Free-standing N-Graphene as conductive matrix for Ni(OH)2 based supercapacitive electrodes

Kush K. Upadhyay, Neli Bundaleska, Miroslav V. Abrashev, Nenad Bundaleski, O. M. N. D. Teodoro, Isabel Fonseca, André Mão de Ferro, Rui Pedro Silva, Elena Tatarova, Maria de Fátima Montemor

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Abstract

Free-standing N-doped graphene (NG2N1O) sheets with 2.3 at. % of nitrogen and residual oxygen content were synthesized using low-pressure microwave plasma. A composite made with Ni(OH)2 and NG2N1O was prepared by the hydrothermal route. Physico-chemical characterizations evidenced the formation of crystalline β-phase of Ni(OH)2 nanoplates interconnected with graphene nanosheets. The electrochemical results of N-graphene electrodes evidenced very good supercapacitive response with a high rate capability of 97%, negligible charge transfer resistance of 0.05 Ω cm2 and very low time constant of 50 ms. The specific capacity of the Ni(OH)2 + NG2N1O composite increased 20% compared to Ni(OH)2 (107 mAh g−1 vs. 86 mAh g−1, respectively) and the rate capability was 75% at current density of 10 A g−1, higher than Ni(OH)2 which retained only 34.4%. The composite showed excellent stability, by retaining 92% of its initial specific capacity after 4000 charge-discharge cycles. Furthermore, electrochemical impedance spectroscopy evidenced that graphene decreased the charge transfer resistance and diffusional contributions while enhancing the capacitive behaviour and the high-frequency response of the electrodes. An asymmetric cell was assembled using activated carbon as negative electrode and the composite as positive electrode. The cell displayed good capacitive response in a potential window of 1.8 V, in aqueous electrolyte, stored a maximum energy density of 38.64 W h kg−1 at a power density of 450 W kg−1 and retained 16 W h kg−1 at a power density of 4.7 kW kg−1.

Original languageEnglish
Article number135592
JournalElectrochimica Acta
Volume334
DOIs
Publication statusPublished - 20 Feb 2020

Keywords

  • Asymmetric supercapacitor
  • Energy storage
  • High-frequency response
  • N-doped graphene
  • Ni(OH)–N-graphene composite

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    Upadhyay, K. K., Bundaleska, N., Abrashev, M. V., Bundaleski, N., Teodoro, O. M. N. D., Fonseca, I., de Ferro, A. M., Silva, R. P., Tatarova, E., & Montemor, M. D. F. (2020). Free-standing N-Graphene as conductive matrix for Ni(OH)2 based supercapacitive electrodes. Electrochimica Acta, 334, [135592]. https://doi.org/10.1016/j.electacta.2019.135592