Highly stable Co3O4 nanoparticles/carbon nanosheets array derived from flake-like ZIF-67 as an advanced electrode for supercapacacitor

Nanosized transition metal oxides (TMOs) are one class of the most potential candidates for supercapacitors due to their short electron transport channels and reversible redox reactions. However, their easy-aggregation characteristics and volume shrinkage/expansion during the charge/discharge process seriously limit the practical application. To address this issue, in this work, a two-step thermal conversion different from traditional approaches is reported to synthesize tightly aligned Co3O4/carbon materials. The architecture of cross-linked nanosheets and uniformly distributed Co3O4 nanoparticles (NPs) is obtained by in-situ reduction of cobalt cations in flake-like zeolitic imidazolate frameworks (ZIFs) within inert gas at 500 degrees C and subsequent mild oxidation of metallic cobalt NPs to Co3O4 NPs (Co304@C-500). As a result, this strategy effectively prevents structural collapse and defect formation, which are usually caused by direct oxidation of ZIF-67 nanosheets. In supercapacitor tests, Co3O4@C-500 shows an appreciable specific capacitance (703.3 F g(-1) at 1 A g(-1)) and excellent cycling stability with the capacitance retention of 100% after 10,000 cycles at 10 A g(-1). Moreover, the Co3O4@C-500//reduced graphene oxide (RGO) asymmetric supercapacitor (ASC) exhibits an energy density of 43.99 Wh kg(-1) at a power density of 824.8 W kg(-1), and excellent cycling performance with a capacity retention of 88% after 10,000 cycles. Such excellent performance might benefit from the rational composition control and unique structure of Co3O4 NPs embedded in the carbon skeleton, which results in short electrolyte diffusion channels as well as electron transport distance and effectively reduce negative effect of volume change of electrode materials during the charge/discharge process.

Automated summary

A two-step thermal conversion method was reported to synthesize tightly aligned Co3O4/carbon materials, featuring a structure of cross-linked nanosheets and uniformly distributed Co3O4 nanoparticles. The material exhibited high specific capacitance and cycling stability in supercapacitor tests, and showed excellent energy density and power density in an asymmetric supercapacitor configuration.