高效能反电渗析盐差能转换技术基础理论研究

The development of salt gradient energy conversion technology by reverse electrodialysis in recent years has mainly focused on improving the energy conversion efficiency, which is mainly determined by the performance of ion exchange membranes as well as the energy consumption of the whole system. For that reason, the present project is devoted to investigate the energy conversion and transportation mechanism in the nanochannel which is the basic functional units in the reverse electrodialysis system. We employ the graphene and molybdenum disulfide layer respectively as the ion exchange membrane material. Using the high precision nanofabrication and characterization techniques of transmission electron microscopy and focused ion beam, we achieve cross micro-nano scale fabrication and characterization on the single layer membrane. In order to regulate the surface charge density of solid - liquid interface, we measure the structure of double electrode layer on surface accurately by atomic force microscope, and analyze the mechanism of the formation of double layer of solid - liquid interface. Then we theoretical analysis the viscous resistance effect of double-layer structure to ion transport in nanochannel reverse electrodialysis system and try to propose a feasible method to reduce the electrical adhesion effect. Finally, we establish and optimize the molecular dynamics model of the ion transport in the nanopore according the experiment data. The influence of ion transportation in nanofludic are ivestigated include the rheological properties, the structure scale effect of nanochannel and the surface effect of solid - liquid interface. The study of this project will provide a scientific improvement for the design and development of a high-performance salt gradient energy conversion system by reverse electrodialysis.

现阶段反电渗析盐差能转换技术发展的重点是提升其能量转换效率，而能量转换效率主要取决于离子交换薄膜的性能以及整个系统的能耗。本项目针对反电渗析系统中的基本功能单元——纳米孔道的转能机理及能量输运规律展开专门性的研究，分别选用石墨烯和二硫化钼这两种二维薄膜作为离子交换薄膜材料，借助透射电子显微镜和聚焦离子束高精度纳米加工与表征技术，实现跨微、纳尺度的加工与性能表征。通过精确测量纳米孔道表面双电层结构，分析不同固液界面双电层产生的机理进而实现固液界面表面电荷的调控，理论分析固液界面双电层结构对纳米孔道反电渗析盐差能转换系统中离子输运的粘滞阻力的影响并提出可以减小电粘附效应的可行性方法。最后依据实验建立并优化离子在纳米孔内输运的分子动力学模型，明确纳尺度下流体的流变特性、结构尺度效应、表面效应对纳通道下离子输运规律的影响。这些工作的开展将为设计和开发高效能反电渗析盐差能转换系统提供科学的改进方案。

现阶段反电渗析盐差能转换技术发展的重点是提升其能量转换效率，而能量转换效率主要取决于离子交换薄膜的性能以及整个体系的能耗。本项目针对反电渗析系统中的基本功能单元——纳米孔道的转能机理及能量输运规律展开专门性的研究。首先针对5nm以下跨尺度纳米孔集成制造做了详细研究，通过项目开展分别研制出不同制备工艺路线，包括聚焦离子束溅射、投射电子显微镜溅射以及介电穿孔制备工艺，该部分研究成果为项目后续研究开展提供了器件基础。在项目研究过程中，对纳米孔内离子输运的迁移率进行了详细的研究，通过实验发现在纳米孔环境下，离子的迁移率随着孔径的下降会比体态的迁移率要低很多，其主要原因是在孔径越小的情况下，孔内离子对形成的概率变大，从而导致离子迁移率的下降。为了进一步研究纳米孔内离子迁移率的输运特性，通过NAMD分子动力学仿真，进一步验证纳米通道内由于纳米孔孔径的减小，离子水合层的剥离，导致纳米受限环境下阴阳离子更容易形成离子对，从而导致离子迁移率下降，这对盐差能发电功率密度有及其重要影响。该研究成果已发表在国际一流期刊杂志《Journal of the American Chemical Society》。针对纳米孔发电渗析盐差能发电研究，分别针对氮化硅与石墨烯两种材料做了相关研究，通过研究分别探索了纳米孔孔径，浓度差比，纳米孔阵列数量以及壁面电荷密度等多个参数对盐差能发电功率影响。同时结合COMSOL仿真建立了基于纳米孔反电渗析盐差能发电理论模型，通过理论计算，以51nm孔径纳米孔为例，如果纳米孔孔隙率达到30%，那么纳米孔发电功率密度可以达到16649Wm-2。 该研究成果已发表《Nano》杂志，同时该纳米孔阵列结构申报专利1项。通过本项目研究，为设计和开发高效能反电渗析盐差能转换系统提供奠定理论基础与科学的改进方案。