高负载量镍钴基纳米阵列超电容电极的原位碱转化研究

Three-dimensional free-standing Ni/Co-based nanoarray electrodes grown on carbon cloth substrate poss unsatisfactory behavior in charge-storage performances due to their low surface area and electrical conductivity, although the smart shape in nanowire arrays is formed. Moreover, the direct growth of active material with a large mass loading on carbon fibers is difficult because of the hydrophobic nature. In-situ alkali conversion of Ni/Co carbonate hydroxide electrode is a facile way to enhance the electrochemical performance with low operation cost. In our previous work, a“two-step”growth route was adopted to achieve Ni-Co carbonate hydroxide nanowire arrays, while an electrochemical pre-activation before the second hydrothermal step was involved to increase the mass loading od active materials on the surface of carbon cloth. Then, in-situ alkali conversion is used to boost the specific and areal capacity by converting Ni-Co carbonate hydroxide nanowires to hydroxide nanowire-supported nanoplate arrays in an alkaline solution. However, the elaborate synthetic way to obtain the advanced precursors of Ni/Co-based nanoarrays, and to increase the conductivity of active materials which is critical for the charge transport kinetics, has not been identified yet. This project will do more work to concern the effect of electrochemical pre-activation on the growth and the alkali conversion of Ni/Co based nanoarrays with high mass loading. Meanwhile, electronic conductivity and surface activity of electrodes can be enhanced via doping effect and chemical reduction, resulting in the high capacity of Ni/Co based hydroxide nanoarrays. The working mechanism and the application potential for in-situ conversion will be illustrated, which provides a novel knowledge for the elaborate design of free-standing electrodes with high-performance.

导电碳布表面生长的三维“自支撑”镍钴基复合化合物纳米线阵列具有良好的结构特征，但局限于比表面积小、电导率低的缺点，其超电容性能并不理想。并且，由于导电碳布基底亲水性较差，在其表面很难实现活性物质的高负载量。碱式碳酸盐电极的原位碱转化是一种成本低、操作灵活的电容量提高手段。在前期工作中，我们通过电化学预活化辅助的“二次生长”过程，实现了负载量的有效提升。所得电极经过原位碱转化，质量和面积比容量都有较大增长。如何获得高负载量镍钴纳米阵列前驱体的合理结构，以及如何提升电极导电能力，目前仍有待探究。在本项目中，我们将深入地研究电化学预活化对所形成纳米阵列以及其后期碱转化过程的影响，实现差异化电极的制备，并希望通过掺杂效应和化学还原方式，提高电极的电导率和表面活性位点数量，从而有效提高电极的电荷存储性能。项目将系统阐述碱转化技术的应用范围及作用机制，为设计高性能“自支撑”电极提供新思路。

高负载量电极是实现超级电容器高容量和高能量密度输出的关键。在本项目中，我们借助表面修饰和电活化方式，提高了镍钴碱式碳酸盐和NiCo LDH等电极材料在导电碳布表面的负载量；借助“差异化”沉积方式，利用氢氧化物在不同溶剂中的沉淀方式差异，制备了多孔纳米结构阵列，增加纳米阵列内部的电解质传递通道数量，提高其活性物质利用率；借助“碱转化”方式，通过阴离子交换手段，减少层状氢氧化物内部的大半径阴离子数量，提高OH-离子在电极材料内的迁移容量；还通过改变金属离子的配位环境，实现了金属离子的价态变化，增强金属离子间的电荷转移作用，实现协同效应增强；借助“差异化”沉积理念，获得了高负载量和高容量的双金属尖晶石型硫化物阵列电极。在对镍钴基纳米阵列结构的生长行为深入认识的基础上，进一步拓展“碱转化”手段的应用领域，在泡沫镍网表面生长镍钴基纳米片阵列，探讨了其结构差异对电荷存储性能的影响，为更深入认识超级电容器工作机制提供借鉴。