Researchers at the Massachusetts Institute of Technology's Department of Mechanical Engineering have recently developed a new type of membraneless hydrogen bromide battery, which has the same performance as a conventional membrane-equipped battery, but has greatly reduced the cost, and achieved a low-cost high-capacity electrochemical energy storage technology. New progress is expected to profoundly change the current energy landscape. The cost of today's energy storage technology is too high In today's energy market, there are abundant sources of electric energy, including traditional coal, electricity, electricity, and hydropower, as well as intermittent energy sources such as wind power and solar energy, which are being vigorously developed. The needs of users are not constant, there are peaks and valleys of electricity use. Therefore, an important technical link that cannot be ignored is energy storage technology. The so-called storage capacity means that when the power supply is sufficient, it can be stored, and when it is needed, it can be provided. Strong energy storage capabilities not only ensure that backbone networks and distributed power grids provide efficient and stable power supply, but also provide strong guarantees for the large-scale use of intermittent energy such as solar energy and wind power, especially in developing countries and the mobile industry. Strong demand. Electrochemical energy storage systems, such as batteries and fuel cells, have broad application prospects in energy storage technology. They can charge and discharge quickly and efficiently. Especially when using solar energy or wind energy, it can store electricity when the sun shines, or store energy when the wind is strong, and then supply electricity in a few minutes when it is cloudy or in a light wind. In addition, they are also very flexible and convenient, where they can be placed wherever they are needed. However, the biggest problem faced by electrochemical energy storage systems is the cost. Even the best electrochemical energy storage devices need to have large capacity, so the cost will be unacceptable. For example, a truck-sized lithium battery can provide a lot of energy, but the cost is too high. Therefore, the development of renewable energy is not so much a technical issue as it is the lack of cost-effective energy storage technology. Isolation Membrane: The Biggest Problem of Hydrogen Bromine Energy Storage System During the research and exploration of large-scale electrochemical energy storage devices, people began to focus on the hydrogen bromide energy storage system. These two reactants have some unique qualities that are of interest. Compared with lithium, bromine is cheap, easy to obtain, and abundant in reserves. Its atomic number is 35, which is a kind of halogen. There are 7 electrons on the outermost layer, and it is easy to form an 8-electron stable structure. Therefore, it is an active non-metallic element, and hydrogen can provide exactly one electron. Therefore, a chemical reaction between hydrogen and bromine occurs extremely rapidly, and the rate of the reaction is faster than that of the oxyhydrogen reaction, and the current is also relatively large. However, the current high-capacity electrochemical energy storage devices mostly rely on the reaction of the hydroxides. However, when hydrogen and bromine react spontaneously, their energy is mostly wasted in the form of heat because of the rapid reaction. To solve this problem, designers of electrochemical energy storage systems usually use expensive insulating membranes to separate them. Another problem with membrane hydrobromide energy storage systems is that over time, when the hydrobromic acid is generated inside the electrochemical energy storage device, it can damage the membrane. Therefore, the development of hydrogen bromide flow batteries has been slow in the past 30 years. In fact, the answer is very clear, if you want to effectively develop the use of hydrogen bromide electrochemical energy storage system, the most important thing is to find ways to get rid of the isolation membrane. There are many people who have such ideas. Not only are current scientists thinking about it, but some people have thought of such methods in the past. In the past 10 years, many scientists have developed a membraneless hydrogen bromide electrochemical energy storage system. These systems use mainly laminar flow technology to separate the reactants. Under the right conditions, the two liquid streams flow in parallel with little or no mixing between the two. However, the electric power of such a membraneless electrochemical energy storage system never exceeds that of a membrane-based system. Therefore, the membraneless electrochemical energy storage system is generally studied as an academic interest and there is no commercial feasibility. The bold innovation of membraneless hydrogen bromide energy storage system Researchers at the Massachusetts Institute of Technology's Department of Mechanical Engineering have developed a bold and novel idea to integrate the advantages of the membraneless energy storage system and the chemical properties of hydrogen bromide, putting two limited systems together to obtain Any single system has good results. This method is expected to get rid of the shortcomings of barrier membranes that hinder the development of fuel cells, and it can also replace the shortcomings of traditional membraneless oxy-cells that perform poorly. One of the characteristics of the hydrogen bromide reaction is its reversibility. The reactants coming out of the membraneless fuel cell are usually different from the products that come out of them, so these systems are usually “direct current†fuel cells and require constant input of fresh reactants. Hydrobromide products are electrolytes. The electrolyte is returned to the battery and charged from the outside to form bromine and hydrogen molecules to achieve the charging effect. This creates a "closed-loop" mode that makes filmless rechargeable batteries possible. At the top of the latest hydrogen bromide electrochemical energy storage system designed by MIT is a porous anode with a small amount of platinum (Pt) catalyst and a solid graphite cathode at the bottom. The electrolyte hydrobromic acid flows between the anode and the cathode, containing negatively charged bromide ions and positively charged hydrogen ions. In the discharge mode, the hydrobromic acid electrolyte enters the main channel from the left and flows between the electrodes. The porous metal mesh at the bottom prevents electrolyte penetration. Hydrogen enters from the top, while hydrobromic acid and a small amount of neutral molecular bromine enter through a separate channel. At the anode, platinum catalyzes the decomposition of hydrogen, forms positively charged hydrogen ions and negatively charged electrons, and then travels through different paths to the cathode. Hydrogen ions pass through the electrolyte, and electrons flow out through an external circuit to provide electrical energy. At the cathode, bromine absorbs electrons and becomes negatively charged ions. The negatively charged bromide ions and the positively charged hydrogen ions form the hydrobromic acid electrolyte. During the charging process, hydrobromic acid is injected back into the battery, hydrogen ions return to the positive electrode, hydrogen gas is formed, and molecular bromine is generated at the anode. The key to relying on laminar flow technology is to prevent reactants from reaching the "wrong" electrode. This phenomenon is called crossover and can cause damage to the anode catalyst. In the new design, the metal mesh allows hydrogen gas to enter the electrolyte. According to the latest numerical model, the researchers found that the concentration of molecular bromine is different in different parts of the battery. At the cathode, bromine becomes hydrobromic acid, and the concentration of bromine decreases as it diffuses into the electrolyte. If time is sufficient, bromine will eventually flow to the anode, causing unnecessary cross-effects. However, the researchers noticed this problem in the design and took measures to ensure that the bromine molecular reactants did not reach the anode. High efficiency and low cost of prototype battery storage In order to test the concept of a membraneless hydrogen bromide energy storage system, the researchers designed a small prototype battery. It consists of two 0.8 mm electrodes, a 1.4 cm long flow channel, and an inlet that directs the reactants into the device. Researchers conducted a series of experiments on prototype batteries based on different flow rates and different reactant concentrations. Even under unoptimized conditions, the battery has a maximum power density of 795 milliwatts per square centimeter (mW/cm2) at room temperature and room pressure. Its performance is comparable to the best membrane hydrogen bromide battery, two to three times higher than other membraneless electrochemical energy storage devices. The prototype battery's charging efficiency is equally exciting. Researchers charged the recovered reaction products into the device in a closed-loop mode. In the reverse operation, hydrogen and bromine were successfully prepared by energizing pure hydrobromic acid. The experimental results in the forward and reverse modes show that the higher the reactant concentration, the higher the power density, and the bidirectional voltage efficiency of more than 90% of 200mW/cm2, which is 25% of the peak power. These results show that the prototype battery has a very large potential for charge and discharge efficiency. The preliminary cost estimate is also very gratifying. Traditional membrane fuel cells, catalysts and separators account for about half of the total cost. The new hydrogen bromide battery does not require a separator, no cathode catalyst, and a small amount of anode catalyst. In addition, due to the higher power density of the hydrogen bromide battery, the amount of energy needed for the system is reduced, which further reduces the cost. Researchers are still continuing to improve their systems, trying to get the electrodes closer together for higher power density. Since all the reactions take place very quickly, there is still a limit to the rate at which hydrogen ions can pass through the electrolyte, even without the limitations of the separator. In addition, they are developing new battery structures that ensure that the electrolyte does not contain bromine molecules during the closed-loop capture and recovery process. 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