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    褶皱石墨烯电极-水系电解液界面性质的分子模拟研究

    Molecular Simulation Study on the Interfacial Properties of Wrinkled Graphene Electrode-Aqueous Electrolyte

    • 摘要: 石墨烯因其高比表面积、优异的导电性和良好的化学稳定性被广泛用作超级电容器电极材料。然而,在实际制备和应用中,石墨烯通常存在褶皱、形变等表面粗糙结构。其对电极/电解液界面性质的调控机制仍需进一步明确。本文构建平坦石墨烯电极及不同振幅褶皱石墨烯电极模型,采用恒电势分子动力学方法研究2 mol/L NaCl水溶液中的界面结构及电容响应。结果表明褶皱结构削弱近界面水分子和Na+/Cl−的规整层化分布,使密度峰表现出峰值降低、峰形展宽和峰位外移,并随振幅增加呈现更明显的多峰化特征。二维密度和水分子结构分析进一步表明,波谷区域更易诱导反离子局部富集和界面水偶极重排,水分子取向及氢键连接均表现出空间非均一性。相应地,电解液侧电荷补偿也呈现明显的形貌依赖性。外加电势引起的电荷重排主要集中在双电层区域,是由离子富集和水分子偶极响应共同决定的。褶皱电极电容高于平坦电极。高振幅体系表现出更强电荷响应。论文系统阐明了褶皱诱导的非均一双电层形成和电荷补偿机制。研究结果可为石墨烯基超级电容器电极形貌调控及绿色储能器件设计提供理论基础。

       

      Abstract: Graphene is widely used as an electrode material for supercapacitors, due to the high specific surface area, excellent electrical conductivity, and good chemical stability. However, during practical preparation and application, rough surface structures are often observed on graphene, including wrinkles and deformations. Their regulatory effects on the electrode/electrolyte interface properties need to be further clarified. In this work, flat graphene electrode models and wrinkled graphene electrode models with different amplitudes were constructed. The interfacial structures and capacitive responses in 2 mol/L NaCl aqueous solution were investigated by constant-potential molecular dynamics method. The results show that the wrinkled structures weaken the regular layered distribution of water molecules and Na+/Cl− near the interface. Density peaks are decreased in height, broadened in width, and shifted outward. More pronounced multi-peak features are observed with increasing amplitude. Further analyses were performed using two-dimensional density distributions and water orientation analyses. It was revealed that the trough regions are more likely to induce local enrichment of counterions and dipole rearrangement of interfacial water. The orientation of water molecules and their hydrogen bonding are uneven in space. Accordingly, the way the electrolyte side balancing charge also clearly depends on the surface shape. The charge rearrangement induced by applied potentials is mainly confined to the electrical double-layer region. This rearrangement is determined jointly by ion enrichment and dipole responses of water molecules. Higher capacitance is exhibited by wrinkled electrodes than by flat electrodes. Stronger charge responses are shown in high-amplitude systems. The formation of heterogeneous electrical double layers and the charge compensation mechanisms induced by wrinkles are systematically elucidated in this paper. Theoretical foundations are provided by these findings for the morphology control of graphene-based supercapacitor electrodes and for the design of green energy storage devices.

       

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