Research, Technology

Sea water could become an endless source of hydrogen

Recently, hydrogen has been considered one of thethe most promising energy sources, as it is able to power not only cars, but also entire industrial sectors. At the same time, its use does not release carbon dioxide into the environment, which has caused global warming. But if hydrogen has so many benefits, why not switch to using it right now? There are several reasons for this. One is that mass production of this gas could exacerbate the problem of fresh water shortages, which are declining every year at a catastrophic rate in many countries. However, scientists proposed another solution - to use sea water for production, and even explained how to overcome the existing technical difficulties.

Scientists propose to produce hydrogen from sea water

Disadvantages of Hydrogen as an Energy Source

Hydrogen is not an ideal sourceenergy, as it has a number of its shortcomings. For example, one kilogram of hydrogen contains as much energy as approximately 4 liters of gasoline. But at normal atmospheric pressure, a kilogram of hydrogen occupies hundreds of times more space. To liquefy hydrogen, it must be cooled to -253 degrees Celsius, or high pressure must be provided.

In addition, it should be taken into account that currentlyThere are no pipelines and distribution systems, which makes it impossible to quickly switch to hydrogen as the main source of energy. However, hydrogen
is currently considered one of the most promising sources of energy for heavy vehicles that cannot be provided by electric batteries.

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These vehicles includetrucks, ships and even planes. Moreover, hydrogen-powered vehicles are already gaining popularity. For example, in China, the production of hydrogen passenger trains has begun. And in the UK they built a hydrogen plane three years ago.

Another likely market for hydrogen is in industries such as the steel industry where high temperature combustion is required.
In addition, over time, the currenthydrogen markets, for example, it is needed for the production of ammonia fertilizers. At present, the world consumption of hydrogen per year is 90 million tons per year.

What is the complexity of hydrogen production

The gradual transition to hydrogen will reducethe amount of carbon dioxide emissions needed to combat global warming. However, for this hydrogen must be produced in an environmentally friendly way. There are currently three main ways to produce hydrogen: green, blue and grey.

Currently, only one of the three ways to produce hydrogen is sustainable, but it is very expensive.

The green way involves the electrolysis of water -a DC power supply is connected to two electrodes that are in the water. As a result, hydrogen is formed at the cathode, and oxygen is formed at the anode. Blue hydrogen is produced by steam reforming of methane from natural gas. Such production emits as much carbon dioxide into the atmosphere as when natural gas is burned. Gray hydrogen is considered the dirtiest source of hydrogen fuel, since all other fossil fuels are used for its production.

It follows that the only optimalThe solution to combat global warming is the production of green hydrogen. However, it costs US$5 per 1 kg, which is twice as expensive as gray hydrogen. Therefore, scientists are currently working on ways to reduce the cost of green hydrogen to at least $ 1 per 1 kg. But high cost is not the only problem.

Electrolyzers are designed to work only withclean water. Increasing green hydrogen production could exacerbate global freshwater shortages. It takes about 10 kg of water to produce 1 kg of hydrogen by electrolysis. Running trucks and key industries on green hydrogen could require roughly 25 billion cubic meters of fresh water per year, according to the International Renewable Energy Agency, the equivalent of water consumption in a country of 62 million people.

The use of hydrogen can solve many problems of hydrogen production

Scientists suggest using salt water to produce hydrogen

Electrodes are used for the electrolysis of hydrogen.precious metals. When using sea water, the electrical discharge that generates oxygen at the anode converts chloride ions in salt water into highly corrosive chlorine gas. This chlorine corrodes electrodes and catalysts within a few hours.

Scientists from RMIT University in Melbourne toTo solve this problem, it is proposed to cover the electrodes with negatively charged compounds such as sulfates and phosphates. They are able to repel negatively charged chlorine ions and thus prevent the formation of chlorine gas. As the researchers report in the journal Small, their electrodes lasted for two months, generating hydrogen from seawater, with no visible signs of damage.

Another team of scientists from the University of Adelaidemade changes to the design of the electrolyzer. Their installation splits water at the anode, and not at the cathode. In doing so, the scientists coated their electrodes with chromium oxide, which attracted bubbles of OH- ions, which repelled chloride ions. According to the study, the apparatus worked with sea water for 100 hours. The team reports this in the journal Nature Energy.

Scientists propose changes to existing electrolysis plants that will allow them to extract hydrogen from salt water

Chemical Engineers from Nanjing TechnologicalThe university proposes not to “reinvent the wheel” at all, but to use the third way to solve the problem, which lies on the surface - to install fine purification membranes in front of the electrolyzers, and thus filter the water before supplying it to the electrodes.

In their experiment, the scientists surrounded the electrodesmembranes that allow only fresh water vapor from the surrounding seawater bath to pass through. As the electrolyzer converts fresh water into hydrogen and oxygen, it creates pressure that pushes more water molecules through the membrane, replenishing the supply of fresh water. That is, a vicious circle is formed, which allows not to spend additional energy on creating high pressure. The researchers report this in the journal Nature. The membrane desalination plant, according to scientists, has worked for 3,200 hours without any signs of damage.

All proposed methods requireadditional studies, as they must be cost-effective and scalable. However, it is already clear that one of the main problems of hydrogen production in large quantities can be solved.

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Finally, we recall that it is quite possible thatin the near future it will not be necessary to produce this gas at all. According to some scientists, there are large reserves of hydrogen in the bowels of the Earth. Moreover, there are already wells from which it is extracted. This is a cheap and environmentally friendly way to get fuel.