LR521 battery.Research and progress of ceramic membrane fuel cell technology

　　Energy is the foundation for the development of the national economy, and the foundation of modern civilization relies on the high development of energy technology. The history of social progress shows that energy utilization methods, technological changes and innovations have all had an important impact on the development of productivity and may even cause major changes in society. However, my country's fossil fuel utilization technology is relatively backward, energy utilization efficiency is low and environmental pollution is serious. Fuel cell technology, which is clean, quiet, efficient and compressible, is one of the most effective technologies to solve the environmental pollution caused by fossil fuels. 1. Overview of solid oxide fuel cells Fuel cells are a new generation of power generation technology after hydraulic, thermal and nuclear power generation. They are energy conversion devices that can directly convert the chemical energy of fuel into electrical energy. Because of its high energy conversion efficiency, almost no environmental pollution problems, and convenient application, it can gradually replace existing power generation technology and effectively improve energy and environmental conditions. It is known as the green energy of the 21st century and will become an emerging new energy technology and New material technology is the protagonist of the fourth industrial revolution. In view of the characteristics of fuel cells with high energy conversion efficiency, easy operation and low environmental pollution, countries around the world have generally paid attention to them and invested heavily in research and development in the past 10 years. After the development stages of alkaline fuel cells, phosphoric acid fuel cells, and molten carbonate fuel cells, it is now internationally recognized that solid oxide fuel cells have outstanding advantages and are called fourth-generation fuel cells. 1.1 The development history of solid oxide fuel cells As early as 1839, W.R. Grove in the UK first reported the world’s first fuel cell device. At the end of the 19th century, the concept of solid oxide fuel cells was first proposed after Nernst discovered Nernst material (solid oxygen ion conductor). In 1935, Schottky pointed out that this Nernst material could be used as a solid electrolyte for fuel cells. In 1937, Baur and Preis introduced a fuel cell using a solid oxygen ion conductor as the electrolyte, thus beginning the development of key materials for solid oxide fuel cells. In 1962, the American Westingouse Company first used hydrocarbon fuel methane as fuel SOFC cell performance. Ceramic membrane fuel cells (CMFC) are the latest development stage of solid oxide fuel cells. [1] 1.2 Advantages of solid oxide fuel cells The outstanding advantages of SOFC are mainly reflected in: ① High power generation efficiency. It is the highest power generation efficiency among fuel cells currently using hydrocarbons (such as natural gas) as fuel. Its primary power generation The efficiency can reach more than 65%; ② A wide range of fuels can be used, hydrogen, natural gas, water gas, liquefied petroleum gas, etc. can be used as fuel, and methanol, ethanol, and even high-carbon chain liquids such as gasoline and diesel can be used as fuel; ③ Waste heat The utilization value is high. Since the operating temperature of SOFC is between 600 and 1000°C, the high-quality waste heat can be used for combined heat and power generation, which can drive micro-turbine to generate electricity. It can also provide heat to achieve combined electricity and heat generation. The total power generation efficiency can be Reaching more than 85%; ④ There is no need to use precious metals as electrode catalysts; ⑤ Since SOFC is an all-solid structure, it is more suitable for modular design and amplification, and it also avoids corrosion and other problems caused by liquid electrolytes. [2] 2. Ceramic Membrane Fuel Cell However, traditional SOFC uses YSZ as the solid electrolyte and must operate at high temperature (1000°C). It has encountered many technical difficulties, which has seriously affected its industrialization process. Exploring high-performance new materials and developing thin-film preparation technologies to achieve medium-temperature SOFCs has been a research trend in recent years, and decisive progress has been made. SOFC with a thin-layered electrolyte as the core can be called a ceramic membrane fuel cell and has satisfactory power output at medium temperatures (600-800°C). CMFC has more advantages than high temperature SOFC. 2.1 New medium-temperature ceramic membrane fuel cell Professor Meng Guangyao, a professor at the University of Science and Technology of China, is keenly aware of the promising development prospects of ceramic membrane fuel cells and has done a lot of research work in this area. In order to achieve medium-temperature ceramic membrane fuel cells, the key issue is the core PEN (positive electrode, electrolyte and cathode) structure, especially the optimization and preparation of ceramic electrolyte materials. One of the preparation technical routes is to thin-film battery components to reduce the internal resistance of the battery and increase useful power output. Another important route is to develop new materials with sufficiently high electrical conductivity at moderate temperatures. The best route is of course a combination of the two aspects, that is, the development of a new thin-film ceramic membrane solid electrolyte, which is the key to the success of the new medium-temperature ceramic membrane fuel cell (IT-CMFC). Based on the "Medium Temperature SOFC" development route, Professor Meng Guangyao's Institute of Solid Chemistry and Inorganic Membranes has made breakthrough progress in the exploration of key new materials and innovative preparation technologies for fuel cells, and has developed a new high-performance medium-temperature operating Ceramic membrane fuel cell (IT-CMFC for short). a. Developed a variety of soft chemical preparation technologies for manufacturing thin-film PEN structures, and applied for a number of invention patents. b. Doped cerium oxide (GDC and SDC) and doped lanthanum gallate-based solid electrolytes were studied. They have conductivities 5 to 10 times higher than YSZ in the medium temperature range. In addition, thin-film SOFC preparation technology is used to reduce the thickness of the electrolyte to 20-30 μm. The output power density of the fuel cell reaches 360mW/cm2 at 650°C, which has entered the international advanced ranks. c. Innovatively developed a new type of composite ceramic membrane solid electrolyte. The fuel cell with this as the core has a power output density of 300-600mW/cm2 in the medium temperature range of 450-650℃. [2] 2.2 Proton Ceramic Membrane Fuel Cell Judging from the current use of electrolytes in solid oxide fuel cells, there are mainly two types of materials: one is oxygen ion conductor, such as Y-stabilized ZrO2 (YSZ); doped CeO2, such as SDC, GDC, etc.; doped LaGaO3, such as LSGM, etc.; the other type is proton conductor, such as doped perovskite SrCeO3 and BaCeO3-based oxide. [3] Doped CeO2 (DCO), as an oxygen ion conductor, has become a hot spot in the research of medium and low-temperature SOFC electrolyte materials due to its high ionic conductivity. But its biggest problem is its reducibility in a low oxygen partial pressure atmosphere, that is, part of Ce4+ is reduced to Ce3+, which introduces electronic conductance into the system and leads to a reduction in the open circuit voltage (OCV) and battery power of the battery. In addition to further optimizing oxygen ion conductor electrolyte materials represented by DCO, researchers are also committed to developing new ion conductors to meet the needs of medium and low temperature SOFC. Since Iwahara discovered that doped SrCeO3 and BaCeO3 are almost pure proton conductive materials under medium and low temperature conditions, they have received widespread attention as electrolyte materials for fuel cells. The proton conductivity of the doped BaCeO3 material is about 10-2S/cm at 600°C, which is higher than the conductivity of YSZ at the same temperature. Although its conductivity is slightly lower than that of DCO, the electronic conductivity of this system is almost negligible at medium and low temperatures. In addition, compared with oxygen ion conductor SOFC, the water produced by the proton conductor SOFC reaction is generated at the cathode end, so that the fuel gas at the anode will not be diluted. [4] The working principle of the proton ceramic membrane fuel cell The working principle of the proton ceramic membrane fuel cell is as shown in the figure: Due to the catalytic effect of the anode, the fuel gas is catalyzed into electrons and H+ at the anode end, and the generated H+ passes through the anode and cathode. The isolated dense ceramic proton-conducting membrane passes toward the cathode, and the electrons flow through the load through the external circuit to reach the cathode. At the cathode end, due to the action of the cathode catalyst, oxygen molecules combine with H+ and electrons transferred from the anode to generate water. 2.3 New composite electrolyte low-temperature ceramic fuel cells In recent years, Dr. B. Zhu from the Royal Swedish Institute of Technology has vigorously advocated and developed a type of DCO-based composite electrolyte materials. This new material is different from traditional single-phase oxide electrolyte materials. , composed of at least two phases, the main phase is the DCO oxide phase, and the second phase is the inorganic compound phase, including carbonates, sulfates, halides, hydroxides and proton conducting oxides (such as BCY, etc.) sometimes for To improve the mechanical strength of the material, there can also be a third phase. Research has found that the ionic conductivity of DCO-inorganic salt composite electrolyte can reach 0.01-1Scm-1 in the low temperature range of 400-600°C, which is ten to ten times higher than the ionic conductivity of currently commonly used electrolyte materials in CFCs such as DCO and YSZ. Hundreds of times, therefore CFC using this new electrolyte material can obtain good medium and low temperature operating performance without the need for thin film by selecting appropriate electrode materials. The anode material of DCO-inorganic salt composite electrolyte CFC usually uses NiO-DCO or NiO-electrolyte composite anode. The cathode material generally uses LSCF, LSC, SSC, Ag2O-lithiated NiO, LiNiO2, etc. or their composite cathode with the electrolyte. [5] Summary Ceramic membrane fuel cells have broad application prospects. At the current level of work, although various functional layers of CMFC have been successfully prepared, battery samples that are comparable in performance to ceramic processes have not yet been successfully prepared. Mainly There is still a lack of basic research on nucleation and growth on porous anode substrates, so that dense and thick electrolyte layers cannot be reproducibly obtained, and a lot of further research work needs to be done in the future.

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