Plasma-grown graphene petals templating Ni–Co–Mn hydroxide nanoneedles for high-rate and long-cycle-life pseudocapacitive electrodes

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Vol. 3; no. 45; pp. 22940 - 22948
• Main Authors: Xiong, Guoping, He, Pingge, Liu, Lei, Chen, Tengfei, Fisher, Timothy S.
• Format: Journal Article
• Language: English
• Published: 01.01.2015
• Subjects: Capacitance; Charge; cobalt; corolla; Devices; electrochemistry; Electrodes; graphene; hot water treatment; Hydroxides; manganese; Nanostructure; Nickel; Petals; specific energy; synergism
• ISSN: 2050-7488; 2050-7496; 2050-7496
• DOI: 10.1039/C5TA05441A

Ni–Co–Mn triple hydroxide (NCMTH) nanoneedles were coated on plasma-grown graphitic petals (GPs) by a facile one-step hydrothermal method for high-rate and long-cycle-life pseudocapacitive electrodes. Structural and compositional characteristics of NCMTHs indicate that the multi-component metal elements distribute homogeneously within the NCMTHs. Comparison of the electrochemical performance of the three-dimensional NCMTH electrodes to Ni–Co double hydroxides reveals that a synergistic effect of the hierarchical structure of GPs and NCMTHs enables their high rate capability and long cycle life. The NCMTH electrode maintains over 95% of its capacitance at a high charge/discharge rate of 100 mA cm −2 relative to its low-current (1 mA cm −2 ) capacitance; and it exhibits very high specific capacitance of approximately 1400 F g −1 (based on the mass of NCMTH), high specific energy density (≈30 W h kg −1 ) and power density (≈39 kW kg −1 ) at a high current density of 100 mA cm −2 , and excellent long-term cyclic stability (full capacitance retention over 3000 cycles). To assess functional behavior, two-terminal asymmetric supercapacitor devices with NCMTHs on graphitic petals as positive electrodes were assembled and tested to reveal ultrafast charge/discharge rates up to 5000 mV s −1 (approx. two orders of magnitude faster than conventional asymmetric devices based on metal hydroxides) with high rate capabilities, and excellent long-term cyclic stability (full capacitance retention over 10 000 cycles).