Electrochemical Performance of MnO₂ Nanorods in Neutral Aqueous Electrolytes as a Cathode for Asymmetric Supercapacitors

Abstract

The electrochemical performance of MnO 2 nanorods prepared by a precipitation reaction was investigated in 0.5 mol/L Li 2 SO 4 , Na 2 SO 4 , and K 2 SO 4 aqueous electrolyte solutions. Results show that at the slow scan rates, the nanorods show the largest capacitance (201 F/g) in Li 2 SO 4 electrolyte since the reversible intercalation/ deintercalation of Li + in the solid phase produces an additional capacitance besides the capacitance based on the absorption/desorption reaction. At fast scan rates they show the largest capacitance in the K 2 SO 4 electrolyte due to the smallest hydration radius of K + , highest ionic conductivity, and lowest equivalent series resistance (ESR). An asymmetric activated carbon (AC)/K 2 SO 4 /MnO 2 supercapacitor could be cycled reversibly between 0 and 1.8 V with an energy density of 17 Wh/kg at 2 kW/kg, much higher than those of the AC/K 2 SO 4 /AC supercapacitor and AC/Li 2 SO 4 /LiMn 2 O 4 hybrid supercapacitor. Moreover, this supercapacitor exhibits excellent cycling behavior with no more than 6% capacitance loss after 23 000 cycles at 10C rate even when the dissolved oxygen is not removed.

Inkjet printing of single-walled carbon nanotube/RuO2 nanowire supercapacitors on cloth fabrics and flexible substrates

“…In contrast to the bare SWNT thin film electrode, the Nyquist plot of the hybrid RuO 2 nanowire/SWNT nanostructured thin film electrode shows that the imaginary part of impedance increases sharply at lower frequency, which indicates that SWNT films retain their electron-transfer capability even with the integration of RuO 2 nanowires [39]. It can be seen that the diameters of the semicircle in the Nyquist plot of the hybrid RuO 2 nanowire/SWNT nanostructured thin film electrode is smaller than that of the bare SWNT thin film electrode, which means that the electrochemical reactions on the electrode/electrolyte interface of hybrid RuO 2 nanowire/SWNT nanostructured thin film electrode are more facile than on the bare SWNT thin film electrode [40]. In addition, the point intersecting with the real axis in the high frequency range (10 kHz) indicates that the ESR of the hybrid RuO 2 nanowire/SWNT nanostructured thin film electrode (22 Ω) is lower than that of the bare SWNT thin film electrode (43 Ω), showing that the integration of RuO 2 nanowires with printed SWNT films increases the conductivity of the printed SWNT thin film electrode.…”

A reduced graphene oxide/Co3O4 composite for supercapacitor electrode

“…Therefore, pseudocapacitors are being developed to improve the energy density of devices since pseudocapacitors store and deliver energy through redox reactions, leading to high specific capacitance [11,12]. Transition metal oxides such as MnO 2 , NiO, Fe 2 O 3 and Co 3 O 4 are being studied as candidate materials for pseudocapacitor electrodes [11][12][13][14][15][16][17][18]. Although metal oxides alone offer high specific capacitance, they deliver low power density and poor rate capability (dramatic drop of specific capacitance with an increase at a high scan rate) due to poor electronic conductivity [19][20][21][22].…”

Development of novel MnO2/nanoporous carbon composite electrodes in capacitive deionization technology

“…Some researchers have done researches dealing with MnO 2 /carbon composites and have known that MnO 2 possesses several advantages on top of carbon material, such as high capacitance, low price, environmental compatibility and natural abundance in other applications, such as supercapacitor and Lithium-ion battery [13][14][15][16]. However, no previous MnO 2 /carbon composite materials as electrodes in CDI studies have been reported.…”