<p>This work seeks to improve electrochemical energy storage in supercapacitors by optimising the synthesis temperature of molybdenum trioxide nanoparticles (MoO₃ NPs) by a hydrothermal method. MoO₃ NPs were synthesised at 160, 180, and 200 ℃, with each temperature sustained for 16&#xa0;h. The MoO₃ NPs were examined by various techniques to evaluate its physiochemical, optical and morphological characteristics. The obtained samples underwent electrochemical research to investigate their electrochemical characteristics, including cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), electrochemical impedance spectroscopy (EIS) studies. The electrochemical performance of the synthesised samples fluctuated with the preparation temperature of the MoO₃ NPs, resulting in distinct morphologies. The M2 electrode demonstrated the greatest specific capacitance (Csp) of 352 Fg⁻¹ at 1 Ag⁻¹. The results underscore the influence of synthesis temperature on the shape, crystalline structure, and electrochemical performance of MoO₃ NPs for supercapacitor applications. The high-performance M2 sample is used in a symmetric supercapacitor device, which exhibits a maximum Csp of 122 F g⁻¹ at 1 Ag⁻¹, achieving maximum energy and power densities of 61.2 W Kg⁻¹ and 1500 Wh. Kg⁻¹ respectively.</p>