For some time thegreen hydrogen, or that produced from renewable sources, considered not only a valid alternative to fossil fuels, but also a key element of change in energy production, at the center of energy strategies of numerous countries and the European Commission itself.
Currently the most consolidated process for producing green hydrogen is the electrolysis of water fed with electricity produced by wind and photovoltaics. The National Agency for New Technologies, Energy and Sustainable Economic Development (Enea), on the other hand, has patented a new method of producing green hydrogen and oxygen from water using solar energy.
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The reactor that splits the water molecule and produces hydrogen
The starting idea is to break the water molecule through thermal decomposition – he explains Silvano Tosti, head of the nuclear technologies laboratory of the Enea– This is a very difficult thing, with the use of traditional processes to achieve it you need to reach 3-4 thousand degrees. To overcome this problem we have created a membrane reactor consisting of a reaction chamber where two types of membranes are present at the same time. A tantalum membrane to separate hydrogen and a ceramic material to separate oxygen. In this way it is possible to significantly lower the temperatures of the process of splitting the water molecule. Already around 1,900 degrees it is possible to obtain quite significant reaction yields.
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The technological limits and the thrust of research
This process goes well with all solar systems where there are mirrors that capture the heat of the solar energy. Since very high temperatures are required, the reactor could be applied in concentrating solar plants, continues Tosti. At the moment, however, there is a technological gap, because concentrating solar systems that reach the highest temperatures do not exceed 1,500 degrees, still too few.
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We believe, however, that this gap can be overcome with the advancement of research on materials capable of operating at very high temperatures – underlines the researcher – a field of activity in which Enea is also involved, in particular studies on nuclear fusion. which concern the development of materials for high heat flows, and research on high temperature solar systems.
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The patented system
The future prospect is to use solar energy directly to produce hydrogen and oxygen, without going through intermediate systems such as electrolysers or the coupling of solar photovoltaics with alkaline electrolysers. With photovoltaics, about 20% of solar energy can be transformed into electricity, while electrolyzers convert electricity into hydrogen with an efficiency of around 50% – says Tosti -. This means that, putting the two together, about 10% of solar energy can be transformed into hydrogen. With the system that we have patented, since we are going to make a direct conversion, it is possible to achieve an efficiency of 20%. Another advantage is to have lower investment costs both in stationary applications, such as civil and industrial electrical users, and in mobile applications such as electric vehicles.
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Oxygen between industry and energy
In addition to hydrogen, the method, born in the laboratories of Enea research centers in Frascati and Casaccia with the involvement of researchers from the departments of Fusion and Technologies for nuclear safety and of Energy Technologies and Renewable Sources, it also allows to separate a large amount of oxygen. This represents a great economic value both for industry and for possible energy applications. In fact, oxygen can be used for combustion and is much more advantageous than air, because emissions are reduced and CO2 is easier to separate. Furthermore, hydrogen and oxygen can be used in fine chemicals, pharmaceuticals, and the electronics industry.
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International research is exploring new ways to make the production of clean hydrogen increasingly efficient and competitive. In particular, Enea is carrying out numerous lines of activity that aim at the realization and validation, on a laboratory scale, of four processes that are potentially more efficient than alkaline and Pem electrolysis or capable of being powered by different energy sources. The technologies considered are AEM electrolysis, electrolysis of steam in molten carbonates, thermochemical cycles of water splitting and reforming of biogas at low temperatures.
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