In this study, a novel hybrid structure of homogeneously distributed Co3O4 nanograins on a hexagonal Co(OH)2 plate is synthesized using a one-pot hydrothermal reaction of ZIF-67. Particularly, because Co-containing ZIF-67 serves as a self-template during the hydrothermal conversion process, various-sized hybrid structures can be prepared using different sizes of ZIF-67 as the precursor material. Owing to their unique structural features, the obtained hybrids effectively boost the electrochemical activation of Co3O4 and Co(OH)2 by preventing aggregation issues. Among the various-sized architectures, large-sized structure exhibits the highest capacity of 184.9 mAh g−1 (at 1 A g−1) in aqueous 1 M KOH electrolyte, indicating that the electrochemical performance is improved as the size of hybrid increases. Furthermore, multifarious all-solid-state hybrid supercapacitors are successfully fabricated with various-sized Co3O4/Co(OH)2 hybrids as the positive electrode and mesoporous plasma-reduced graphene oxide as the negative electrode. Notably, the as-prepared hybrid supercapacitors deliver a maximum energy density of 37.6 Wh kg−1 and peak power density of 47 kW kg−1 with excellent cycling stability (91% capacity retention after 5000 cycles).