Rare-earth-based nanomaterials with exceptional electrochemical properties can be obtained via 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 via 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 Nd3GaxOy 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 Nd3GaxOy in terms of its electrochemical performance indicate its significant promise for potential application in energy-storage devices.