On June 1st, the National Development and Reform Commission and nine other departments issued the "14th Five Year Plan" for the development of renewable energy. It is required to promote green hydrogen substitution in key areas such as chemical industry, coal mining, and transportation. Promote the demonstration application of fuel cells in industrial and mining areas, port areas, ships, key industrial parks, etc., coordinate the construction of green hydrogen terminal supply facilities and capacity, and increase the proportion of green hydrogen use in the transportation sector. However, currently, over 95% of hydrogen is generated through fossil fuels such as methanol cracking, coal gasification, and partial oxidation of hydrocarbons. This is mainly due to its low cost and simple process. However, with the requirements of the "dual carbon" goal, the development of hydrogen production through electrolysis of water will become an important link in the development of renewable energy and gradually replace traditional fossil energy hydrogen production.

At present, electrolysis of water for hydrogen production accounts for about 4% of the world's hydrogen production [1], and the purity of hydrogen produced can reach 99.999%. The "heart" of electrolysis of water for hydrogen production is proton exchange membranes. In the previous article, we introduced cation exchange membranes (proton exchange membranes). In addition to the most commonly used cation exchange membranes, there are also solid oxide electrolysis of water, alkaline electrolysis of water, and anion exchange membrane electrolysis of water. Due to its low cost and stable hydrogen production, research on anion exchange membrane electrolysis of water for hydrogen production is constantly receiving attention and development. The principle of anion exchange membranes is mainly to use positively charged functional groups (including quaternary ammonium salts, imidazole salts, quaternary phosphine salts, etc.), which form a positive electric field to attract OH - and achieve the transfer of OH - ions in the electrolyte, while blocking the passage of cations.

At present, anion exchange membrane electrolysis of water combines the advantages of low cost of anion exchange membranes and high efficiency and convenience of proton exchange membrane electrolysis of water. It is the latest developed electrolysis technology and is still in the laboratory research stage. Anion exchange membrane electrolysis of water can use transition metal catalysts instead of precious metal catalysts in PEM electrolysis, reducing costs. In addition, anion exchange membrane electrolysis of water can use pure water or low concentration alkaline aqueous solutions as electrolytes, alleviating the corrosion of equipment caused by strong alkaline solutions. At the same time, anion exchange membrane electrolysis of water does not require the use of expensive perfluorosulfonic acid membranes, which can further reduce material costs. However, it also faces many problems such as stability, durability, and electrolysis efficiency that need to be solved urgently.

     The main categories of anion exchange membranes (AEMs) currently include polyarylether anion exchange membranes, aryl ether free anion exchange membranes, and other anion exchange membranes. There have been many studies on polyarylethers based anion exchange membranes, mainly focusing on inexpensive and readily available categories such as polysulfone (PSF), polyphenylene oxide (PPO), and polyaryletherketone (PEAK) [3]. A large number of studies have found that anion exchange membranes have poor alkali resistance and insufficient ion conductivity in alkaline environments, which urgently need to be solved. During the operation of the anion exchange membrane electrolysis water device, the local strong alkaline environment formed on the membrane surface causes the anion exchange membrane to degrade under the attack of hydroxide ions. The resulting membrane perforation can cause battery short circuit, making the anion exchange membrane electrolysis water device unable to operate for a long time. Therefore, the development of high-performance anion exchange membranes under strong alkaline conditions is of great significance.

The anion exchange membrane is composed of a polymer main chain and ion exchange groups. The polymer main chain serves as the structural framework and is mainly responsible for providing certain mechanical strength, while the ion exchange groups are mainly responsible for ion conduction [2]. In polyarylethers anion exchange membranes, the polymer main chain often contains ether oxygen bonds. Under high temperature and alkaline conditions, the ether oxygen bonds are easily broken, causing structural instability and the rupture of the anion exchange membrane, greatly reducing the mechanical strength of the anion exchange membrane. Therefore, recently developed six membered cyclic organic compounds without ether oxygen bonds, such as piperidine groups, as well as other organic anion exchange membranes without ether oxygen bonds, have shown excellent alkali resistance and ion conductivity [4].

For ion exchange groups, the first quaternary ammonium salt groups used are also easily replaced and eliminated by hydroxide ions in high-temperature alkaline environments, resulting in the loss of ion exchange ability in anion exchange membranes. Therefore, in recent years, various chemically stable functional groups such as aromatic quaternary ammonium salts, non aromatic cyclic amine salts, and metal center cations have been continuously developed as ion exchange groups in anion exchange membranes. In addition to using structurally stable ion exchange groups, increasing the density of cation groups in the anion exchange membrane to enhance the overall hydroxide ion conductivity of the membrane is also an effective strategy [5]. At present, research is focused on more effective directional arrangement of ion groups within the membrane, in order to form certain ion channels. The formation of such channels is often achieved by introducing and regulating various intermolecular forces, thereby promoting the spontaneous assembly and arrangement of functional groups on the anion exchange membrane, and forming microphase separation within the polymer, thereby obtaining anion exchange membrane materials with higher hydroxide ion conductivity [6].

Currently, electrolysis of water for hydrogen production still has significant cost constraints and limitations. However, according to a research report by Fotile Securities, with the continuous decrease in electricity costs brought about by increased production capacity, advancements in electrolysis of water technology, and the maturity of renewable energy generation, the cost of renewable energy electrolysis for hydrogen production (green hydrogen) will continue to decline, which will also contribute to the widespread promotion of renewable energy electrolysis for hydrogen production technology. At present, the installed capacity of electrolytic water worldwide is growing rapidly. According to IEA statistics, the annual installed capacity of electrolytic water worldwide has increased rapidly in recent years. In 2014, the global installed capacity of electrolytic water was only 9.1 MW; By 2019, the newly added scale of global electrolysis water facilities reached 25.4MW that year. Meanwhile, based on published project data, IEA predicts that it will reach 1433.1 MW by 2023.

     With such rapid growth in installed capacity of electrolytic water, both mainstream proton exchange membranes and developing anion exchange membranes have unlimited prospects. With the continuous support of national policies and technological advancements, it is easy to anticipate that the hydrogen energy industry will become an important component of the energy industry in the coming decades. Clean and green electrolytic water hydrogen production will undoubtedly gradually achieve development goals and achieve comprehensive promotion in the near future.

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Reference materials

[1] Yang Xiong Preparation and Performance Study of Ether Free Alkaline Polymer Membranes for Electrolysis of Water [D]. Dalian University of Technology, 2020. DOI: 10.26991/dcnki.gdllu.2020.002887

[2] Su Xiangdong Preparation and water electrolysis performance of piperidine functionalized anaerobic polymer membranes [D]. Dalian University of Technology, 2019 DOI: 10.26991/dcnki.gdllu.2019.000826

[3] You W, Noonan K J T, Coates G W. Alkaline table any exchange members: a review of synthetic approaches [J] Progress in Polymer Science, 2020, 100:101177.

[4] Xu Ziang, Wan Lei, Liu Kai, et al. Research progress in molecular design for highly stable alkaline ion membranes [J]. Journal of Chemical Engineering, 2021, 72 (8): 3891-3906. Xu Z A, Wan L, Liu K, et al. Recent progress of molecular design for highly stable alkaline ion exchange membranes [J] CIESC Journal, 2021, 72 (8): 3891-3906

[5] Lu W T, Yang Z Z, Huang H, et al. Piperidinium functionalized poly (vinylbenzyl chloride) cross linked by polybenzimidazole as an ion exchange membrane with a continuous ionic transport pathway [J] Industrial&Engineering Chemistry Research, 2020,59 (48): 21077-21087

[6] Wang Peican, Wan Lei, Xu Ziang, Xu Qin, Wang Baoguo. Current Status and Prospects of Alkaline Membrane Electrolytic Water Hydrogen Production Technology [J]. Journal of Chemical Engineering, 2021, 72 (12): 6161-6175

More content

Mechanism and Types of Proton Exchange Membranes Used for Hydrogen Production from Electrolytic Water

Domestic production and non fluorination progress of ion exchange membranes for flow batteries

Progress in the application of polybenzimidazole (PBI) film in fuel cells



Reference materials

[1] Yang Xiong Preparation and Performance Study of Ether Free Alkaline Polymer Membranes for Electrolysis of Water [D]. Dalian University of Technology, 2020. DOI: 10.26991/dcnki.gdllu.2020.002887

[2] Su Xiangdong Preparation and water electrolysis performance of piperidine functionalized anaerobic polymer membranes [D]. Dalian University of Technology, 2019 DOI: 10.26991/dcnki.gdllu.2019.000826

[3] You W, Noonan K J T, Coates G W. Alkaline table any exchange members: a review of synthetic approaches [J] Progress in Polymer Science, 2020, 100:101177.

[4] Xu Ziang, Wan Lei, Liu Kai, et al. Research progress in molecular design for highly stable alkaline ion membranes [J]. Journal of Chemical Engineering, 2021, 72 (8): 3891-3906. Xu Z A, Wan L, Liu K, et al. Recent progress of molecular design for highly stable alkaline ion exchange membranes [J] CIESC Journal, 2021, 72 (8): 3891-3906

[5] Lu W T, Yang Z Z, Huang H, et al. Piperidinium functionalized poly (vinylbenzyl chloride) cross linked by polybenzimidazole as an ion exchange membrane with a continuous ionic transport pathway [J] Industrial&Engineering Chemistry Research, 2020,59 (48): 21077-21087

[6] Wang Peican, Wan Lei, Xu Ziang, Xu Qin, Wang Baoguo. Current Status and Prospects of Alkaline Membrane Electrolytic Water Hydrogen Production Technology [J]. Journal of Chemical Engineering, 2021, 72 (12): 6161-6175

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