Hierarchical graphene network sandwiched by a thin carbon layer for capacitive energy storage

A simple yet efficient one-step route is reported to prepare a three-dimensional interconnected thin-layer carbon network consisting of graphene sheets sandwiched by a porous carbon layer (PCG). Our route relies on the direct pyrolysis of ethylene diamine tetraacetic acid tripotassium salt (EDTA-3K) in the presence of polyelectrolyte-functionalized graphene oxide (GO) at 750 °C. The decomposition of EDTA-3K at elevated temperature yields carbon and potassium species, which in turn serves as an activation agent to generate highly porous carbon layer on graphene sheets. Due to the reduced ion diffusion length, improved wettability and electrical conductivity, PCG electrode exhibits a higher specific capacitance, better rate capability together with smaller ion transport resistance in both aqueous KOH and organic electrolyte as compared with the counterpart carbon electrode prepared by direct pyrolysis of EDTA-3K in the absent of GO. Moreover, PCG electrode shows excellent cycling stability with 97% and 94.3% capacitance retention after 20,000 and 5000 consecutive charge-discharge cycles in aqueous and non-aqueous electrolytes, respectively. Further constant voltage floating experiment by holding the cell voltage at 2.5 V for 200 h confirms the high stability of PCG electrode in TEABF4/AN electrolyte. These performance demonstrate that PCG hybrid could be one of promising candidates for electrochemical energy storage.

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