Nickel Hydride No. 5 battery

Current status of Nickel Hydride No. 5 battery proton exchange membrane technology

Nickel Hydride No. 5 batterys are electrochemical reaction devices that directly convert dye chemical energy into electrical energy. The combined heat and power efficiency can reach more than 95%. At the same time, they also have the advantages of no noise, green environmental protection, high reliability, and easy maintenance. They are considered to be the most promising new power generation technology in contemporary times. Proton exchange membrane Nickel Hydride No. 5 batterys (PEMFC) use proton conductive materials as electrolytes. Compared with ordinary Nickel Hydride No. 5 batterys, they have fast start-up speed at room temperature, no electrolyte loss, and high specific power and specific energy. Therefore, they have been widely used in decentralized power stations, mobile power sources, and special aerospace. As the core material of Nickel Hydride No. 5 batterys, the performance of proton exchange membrane (PEM) directly affects the stability and durability of Nickel Hydride No. 5 batterys.

1. Classification of proton exchange membranes

According to the fluorine content, proton exchange membranes can be divided into perfluorinated proton exchange membranes, partially fluorinated polymer proton exchange membranes, non-fluorinated polymer proton exchange membranes, and composite proton exchange membranes. Among them, since the main chain of the perfluorosulfonic acid resin molecule has a polytetrafluoroethylene (PTFE) structure, it brings excellent thermal stability, chemical stability and high mechanical strength; the polymer membrane has a long life, and because of the presence of hydrophilic sulfonic acid groups on the molecular side chains, it has excellent ion conduction properties. Non-fluorinated proton membranes require a relatively harsh working environment, otherwise they will be quickly degraded and destroyed, and will not have the excellent performance of perfluorosulfonic acid ion membranes.

Current Development Status of Nickel Hydride No. 5 battery Proton Exchange Membrane Technology

Perfluorinated proton exchange membranes were the first to be industrialized. Perfluorinated proton exchange membranes include ordinary perfluorinated proton exchange membranes, enhanced perfluorinated proton exchange membranes, and high-temperature composite proton exchange membranes. The production of common perfluorinated proton exchange membranes is mainly concentrated in the United States, Japan, Canada and China. The main brands include Nafion series membranes of Dupont, Dow membranes and Xus-B204 membranes of Dow Chemical Company, 3M perfluorocarbon membranes, Alciplex of Asahi Kasei Corporation, Flemion of Asahi Glass Company, C series of Japan Chlorine Engineering Company; BAM series membranes of Ballard Company of Canada, Solvay series membranes of Solvay Company of Belgium; DF988 and DF2801 proton exchange membranes of Shandong Dongyue Group of China. The main companies and products are shown in Table 2.

Current status of Nickel Hydride No. 5 battery proton exchange membrane technology

Since the early 1980s, Ballard Company of Canada used perfluorosulfonic acid proton exchange membranes for PEMFC and achieved success, perfluorosulfonic acid membranes have become the only commercial membrane material common perfluorinated proton exchange membranes for modern PEMFC. Enhanced perfluorinated proton exchange membranes mainly include PTFE/perfluorosulfonic acid composite membranes and glass fiber/perfluorosulfonic acid composite membranes. High-temperature composite proton exchange membranes mainly include heteropolyacid/perfluorosulfonic acid composite membranes and inorganic oxide/perfluorosulfonic acid composite membranes. The classification of perfluorosulfonic acid membranes is shown in Table 3.

Current Development Status of Nickel Hydride No. 5 battery Proton Exchange Membrane Technology

1. Perfluorosulfonic Acid Proton Exchange Membrane

Perfluorosulfonic acid proton exchange membranes have been commercialized and have become an important Nickel Hydride No. 5 battery diaphragm material on the market. The perfluorosulfonic acid PEMs currently on the market mainly include Nafion series PEMs (Nafion117, Nafion115, Nafion112, etc.) from Dupont in the United States, XUS-B204 membranes from Dow, Aquivion membranes from Solvay in Belgium, Alciplex from Asahi Kasei in Japan, Flemion from Asahi Glass, C series from Chlorine Engineering, and BAM membranes from Baliard in Canada. Fleminon membrane, Aciplex membrane and Nafion membrane are similar, all of which have long side chains; XUS-B204 membrane has shorter fluorinated side chains, and its conductivity is significantly improved, but at the same time, the difficulty and cost of synthesis are also greatly increased, and it has been discontinued. Solvay has solved this problem by introducing a higher content of sulfonate groups to maintain the water content in the membrane. The performance of the short-chain Aquivion membrane it produces has exceeded that of Nafion112 membrane.

The most widely used PEM in the market is Dupont's Nafion membrane. Compared with other proton exchange membranes, Nafion membrane has higher chemical stability and higher mechanical strength, and can maintain high conductivity in a high humidity working environment. Currently, almost all commercial perfluorosulfonic acid PEMs are based on Nafion structure. However, the membrane material has high requirements for temperature and water content (proton conductivity performance is seriously reduced at medium and high temperatures). When used in direct methanol Nickel Hydride No. 5 batterys, the methanol permeability is high and the preparation process is difficult. Beijing University of Chemical Technology has prepared Nafion nanofiber membrane, which has a conductivity 5 to 6 times that of Nafion membrane, and has improved the properties of Nafion membrane.

2. Partially fluorinated proton exchange membrane

General Electric (GE) of the United States used PEM Nickel Hydride No. 5 batterys with sulfonated polystyrene proton membrane on spacecraft in the 1960s. In order to improve the performance of sulfonated polystyrene proton PEM, Ballard Company of Canada developed the BAM series PEM. This is a typical partially fluorinated polystyrene PEM. Its thermal stability, chemical stability and water content have been greatly improved, exceeding the performance of Nafion117 and Dow membranes. At the same time, its price is lower than that of perfluorinated membranes, and in some cases it can replace perfluorinated sulfonic acid membranes. However, due to the small molecular weight and insufficient mechanical strength of polystyrene PEM, its wide application is limited to a certain extent.

3. Fluorine-free proton exchange membrane

In order to meet the requirements of PEM in both chemical stability and mechanical strength, fluorine-free PEM is generally prepared using aromatic polymers containing benzene ring structures on the main chain. Sulfonated aromatic polymers mainly include sulfonated polyaryletherketone, sulfonated polysulfide sulfone, sulfonated polyetheretherketone, sulfonated naphthalene polyethersulfoneketone, sulfonated polyimide, sulfonated polybenzimidazole, etc. The water absorption and alcohol resistance of PEM prepared in this way are significantly higher than those of Nafion membrane. DAIS Company of the United States uses sulfonated block ionic copolymer as PEM raw material to develop sulfonated styrene-butadiene/styrene block copolymer membrane. When the sulfonation degree of the PEM is controlled between 50% and 60%, its conductivity can reach the level of Nafion membrane; when the sulfonation degree is greater than 60%, it can simultaneously obtain higher electrochemical performance and mechanical strength, achieving a balance between the two; the battery life at 60°C reaches 2500h, and the room temperature life is 4000h, which is expected to be used in low-temperature Nickel Hydride No. 5 batterys.

II. Modification of proton exchange membranes

1. Composite proton exchange membranes

In order to solve the problems of high difficulty in synthesizing raw materials, complex preparation processes and high costs of perfluorosulfonic acid proton exchange membranes, researchers have used composite membrane materials to develop new proton membranes. Composite proton exchange membranes mainly include mechanically enhanced proton exchange membranes, high-temperature proton exchange membranes and self-humidifying proton exchange membranes.

(1) Mechanically enhanced proton exchange membranes

Proton conductors are combined with reinforcing components to achieve mechanically enhanced proton exchange membranes. Among them, proton conductors can form continuous proton transport channels and improve the conductivity of protons, such as the modification and application of Nafion membranes. Mechanically reinforcing components effectively improve the mechanical strength of membrane materials, such as the modification and application of PTFE porous membranes. The enhanced composite PEM obtained by modifying PTFE porous membranes has increased its own mechanical strength and stability, while the membrane thickness has also been greatly reduced. As the polymer content decreases, the production cost is also reduced; the improvement of the water content and transfer in the membrane by the modification operation can further reduce the resistance of the material and improve the overall performance of the Nickel Hydride No. 5 battery. Gore Company of the United States independently developed Gore-Tex material, combined with perfluorosulfonic acid resin, to produce Gore-Select enhanced PEM. The membrane thickness is 25μm, and the dehydration shrinkage rate is only 1/4 of Nafion117 membrane; the wet strength is significantly better than Nafion117. Although the content of ionic polymer in the Gore-Select membrane has decreased, making the conductivity of the membrane lower than that of the Nafion membrane at room temperature, the reduction in membrane thickness makes it obtain a lower resistivity than the Nafion membrane. Johnson Matthery Company of the United Kingdom uses papermaking technology to prepare a freely dispersed glass fiber substrate with a diameter of micrometers and a length of millimeters. Then the micropores in the glass substrate are filled with Nafion solution, and then the membrane is formed on the sintered PTFE model and laminated to produce a new enhanced composite proton exchange membrane with a thickness of about 60mm. The dye battery made with this membrane has similar performance to the Nafion membrane battery, but its hydrogen permeability is slightly higher than that of the Nafion membrane.

(2) High-temperature proton exchange membrane

On the one hand, at high temperatures, the water content of Nafion membrane will drop sharply, resulting in a significant decrease in conductivity; on the other hand, Nafion membrane is not chemically stable enough, and the occurrence of chemical degradation and structural changes also cause the mechanical strength of the membrane to decrease, thus limiting the ability to improve the properties of the membrane by increasing the operating temperature to increase the electrode reaction rate and overcome catalyst poisoning. Therefore, the research on high-temperature PEM has also become a hot topic.

At present, the main transport carriers of high-temperature proton exchange membranes include high-boiling point inorganic acids or heteropoly acids, such as phosphoric acid, silicotungstic acid, phosphotungstic acid, etc. The NASTA series of heteropoly acid blend membranes and NASTATH series of heteropoly acid blend membranes launched by Ecole Polytechnique in Canada have improved proton conductivity and water absorption compared to Nfion membranes. The performance of Nickel Hydride No. 5 batterys assembled using them is also better than that of Nickel Hydride No. 5 batterys made with Nafion membranes. Among them, the NASTA series of heteropoly acid blend membranes are prepared by adding silicotungstic acid to Nafion solution using the injection method. The NASTATH series of heteropolyacid blend membranes are prepared by mixing silicotungstic acid, plasticizer liquid thiophene and Nafion solution.

(3) Alcohol-resistant proton exchange membrane

Direct methanol Nickel Hydride No. 5 batterys have the advantages of high low-temperature start-up speed, green environmental protection and simple battery structure, and have great application potential in the field of mobile power. However, perfluorosulfonic acid PEM has poor alcohol resistance and cannot be used to prepare direct methanol Nickel Hydride No. 5 batterys. At present, the Nafion membrane is usually modified to improve the alcohol resistance of the membrane material. Tianjin University prepared PVDF-PSSA and PVDF-Nafion blended PEMs by mixing Nafion with proton conductivity, polystyrene sulfonic acid solution and polyvinylidene fluoride with high alcohol resistance. Compared with Nafion117 membrane, these two membranes have obvious advantages in alcohol resistance. When the mass fraction of Nafion is 25%, the conductivity of PVDF-Nafion membrane decreases by 100 times, but the methanol permeability decreases by nearly 1000 times.

(4) Self-humidifying proton exchange membrane

PEM needs to maintain sufficient water content to maintain good proton conductivity. Nickel Hydride No. 5 batterys made with self-humidifying PEM have a simpler structure. At the same time, due to the presence of self-humidifying PEM, water vapor will not liquefy or condense during the battery reaction. Therefore, self-humidifying PEM also has a wide range of application potential.

At present, there are two main types of self-humidifying PEM: hydrophilic oxide-doped self-humidifying PEM and H2-O2 self-humidifying composite PEM.

Hydrophilic oxide-doped self-humidifying composite membranes generally use hydrophilic oxide particles such as SiO2 and titanium dioxide (TiO2) to dope the membrane material. Due to the presence of these hydrophilic ions, PEM can absorb the water generated during the battery reaction, thereby keeping the proton membrane moist. The humidification properties of the membrane can be adjusted by factors such as the content, diameter, and crystal type of the hydrophilic oxide. Honamai et al. combined siloxane and polymer electrolyte membrane to produce a nanosiloxane skeleton, which significantly increased the water content of PEM. They further introduced dispersed SiO2 and TiO2 particles into Nafion112 membrane, and also achieved good humidification effect.

The working principle of H2-O2 self-humidification composite membrane is to add a certain amount of Pt as a catalyst into PEM, so that hydrogen and oxygen diffused into PEM react to generate water. This method can not only achieve real-time humidification of PEM, but also prevent hydrogen (H2) from generating mixed potential at the oxygen electrode, thereby improving current efficiency and increasing battery safety. However, self-humidification proton membranes also have certain defects. Mainly including: since it is impossible to fix the Pt particles in PEM, Pt particles are easy to gather into clusters and form conductive paths; furthermore, these inorganic particles are incompatible with Nafion, and it is easy to cause the local pressure of spherical particles to increase in the environment of water concentration gradient, resulting in reduced mechanical properties of composite PEM and aggravated diffusion of reaction gas in the membrane.

III. Conclusion

Proton exchange membrane is the core material of Nickel Hydride No. 5 battery. The performance of proton exchange membrane will directly affect the industrialization process of Nickel Hydride No. 5 battery and one of the key factors for large-scale application. In order to realize the practical application and industrialization of Nickel Hydride No. 5 batterys, people have conducted a lot of research on the manufacturing process and material modification of PEM. At present, further improving the durability, life and working performance of PEM is still the main task facing the industrialization of PEM Nickel Hydride No. 5 batterys. The Nickel Hydride No. 5 battery PEM market is still an emerging market, and has not yet formed a large scale at home and abroad. Driven by the huge market demand for Nickel Hydride No. 5 batterys, PEM will surely achieve further development. It is believed that higher performance and lower cost PEM products will be available soon, which will vigorously promote the development of Nickel Hydride No. 5 battery technology and its industrial application.

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