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    Phosphorus-doped carbon/carbon nanotube hybrids as high-performance electrodes for supercapacitors

    Year: 2020

    Journal: Electrochim. Acta, Volume 354, SEP 10

    Authors: Rey-Raap, Natalia; Granja, Miguel A. C.; Pereira, Manuel Fernando R.; Figueiredo, Jose Luis

    Organizations: Project UNIRCELL [POCI-01-0145-FEDER-016422]; European Structural and Investment Funds (FEEI) through - Programa Operacional Competitividade e Internacionalizacao - COMPETE2020; FCT - Fundacao para a Ciencia e a Tecnologia, I.P; Associate Laboratory LSRE-LCM [UIDB/50020/2020]; FCT/MCTES (PIDDAC)

    Keywords: Hydrothermal carbons; Carbon nanotubes; Phosphorus functionalities; Pseudocapacitance; Electric double-layer capacitor

    P-doped carbon hybrids were prepared by hydrothermal carbonization of glucose in the presence of CNT followed by chemical activation with phosphoric acid. The role played by phosphoric acid on the final textural and chemical properties of the samples was thoroughly investigated by varying the temperature of activation. Temperatures higher than 700 degrees C were needed to chemically activate the samples, while 800 degrees C is the optimum temperature to generate the largest amount of micropores. In addition to oxygen functional groups such as carboxylic acids, anhydrides, lactones, phenols and carbonyl quinones, several phosphorus functional groups are also detected. At 700 degrees C, only C-O-P-O-3 and C-P-O-3 groups are observed; meanwhile, C-3 -P=O and C-3-P groups appear at 800 degrees C and 900 degrees C, respectively. The oxygen moieties bonded to carbon and the phosphates (C-O-P-O-3) contribute significantly to the pseudocapacitance; the oxygen groups linked to phosphorus (C-P-O-3 and C-3-P=O) enhance the electrostatic charge and the non-oxygen functional group (C-3-P) increases the capacitance retention. The P-doped hybrid treated at 800 degrees C resulted in a porous carbon material with 806 m(2) g(-1) active surface area and high phosphorus content (6.6%) that increases the total capacitance from 26 (non-doped hybrid treated at 700 degrees C) to 124 F g(-1) at 1 A g(-1). Besides, its high content of phosphorus increases the rate capability (115 F g(-1) at 10 A g(-1)), resulting in an electrode material with higher performance at large current density than that of commercial activated carbon Supra50. (C) 2020 Elsevier Ltd. All rights reserved.
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