Green hydrogen: energy from dry air

Status: 06.09.2022.000| Reading time: 3 minutes

DrHydrogen generation through electrochemical separation of water is an essential technology for the production of climate-neutral energy carriers. If the electrical energy needed for this comes from solar or wind energy, the green hydrogen produced in this way is a chemical energy source that does not release carbon dioxide when burned. Hydrogen can be stored, transported, and used in many ways – from the tiny fuel cell in smartphones to the climate-neutral fuel for aircraft.

So many scientists are working to improve the electrolyzer, systems in which water is broken down into hydrogen and oxygen on a large scale. It should be as efficient as possible, last as long as possible without maintenance and be inexpensive to produce.

However, there is one aspect that has not been focused so far: can the electrolyzer also run when fresh water is scarce? After all, more than a third of the Earth’s surface is desert or at least semi-arid. However, many people live in these areas – 20 percent of the world’s population.

Salt water is not suitable for electrolysis

In any case, using salt water where there is at least an outlet to the sea is not a solution for electrolyzers. Then it produces chlorine gas when the seawater decomposes is not only a problem for catalysts, it is also a toxic waste product.

First of all, seawater desalination plants will be needed in order to be able to operate an electrolyzer and produce hydrogen with fresh water obtained in this way. This greatly increases energy requirements and makes hydrogen production completely inefficient.

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But now scientists have University of Melbourne Presented a new technology in the journal Nature Communications that makes it possible to produce hydrogen without, so to speak, water. With so-called direct air electrolysis (DAE), only ambient air is used, which still contains little water even in dry areas.

Sulfuric acid as a water scavenger

Researcher Gang Kevin Lee reports that the thing can still work with dry air. The DAE system still operates without problems at only four percent humidity and saves hydrogen.

Electricity for the experiment was provided by solar cells. But of course it works well if the electric power comes from wind turbines. The five interconnected electrolyte units operated continuously for a full twelve days before the researchers finished the experiment. The daily volume of hydrogen production per square meter of the cathode was 745 liters. Scientists estimated the efficiency at 95 percent.

The heart of the air electrolysis cell is a sponge moistened with sulfuric acid, which not only does the job of the electrolyte. Sulfuric acid (H₂So₄) is an extremely hydrophilic substance that eagerly absorbs water molecules that are still present in the dry ambient air and thus feeds them to the system to break them down into hydrogen and oxygen. The test was performed at 25°C.

Technology is scalable

This basically proves that hydrogen can be easily obtained from the air, even in the driest regions of the world, using only wind or solar energy. According to researchers, the air in the entire Earth’s atmosphere contains about 13 trillion tons of water.

In the end, the question remains whether economically feasible quantities can be obtained using this electrolysis technique. The researchers stress that their technology is scalable, that is, you just need to connect enough units in parallel to get the required amount of hydrogen.