[Edit this paragraph] Characteristics of fuel cells
Fuel cell is very complex, involving the theories of chemical thermodynamics, electrochemistry, electrocatalysis, material science, power system and automatic control, and has the advantages of high power generation efficiency and less environmental pollution. Generally speaking, fuel cells have the following characteristics:
(1) High energy conversion efficiency. He directly converts the chemical energy of fuel into electric energy without combustion process, so it is not limited by Carnot cycle. At present, the energy conversion efficiency of fuel cell system is 45% ~ 60%, while the efficiency of thermal power generation and nuclear power is about 30% ~ 40%.
(2) The emission of harmful gases SOx, nitrogen oxides and noise is very low, and the emission of CO2 is greatly reduced due to high energy conversion efficiency, and there is no mechanical vibration.
(3) the fuel has a wide application range
(4) The building blocks are large in scale and flexible in installation position. The fuel cell power station occupies a small area and has a short construction period. The power of the power station can be assembled by the battery stack as needed, which is very convenient. Fuel cells are very suitable as centralized or distributed power stations, or as independent power stations in residential areas, factories and large buildings.
(5) The fuel cell with fast load response and high operation quality can be converted from the lowest power to the rated power in a few seconds, and the power plant can be very close to the load, thus improving the principle rate deviation and voltage fluctuation of the local frequency fuel cell, reducing the existing substation equipment and current-carrying capacity, and reducing the investment and line loss of power transmission and transformation lines.
[Edit this paragraph] "Fuel" and "Battery"
In order to understand its value, let's study the words "fuel" and "battery" respectively.
In order to use fuel such as coal or oil to generate electricity, coal or oil must be burned first. The energy generated by their combustion can heat water and turn it into steam, which can be used to make the turbine generator rotate in the magnetic field. This produces an electric current. In other words, we convert the chemical energy of fuel into heat energy, and then convert heat energy into electric energy. In this double transformation process, a lot of original chemical energy is wasted. However, fuel is very cheap, although there is such a waste, it does not prevent us from producing a lot of electricity without expensive expenses. It is also possible to directly convert chemical energy into electrical energy without first converting chemical energy into thermal energy. To do this, we must use batteries. This battery consists of one or more chemical solutions in which two metal rods called electrodes are inserted. A special chemical reaction takes place on each electrode, and electrons are either released or absorbed. The potential on one electrode is greater than that on the other, so if the two electrodes are connected by wires, electrons will flow from one electrode to the other through the wires. Such an electron flow is an electric current, which will continue as long as there is a chemical reaction in the battery. The battery of a flashlight is an example of this kind of battery. In some cases, when the battery runs out, people force the current to flow back into the battery, and the battery will react in turn, so the battery can store chemical energy and use it to regenerate the current. The battery in the car is an example of this reversible battery. In the battery, much less chemical energy is wasted, because it takes only one step to convert chemical energy into electrical energy. However, the chemicals in the battery are very expensive. Zinc is used to make batteries for flashlights. If you try to use enough zinc or similar metals to prepare electricity for the whole city, it will cost billions of dollars every day.
Fuel cell is a device that combines the concepts of fuel and battery. It is a kind of battery, but it doesn't need expensive metal, and only uses cheap fuel for chemical reaction. The chemical energy of these fuels is also converted into electric energy in one step, which is much less than the energy loss usually through two steps. Therefore, the amount of electricity that can be provided for human beings has greatly increased.
At present, six types of fuel cells have been developed based on electrolytes, namely alkaline fuel cell (AFC), phosphoric acid fuel cell (PAFC) and molten carbonate fuel cell (MCFC), SOFC (solid oxide fuel cell), SPFC (solid polymer fuel cell), PEMFC (proton exchange membrane fuel cell) and BEFC (biofuel cell). According to the working temperature, it is divided into high, medium and low temperature fuel cells. Normal temperature fuel cells, such as Such, operate from room temperature to 373 K (100℃); Medium temperature fuel cells, such as PAFC；; , working at 373 K (100℃) ~ 573 K (300℃). High-temperature fuel cells, such as MCFC and SOFC, operate at temperatures over 873K(600℃).
Fuel cells are essentially designed with the concept of controlling the explosion of hydrogen bombs. The fuel cell on the spacecraft is used to collect the energy generated by hydrogen during interstellar travel. Electromagnetic and solar energy collected by solar panels of spacecraft will be converted into electric energy, which will be used to slowly replace hydrogen stored in fuel cells with fuel. Fuel cells also contain a small amount of controlled substances that can undergo nuclear fission, which in turn are used for nuclear reactions with hydrogen nuclei. The nuclear reaction is carried out in the fuel cell, which provides high energy during the space journey and accelerates the ion engine to propel the spacecraft. In the final stage of the journey, the fuel cell provides the hydrogen needed to power the fuel rocket. The whole process is controlled by powerful electromagnetism, which can provide energy and avoid excessive energy leakage leading to reactor core melting. Thermal energy is a by-product of nuclear reaction, which is absorbed by the outer wall of fuel cell and converted into electrical energy for computer, life support system and other necessary functions.
After years of exploration, the most promising fuel cell for automobiles is proton exchange membrane fuel cell. Its working principle is that hydrogen is sent to the negative electrode, and two electrons in the hydrogen atom are separated under the action of catalyst (platinum). Attracted by the positive electrode, these two electrons generate current through the external circuit, and hydrogen ions (protons) that lose electrons can pass through the proton exchange membrane (i.e. solid electrolyte) and recombine with oxygen atoms and electrons at the positive electrode to form water. Because oxygen can be obtained from air, as long as hydrogen is continuously supplied to the negative electrode and water (steam) is taken away in time, the fuel cell can continuously provide electric energy.
The smallest fuel cell in the world-only 3 mm in diameter
American scientists have recently developed the world's smallest fuel cell, with a diameter of only 3 mm, which can generate 0.7 volts for 30 hours. This fuel cell can generate electricity without consuming electric energy, and it consists of four parts. The upper layer is a water storage tank, and the lower layer is a fuel hall filled with metal hydride, separated by a film, and there is a group of electrodes below the fuel hall of metal hydride. There are also many small holes in the film, which allow water molecules in the water storage tank to enter the fuel hall in the form of water vapor. After entering the fuel hall, water molecules react with metal hydride to generate hydrogen. Hydrogen will fill the entire fuel hall and impact the membrane upward. Stop the inflow of water, and then hydrogen will react chemically on the electrode below the fuel hall to form an electric current.
The new battery is very small, measuring 3x6x1mm. There is no gravity. Its tension can control the water flow, which means that it can work well even when moving and rotating. So it is most suitable for some small household appliances. Now, this battery can generate 0.7 volts and 1 ma, and the electric fuel can last for about 30 hours.
[Edit this paragraph] The invention of the fuel cell
Although the term fuel cell has not appeared for a long time, its history can be traced back to 100 years ago. 1889, two chemists, Ludwig Mond and Charles Langer, wanted to make a practical device that could provide electricity with air and industrial gases, and the word "fuel cell" was born with their invention. Modern fuel cell technology emerged in the 1960s. In order to find an efficient power plant for the space shuttle, NASA cooperated with GE Company to develop the first modern fuel cell-proton exchange membrane fuel cell, which is also the beginning of fuel cell commercialization. Since then, after more than 40 years of development, the fuel cell family has become more and more prosperous, and its application fields are everywhere.
[Edit this paragraph] The development status of fuel cell technology in China.
China began to study fuel cells as early as 1950s. China has made many breakthroughs in key materials and technological innovation of fuel cells. China government attaches great importance to the research and development of fuel cells, and has successively developed 10W -30kW hydrogen-oxygen fuel electrode and fuel cell electric vehicle. Fuel cell technology, especially proton exchange membrane fuel cell technology, has also developed rapidly. Proton exchange membrane fuel cells with various specifications such as 60kW and 75kW have been developed, and fuel cell engines with a net output of 40kW for electric vehicles and 0/00 kW for city buses have been developed, making China's fuel cell technology enter the ranks of advanced countries in the world.
In today's era of global energy shortage and high oil prices, it is urgent to find new energy sources to replace fossil fuels. Due to its obvious advantages, cleanness and high efficiency, hydrogen energy has won strong support from governments all over the world, and various energy and power companies are full of confidence in the development of fuel cells, so the future market of fuel cells will have huge growth space.
Although the current market demand for fuel cells is quite small, it is predicted that in the next decade, with the technological progress and economies of scale, the production cost and use cost of fuel cells will be reduced, the competitiveness will be improved, and the potential market of fuel cells will gradually develop. There is little demand for portable fuel cells now, but the portable fuel cell market will be the fastest growing market from now until 20 1 1 or even longer. Fuel cell systems used in consumer electronics will be commercialized in recent years.
[Edit this paragraph] fuel cell technology classification
According to different methods, the types of fuel cells can be roughly classified as follows:
1. According to the working mechanism of fuel cell.
It is divided into acid fuel cells and alkaline fuel cells.
2. According to the type of electrolyte, there are acidic, alkaline, molten salt or solid electrolyte.
Therefore, fuel cells can be divided into alkaline fuel cells (AFC), phosphoric acid fuel cells (PAFC), molten carbonate fuel cells (MCFC), solid oxide fuel cells (SOFC), proton exchange membrane fuel cells (PEMFC) and so on. Among the fuel cells, phosphoric acid fuel cell (PAFC) and proton exchange membrane fuel cell (PEMFC) can be cold-started and fast-started, and can be used as mobile power sources, which meet the requirements of FCEV and are more competitive.
3. According to the fuel type.
There are organic fuels such as hydrogen, methanol, methane, ethane, toluene, butene and butane, and gas fuels such as gasoline, diesel and natural gas. Organic fuel and gaseous fuel can only become fuel cells after being "reformed" into hydrogen by reformer.
4. According to the operating temperature of the fuel cell.
Low temperature type, the temperature is lower than 200℃; Medium temperature type, the temperature is 200 ~ 750℃; High temperature type, the temperature is higher than 750℃.
Fuel cells operating at room temperature, such as proton exchange membrane fuel cells (PEMFC), need to use precious metals as catalysts. Most of the chemical energy of fuel can be converted into electric energy, and only a small amount of waste heat and water are produced, and no nitrogen oxides that pollute the atmospheric environment are produced. No waste heat recovery device is needed, and it is small in size and light in weight. However, the catalyst platinum (Pt) will react with carbon monoxide (CO) in the working medium, resulting in "poisoning" and failure, thus reducing the efficiency of the fuel cell or completely damaging the fuel cell. In addition, the price of platinum (Pt) is very high, which increases the cost of fuel cells.
The other is the fuel cells operating at high temperature (600 ~ 1000℃), such as molten carbonate fuel cells (MCFC) and solid oxide fuel cells (SOFC), which do not need to use precious metals as catalysts. However, due to the high working temperature, it is necessary to use a compound waste heat recovery device to utilize the waste heat, which is bulky and heavy, and is only suitable for high-power power stations.
The most practical fuel cell uses hydrogen or gas fuel rich in hydrogen, but hydrogen is not directly available in nature, and the fuel cell is hydrogen; The sources are usually petroleum fuel, methanol, ethanol, biogas, natural gas, naphtha and gas. Hydrogen-rich gas fuel is made by chemical treatment such as reforming and cracking. The oxidant is oxygen or air, and air is the most common oxidant.