The PBI membrane achieves an energy efficiency of over 80% at an electric density of 200mA/cm²
Classification：Industrial News
- Author：ZH Energy
- Release time：Dec-23-2024
【 Summary 】Central South University, in collaboration with ZH Energy Storage, is dedicated to the industrialization of non-fluorinated ion-exchange membranes and has proposed a new strategy to enhance the proton
Research Question: Central South University, in collaboration with ZH Energy Storage, is committed to the industrialization of non-fluorinated ion-exchange membranes. This work explores the impact of molecular interaction regulation in polybenzimidazole (PBI) membranes on the energy efficiency of vanadium redox flow batteries (VRFBs) and proposes a new strategy to enhance the proton conductivity of PBI membranes. The related achievements have been published in ChemSusChem under the title "Regulating Molecular Interactions in Polybenzimidazole Membrane for Efficient Vanadium Redox Flow Battery."
Research Challenge: Traditional PBI membranes, due to their tightly bound structure, exhibit poor proton conductivity, which limits their application in VRFBs. How to effectively relax the membrane structure to improve proton conductivity is a challenge.
Key Arguments
By regulating the molecular interactions within PBI membranes, the proton conductivity of the membranes can be significantly improved, achieving an increase of up to 3850%. The strategy of using DMSO/water and acid treatment can effectively switch the interactions within the membrane, thereby optimizing its performance. The study reveals the structure-performance relationship of PBI membranes, providing important theoretical support for the development of VRFB membranes. Previous research has mainly focused on the selection of membrane materials and their physicochemical properties, while this paper improves membrane performance by regulating molecular interactions, offering a new perspective.
This paper proposes a method for designing high-performance PBI membranes by regulating molecular interactions, which mainly includes the following aspects:
Membrane Preparation: PBI membranes are treated with a DMSO/water mixed solution to regulate the molecular interactions within the membrane. Experiments have shown that when the proportion of DMSO reaches 67 mol%, the membrane's texture significantly softens and exhibits gel-like characteristics.
Proton Conductivity Testing: After acid treatment, the proton conductivity of the membrane increases from 1.9 mS/cm to 76.3 mS/cm, confirming the significant improvement in membrane performance. The key to this process is the formation and transformation of hydrogen bonds within the membrane. The formula is as follows:
Molecular Interaction Analysis: Changes in molecular interactions within the membrane were analyzed using Fourier Transform Infrared Spectroscopy (FT-IR) and Electrostatic Potential (ESP) methods, revealing the formation of hydrogen bonds between DMSO and PBI molecules.
Theoretical Simulation: Molecular Dynamics (MD) simulation was used to analyze the impact of varying DMSO proportions on molecular interactions within the membrane, finding that the primary molecular interactions in E-PBI membranes shifted from van der Waals forces to hydrogen bonds.
Material Selection: Selection and processing of materials such as polybenzimidazole (PBI) powder, DMSO, and acid to ensure that the membrane preparation process meets experimental requirements;
Membrane Treatment: The membrane was soaked in a mixed solution with different DMSO/water ratios for 24 hours, followed by acid treatment to achieve protonation and phase separation within the membrane;
Performance Testing: The proton conductivity, energy efficiency, and other properties of E-PBI-H+ membranes were tested in comparison with regular PBI membranes and Nafion 212 membranes to assess their potential for practical application. Experimental results showed that the energy efficiency of E-PBI-H+ membranes reached 80.5%;
Data Collection: Data on liquid absorption, expansion ratio, and proton conductivity of membranes at different DMSO ratios were collected to analyze their relationship with molecular interactions within the membrane.
The experimental results of this paper show that the strategy of regulating molecular interactions significantly improved the performance of PBI membranes:
1. Proton Conductivity Improvement: The proton conductivity of E-PBI membranes increased from 1.9 mS/cm to 76.3 mS/cm, surpassing the performance of commercial Nafion 212 membranes, validating the effectiveness of regulating molecular interactions;
2. Energy Efficiency: At 200 mA/cm², VRFBs assembled with E-PBI-H+ membranes achieved an energy efficiency of 80.5%, significantly better than the 76.1% of Nafion 212;
3. Stability Testing: E-PBI-H+-VRFB maintained high efficiency in 600 cycle tests, demonstrating its good stability and low vanadium ion permeability;
4. Formation of Porous Structure: After acid treatment, the porosity of E-PBI membranes exceeded 50%, providing space for the introduction of acid and further improving proton conductivity.
Conclusion: By regulating the molecular interactions within polybenzimidazole membranes, this paper successfully designed high-performance E-PBI-H+ membranes, significantly enhancing their proton conductivity and energy efficiency. The study shows that when the DMSO proportion reaches 67 mol%, the membrane structure is optimized, with proton conductivity increasing from 1.9 mS/cm to 76.3 mS/cm. The membrane exhibits good performance and stability in VRFB applications, providing a new direction for the development of high-performance membranes in the future.
Figure 1 illustrates the changes in molecular interactions within PBI membranes under different DMSO ratios, including hydrogen bonding patterns and FT-IR spectra. As the proportion of DMSO increases, the molecular interactions within the PBI membrane shift from hydrogen bonds between PBI molecules to hydrogen bonds between DMSO and PBI molecules. This transition leads to a relaxation of the membrane structure, thereby enhancing proton conductivity. Changes in the FT-IR spectra indicate that the introduction of DMSO strengthens the hydrogen bonding interactions within the membrane, providing better channels for proton conduction.
Figure 2: Cohesion Energy Density (CED) analysis of E-PBI membranes.
Figure 2 shows the proportion of different molecular interactions in regular PBI and E-PBI membranes, including the contributions of electrostatic forces and van der Waals forces. The proportion of electrostatic forces in E-PBI membranes significantly increases, indicating that hydrogen bonding interactions play a dominant role in the structure of the membrane, which is consistent with the enhancement of the membrane's proton conductivity, as the strengthening of hydrogen bonds aids in the migration of protons. Dynamic simulation analysis shows that the hydrogen bond strength between DMSO and PBI is high, supporting the important role of DMSO in membrane modification.
Figure 3: Changes in the surface morphology and chemical environment of the membranes.
Figure 3 displays the surface morphology of regular PBI membranes and E-PBI-H+ membranes, along with a comparison of their FT-IR spectra. The surface morphology of E-PBI-H+ membranes exhibits a distinct porous structure, which provides more space for proton transfer and helps to enhance the proton conductivity of the membrane. The comparison of FT-IR spectra shows that the characteristic peaks of DMSO in E-PBI-H+ membranes disappear, indicating that DMSO has been removed by acid treatment, and the imidazole rings in the membrane have been protonated, further improving the membrane's proton conductivity.
Figure 4: Comparison of VRFB performance.
Figure 4 compares the coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) of VRFBs assembled with Nafion 212, E-PBI-H+, and regular PBI-H+ at different current densities. The VRFB assembled with E-PBI-H+ membranes shows significantly higher CE and EE at all current densities compared to Nafion 212 and regular PBI-H+, demonstrating its superior performance in practical applications. This result validates the effectiveness of the E-PBI-H+ membrane obtained by regulating molecular interactions in enhancing VRFB performance, indicating its potential application value in clean energy storage.
Figure 5: The effects of other solvent-nonsolvent formulations.
Figure 5 presents the liquid absorption ratio and proton conductivity of membranes treated with different solvent-nonsolvent formulations, such as DMSO/ethanol and DMF/water. The results indicate that using different solvent-nonsolvent formulations can also optimize membrane performance, further validating the broad applicability of the strategy for regulating molecular interactions. This provides new ideas for future membrane material design, suggesting that different solvent combinations can effectively modulate the microstructure and properties of membranes.
These key figures quantitatively and qualitatively demonstrate the effectiveness of regulating molecular interactions within PBI membranes and their impact on membrane performance, emphasizing the important role of DMSO in membrane modification, and providing experimental evidence for the high efficiency of VRFBs. Through the analysis of these figures, the article not only reveals the mechanism of membrane performance optimization but also offers important references for future research directions.
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