Synthesis and Electrochemical Performance of Hydrothermally Synthesized Nanoplates and Nanowhiskers NiCo2O4 Particles

Among oxides, Nickel cobaltite (NiCo2O4), with excellent electrochemical performance, has become a new class of energy storage material for electrochemical supercapacitors. This thesis work pursues comparative study on the physical, magnetic, and electrocapacitive performance of two sets of NiCo2O4 nanoparticles prepared in the absence and presence of NH4F via hydrothermal technique. Furthermore, novel Ni nanoparticle assisted the growth of NiCo2O4 is also explored in this study. NiCo2O4 nanowhisker (absence of NH4F) turns into nanoplates (presence of NH4F) nanoarchitecture, while the presence of Ni nanoparticle makes these structures denser. Based on X-ray diffraction, FTIR, surface area measurement and magnetic study, it was concluded that Ni nanoparticles were completely dissolved during the hydrothermal reaction and occupy octahedral (B) sites in NiCo2O4 unit cell. Based on this observation, the chemical reaction is proposed for the formation of NiCo2O4 in the presence of Ni nanoparticles. The electrocapacitive performance of Ni-doped nanoplates and nanowhiskers NiCo2O4 evaluated in 3M KOH electrolyte were lower than the pristine NiCo2O4; however, both sets of samples showed improved electrocapacitive performance at higher Ni nanoparticle content. Nanoplates and nanowhiskers NiCo2O4 displayed specific capacitance of 473.33 F/g (Ni-00) and 471.61 F/g (Ni-200mg) and 576.33 F/g (Ni-00) and 475.95 F/g (Ni-200mg) at 2mV/s scan rate, respectively. Furthermore, better energy and power density were observed for nanoplates, as compared to nanowhiskers NiCo2O4. Still, the overall lower electrocapacitive performance of Ni-doped NiCo2O4 as compared to pristine NiCo2O4 was observed and attributed to the increased disorder in NiCo2O4 unit cell upon Ni substitution for Co ions, likely reduction of overall electroactive sites, and increased hydrophobic nature of electrode surface. In conclusion, this detailed study clearly elucidates the role of nanoarchitecture of NiCo2O4 in determining the electrocapacitive performance of NiCo2O4