A green and high energy density asymmetric supercapacitor based on ultrathin MnO₂nanostructures and functional mesoporous carbon nanotube electrodes

Abstract

A green asymmetric supercapacitor with high energy density has been developed using birnessite-type ultrathin porous MnO(2) nanoflowers (UBMNFs) as positive electrode and functional mesoporous carbon nanotubes (FMCNTs) as negative electrode in 1 M Na(2)SO(4) electrolyte. Both of the electrode materials possess excellent electrochemical performances, with high surface areas and narrow pore size distributions. More significantly, the assembled asymmetric supercapacitor with optimal mass ratio can be cycled reversibly in the high-potential range of 0-2.0 V and exhibits an excellent energy density as high as 47.4 W h kg(-1), which is much higher than those of symmetric supercapacitors based on UBMNFs//UBMNFs and FMCNTs//FMCNTs supercapacitors. Furthermore, our asymmetric supercapacitor (ASC) device also exhibits a superior cycling stability with 90% retention of the initial specific capacitance after 1000 cycles and stable Coulombic efficiency of ~98%. These intriguing results exhibit great potential in developing high energy density "green supercapacitors" for practical applications.

Asymmetric supercapacitor based on nanostructured graphene foam/polyvinyl alcohol/formaldehyde and activated carbon electrodes

“…Where x CH stands for the hydrogen inserted into the nano-textured carbon during charging and oxidized during discharging Transition metal oxides (TMOs), conducting polymers and their corresponding composites materials are promising candidates for ECs applications and are mostly used as positive electrode [11][12][13]. TMOs are widely considered as positive electrode because of their inherent "pseudocapacitance" which is due to rapid and reversible electron exchange reactions at the electrode interface.…”

“…Some of these studies include, activated carbon (AC)//manganese oxides (MnO 2 ) [15,16], carbon nanotube//MnO 2 [13], AC//Ni(OH) 2 [17]. Conducting polymers, polymer composite materials and carbon materials such as CNT have also been reported for ASC applications some of which are: AC//conducting polymers [6,18], CoO@polypyrrole//activated carbon [19] and carbon nanotube/PANI (CNT/PANI) [20] just to mention a few.…”

In situ anchoring uniform MnO2 nanosheets on three-dimensional macroporous graphene thin-films for supercapacitor electrodes

“…4,5 Given that pseudo-capacitance is primarily generated by surface faradaic redox reactions, developing MnO 2 nanostructures with an ultrathin morphology is expected to achieve the full potential of MnO 2 for advanced supercapacitors. [6][7][8] However, the poor electrical conductivity of MnO 2 (10 À5 to 10 À6 S cm À1 ) severely limits its specic capacitance far low from the theoretical value (1340 F g À1 ).…”

Synthesis of amorphous cobalt-boron alloy/highly ordered mesoporous carbon nanofiber arrays as advanced pseudocapacitor material

“…At high scan rates, the diffusion effect, limiting the migration of the electrolytic ions, leads to inaccessible active surface areas for charge storage. In addition, the amorphous alloy exhibits much higher specific capacitance than some transition metal oxides, such as MnO 2 (85.8 F g −1 ) [23], NiO (232 F g −1 ) [24], Fe 2 O 3 (255 F g −1 ) [25], and Co 3 O 4 (358 F g −1 ) [26], which are studied as candidate materials for pseudocapacitor electrodes.…”