Stable neodymium gallium oxide (Nd₃Ga₅O₁₂ and Nd₃GaO₆) phases: a study on their asymmetric supercapacitor applications

Rare-earth-based nanomaterials with exceptional electrochemical properties can be obtained <i>via</i> a simple, low-cost, environment-friendly citrate-gel-matrix approach. Owing to their high specific capacitance, strong conductivity, and electrochemical stability, gallium-based materials are capable of withstanding numerous charge-discharge cycles, thus extending the life cycle of a supercapacitor. This tunability enabled researchers to alter the morphology and composition of the electrode to enhance supercapacitor performance. This research describes the investigation of stable neodymium gallium oxides, namely, Nd₃Ga₅O₁₂ and Nd₃GaO₆, synthesised <i>via</i> a citrate-gel-matrix method for asymmetric supercapacitor applications. Structural, morphological and optical studies elucidated the outstanding supercapacitor performance of Nd₃Ga₅O₁₂ and Nd₃GaO₆. XRD revealed the formation of cubic Nd₃Ga₅O₁₂ and orthorhombic Nd₃GaO₆. The vibrational modes, optical properties, surface morphology and oxidation states of Nd₃Ga_<i>x</i>O_<i>y</i> phases were examined using Raman spectroscopy, UV-visible spectroscopy, scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. Electrochemical studies using cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy revealed that the fabricated Nd₃Ga₅O₁₂ electrode resulted in a greater specific capacitance of about 418 F g^-1 than Nd₃GaO₆, thereby displaying superior electrochemical characteristics. An asymmetric device fabricated with Nd₃Ga₅O₁₂ demonstrated a specific capacitance of about 64 F g^-1, energy density of 20 W h kg^-1 and a power density of about 750 W kg^-1. Thus, the favorable attributes of Nd₃Ga_<i>x</i>O_<i>y</i> in terms of its electrochemical performance indicate its significant promise for potential application in energy-storage devices.