Hydrated and non-hydrated rGO-MnMoO4 nanocomposites (rGO-MnMoO4 and rGO-MnMoO4.1H2O) are synthesized by an easy hydrothermal method for use as supercapacitor electrodes. These nanocomposites are in situ grown onto the nickel foam. These nanocomposites are characterized via their structure, morphology, and chemical bonding. The electrochemical performance of these nanocomposites was measured as the supercapacitor electrodes. The morphological study of the samples reveals that the calcination process changes the morphology of nanocomposites from nanofakes to cross-nanosheets for the hydrated and non-hydrated nanocomposites, respectively. The results showed that the cooperation of both the GO and the hydrated compound has a synergistic efect on the electrochemical performance of nanocomposites. The rGO-MnMoO4.1H2O nanocomposite at a scan rate of 5 mV s−1 in 1 M KOH electrolyte shows the highest specifc capacitance of 855.6 F g−1. It was found that the difusion-limited process has a main contribution (than the capacitive process) to the storage mechanism of hydrated and non-hydrated rGO-MnMoO4 nanocomposites. Also, the investigation of the storage mechanism contribution reveals that this mechanism depends on the scan rate. The designed quasi-solid-state symmetric supercapacitor device of rGO-MnMoO 4.1H2O with KOH/PVA gel electrolyte can deliver a high energy density of 7.81 Wh kg−1 and a high power density of 2500 W kg−1. Also, the assembled quasi-solid-state symmetric supercapacitor (SSC) exhibits a capacitance retention of 77.7% after 5000 cycles.

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