CHEMICAL SCIENCE

Hydrogen by air: the solution for the future of green hydrogen energy


On September 6, 2022, Kevin Gang Li from the University of Melbourne in Australia, Hu Guoping from the Ganjiang Institute of Innovation of the Chinese Academy of Sciences, Fan Xiaolei of the University of Manchester in the United Kingdom, and Guo Jining, a doctoral student they co-supervised, published a new study titled “Hydrogen production from the air” in the journal Nature Communications. The research team has developed a method to produce hydrogen from the air, decoupling hydrogen production from freshwater resources, providing a new direction for future carbon neutrality.

Background

Hydrogen, especially hydrogen (green hydrogen) from water using renewable energy sources, is widely considered to be the ultimate clean energy source. The burning of fossil fuels causes large amounts of carbon dioxide emissions, which can lead to the greenhouse effect and global warming. Hydrogen combustion does not release carbon dioxide or any other greenhouse gas. Green hydrogen goes a step further, using only water and renewable clean energy in the production of hydrogen. Green hydrogen is usually produced by electrolyzing water, that is, using electrical energy to break down water into hydrogen and oxygen. Electricity, on the other hand, can come from renewable sources such as solar, wind, geothermal or tidal. Since hydrogen can be used as a “storage” medium for renewable energy, it can be further converted back energy through fuel cells and other means to ensure the continuous supply of clean energy. For a low-carbon economy, green hydrogen is essential.

Do you want fresh water or hydrogen?

Electrolysis of water to hydrogen relies heavily on clean water resources. However, according to UNWR, 2.3 billion people worldwide live in water-stressed countries and regions, of which 733 million live in areas of high or severe water scarcity (UNW, 2021). At present, power plants, agriculture and other industries need a large amount of water resources to meet their production needs, and form a certain competitive relationship with the drinking water resources on which human beings depend. Although the water treatment device can alleviate the above problems to a certain extent, the additional purification process undoubtedly increases the complexity and cost of electrolyzing water to hydrogen, which poses great challenges to its feasibility. In addition, there is a high geographical mismatch between renewable energy and freshwater supplies.

Specifically, the ideal location for producing green hydrogen is in solar and wind-rich regions, including Central Asia, West Asia, much of India, North Africa, western North America and much of Australia, which are often also areas of extreme water scarcity, leading to a competitive relationship between drinking water and industrial water. Therefore, the use of surface or groundwater as a raw material for hydrogen production will further exacerbate the shortage of water resources, which in turn will trigger a water crisis. In addition, the green hydrogen economy will also exacerbate the risk of global freshwater shortages.

Figure 1: Contradiction between freshwater supply and solar (a) and wind (b).

Turns the air into hydrogen

Researchers from the University of Melbourne and the University of Manchester offered a way to overcome the above problems, designing and validating a device that could produce hydrogen without consuming fresh water. The technology, recently published in Nature Communications and known as the Air Electrolyzer (DAE), works by absorbing water directly from the air and then electrolyzing the water to produce hydrogen from renewable electrical energy.

Lead researcher Dr Kevin Gang Li of the University of Melbourne, a senior lecturer in chemical engineering, said the idea arose when considering producing hydrogen in areas with difficult water supply. “It has been argued that an area without groundwater is not suitable for hydrogen production. But in fact, there is a lot of water in the air. Even Alice Springs, located in the central Australian desert, has a relative humidity of about 20%. This is more than enough for us to produce hydrogen from renewable sources. ”

The DAE that Dr. Li studied with researchers such as PhD student Guo Jining, like other electrolyzers, consists of metal plate electrodes that provide energy for the decomposition process of water (from renewable sources). But at its core lies a porous medium between metal plates filled with an absorbent ionic solution — a chemical that spontaneously absorbs moisture from the air. “This type of substance is simple, and it likes to trap water molecules from the air. When water molecules are captured from the air, they become raw materials for electrolysis. This is the core of this invention. If you expose this device to air, it can produce hydrogen. That’s why we call it a direct air electrolyzer. You use air as feed for your device, rather than liquid water as current electrolyzers do. “This is the first report we currently know of producing high-purity hydrogen directly from the air.

Figure 2: Air Hydrogen Roadmap

Remove barriers to green hydrogen production

By realizing the direct production of hydrogen from the air, this technology decouples hydrogen production from freshwater resources and opens up new channels for green hydrogen manufacturing, which will bring a series of economic and environmental benefits. For industries with high carbon emissions, such as metallurgy, DAE can achieve zero carbonization by combining this technology with solar energy or other renewable energy sources to provide it with a stable renewable energy supply. By harnessing renewable energy, DAE technology can also be used independently in remote areas where there is no stable power supply, providing clean hydrogen energy. In addition, the technology can be integrated with existing systems to facilitate green hydrogen production and delivery. For example, in the existing natural gas pipeline network, the green hydrogen prepared by DAE can be mixed with natural gas for transmission, solving the problem of excess electricity on solar farms and exporting green hydrogen to the desired area.

Dr Lee said: “If we are to develop a hydrogen-based economy, providing local methods of hydrogen production for remote communities or those arid or semi-arid areas is a top priority. I think this technology is of great significance to solve this problem. A large part of the planet does not actually have enough fresh water supply, and it is crucial to ensure that there is enough green hydrogen supply in these areas. Residents in remote areas can use renewable electricity during the day, while DAEs can convert excess electricity into hydrogen and store it, and then convert hydrogen into electricity again when there is a lack of electricity, thus achieving a continuous power supply and eliminating dependence on fossil fuels. “

Figure 3: Schematic of DAE technology

A new direction for hydrogen production driven by sustainable energy

The purpose of this DAE technology is not to replace the traditional hydrogen production process, but to complement it perfectly. When freshwater is abundant and inexpensive, traditional hydrogen production processes still have advantages. After two and a half years of research and development and laboratory demonstrations, the team members believe that the device can be easily scaled up and combined with renewable energy sources, and can continuously produce high-purity hydrogen with relative humidity as low as 4%, which is technically and structurally feasible, and has low maintenance costs. Based on this DAE technology, green hydrogen can be produced anywhere on the planet and has great potential application value.

The technology has completed the patent layout and laboratory stage demonstration, the next step is to scale up hydrogen production, as well as testing under different geographical and climatic conditions to understand its ability to adapt to different conditions and work performance under different conditions. “We’re scaling up the DAE — from five-story stacks to 1 square meter, then 10 square meters, and so on. Although we can simulate a dry climate in the laboratory, it is not really a desert after all. So we wanted to take it to Alice Springs and spend a few weeks seeing how it went. “After that, the focus of making it a commercial product in the final phase will be energy consolidation, storage and supply.

The upgrade of DAE technology has attracted investment from the world’s top venture capital. How close this technology is to reality remains to be seen. But the technology offers a low-cost, simple solution to produce green hydrogen, which in turn promises to overcome the poor economics of green hydrogen production without consuming limited freshwater resources.

Figure 4: DaE prototype physical drawing

(Source: Science Network Tess Ritchie Guo Jining)

Related paper information:https://doi.org/10.1038/s41467-022-32652-y

Original link:https://research.unimelb.edu.au/research-at-melbourne/climate-hub/our-climate-capability/a-new-device-creates-hydrogen-from-air



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