Hierarchically porous CuO microspheres and their r-GO based nanohybrids for electrochemical supercapacitors applications

In this work, we are reporting the facile synthesis of hierarchically porous CuO microspheres and their r-GO based nanohybrid as an electrode material for supercapacitor applications. The fabricated product was characterized by powder X-ray diffraction technique (PXRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis, and Brunauer-Emmett-Teller (BET) analysis. PXRD analysis showed the existence of the monoclinic phase of CuO. The compositional study of the synthesized product was completed via EDX analysis. The FESEM analysis confirmed the hierarchical porous micro-spherical architecture of the product with smaller CuO grain-size particles, quasi- microporous spindle-like nanosheets assembled by nano-grains, and their aggregation to mesoporous nature. The BET analysis revealed that the BET and Langmuir surface area of the hierarchically porous CuO microspheres was 60.02 m(2)/g and was 86.68 m(2)/g. Furthermore, the BET results also confirmed the mesoporous structure of the fabricated sample. The hierarchically porous CuO microspheres showed a specific capacitance of 402 F/g at 1 A/g with 75.4% capacitance retention whereas their r-GO based nanohybrid showed 712 F/g at 1 A/g with 96.9% capacitance retention. The greater electrochemical response of r-GO based nanohybrid was due to the greater surface area and higher electrcial conductivity arise from the synergistic effects between the novel structure and r-GO nanosheets. Moreover, apart from the condcutive matrix r-GO also behaves as a capacitive supplement and contributes toward the total capacitance of the nanocomposite. The electrical impedance spectroscopy (EIS) experiments reveal that the addition of the r-GO matrix also facilitates the charge transfer and improves the kinetics of the redox reaction. In short, it can be concluded that r-GO based hierarchically porous CuO microspheres found themselves as a potential candidate in the field of hybrid supercapacitors. (C) 2020 The Author(s). Published by Elsevier B.V.