(152373)Synthesis of porous Co_3O_4/Reduced graphene oxide by a two-step method for supercapacitors with excellent electrochemical performance

摘要

Porous Co_3O_4/reduced graphene oxide (RGO) composites with excellent supercapacitive performance were successfully synthesized on nickel foam (NF) by electrophoretic deposition followed by thermal reduction, and a hydrothermal method. The effects of the introduction of RGO and molar ratio of hexamethylenetetramine (HMT) and Co(NO_3)_2 on morphology and electrochemical performance of the deposits were investigated. The morphological evolution of Co_3O_4 prepared on RGO with the increase in molar ratio was followed: dispersed flower-like clusters composed of fine nanosheets (1:2) → coarse flower-like clusters (1:1) → a honeycomb-like structure consisting of fine nanosheets (2:1) →two layers of structures (initial honeycomb-like structure covered with coarse flower-like structure in 3:1 and 4:1). A highest specific surface area was obtained in the sample prepared in the HMT/Co(NO_3)_2 M ratio of 2:1. The introduction of RGO contributed to the increase in specific surface area of the deposits. For the three-electrode testing system, the specific capacitance of the Co_3O_4/RGO deposit at the molar ratio of 2:1 reached the highest values of 1138.11 Fg~(-1) at a current density of 1 Ag~(-1), 800.71 Fg~(-1) at a scanning rate of SmVs~(-1), which were higher than those of Co_3O_4. This C03O4/RGO deposit also demonstrated the outstanding cycling stability (the specific capacitance of the 80.67% of initial value was retained after 5000 cycles). For the two-electrode testing system, the as-fabricated asymmetric supercapacitor device achieved a high specific capacitance of 108.87Fg~(-1) at a current density of 1 Ag~(-1) with a stable operational voltage of 1.45 V and a high energy density of 647.05 Wh-kg~(-1).