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. 2022 Oct 8;12(19):3514.
doi: 10.3390/nano12193514.

Pseudocapacitive Effects of Multi-Walled Carbon Nanotubes-Functionalised Spinel Copper Manganese Oxide

Christopher Nolly  1 , Chinwe O Ikpo  1 , Miranda M Ndipingwi  1 , Precious Ekwere  1 , Emmanuel I Iwuoha  1
Affiliations

Pseudocapacitive Effects of Multi-Walled Carbon Nanotubes-Functionalised Spinel Copper Manganese Oxide

Christopher Nolly et al. Nanomaterials (Basel). .

Abstract

Spinel copper manganese oxide nanoparticles combined with acid-treated multi-walled carbon nanotubes (CuMn2O4/MWCNTs) were used in the development of electrodes for pseudocapacitor applications. The CuMn2O4/MWCNTs preparation involved initial synthesis of Mn3O4 and CuMn2O4 precursors followed by an energy efficient reflux growth method for the CuMn2O4/MWCNTs. The CuMn2O4/MWCNTs in a three-electrode cell assembly and in 3 M LiOH aqueous electrolyte exhibited a specific capacitance of 1652.91 F g-1 at 0.5 A g-1 current load. Similar investigation in 3 M KOH aqueous electrolyte delivered a specific capacitance of 653.41 F g-1 at 0.5 A g-1 current load. Stability studies showed that after 6000 cycles, the CuMn2O4/MWCNTs electrode exhibited a higher capacitance retention (88%) in LiOH than in KOH (64%). The higher capacitance retention and cycling stability with a Coulombic efficiency of 99.6% observed in the LiOH is an indication of a better charge storage behaviour in this electrolyte than in the KOH electrolyte with a Coulombic efficiency of 97.3%. This superior performance in the LiOH electrolyte than in the KOH electrolyte is attributed to an intercalation/de-intercalation mechanism which occurs more easily in the LiOH electrolyte than in the KOH electrolyte.

Keywords: galvanostatic charge/discharge; nanocomposite electrode; pseudocapacitor; specific capacitance; spinel metal oxide.

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Conflict of interest statement

The authors do not have any conflict of interest to declare.

Figures

Figure 1
Figure 1
Experimental diagram for the synthetic procedures of Mn3O4 (a), CuMn2O4 (b) and CuMn2O4/MWCNTs (c) electrode materials.
Figure 1
Figure 1
Experimental diagram for the synthetic procedures of Mn3O4 (a), CuMn2O4 (b) and CuMn2O4/MWCNTs (c) electrode materials.
Figure 2
Figure 2
SEM image of Mn3O4 (a) viewed at a 100 nm scale, with the corresponding PDDF profile (b). SEM image of CuMn2O4 (c) at the 100 nm scale with its related PDDF profile (d). SEM image of CuMn2O4/MWCNTs (e) at the 100 nm scale with its complementary PDDF profile (f).
Figure 3
Figure 3
HR-TEM images of Mn3O4 viewed at 50 nm scale (a) and 2 nm scale (b). HR-TEM images of CuMn2O4 at the 50 nm scale (c) and 2 nm scale (d). HR-TEM images of CuMn2O4/MWCNTs at the 50 nm scale (e) and 2 nm scale (f).
Figure 4
Figure 4
XRD patterns (a), Raman spectra (b) and FTIR spectra (c) of Mn3O4, CuMn2O4 and CuMn2O4/MWCNTs electrode materials.
Figure 4
Figure 4
XRD patterns (a), Raman spectra (b) and FTIR spectra (c) of Mn3O4, CuMn2O4 and CuMn2O4/MWCNTs electrode materials.
Figure 5
Figure 5
CV curves of individual materials scanned at 20 mV s−1 in 3 M KOH (a) and 3 M LiOH (b) aqueous electrolytes; CV curves of CuMn2O4/MWCNTs electrode material in 3 M KOH (c) and 3 M LiOH (d) aqueous electrolytes at different scan rates.
Figure 5
Figure 5
CV curves of individual materials scanned at 20 mV s−1 in 3 M KOH (a) and 3 M LiOH (b) aqueous electrolytes; CV curves of CuMn2O4/MWCNTs electrode material in 3 M KOH (c) and 3 M LiOH (d) aqueous electrolytes at different scan rates.
Figure 6
Figure 6
Nyquist plots of all analysed electrode materials in 3 M KOH (a) and 3 M LiOH (b) aqueous electrolytes; comparative Nyquist plot of CuMn2O4/MWCNTs in both 3 M KOH and 3 M LiOH aqueous electrolytes (c); corresponding Bode phase impedance plot of all electrode materials in 3 M KOH (d) and 3 M LiOH (e) aqueous electrolytes.
Figure 6
Figure 6
Nyquist plots of all analysed electrode materials in 3 M KOH (a) and 3 M LiOH (b) aqueous electrolytes; comparative Nyquist plot of CuMn2O4/MWCNTs in both 3 M KOH and 3 M LiOH aqueous electrolytes (c); corresponding Bode phase impedance plot of all electrode materials in 3 M KOH (d) and 3 M LiOH (e) aqueous electrolytes.
Figure 7
Figure 7
Graphs of log impedance against log frequency for all analysed electrode materials in 3 M KOH (a) and 3 M LiOH (b) aqueous electrolytes; Nyquist (c) and Bode (d) plots of CuMn2O4/MWCNTs electrode material before and after 6000 cycles in 3 M LiOH aqueous electrolyte.
Figure 8
Figure 8
GCD curves of all electrode materials obtained at 0.5 A g−1 in 3 M KOH (a) and 3 M LiOH (b) aqueous electrolytes; GCD curves of CuMn2O4/MWCNTs electrode material in 3 M KOH (c) and 3 M LiOH (d) aqueous electrolytes.
Figure 9
Figure 9
Histogram of the specific capacitance of CuMn2O4/MWCNTs electrode material in 3 M KOH and 3 M LiOH aqueous electrolytes (a); cycling performance of CuMn2O4/MWCNTs electrode material in 3 M KOH and 3 M LiOH aqueous electrolytes after 6000 cycles at 1 A g−1 current load (b); Coulombic efficiency of CuMn2O4/MWCNTs electrode material in 3 M KOH and 3 M LiOH aqueous electrolytes over 6000 cycles obtained at 1 A g−1 current loading (c); GCD curves of CuMn2O4/MWCNTs electrode material before and after 6000 cycles at 1 A g−1 in 3 M LiOH aqueous electrolyte (d).
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