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, Nd 3 Ga 5 O 12 and Nd 3 GaO 6 , synthesised via a citrate–gel–matrix method for asymmetric supercapacitor applications. Structural, morphological and optical studies elucidated the outstanding supercapacitor performance of Nd 3 Ga 5 O 12 and Nd 3 GaO 6 . XRD revealed the formation of cubic Nd 3 Ga 5 O 12 and orthorhombic Nd 3 GaO 6 . The vibrational modes, optical properties, surface morphology and oxidation states of Nd 3 Ga x O y 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 Nd 3 Ga 5 O 12 electrode resulted in a greater specific capacitance of about 418 F g −1 than Nd 3 GaO 6 , thereby displaying superior electrochemical characteristics. An asymmetric device fabricated with Nd 3 Ga 5 O 12 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 Nd 3 Ga x O y in terms of its electrochemical performance indicate its significant promise for potential application in energy-storage devices.