecule's two subunits -- one of which is responsible for absorbing photon energy from sunlight and the other for acquiring free electrons.

With this super-molecular complex at its core, it is possible to form a special device that uses sunlight energy to extract hydrogen atoms from water. This cheap and efficient method can obtain large quantities of hydrogen for driving cars, airplanes, trains, etc., or they can be used to produce clean water and energy by burning them with oxygen in the air, and of course to make fuel cells to produce electricity.

Giant molecules that can be magically combined

Years ago, scientists discovered that biological macromolecules containing the metal element ruthenium are very efficient at absorbing sunlight and can generate enough energy to reduce the oxidized state of the elemental hydrogen to a hydrogen product. The specific chemical process is that this ruthenium-containing macromolecule can produce more than two electrons each time it "eats" a photon, and the energy of these electrons splits the water molecule apart to form separate hydrogen molecules and oxygen atoms.

Recently, scientists have created a giant molecule made of rhodium, ruthenium, chlorine, carbon, nitrogen, hydrogen and six other elements. This giant molecule is shaped like a long magic wand, its two ends are two subunits containing the metal ruthenium, which are used to capture the sun's photon energy and produce free electrons; the center is a subunit containing the metal rhodium, which is used to crack the chemical bond between water molecules with the energy (free electrons) coming from the ruthenium subunit, so as to separate out the hydrogen; and, of course, there is also a very important part, which is that, in between the two parts, there are two to put them subunits that link them for electron transfer. These subunits can accomplish their own functions alone, and when combined with other subunits they can accomplish new and more complex tasks, just like some general-purpose mechanical parts, which can be assembled in different ways to form different machines with different functions that can accomplish different tasks.

It took researchers a full decade to complete the design and preparation of this amazing macromolecule, and to bring it to the practical stage of harvesting electrons using light energy. Now that the principles of the giant molecule's components are well understood, it is no longer difficult to design a system to extract hydrogen atoms from water. Researchers continue to tweak the giant molecule to make it more productive and stable.

The giant molecule system can also add new functionality by installing subunits with new capabilities to get the remaining part -- oxygen -- from the cracked water molecule. In addition to fracking water, scientists believe that using solar energy and the design ideas of this giant molecule, a number of cost-effective and versatile chemical reactions will appear in everyday life, allowing people to make the chemical products they want themselves.

1. Laboratory production/200406/ca488216.htm

2. Industrial production

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