Effects of graphene oxide doping content and pH on energy storage performance of graphene aerogel
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摘要: 采用溶胶凝胶法制备石墨烯气凝胶（GA），并研究了前驱液中的pH值与氧化石墨烯（GO）的质量分数对GA材料储能性能的影响。使用X射线粉末衍射（XRD）、X射线光电子能谱（XPS）、氮气吸脱附分析、扫描电子显微镜（SEM）对样品微观结构与形貌进行表征。用循环伏安（CV）、恒流充放电（CP）、电化学交流阻抗（EIS）测试了样品的电化学性能。结果表明，前驱液中的pH值及GO质量分数的不同会影响GA中团簇颗粒的大小和数量，进一步影响GA三维结构。在pH值为6.3、GO 的质量分数为1%时，制得的GA比表面积最大为530 m2·g−1，在1 A·g−1的电流密度下比电容高达364 F·g−1。此外，将该材料制成对称超级电容器具有高的库伦效率，在1 A·g−1下进行CP测试，得到电容器的比电容为98 F·g−1，循环800次后其循环稳定性能为初始比电容值的95.9%。Abstract: The preparation of graphene aerogel (GA) by the sol-gel method has wide application prospects. In this study, the sol-gel method was used to prepare GA composites using resorcinol (R), formaldehyde (F), and graphene oxide (GO) as precursor materials and sodium carbonate (C) as the catalyst. The effects of the pH value and GO in the precursor solution on the energy storage performance of GA materials were studied. The microstructure and morphology of the samples were characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nitrogen desorption analysis, and scanning electron microscopy (SEM). Cyclic voltammetry (CV), constant current charge–discharge (CP) and electrochemical impedance spectroscopy (EIS) were used to measure the electrochemical properties of the samples in 1 mol·L−1 Na2SO4 electrolyte. The results show that different pH values and GO affect the size and number of cluster particles in GA and the three-dimensional structure of GA. When the pH value was 6.3 and the mass fraction of GO was 1% in the precursor solution, the obtained GA sample exhibited superior surface properties and electrochemical performance. At a current density of 1 A·g−1, the specific surface area of the GA was 530 m2·g−1, and the specific capacitance was 364 F·g−1. If the current density was increased to 10 A·g−1, the specific capacitance still reached 229 F·g−1, indicating that the GA sample had better multiplier performance. After 800 cycles at a current density of 1 A·g−1, the specific capacitance retention rate was 76%. In addition, the GA sample was utilized as a symmetrical supercapacitor with high coulomb efficiency. The specific capacitance of the capacitor remained at 98 F·g−1 in a constant current charge–discharge test at a current density of 1 A·g−1. After 800 cycles, a specific capacitance retention rate of 95.9% was maintained by the symmetrical supercapacitor. This study provides a method for improving the electrochemical properties of GA to realize supercapacitors with better performance.
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Key words:
- graphene oxide /
- graphene aerogel /
- pH /
- supercapacitor /
- electrochemical performance
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图 2 样品的SEM图。（a） GA–1–4；（b） GA–0–6.3；（c） GA–0.4–6.3；（d） GA–1–6.3；（e） GA–1–8
Figure 2. SEM images of samples：(a) GA–1–4; (b) GA–0–6.3; (c) GA–0.4–6.3; (d) GA–1–6.3; (e) GA–1–8
图 4 GA的XPS图。（a）样品GA–1–6.3的XPS图谱；（b）样品GA–1–6.3的高分辨率C 1s XPS图谱
Figure 4. XPS spectra of GA：(a) XPS spectra of GA–1–6.3; (b) high-resolution spectra of C 1s of GA–1–6.3
图 5 GA制备过程图。（a）前驱混合液照片；（b）水凝胶照片；（c）高温炭化后照片
Figure 5. Preparation process photos of GA: (a) precursor mixture; (b) hydrogel; (c) hydrogel after carbonization at high temperature
图 6 GA的CV曲线图。（a），（b） 5 mV·s−1扫描速率下样品的CV曲线图；（c）不同扫描速率下样品GA–1–6.3的CV曲线图
Figure 6. CV curves of GA: (a), (b) CV curves of sample at scanning rate of 5 mV·s−1; (c) CV curves of GA–1–6.3 at different scanning rates
图 7 GA的CP曲线图。（a），（b） 1 A·g−1电流密度下五组样品的CP曲线图；（c）样品GA–1–6.3在1 A·g−1电流密度下的循环寿命曲线图（插图为不同电流密度下样品GA–1–6.3的CP曲线图）
Figure 7. CP curves of GA: (a), (b) CP curves of sample at 1 A·g−1 current density; (c) cycle life curve of GA–1–6.3 at a current density of 1 A·g−1 (inset: CP curves of GA–1–6.3 at different current densities)
图 8 GA的EIS图及其等效电路图。（a）（b）样品的EIS曲线图；（c）电化学阻抗谱的等效电路
Figure 8. Nyquist plots and equivalent circuit of GA: (a), (b) Nyquist plots of samples; (c) the equivalent circuit for the electrochemical impedance spectra
图 9 超级电容器的CP图以及其Ragone图。（a）不同电流密度下超级电容器的CP曲线图；（b）在1 A·g−1电流密度下超级电容器的循环寿命曲线图（插图为超级电容器在1 A·g−1电流密度下第1次、第500次、第800次的CP曲线图）；（c）能量密度与功率密度的曲线
Figure 9. CP curves and Ragone plot of the supercapacitors: (a) CP curves of the supercapacitors at different current densities; (b) cycle life curves of the supercapacitors at a current density of 1 A·g−1 (inset: CP curves of the first, 500th, and 800th cycles of the super capacitors at 1 A·g−1 current density); (c) curve of energy density vs power density
表 1 五组样品的比表面积
Table 1. Specific surface areas of the samples
Sample Mass fraction of GO/% pH BET/(m2·g−1) GA–1–4 1 4 231 GA–0–6.3 0 6.3 115 GA–0.4–6.3 0.4 6.3 370 GA–1–6.3 1 6.3 530 GA–1–8 1 8 203 
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