Hydrogen is a combustible gas, so engines can burn hydrogen directly. The exhaust gas it emits is water, which is not polluting. It is even possible to realize the actual use of hydrogen engines without much modification to current gasoline engines (in the same way that many taxis are now converted to natural gas, there are actually cars running on hydrogen, but there are very few, like the Mazda RX). -8
Hydrogen RE is a car that burns hydrogen directly, but the reason it has not developed in this way is due to some practical reasons, the most important of which are the cost and operability.
Green car concept
Hydrogen car
BMW i8 hydrogen fuel cell
First of all, let's talk about the preparation of hydrogen. gas. I know that the preparation of hydrogen is very simple, electrolysis, I learned it in college, but the current industrial hydrogen production efficiency is only 60-70%, and the electricity generation efficiency is about 50%, plus the cost of electricity generation it -even, more The additional costs of storing and transporting hydrogen make the cost of large-scale hydrogen production very high, even higher than that of currently used petroleum products, such as gasoline, so it is difficult to promote it from a cost point of view.
Hydrogen cars
Second, let's talk about hydrogen storage. Hydrogen is gaseous at room temperature, but if you store hydrogen gas in the car (a volume as large as an existing fuel tank) the car basically cannot go many miles. There are two common ways to increase hydrogen storage capacity: pressing hydrogen into a liquid by increasing thepressure and cooling it, and use a special alloy to combine with hydrogen to form a hydride, which can be heated and released again if necessary.
The temperature of liquid hydrogen is very low, below minus 250 degrees. At normal temperature, it continually evaporates to form hydrogen gas and is lost. Therefore, storing liquid hydrogen requires a special material with excellent thermal insulation. and the pressure resistance of the container, the cost of this container is very high, but even this cannot completely prevent the loss of hydrogen. It's possible that your hydrogen car has just added a large tank of liquid hydrogen, and you are coming back from one tank. on a business trip, you find that the car has no fuel, wouldn't that be inconvenient? In addition, for us, owners of ordinary cars, space in the car is precious. Whoever isready to carry a large container in the car to take up space (the density of liquid hydrogen is 1/15 of water and its volume is 45). liters of water can contain more than 3 kilograms) of liquid hydrogen, so it remains a large tank).
Hydrogen storage alloy refers to an intermetallic compound that can reversibly absorb, store and release a large amount of hydrogen under a certain hydrogen temperature and pressure. The principle is that metal and hydrogen form ionic compounds, covalent compounds. etc. Metal hydrides, metal phase hydrides-intermetallic compounds, and other combinations can release hydrogen under certain conditions. The material of this alloy is a rare metal, difficult to manufacture and expensive, therefore even more difficult to promote.
The reason why hydrogen fuel cells have become the development directionis that they not only have the advantages of pollution-free hydrogen combustion, but also have the advantages of low noise and high efficiency. fuel cells can reach more than 50%, which directly converts chemical energy into electrical energy without thermal or mechanical intermediate energy conversion (generator), and does not have the disadvantages of high preparation cost and low cost. 'a storage difficulty, it therefore became the first choice.
Are hydrogen fuel cells the same as hydrogen-oxygen fuel cells
1 Closed-loop air cooling
For steam turbines. below 50,000 kilowatts Generators often use a closed-loop air cooling system, using a fan in the motor to blow the heating components to cool them.
2. Hydrogen cooling
For generatorswith a capacity of 50,000 to 600,000 kilowatts, hydrogen cooling is widely used. The heat dissipation performance of hydrogen (purity 99%) is better than that of air, and the heat dissipation effect is good. It can significantly reduce the ventilation friction loss of the engine, thereby greatly improving the efficiency of the generator. Explosion-proof and leak-proof measures must be taken when using hydrogen cooling, which makes the engine structure more complex and increases the consumption and cost of electrode materials.
3. Liquid Cooling
The relative cooling capacity of water is 50 times that of air. To remove the same heat, the flow rate of water required is much lower than that of air. air. Therefore, using hollow wires in the coil and passing water through the wires for cooling cansignificantly reduce motor temperature rise, delay insulation aging, and extend motor life.
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Strictly treated hydrogen for cooling can ensure that the inside of the generator is clean, the ventilation and cooling effect heat dissipation is stable, and there will be no problems caused by dirt.
Hydrogen contains very little oxygen, less than 2%, and does not support combustion. Even if a short circuit fault occurs inside the generator, there is no risk of fire, which can greatly reduce the degree of combustion. Damage caused by fault. In hydrogen there is less noise and the insulating materials are less susceptible to oxidation and corona damage.
The hydrogen in the generator must maintain the specified purity to ensure the operating performance of the generator andavoid explosions. For this purpose, a hydrogen supply device must be installed.
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Hydrogen fuel cells use the chemical element hydrogen to create batteries that store energy. The basic principle is the reverse reaction of water electrolysis, supplying hydrogen and oxygen to the cathode and anode, respectively. Once the hydrogen diffuses outward through the cathode and reacts with the electrolyte, the electrons are released and reach the anode via an external charge.
Characteristics of hydrogen fuel cells:
1. No pollution
Fuel cells do not pollute the environment. It is by electrochemical reaction rather than by combustion (petrol, diesel)or energy storage (battery) - the most typical traditional backup power solution. Combustion releases pollutants such as COx, NOx, SOx gases and dust. As mentioned above, fuel cells only produce water and heat. If hydrogen is produced from renewable sources (photovoltaic panels, wind energy, etc.), the entire cycle is completely emission-free.
2. Quiet
The fuel cell operates quietly, with only approximately 55 dB of noise, which is equivalent to the level of a normal conversation. This makes the fuel cell suitable for indoor installation or where there are exterior noise restrictions.
3. High efficiency
The power generation efficiency of fuel cells can reach more than 50%. This is determined by the conversion properties of the fuel cells. It directly converts energychemical in electricity. energy without the need After the intermediate conversion of thermal energy and mechanical energy (generator).
The hydrogen-oxygen fuel cell is a promising new energy source. It generally uses hydrogen, carbon, methanol, borohydride, coal gas or natural gas fuel as the negative electrode and air oxygen as the positive electrode. . The main difference from ordinary batteries is that the active materials of ordinary batteries are pre-placed inside the battery, so the capacity of the battery depends on the amount of active materials stored while the active materials (fuel and oxidizer) fuel cells are supplied continuously; While reacting to earth input, this type of battery is actually just an energy conversion device. This type of battery has the advantages of high conversion efficiency.high capacity, high specific energy, wide power range and no recharging. However, due to its high cost and complex system, it is limited to some special uses, such as spacecraft. , submarines, military, TV transfer stations, aspects such as lighthouses and buoys.
Hydrogen-oxygen fuel cells use hydrogen as a fuel as a reducing agent and oxygen as an oxidant.
Hydrogen-oxygen fuel cells are batteries that convert chemical energy into electrical energy through the combustion reaction. fuel. Primary batteries work on the same principle.
When a hydrogen-oxygen fuel cell operates, it supplies hydrogen gas to the hydrogen electrode and oxygen to the oxygen electrode. Hydrogen and oxygen pass through the electrolyte to generate water under the action of a catalyston the electrode. At this time, there is an excess of electrons on the hydrogen electrode and they are negatively charged, and the oxygen electrode is positively charged due to the lack of electrons. Once the circuit is ignited, this combustion-like reaction process can continue.
When working, fuel (hydrogen) is supplied to the negative electrode and oxidant (oxygen) is supplied to the positive electrode. Hydrogen decomposes into positive H+ ions and e- electrons under the action of the catalyst on the negative electrode. Hydrogen ions enter the electrolyte, while electrons move along the external circuit towards the positive electrode. The electrical load is connected to the external circuit. On the positive electrode, the oxygen and hydrogen ions present in the electrolyte absorb the electrons arriving at the positive electrode to form water. This is the reverse process of the water electrolysis reaction.
Hydrogen-oxygen fuel cells do not require a device to store all the reducing and oxidizing agents inside the battery.
The reactants in hydrogen-oxygen fuel cells are all found inside the battery. outside the battery, it simply provides a container for the reaction 2H2+O2==2H2O
Hydrogen and oxygen can be supplied outside the battery
The fuel cell is a chemical battery that uses the energy released when substances undergo chemical reactions to convert it directly into electrical energy. From this point of view, it is similar to other chemical batteries such as zinc-manganese dry batteries, lead-acid batteries, etc. However, when it works, it needs to continuously supply reaction substances, fuel and oxidant, which is different from other ordinary chemical batteries. Because it converts the energy released by the fuel whenchemical reactions into electrical energy, it is called a fuel cell.
More precisely, a fuel cell is a “generator” that uses the reverse reaction of the electrolysis of water. It consists of a positive electrode, a negative electrode, and an electrolyte plate sandwiched between the positive and negative electrodes. Initially, electrolyte plates were formed by infiltrating electrolytes into porous plates. In 2013, they were developed to directly use solid electrolytes.
When working, fuel (hydrogen) is supplied to the negative electrode and oxidizer (air, the active ingredient is oxygen) is supplied to the positive electrode. Hydrogen is broken down into positive H+ ions and e- electrons at the negative electrode. When hydrogen ions enter the electrolyte, electrons move toward the positive electrode along the external circuit. The electric charge est connected to the external circuit. On the positive electrode, oxygen from the air and hydrogen ions from the electrolyte absorb electrons arriving at the positive electrode to form water. This is the reverse process of the water electrolysis reaction. Water can be reused in this process, and the principle of generating electricity is similar to solar cells that can be used at night.
The electrode materials of fuel cells are generally inert electrodes with strong catalytic activity, such as platinum electrodes, activated carbon electrodes, etc.
Thanks to this principle, the fuel cell can continuously transmit energy to the outside during its operation, so it can also be called a “generator”.
Generally speaking, writing the equation for the chemical reaction of a fuel cell requires careful attention to the acidity and alkalinity of the electrolyte. The electrode reaction that occurs on the positive and negative electrodes is not isolated, but is often closely related to the electrolyte solution. For example, there are two types of hydrogen-oxygen fuel cells: acid type and alkaline type:
If the electrolyte solution is alkaline or saline solution, the reaction formula of the negative electrode is: 2H2 + 4OHˉ-4eˉ == 4H20 Anode: O2 + 2H2O + 4eˉ== 4OHˉ
If the electrolyte solution is an acidic solution, the reaction formula of the negative electrode is: 2H2-4eˉ =4H+ (cation), and the positive electrode: O2+4eˉ+4H+=2H2O
In an alkaline solution, H+ cannot appear, and in an acidic solution, OHˉ cannot appear.