| Supercapacitor, also known as electrochemical capacitor, is a novel energy storage device that has drawn considerable attentions because of its high specific power density, fast charging/discharging rate, long cycle life and wide operation temperature. As the crucial component in supercapacitor, the electrode materials determine the overall performance of a supercapacitor. Graphene holds great promises supercapacitor in view of its good electrical conductivity, extremely high theoretical surface area (2630 m2/g) and stable physiochemical properties. However, the strong Van der Waals interctions between graphene layers usually leads to serious agglomeration which not only decreases the ion-accessible surface area, but also brings in a large ion diffusion resistance.Introducing nanopores on 2D graphene planes can not only increases the specific surface area for effective charge storage, but also promotes the ion kinetics, leading to an excellent rate capability. In this work, graphene-like materials with abundant in-plane nanopores were prepared by a chemical vapor deposition (CVD) method with ferrocene as precursor and the in-situ generated Fe2O3 as etching reagent. The inorganic template including flake-like MgO and hexagonal MgAl-LDO flakes were successfully applied as sascifical template to grow graphene nanomesh that is characterized by less aggregated structure, abundant in-plane nanopore and large specific suface area. The main achievements were summarized as following:GNM with few-layers, less-stacking and high specific surface area up to 1754 m2/g has been successfully prepared through a CVD method with ferrocene as the carbon precursor and ultrathin MgO as sacrificial template. Structural characterization shows that there are numberous mesopores of 4-8 nm and the large mesopore of 10-20 nm, along with the macropores of 100-200 nm on the graphene sheets. The specific capacitance of GNM reached 303 F/g at current density of 0.5 A/g in 6.0 mol/L K.OH electrolyte. A rectangular CV curve is kept for a symmetric GNM-based supercapacitor even at a very high scan rate of 1.0 V/s in 6.0 mol/L KOH electrolyte. The relaxation time constant (τ0) of GNM-based supercapacitor was measured to be 473 ms and 3.5 s in aqueous KOH and TEABF4/AN electrolyte, respectively, which were significantly less than those of graphene electrode without in-plane nanopores.Hexagonal carbon nanomesh (CNM) was prepared by the same CVD method whilst using MgAl-layered double oxides (MgAl-LDO) as template. The in-situ generated Fe2O3 nanoparticles play important role in pore generation. It was found that both the pore size and pore density strongly depend on the CVD times and annealing time. Under the optimized preparation conditions, CNM-60-90 sample (prepared at CVD times of 60 min, following by thermal annealing in flowing N2 at 800 ℃ for 90 min) exhibited a surface area of 1440 m2/g with mesoporous of 1-8 nm and the larger mesoporous about 20 nm in the 2D planes and the pore surface density of 2.11 x 103 μm-2. A high capacitance value as large as 271 F/g can be achived at current density of 1.0 A/g in 6.0 mol/L KOH electrolyte. A supercapacitor assemblied with the GNM-60-90 as symmetric electrode showed an excellent cycling stability with 97.5% capacitance retention after 3000 cycles at current density of 3.0 A/g. In control experiment, we obtained carbon sheets by etching the MgAl-LDO template before thermal annealing treatment. Unde the identical measurement condition, the GNM exhibited superior capacitive performances as compared with carbon sheets with respect in the specific capacitance, rate capacitance and relaxtion time constant. |
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