Biomorphic composites composed of octahedral Co3O4 nanocrystals and mesoporous carbon microtubes templated from cotton for excellent supercapacitor electrodes

•Biomorphic composite was prepared via a simple cotton-assisted hydrothermal route.•Co3O4 nanocrystals exhibit high exposed {1 1 1} facets.•Co3O4 nanocrystals are supported on the porous carbon microtubes.•Its specific capacitance is 284.2 F⋅g−1 at 1 A⋅g−1.