File Name : figure s1-.tif

Caption : fig. s1 (a) photograph of pre-co@nc (purple) and pre-co@nc-cnt (pink); (b) xrd pattern of pre-co@nc; (c) xrd pattern of pre-co@nc-cnt.

File Name : fig. s2-.tif

Caption : fig. s2. ft-ir spectra of pre-co@nc and pre-co@nc-cnt.

File Name : fig. s3-.tif

Caption : fig. s3. magnified sem images of (a) co@nc and (b) co@nc-cnt

File Name : fig. s4-.tif

Caption : fig. s4. tg curves of pre-co@nc and pre-co@nc-cnt measured from room temperature to 550 oc with a ramping rate of 10 oc min-1 under nitrogen atmosphere.

File Name : fig. s5-.tif

Caption : fig. s5. xrd patterns of (a) pyrolyzed pre-co@nc at 220 oc; (b) pre-co@nc and pre-co@nc-cnt pyrolyzed at 350 oc.

File Name : fig. s6-.tif

Caption : fig. s6. (a) tem images of co@nc-cnt; (b) pore size distribution of co@nc-cnt calculated according to the left tem images.

File Name : fig. s7-.tif

Caption : fig. s7. xps survey spectra of co@nc and co@nc-cnt.

File Name : fig. s8-.tif

Caption : fig. s8. cv curves of co@nc, co@nc-cnt and pt/c measured in n2- and o2-saturated electrolyte at a scanning rate of 50 mv s-1

File Name : fig. s9-.tif

Caption : fig. s9 (a) lsv curves of co@nc at different rotating speed in o2-saturated electrolyte with a scanning rate of 5 mv s-1; (b) koutechky-levich (k-l) plots of co@nc.

File Name : fig. s10-.tif

Caption : fig. s10 lsv curves of co@nc-cnt obtained using various co content in precursor.

File Name : fig.s11-.tif

Caption : fig. s11 chronoamperometry curves of co@nc-cnt exhibited from 15000 s to 40000 s.