Effects of graphene oxide doping content and pH on energy storage performance of graphene aerogel
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摘要: 采用溶膠凝膠法制備石墨烯氣凝膠（GA），并研究了前驅液中的pH值與氧化石墨烯（GO）的質量分數對GA材料儲能性能的影響。使用X射線粉末衍射（XRD）、X射線光電子能譜（XPS）、氮氣吸脫附分析、掃描電子顯微鏡（SEM）對樣品微觀結構與形貌進行表征。用循環伏安（CV）、恒流充放電（CP）、電化學交流阻抗（EIS）測試了樣品的電化學性能。結果表明，前驅液中的pH值及GO質量分數的不同會影響GA中團簇顆粒的大小和數量，進一步影響GA三維結構。在pH值為6.3、GO 的質量分數為1%時，制得的GA比表面積最大為530 m2?g?1，在1 A?g?1的電流密度下比電容高達364 F?g?1。此外，將該材料制成對稱超級電容器具有高的庫倫效率，在1 A?g?1下進行CP測試，得到電容器的比電容為98 F?g?1，循環800次后其循環穩定性能為初始比電容值的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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圖 2 樣品的SEM圖。（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
圖 4 GA的XPS圖。（a）樣品GA–1–6.3的XPS圖譜；（b）樣品GA–1–6.3的高分辨率C 1s XPS圖譜
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
圖 5 GA制備過程圖。（a）前驅混合液照片；（b）水凝膠照片；（c）高溫炭化后照片
Figure 5. Preparation process photos of GA: (a) precursor mixture; (b) hydrogel; (c) hydrogel after carbonization at high temperature
圖 6 GA的CV曲線圖。（a），（b） 5 mV?s?1掃描速率下樣品的CV曲線圖；（c）不同掃描速率下樣品GA–1–6.3的CV曲線圖
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
圖 7 GA的CP曲線圖。（a），（b） 1 A?g?1電流密度下五組樣品的CP曲線圖；（c）樣品GA–1–6.3在1 A?g?1電流密度下的循環壽命曲線圖（插圖為不同電流密度下樣品GA–1–6.3的CP曲線圖）
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)
圖 8 GA的EIS圖及其等效電路圖。（a）（b）樣品的EIS曲線圖；（c）電化學阻抗譜的等效電路
Figure 8. Nyquist plots and equivalent circuit of GA: (a), (b) Nyquist plots of samples; (c) the equivalent circuit for the electrochemical impedance spectra
圖 9 超級電容器的CP圖以及其Ragone圖。（a）不同電流密度下超級電容器的CP曲線圖；（b）在1 A?g?1電流密度下超級電容器的循環壽命曲線圖（插圖為超級電容器在1 A?g?1電流密度下第1次、第500次、第800次的CP曲線圖）；（c）能量密度與功率密度的曲線
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
久色视频表 1 五組樣品的比表面積
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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