In view of the current global environmental pollution, fossil fuel shortages, and energy security issues, renewable energy has become the focus of attention of governments and scientists in all countries, but the randomness and instability of renewable energy sources such as solar, wind, and tidal power make them Development and application are limited. All vanadium redox flow batteries (referred to as vanadium batteries) have the advantages of long life, good flexibility, deep discharge, small cross-contamination, and good stability, and can be used as a clean, efficient, large-scale energy storage device. Provide technical support for the continuous use of renewable energy.
As a key material for vanadium batteries, proton exchange membranes can not only provide H+ transmission channels for positive and negative electrolytes, but also can prevent self-discharge effects caused by cross-contamination of positive and negative electrolytes. Proton exchange membranes have become the bottleneck for the development of vanadium batteries. At present, vanadium batteries are mainly commercialized perfluorinated sulfonic acid ion exchange membranes, mainly Nafion membranes (United States, Dupont), and Nafion membranes are strongly acidic. The electrolyte is relatively stable, and the proton conductivity is also high, but the penetration of vanadium ions is relatively serious, which can easily lead to the battery's self-discharge effect to reduce the battery efficiency, and the price is expensive.
The separator of vanadium battery can be divided into anion exchange membrane (AEM) and cation exchange membrane (PEM). The application of PEM (such as Nafion membrane) to vanadium battery after modification treatment also shows certain vanadium resistance performance, due to the The negatively charged groups can attract positively charged vanadium ions, and cannot fundamentally reduce the permeability of vanadium ions; relatively speaking, the Donan repulsion between positively charged groups on the AEM and vanadium ions can effectively prevent vanadium The permeation of ions fundamentally prevents self-discharge effects caused by cross-contamination of electrolytes on both sides of the membrane. Therefore, the development of AEMs with high proton conductivity, good resistance to vanadium, good chemical stability, and low cost has very important research and practical significance.
Recently, the vanadium battery group of the Environmental Protection Functional Membrane Materials and Applications Division of the Polymer Division of the Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences has successfully prepared polyetherether sulfones containing imidazole salt side groups that can be used for different degrees of bromination of vanadium batteries. Anion exchange membranes (QIm-PEES-AEMs), in order to better elucidate the relationship between the “structure-performance†of AEMs, the proton conductivity, water absorption, swelling degree, stability, vanadium ion permeability and the prepared AEMs Its battery performance in vanadium batteries was tested and compared with the relative performance of Nafion 117.
Tests have shown that the optimized polyetherethersulfone anion exchange membranes can achieve a conductivity of 7.3 x 10-2 S/cm (VS 8.3 x 10-2 S/cm) and a vanadium ion permeability of only 5.5 x 10-9 cm 2 . At min (VS 6.49 x 10-7 cm2/min), at a current density of 60 mA/cm2, the Coulomb efficiency of the film reached 93.4% (VS 89.3%), and the energy efficiency reached 77.6% (VS 78.8%), which was comparable to that of Nafion 117. Comparable conductivity and energy efficiency, as well as lower vanadium ion permeability and better stability than Nafion 117. It is worth noting that QIm-PEES-AEMs are only one-tenth the cost of preparation of Nafion117 membranes and the preparation process is simple and effectively avoids the use of the carcinogenic agent chloromethyl ether in the traditional chloromethylation process.
This part of the research work was supported by the project funding of the Ministry of Science and Technology (2014BAJ02B02) and the Ningbo Municipal Science and Technology Bureau (2014B81004, 2014S10007).
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