To boost the energy storage of microsupercapacitors (MSCs), a nanocomposite electrode combining carbonaceous materials with metal oxides was developed, i.e. combining capacitive and faradaic currents. Our method involves a one-step hydrothermal process, the initial components being graphene oxide, dopamine and Co2+ ions, resulting in a reduced graphene oxide–polydopamine–Co3O4 composite. Dopamine acts as a reducing agent and prevents graphene oxide agglomeration. Co2+ ions are expected to be chelated by polydopamine, likely leading to uniform dispersion of Co3O4 particles on the graphene surface. Using this composite as an active material, thin film electrodes were prepared, thoroughly characterized via various chemical techniques, and their electrochemical properties were tested in KOH. In situ electrochemical quartz crystal microbalance was used to elucidate the charge storage process, which showed the presence of a “point of maximum mass” separating a dominant anionic contribution due to the pseudocapacitive response of Co3O4 and a cationic contribution reflecting the electroadsorption/desorption of cations on the rGO surface. Lastly, we extended our study to the fabrication of a current collector-free microsupercapacitor device, composed of interdigitated rGO–PDA–Co3O4 electrodes, which demonstrates excellent cycling stability over 3000 cycles at a scan rate of 50 mV s−1 and remarkable energy density of 12.25 mW h cm−3 at a power density of 0.26 W cm−3.