非对称超级电容器用棉秆韧皮碳纳米片的控制制备及性能研究

As an effective energy-storage device, aqueous asymmetric supercapacitor integrates electric double layer and surface redox charge storage modes, which have many advantages such as large voltage window, high energy density and low cost. Carbon is one of mostly used supercapacitor materials, where pore size distribution and specific surface area often effects is capacitance performance. Cotton stalk as the green renewable biomass resources are rich in organic carbon, which can be transformed into the graphitic carbon material. The project is to select waste cotton stalk bast as raw material for controlled preparation of carbon nanosheets with high graphitization degree, large specific surface area, and ideal pore size distribution by hydrothermal treatment and high temperature pyrolysis chemical activation and oxidation method. On the basis of data analysis about the structure, morphology and electrochemical performance, we try to clarify electrochemical energy storage mechanism of cotton stalk bast carbon nanosheets. Furthermore, to enhance energy density, asymmetric supercapacitors can be constructed with the as-prepared Co3O4 electrode material as the positive electrode and cotton bast-based carbon nanosheets material as negative electrode. For application of cotton stalk bast carbon materials in asymmetric supercapacitor, theoretical and practical theory will be provided in this project, and the utilization rate of waste cotton stalk can be improved in the future.

水系非对称超级电容器是集物理和化学储能于一体的高效储能器件，它具有电位窗口宽、成本价、能量密度和功率密度大等特点。碳材料是超级电容器中常用的电极材料之一，其自身孔径分布和比表面积大小严重影响着电容器性能。棉秆为绿色可再生生物质资源，它来源广泛、富含有机碳，选用适当的方法可以将其转化为石墨化碳材料。本项目拟以废弃棉秆韧皮为原料，采用水热处理、高温热解化学活化氧化的方法，制备石墨化程度、比表面积、孔径分布和形貌可控的碳纳米片；在研究其结构和形貌以及电化学性能的基础上通过数据分析，努力阐明棉秆韧皮碳纳米片的控制制备原理及其电化学储能机制。将所制备的材料与四氧化三钴组装非对称电容器，增大电容器工作电压，进而有效提高其储能密度。为棉秆韧皮石墨化碳材料成为非对称超级电容器电极材料提供理论依据和实践基础，进而提高棉秆废弃物的利用率。

棉秆是一种存量巨大的农业废弃物，利用科学合理的方法和技术将其“变废为宝”实现价值升级具有重要的科学意义和研究价值。棉秆韧皮作为棉秆中纤维素最集中的部分其韧皮细胞腔体炭化后可作为电解质溶液的微储池，展现出可应用于电化学储能方面的潜在优势。项目研究中通过水热反应在活化剂的作用下对棉秆韧皮进行了初步活化处理，促进活化剂渗透到结构内部，有利于高温条件下韧皮纤维的深度刻蚀。利用高温碳化活化制备了厚度和孔径分布可控的棉秆韧皮生物质炭纳米片，及其相关的炭基复合材料。对所得材料进行物理性质表征和电化学性能测试。结果表明，棉秆韧皮生物质炭纳米片的主要孔径分布可控制在0.5-5 nm，在电流密度为0.5 A/g时比电容达330 F/g；进一步组装非对称超级电容器并进行测试分析，2-NTQ-RGO//AC在功率密度为812 W/kg时，能量密度为16.7 Wh/kg，2-NTQ-RGO//DQ-RGO在功率密度为900 W/kg时能量密度为23.4 Wh/kg。通过实验研究明确了制备条件对碳纳米片微结构的调控和表面缺陷程度的影响。水热反应中醋酸和双氧水等体积的混合溶液对棉秆韧皮中半纤维素和果胶等的活化溶解效果最好，碳化活化剂ZnCl2的刻蚀效果优于KOH和NaOH。碳化活化温度过高、时间过长容易造成细胞壁所形成的纳米片结构的坍塌，进而影响材料的电化学性能。本项目的研究为棉秆废弃物的高效利用提供了一条可行的路径，对环境保护具有重要意义。