Improving electron and ion transport by constructing 3D graphene nanosheets sandwiched between porous carbon nanolayers produced from resorcinol-formaldehyde resin for high-performance supercapacitor electrodes
摘要: 理想的电极结构应由具有较短传输距离的三维互穿电子和离子通道组成。本文通过在石墨烯表面构建厚度可调的间苯二酚-甲醛树脂碳，制备石墨烯纳米片三明治状多孔石墨烯基电极，并通过化学活化进一步提高树脂碳孔隙率。三维交联结构为离子提供丰富的输运通道，同时缩短离子扩散路径。此外，石墨烯网络增强电导率，促进电子传输。基于其结构特点，具有较薄树脂碳层的三明治状多孔石墨烯基纳米片电极在电流密度为0.2 A g−1的情况下，其比电容最高可达324 F g−1。与初始电容相比，在5 A g−1的大电流密度下，经过8000次充放电后，仍具有99%的容量保持率，具有良好的循环稳定性。研究结构揭示了其结构与电化学性能之间的关系，为开发高电子和离子输运效率的电极材料提供了有效策略。Abstract: An ideal supercapacitor electrode should contain three-dimensional (3D) interpenetrating electron and ion pathways with a short transport distance. Graphene-based carbon materials offer new and fascinating opportunities for high performance supercapacitor electrodes due to their excellent planar conductivity and large surface area. 3D graphene nanosheets coated with carbon nanolayers of controllable thickness from resorcinol-formaldehyde (RF) resin are constructed and activated by KOH to develop pores. Such a sandwich structure provides abundant transport channels for ions with short paths. The porous carbon nanolayers accelerate ion transport, while the graphene networks improve the conductivity, boosting electron transport. As expected, the prepared porous carbon has a high surface area of 690 m2 g−1 and a high specific capacitance of up to 324 F g−1 in a 6 mol L−1 KOH aqueous electrolyte at a current density of 0.2 A g−1. More than 99% of the capacitance is retained after 8000 charge–discharge cycles at a high current density of 5 A g−1, indicating good cycling stability. This research provides an effective strategy for the development of outstanding electrode materials for the enhanced transport of both electrons and ions.
Figure 5. Electrochemical performances of KACGS, (a) cyclic voltammograms at different scan rates, (b) galvanostatic charge/discharge cycling at different currents densities, (c) nyquist plots of the experimental impedance data, the inset shows the expanded high–frequency region of the plots (10 mHz to 100 kHz, ac amplitude, 5 mV). (d) cycling stability tests (8000 cycles) at current density of 5 A g–1 within the potential window range from 0 to –1 V.
Table 1. Comparison of electrochemical performance of KACGS with some representative active carbon-based electrodes for supercapacitors (All were tested in three electrode system).
Electrode Electrolyte Specific capacitance (F g–1) Ref. Sandwich–like hierarchical porous carbon/graphene/carbon 6 mol L−1 KOH 324 (0.2 A g−1)
224 (1A g−1)
This work N-doped ordered
6 mol L−1 KOH 227 (0.2 A g−1)  KOH-activated carbon 6 mol L−1 KOH 152.6 (0.5 A g−1)  Hollow porous carbon spheres 6 mol L−1 KOH 303.9 (0.1 A g−1)  N-containing hierarchical
porous carbon spheres
7 mol L−1 KOH 276 (0.1 A g−1)  N/S-co-doped carbon nanobowls 6 mol L−1 KOH 279 (0.1 A g−1)  MXene-bonded activated carbon 1 mol L−1 Et4NBF4/AN 126 (0.1 A g−1)  N-doped mesoporous carbon 6 mol L−1 KOH 218 (0.5 A g−1)  3D Carbon aerogels 6 mol L−1 KOH 151 (0.5 A g−1)  Branched carbon nanotube/carbon nanofiber composite 1 mol L−1 H2SO4 207 (1 A g−1) 
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