Various technologies that promote the development of new energy have received more and more attention. This is more obvious when the cyclone in Copenhagen is blowing all over the world. MIT chemists have invented a catalyst that uses sunlight to turn water into hydrogen. If the process can be scaled up, it can make solar energy a major source of energy. More meaningfully, this technology may be applicable to seawater, so our energy and water resources issues will have more choices. If this is true, the “senior photos†of leaders of various countries will no longer be taken out by the organizers of the General Assembly and forced to bear more environmental protection responsibilities, especially in developed countries.
"Photosynthesis" turns water into hydrogen fuel
This summer, in an auditorium full of scientists and energy officials from the US government, MIT professor Daniel Nosila demonstrated a video: A reaction that produces oxygen from water is like photosynthesis of green plants. This is an achievement that may have a profound impact on the energy debate. With the help of the catalyst he developed, the reaction is the first and most difficult step in the decomposition of water to produce hydrogen.
Nosila said that effectively producing hydrogen from water can overcome one of the main obstacles that prevent solar energy from becoming an important source of electricity. That is, there is no cost-effective way to store the energy collected by solar panels for use at night or cloudy days.
Solar energy, like wind energy, is clean energy and is almost inexhaustible. But because there is no cheap storage method, solar energy cannot replace fossil fuels on a large scale.
In Nocera ’s proposal, sunlight can split water to produce multifunctional, easily stored hydrogen fuel, which can then be burned in an internal combustion generator or recombined with oxygen in a fuel cell.
In fact, as early as the early 1970s, scientists began to try to imitate photosynthesis to store energy from the sun, but they all have restrictions on demanding reaction conditions and high costs.
Nocera manufactures an inexpensive catalyst that can produce oxygen from water at room temperature and without corrosive chemicals, which is the same as the excellent conditions found in plants. Several other catalysts, including another developed by Nocera, can be used to help complete the process and produce hydrogen. Nosila believes that there are two ways to use its breakthrough. In the first, traditional solar panels capture sunlight and generate electricity; this electricity starts an electrolyzer device that uses his catalyst to split water. The second method will use a system that more closely mimics the structure of leaves. The catalyst will be side by side with a special dye molecule used to absorb sunlight; the energy captured by the dye will drive the water decomposition reaction. Both methods convert solar energy into hydrogen fuel, which can be easily stored and used at night, or whenever needed.
The dark side of solar
Sunlight is the largest potential source of renewable energy in the world, but this potential is also unstable. In China, many solar thermal utilization companies are developing new technologies so that solar water heaters and other products can be applied in more places, such as cold and rainy areas.
It is reported that even in the United States, solar power can only meet about 1% of the total US demand. Most solar panels are connected to the grid. When the sunlight is sufficient, when the solar panels are running at peak, homeowners and businesses can sell excess electricity to public utilities. But at night or in rainy weather, they have to rely on the power grid. Moreover, as the contribution of solar energy grows, its unreliability will become an increasingly serious problem.
Ryan Wiser, a scientist at the Lawrence Berkeley National Laboratory in Berkeley, California, who studies the electricity market, said that if solar energy develops enough to supply 10% of total electricity, utilities will The problem of rainy weather during peak demand needs to be resolved. "Either you need to operate an additional natural gas power plant that can quickly start to make up for the lost electricity, or you need to invest in energy storage. The first option is relatively cheaper because the electricity storage is too expensive."
None of the current storage methods have economies of scale and economy. Nathan Lews, a professor of chemistry at the California Institute of Technology, said that the cheapest method was used as an example: pumping water uphill with electricity, and then letting water pass through a turbine to generate electricity. Pumping one kilogram of water 100 meters high stores approximately 1 kilojoule of energy. In comparison, one kilogram of gasoline stores approximately 45,000 kilojoules of energy. To store enough energy in this way requires a large number of dams and huge reservoirs, which are evacuated and filled every day. Moreover, in places where the sun is particularly abundant, there is not necessarily large-scale water available.
Another common way is battery storage, which has the disadvantage of high cost. This approach will add $ 10,000 to the cost of a typical home solar system, and the energy stored is limited. Lewis said that the best batteries store 300 watt-hours of energy per kilogram and 13,000 watt-hours of gasoline per kilogram. Chemical fuel is the only way to obtain intensive energy storage. "Among those fuels, hydrogen not only has the potential to be cleaner than gasoline, but by weight, it can store more energy (about three times)."
Artificially produce "photosynthesis"
From small to large, it can be seen everywhere that plants can easily use sunlight to turn enough materials into energy-rich molecules. This fact mocked chemists looking for new energy technologies for decades. Nocera's research direction is to imitate photosynthesis to make solar energy use more economical. The field of artificial photosynthesis started very quickly. There was research in this area in the early 1970s, but there was no breakthrough that could be generalized to the application level. For decades, scientists have studied the structure and energy absorption of sunlight by plants Materials, but did not find a clear "road map".
Until 2004, researchers at Imperial College London determined the structure of a group of proteins and metals, which played an important role in plants releasing oxygen from water. Nosila said, "After seeing this, we can start designing the system."
He said that artificial photosynthesis can provide a viable method of storing energy produced by solar energy, so that people's houses do not have to rely on the grid. In this plan, electricity from solar panels drives the electrolysis cell, which splits the water into hydrogen and oxygen. Hydrogen is stored, and at night or on cloudy days, it is installed in fuel cells to generate electricity for electric lights, appliances, and even electric cars. In sunny weather, some solar energy is used directly, bypassing the step of making hydrogen.
Nosila's discovery has aroused great concern, but there are also many voices of doubt. Many chemists feel that it is too optimistic. Thomas Meyer, who was a Nosila mentor, said that although Nosila ’s catalyst “may prove to be technically important, it is a research finding that it cannot be guaranteed to scale up or even It becomes practical. "
Another suspicion is that Nosila's laboratory can't split water as fast as a commercial electrolyzer. The faster the system, the smaller the commercial units that produce a certain amount of hydrogen and oxygen, and usually the smaller the system, the cheaper it is. Some scientists also questioned the whole principle of turning sunlight into electricity, then into chemical fuel, and then back to electricity. They suggest that although batteries store far less energy than chemical fuels, they are much more efficient because every step is wasted energy in the process of using electricity to make fuel and then use the fuel to generate electricity. "It is better to focus on improving battery technology or other similar forms of energy storage rather than developing water electrolysis and fuel cells."
Seawater can also become energy
However, Michael G ratzel, a professor of chemistry and chemical engineering at the Swiss Federal Institute of Technology in Lausanne, may turn Nocera ’s discovery into a practical one. In 1991, Krazer invented a new type of solar cell. It uses a ruthenium containing dye, like chlorophyll in plants, absorbs sunlight and releases electrons. However, in Krazer's solar cells, electrons do not cause water decomposition reactions. Instead, they are collected by a titanium dioxide film and are instructed by an external circuit to generate electricity. Krazer's vision was to integrate his solar cell and Nocera's catalyst into a device to capture energy from the sun and use it to split water.
The principle is that Krazer's dye will replace the electrode formed around the catalyst in the Nocera system. When exposed to sunlight, the dye itself can generate the voltage needed to aggregate the catalyst. "The dye is like a conductive molecular wire," Krazer said, and then the catalyst gathers where it is needed. Once the catalyst is formed, the sunlight absorbed by the dye drives the reaction that splits the water. Krazer said that the equipment is more efficient and cheaper than using solar panels and electrolyzers separately.
Nocera is studying another possibility, whether its catalyst can be used to decompose seawater. Nocera's research found that in the initial test, the salt performed well in the presence of the salt. Others are testing to see if it can handle other compounds in seawater. If successful, Nosila ’s system will not only be able to deal with the energy crisis, it will also help solve the world ’s freshwater shortage.
In any case, artificial green leaves are a good vision. Paul A livisatos, a professor of chemistry and materials science at the University of California, Berkeley, said that he is also leading a project to organize the Lawrence Berkeley National Laboratory, Use chemical methods to simulate photosynthesis.
"Artificial leaves" make hydrogen fuel in a glass
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