Morphology and crystalline structure of electrode materials control the capacitive properties of a supercapacitor device. Among the commonly studied electrode materials, Ni-Co-based bimetallic selenides are recognized as a promising supercapacitor electrode. Herein, NiCo2Se4/reduced graphene oxide (NCSRG) composites are synthesized by a two-step facile hydrothermal reaction for high-performance supercapacitor applications. The synthesis process is explored using a time-dependent experiment. The duration of the hydrothermal reaction controls the morphology of the electrode materials, which further affect the electrochemical performance. Specific capacitance of nickel-cobalt carbonate hydroxides (NCRGs) improves remarkably after Se interrogation. It is found that 12 h reaction products exhibit the highest capacitance properties among the intermediate NCRGs and final products (NCSRGs). An asymmetric supercapacitor (ASC) cell is fabricated using positive (NCSRG-12) and negative (TRGO) electrodes (TRGO//NCSRG-12). It is found that the specific capacitance of the ASC device is similar to 139 F g(-1) at a 2 A g(-1) current density with a working potential of similar to 1.4 V. The device delivers an energy density of similar to 37.83 W h kg(-1) and a power density of 1433.55 W kg(-1). The loss of specific capacitance is similar to 12.73% after 5000 galvanostatic charge-discharge (GCD) cycles.