Extremely efficient photocatalysis converts tap water into hydrogen using only sunlight
Hydrogen as an energy source is an important building block for a sustainable economy. Not only do trucks, trains and cars already run on H2 thanks to fuel cells. It is also used in steel production, in the chemical industry and as a storage medium for renewable energy.
However, there is still room for improvement in its production. While production from natural gas is likely to be ruled out in the future anyway, but is currently unbeatably cheap, electrolysis requires electricity. And as long as this is not available in abundance from renewable sources, hydrogen production is more inefficient than direct use or, for example, the use of battery storage.
This makes the approach taken by a research group at Oregon State University has taken all the more elegant. A frame construction made of metal and organic elements with pores in the nanometer range only requires direct sunlight to extract pure hydrogen from normal water.
Leap in efficiency
The principle is called photocatalysis. A chemical process is triggered solely by the absorption of photons from sunlight. The basic technology is already known. However, previous designs using zinc, indium or titanium were only able to use between 0.3 and 0.7 percent of the incident solar energy to produce hydrogen.
With the optimized structure and the use of ruthenium, a very rare transition metal, the efficiency could be increased to 10.0 percent, i.e. 15 to 30 times better. Although the value is still well below the conversion rates of a commercial solar cell, hydrogen is obtained directly without detours and therefore without any further energy losses.
In the experiments, 10,000 micromoles of hydrogen per hour and gram of water were obtained. While chemists and materials researchers would already be impressed, a conversion may help everyone else.
Almost 20 percent of the H2 contained in water can be dissolved out within an hour. This means that 50 liters (13 US gal) of water are enough to obtain one kilogram of hydrogen in one hour. In the tests with normal power water, the rate was slightly worse. Around 60 liters (16 US gal) would then be necessary.
An area of not quite 100 square meters (1,000 sq. ft.) would be sufficient. After all, one kilogram of hydrogen is enough to drive almost 100 kilometers (60 miles) or heat a house for a few hours.
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