• Bundaleska, Neli
• Abrashev, Miroslav V.
• Montemor, Maria De Fátima
• Teodoro, Orlando
• Upadhyay, Kush K.
• Bundaleski, N.
• Silva, Rui Pedro
• Tatarova, Elena
• Fonseca, I. M.
• Ferro, André Mão De

Abstract

<p>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.</p>

Topics

• density
• impedance spectroscopy
• Carbon
• energy density
• phase
• Oxygen
• Nitrogen
• composite
• mass spectrometry
• current density
• oxygen content