Core–shell shaped Ni₂CoHCF@PPy microspheres from prussian blue analogues for high performance asymmetric supercapacitors

Abstract

Recently, prussian blue analogues (PBAs), as the most classical class of metal-organic frameworks, have been widely studied by scientists. Nevertheless, the inferior conductivity of PBAs restricts the application in supercapacitors. In this work, nickel cobalt hexacyanoferrate (Ni 2 CoHCF) had been produced via a simple co-precipitation approach and coated with polypyrrole on its surface. The conductivity of PBAs was improved by the polypyrrole coating. The Ni 2 CoHCF@PPy-400 microspheres were demonstrated to the outstanding specific capacity of 82 mAh g −1 at 1 A g −1 . After 3000 cycles, the Ni 2 CoHCF@PPy-400 microspheres had a long cycle life and 86% specific capacity retention rate at 5 A g −1 . Additionally, it was coupled with activated carbon to build high performance asymmetric supercapacitor (Ni 2 CoHCF@PPy-400//AC), which displayed a high energy density of 21.7 Wh kg −1 at the power density of 888 W kg −1 and good cycle stability after 5000 cycles (a capacity retention rate of 85.2%). What is more, the results reveal that the Ni 2 CoHCF@PPy-400 microspheresare a prospective candidate for exceptional energy storage devices.

The synthesis of Ni/Mn hexacyanoferrate microcubes and nanorods for high‐performance asymmetric supercapacitor in neutral electrolyte

“…The Raman spectrum of Ni/Mn-HCF displays the characteristic peak at 2094 cm À1 , which is attributed to the C ≡ N stretching mode (Figure 2B). 35,41,46 The morphology of Ni/Mn-HCF on carbon cloth was observed with SEM. The carbon cloth was uniformly and tightly coated with Ni/Mn-HCF (Figure 3A,B).…”

“…The Raman spectrum of Ni/Mn‐HCF displays the characteristic peak at 2094 cm −1 , which is attributed to the C ≡ N stretching mode (Figure 2B). 35,41,46 …”

“…TM‐HCFs and their numerous composites such as TM‐HCF/carbon‐based nano/micromaterials, 28,37,41,42,46,48 TM‐HCF/TM‐oxides, 33,44,45 TM‐HCF/polymer 35,52 and TM‐HCF/TM‐LDH 53 have been widely used as the positive electrodes of supercapacitors. Theoretically, binary TM‐HCFs such as Ni 2 CoHCF, Co 2 Fe(CN) 6 have higher specific capacitance than unary TM‐HCF because of their much richer oxidation states 35,38 . Thus, investigation on the possible application of binary TM‐HCF has become a hot spot in recent years.…”

“…Recently, the application of transition metal hexacyanoferrates (TM‐HCFs) as the electroactive materials of supercapacitor has also been investigated by many researchers due to their excellent redox reversibility, high ionic conductivity, superior environmental benignancy, low cost, and insolubility upon oxidation/reduction 27‐52 . TM‐HCFs and their numerous composites such as TM‐HCF/carbon‐based nano/micromaterials, 28,37,41,42,46,48 TM‐HCF/TM‐oxides, 33,44,45 TM‐HCF/polymer 35,52 and TM‐HCF/TM‐LDH 53 have been widely used as the positive electrodes of supercapacitors. Theoretically, binary TM‐HCFs such as Ni 2 CoHCF, Co 2 Fe(CN) 6 have higher specific capacitance than unary TM‐HCF because of their much richer oxidation states 35,38 .…”

“…Because of the rich valence states of transition metals (TM), the oxides, 4‐6,9‐11 sulfides, 12‐16 hydroxides 17‐26 of transition metals, and their numerous composites have been widely investigated as the supercapacitor electrode materials of faradic supercapacitor. Recently, the application of transition metal hexacyanoferrates (TM‐HCFs) as the electroactive materials of supercapacitor has also been investigated by many researchers due to their excellent redox reversibility, high ionic conductivity, superior environmental benignancy, low cost, and insolubility upon oxidation/reduction 27‐52 . TM‐HCFs and their numerous composites such as TM‐HCF/carbon‐based nano/micromaterials, 28,37,41,42,46,48 TM‐HCF/TM‐oxides, 33,44,45 TM‐HCF/polymer 35,52 and TM‐HCF/TM‐LDH 53 have been widely used as the positive electrodes of supercapacitors.…”