Anode (negative):
Cathode (positive electrode):
Because the proton exchange membrane can only conduct protons, hydrogen ions (protons) can directly pass through the proton exchange membrane to reach the cathode, while electrons can only reach the cathode through the external circuit. When electrons flow to the cathode through an external circuit, direct current is generated. When the anode is taken as a reference, the cathode potential is 1.23V, that is to say, the theoretical upper limit of the generation voltage of each single battery is1.23v. When the load is connected, the output voltage depends on the output current density, usually between 0.5-1v.. A fuel cell stack (referred to as stack) whose output voltage meets the actual load demand can be composed of a plurality of single cells stacked together. Proton exchange membrane fuel cell has the following advantages: its power generation process does not involve hydrogen and oxygen combustion, so it is not limited by Carnot cycle and has high energy conversion rate; The power generation process is pollution-free, the generator set is modular, with high reliability, convenient assembly and maintenance, and no noise when working. Therefore, proton exchange membrane fuel cell power supply is a clean and efficient green power supply.
Usually, the operation of proton exchange membrane fuel cells needs a series of auxiliary equipment to form a power generation system. The power generation system of proton exchange membrane fuel cell consists of stack, hydrogen and oxygen supply system, hydrothermal management system, electric energy conversion system and control system. Electric pile is the core of power generation system. When the power generation system is running, the reaction gases hydrogen and oxygen enter the stack after passing through the pressure regulating valve and humidifier (humidification and heating) respectively, and react to generate direct current, which is supplied to the load after voltage stabilization and conversion. When the stack works, the water generated by the hydrogen-oxygen reaction is taken away by the excess oxygen (air) flow at the cathode. Unreacted (excessive) hydrogen and oxygen flow out of the stack, then are dehydrated by the steam-water separator, and can be recycled by the circulating pump or directly discharged into the air in the open space. In order to ensure the normal operation of proton exchange membrane fuel cell stack, the stack, hydrogen and oxygen treatment system, hydrothermal management system and corresponding control system are usually mechatronics to form a proton exchange membrane fuel cell generator. According to different load and environmental conditions, hydrogen and oxygen storage system, waste heat treatment system and power conversion system are configured, and proton exchange membrane fuel cell power station can be formed through electromechanical integration.
Generally speaking, a proton exchange membrane fuel cell power station consists of a proton exchange membrane fuel cell generator, hydrogen production and storage devices, a gas supply guarantee system, a hydrogen safety monitoring and discharge device, a cooling water tank and a waste heat treatment system, a power station electrical system and an automatic control system.
The hydrogen storage device provides hydrogen for the generator, and its reserve is determined according to the power generation required by the load. There are gaseous hydrogen storage, liquid hydrogen storage and solid hydrogen storage, and there are many corresponding hydrogen storage materials, which are mainly determined by the environmental conditions and technical and economic indicators of the power station. Hydrogen storage is one of the key problems in the construction of proton exchange membrane fuel cell power station, and the selection of hydrogen storage methods and materials is related to the safety and economy of the whole power station. The gas supply system is not a problem for the application of proton exchange membrane fuel cells in open space on the ground (such as fuel cell electric vehicles), but it is a very important problem for the application of underground engineering or closed space. How to set the air inlet must be strictly demonstrated. Hydrogen safety monitoring and discharge device is a unique problem of hydrogen power station. Because hydrogen is the lightest flammable and explosive gas, the scheduled evacuation of hydrogen storage devices, pipelines, valve fittings, proton exchange membrane fuel cell stacks and stacks may all cause hydrogen leakage. In order to prevent the concentration of hydrogen accumulated in the power station space from exceeding the explosion limit, it is necessary to detect, alarm and eliminate emissions in real time. Hydrogen safety monitoring and emission elimination device consists of hydrogen sensor, monitoring alarm, exhaust fan, pipeline and hydrogen eliminator. The sensor must be installed at the highest position in the power station space. The cooling water tank or waste heat treatment system absorbs or processes the heat generated by the operation of the proton exchange membrane fuel cell generator to ensure that the power station environment is not too hot. Reusing the waste heat of proton exchange membrane fuel cell power station, such as engineering dehumidification, air conditioning, heating or decontamination, can greatly improve the fuel utilization efficiency and has good development and application prospects. According to the overall power supply mode and structure of the project, the electrical system processes the power generated by the proton exchange membrane fuel cell generator and then runs in parallel with the power grid or/and directly supplies power to the load, involving power flow, switchgear, dial and relay protection. Using proton exchange membrane fuel cell power station can realize the multi-power distributed power supply mode of engineering emergency power grid, so its electrical and distribution system is a problem worthy of in-depth study. Power plant automation system is an automation device based on computer parameter detection and coordinated control to ensure the normal and reliable operation of proton exchange membrane fuel cell power plant. Generally, distributed control system (DCS) or field bus control system (FCS) should be adopted. The main equipment includes field intelligent instruments or sensors, transmitters, communication buses and controllers, and provides an interface for networking communication with the engineering control center. Its main functions include parameter detection, display, alarm, historical data storage, fault diagnosis, accident recall, operation guidance, control and protection output and data information management. It is the core of information and intelligence of proton exchange membrane fuel cell power station. Up to now, the most commonly used proton exchange membrane is Nafion proton exchange membrane of DuPont Company, which has the advantages of high proton conductivity and good chemical stability. Most PEMFC adopts perfluorosulfonic acid membranes such as Nafion, and the PEM used to assemble PEMFC in China mainly depends on imports. However, Nafion proton exchange membrane still has the following disadvantages: (1) it is difficult to make and its cost is high, the synthesis and sulfonation of perfluoro substances are very difficult, and the hydrolysis and sulfonation in the process of film formation are easy to denature and degrade the polymer, which makes the film formation difficult and leads to high cost; (2) It requires high temperature and water content, and the best working temperature of Nafion series membranes is 70 ~ 90℃. If it exceeds this temperature, the water content and conductivity of Nafion series membranes will decrease rapidly, which hinders the improvement of electrode reaction speed and overcomes catalyst poisoning by increasing the working temperature appropriately. (3) Some hydrocarbons, such as methanol, have high permeability and are not suitable for proton exchange membrane (DMFC) in direct methanol fuel cells.
The price of Nafion membrane is about $600 per square meter, which is equivalent to $0/20 per kilowatt/kloc (unit battery voltage is 0.65V). In the fuel cell system, the cost of membrane accounts for almost 20%~30% of the total cost. In order to realize the commercial application of fuel cells as soon as possible, it is urgent to reduce the price of proton exchange membrane. Ballard Company of Canada has done very well in the field of proton exchange membrane, which makes people see the hope of commercialization of exchange membrane. According to the research plan, its third generation proton exchange membrane BAM3G is a partially fluorinated sulfonic acid proton exchange membrane. Its demonstration life has exceeded 4500h, and the price has dropped to 50 US dollars per cubic meter, which is equivalent to 0/0 US dollars per kilowatt/kloc (the unit battery voltage is 0.65V).
The world's largest proton exchange membrane fuel cell demonstration power station was built in South China University of Technology. As a kind of electric vehicle, fuel cell vehicle is considered as the best and final solution to solve automobile pollution and automobile dependence on oil. This is because the chemical reaction process of fuel cell does not produce harmful substances, but only emits a small amount of water vapor, and its energy conversion efficiency is 2~3 times higher than that of internal combustion engine. A car equipped with this battery only needs to be filled with hydrogen like refueling, and it can continue driving.
Besides being used in automobiles, fuel cells also have broad application prospects in transportation, military, communication and other fields. Developed countries have invested huge manpower and material resources in the research and development of this technology, and there are more than 30 research units engaged in fuel cells in China.
This includes South China University of Technology. Why build the world's largest demonstration power station? Liao Shijun told reporters: "Demonstration is a necessary step for the commercialization of a new technology. The gradual enlargement of fuel cell technology involves many problems. Only by reaching a certain capacity demonstration can the technology mature and finally be commercialized. The demonstration power station is built not only to show the new energy technology of proton exchange membrane fuel cell to the public, but also to test the feasibility of this technology and understand what problems exist in this technology and how to improve it. The bigger the power station, the more difficult it is to build and the more obvious the problem will be. "
The demonstration power station can run for 24 hours, and the generated current can be directly transmitted to the 380V low-voltage power grid of the school. At full load, it can meet the normal operation of the international academic center of South China University of Technology, a luxury quasi-five-star hotel near the power station. "The by-product hot water of the demonstration power station is about 50 degrees Celsius, which is very suitable for domestic hot water. When both heat and electricity are fully utilized, the energy utilization rate of fuel cell power stations will reach 90%. " Liao Shijun said.
In the demonstration power station, natural gas is first converted into hydrogen, which enters the fuel cell generator set to generate current and hot water.
According to reports, the hydrogen production process designed and developed by South China University of Technology, the hydrogen production efficiency of natural gas is close to 2.0, that is, 1 cubic meter of natural gas can produce nearly 2 cubic meters of hydrogen, which is 20%~30% higher than some similar hydrogen production devices in China. Power generation is at least 30% higher than that of direct combustion of natural gas, and pollutant emissions are reduced by 60% year-on-year. It fully demonstrates the advantages of high efficiency and low emission of fuel cell power generation. Fuel cell technology has been developed for decades, but it has not been widely promoted. Besides stability and durability, high cost is also the bottleneck of commercialization.
Liao Shijun told reporters that the price of proton exchange membrane fuel cells abroad is as high as 70,000 yuan per kilowatt. Installing a 50 kW battery system for a car will cost 3.5 million yuan for photovoltaic cells. Therefore, while tackling key technical problems, how to effectively reduce the cost of fuel cells has always been an important research content of the research group.
Due to the use of various new technologies, the cost of fuel cells developed by South China University of Technology has been reduced to 6000~7000 RMB per kilowatt, which is only110 of the international market price.
"Compared with traditional power generation technology, this cost is still high, but compared with other new energy sources such as solar energy, it is much cheaper." Liao Shijun calculated an account. According to the calculation of 6000 yuan per kilowatt, the cost of fuel cell vehicles is still not cheap. However, by contrast, hydrogen is much cheaper than gasoline!
In order to promote the development and utilization of fuel cells, China has introduced a subsidy policy, and directly subsidizes 300,000 yuan to buy a fuel cell vehicle. In addition, after mass production of fuel cells, there is still a lot of room for cost reduction. At the same time, many governments have said that once the fuel cell is commercialized on a large scale, it will not be a problem to build hydrogen refueling stations in various places, and the fuel cell will enter the homes of ordinary people just around the corner.
In recent years, in addition to successfully completing the power station construction, South China University of Technology has also made a series of important achievements in tackling key technologies of proton exchange membrane fuel cells, including the preparation technology of highly dispersed and highly active catalysts, the preparation technology of membrane electrodes by direct coating under illumination, the preparation technology of low platinum catalysts, and the preparation technology of membrane electrodes by ultra-low platinum loading. The research group * * * applied for 8 patents of fuel cell core technology, authorized 4 patents, and applied for international invention patent 1 item.
When talking about the next step, Liao Shijun said: "We will use the platform of Guangzhou Institute of Modern Industrial Technology to carry out fuel cell industrialization and devote ourselves to developing a series of products such as fuel cell backup power supply, base station communication power supply and household cogeneration system. We hope to further reduce the cost of fuel cells and promote the development and commercialization of fuel cell technology in Guangdong Province. "