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Photo Source: after Pixabay eats bananas, we always take banana peels for granted and throw them into the trash can. But there are always scientists who have to do something unusual, coupled with the fact that they have "high-end" devices, so they decide to take a look at what happens with only a xenon lamp. But before we talk about what these scientists do, we have to know why they have to put the banana peel in the oven and bake it.

When you see an electric car driving on the street, some people may think: it should use lithium batteries. After all, each of us is most familiar with the "lithium battery" (smartphone) we are holding in our hands or in our pockets. Moreover, even in the electric vehicle industry, lithium batteries take the lead, such as the power lithium batteries used by Tesla. But in fact, lithium batteries also have a strong competitor-hydrogen fuel cells.

Although hydrogen fuel cells and lithium batteries are still vying for the top spot in the future electric vehicle industry, they do have one thing in common: "hydrogen" and "lithium" are in the "front row" of the periodic table, first and third, respectively. Interestingly, these two simplest elements (excluding helium) play an important role in the electric vehicle or new energy industry of the future. However, we are more familiar with the reaction of hydrogen fuel cell utilization than lithium battery.

Hydrogen is "power" if you haven't forgotten the "electrolytic water" reaction in high school chemistry textbooks, you can easily understand how hydrogen fuel cells work-the reverse process of electrolyzing water. In general, hydrogen reacts with oxygen to form water, and this part of the chemical energy is converted into electricity.

In addition, hydrogen has a longer history in power applications than lithium. In 1766, Henri Cavendish (Henry Cavendish) first discovered hydrogen in the laboratory. At that time, Cavendish dripped dilute hydrochloric acid on the zinc tablet, creating bubbles. He not only analyzed "bubbles", but also found that such bubbles can produce water after combustion.

Subsequently, the gas made a big difference in man's dream of flying and as a source of lift. In 1783, Jacques Jacques Charles first invented the hydrogen balloon. Hydrogen is very light and less dense than air, so balloons filled with hydrogen can float in the air. On this basis, Henri Giffard built the first airship powered by hydrogen in 1852. Such airships safely transferred 35000 people during World War I without any accident. Unfortunately, in 1937, the German airship Hindenburg was burned in the air by a hydrogen explosion. Since then, the era of airships with hydrogen as lift has come to an end.

Photo: Pixabay, but in recent years, "hydrogen can burn, and only water" has once again attracted the attention of scientists, especially because water is not harmful to the environment. This time, when scientists want to use hydrogen as a power, they have to rely on its combustible properties.

However, there is almost no hydrogen in nature. Most of the hydrogen elements on earth exist in the form of compounds, such as water and organic matter. But the good news is that, in theory, it is not difficult to produce hydrogen. For example, when hydrogen was first discovered, acids reacted with metal iron or zinc to produce hydrogen. However, to use hydrogen as a source of energy, we still need to find ways to produce on a large scale.

Hydrogen production faces challenges for hydrogen fuel cells, hydrogen production is one of the most challenging links. Considering the impact of fossil fuels on the environment, scientists have been looking for clean energy alternatives to fossil fuels. But their idea of clean energy, hydrogen, is not really free from the limitations of fossil fuels: at present, industrial hydrogen production is mainly through methane steam reforming, oil catalytic reforming or coal gasification, but their raw materials are still fossil fuels. When thinking about how to make really clean hydrogen, the first thing that comes to mind is the experiment of "electrolyzing water" in textbooks.

But hydrogen production by electrolysis of water in industrial production is not as simple as drawing a diagram or writing an equation in a book. From the selection of electrodes, electrolytes and catalysts to proton exchange membranes, every step needs to be optimized because the efficiency of hydrogen production by electrolysis of water is still very low.

Photo source: in addition to electrolyzing water, Wikimedia commons has another method that is becoming more and more popular among scientists: biomass pyrolysis. Biomass refers to all kinds of organisms formed by photosynthesis, such as corn, fallen leaves, fruit shells and other organic wastes. Before becoming "waste", these organisms have been absorbing carbon dioxide and are "containers" for natural storage of carbon dioxide. Therefore, if organic waste is directly discarded in the environment, it may lead to the release of a large amount of carbon dioxide. Carbon, hydrogen and oxygen are the main components of organisms, so scientists are thinking that if organic waste is collected, it may be converted into useful substances. Getting hydrogen from it is also part of scientists' plans.

Recently, a team led by Hubert Giraud (Hubert Girault) of the Department of basic Sciences at the Federal Institute of Technology (EPFL) in Lobsang, Switzerland, has developed a new method of decomposing biomass. They used banana peels, which are regarded as garbage, to get hydrogen and a substance called biochar. The results are published in the journal Chemical Science.

What happens with banana peels? In this study, the key to turning banana peels into hydrogen is the xenon lamp. A xenon lamp is an electric light source that glows by means of xenon discharge. Xenon lamps are no stranger to the research team, who have used xenon lamps to prepare nanoparticles. But in this study, they decided to use a high-power xenon flash as a light source to cause photopyrolysis of banana peels that are often thrown away, and then see what happens.

High-power xenon flash lamp can not only provide higher power energy, but also provide short pulses. In other words, it is necessary to produce a powerful flash in order to quickly trigger the photochemical reaction of the banana peel.

Before using light, they also need to dry the wet banana peel at 105 degrees Celsius, and then grind the dried banana peel into powder. The powders are then transferred to a stainless steel reactor filled with inert gas. It is worth noting that the reactor can withstand a certain amount of pressure and has a glass window, which allows the researchers to see the changes taking place in real time. However, the ordinary reactor does not have a glass window, because the combination of several atmospheric pressure and glass still deters many scientists.

A graphical summary of the study. Photo: EPFL under this xenon flash, the transformation of the banana peel ends in 14.5ms. As a result, about 100 litres of hydrogen and 330 grams of biochar are produced per kilogram of banana peel (dry weight). In addition, the researchers believe that the biochar is also valuable, for example, to improve the soil and to produce electrodes, because the cathodes of many batteries are carbon-based materials.

Bhawna Nagar Naggar, co-author of the study, believes that the most important aspect of the study is that they indirectly converted the carbon dioxide stored in banana peels into valuable substances. This is also the significance of biomass research.

The study did not use any catalysts, only xenon lamps. But it is clear that researchers need to do more to increase hydrogen production. The similarity between "biomass" and "electrolytic water" is that progress in any area is likely to lead to new ideas.

Perhaps one day, hydrogen production from banana peels will no longer be a small discovery in the laboratory, but will really be used for hydrogen production on a large scale.

Reference link:

Https://doi.org/10.1039/D1SC06322G

Https://techxplore.com/news/2022-01-hydrogen-banana.html

Https://periodic-table.com/hydrogen/#:~:text=Hydrogen%201%20Discovery%20and%20History%20The%20informal%20discovery,Hydrogen%20Gas%20...%208%20Isotopes%20of%20Hydrogen%20

Https://en.wikipedia.org/wiki/Hydrogen

This article comes from the official account of Wechat: global Science (ID:huanqiukexue), written by Wang Yibo, revision: 27

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