## 4 Conclusions  
In summary, porous thin-wall hollow Co\({}_{3}\)O\({}_{4}\) spheres were successfully prepared through a simple approach and were characterized in detail. The electrochemical studies above unambiguously illuminate that the Co\({}_{3}\)O\({}_{4}\) in this work shows prominent specific capacitance and cycling stability, which are attributed to its favorable structural features. Particularly, in comparison with other Co\({}_{3}\)O\({}_{4}\)-based electrode materials, it demonstrates an overwhelming rate capability (limited decay of 6.4% from  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Material** &
\begin{tabular}{c} **Specific** \\ **Capacitance** \\ \end{tabular} & **Rate Capability** & **Stability-Cycles** & **Ref.** \\ \hline hollow Co\({}_{3}\)O\({}_{4}\) spheres & 474.8 F/g at 1 A/g & 79\% at 10 A/g & 99\%-1000 & [37] \\ hollow Co\({}_{3}\)O\({}_{4}\) spheres & 394.4 F/g at 2 A/g & 81\% at 20 A/g & 92\%-500 & [45] \\ hollow Co\({}_{3}\)O\({}_{4}\) spheres & 342.1 F/g at 0.5 A/g & 69\% at 10 A/g & 90\%-2000 & [46] \\ hollow Co\({}_{3}\)O\({}_{4}\) nanotubes & 1006 F/g at 1 A/g & 51\% at 10 A/g & 91\%-1000 & [29] \\ hollow Co\({}_{3}\)O\({}_{4}\) cages & 948.9 F/g at 1 A/g & 56.6\% at 40 A/g & – & [30] \\ hollow Co\({}_{3}\)O\({}_{4}\) nanotubes & 404.9 F/g at 0.5 A/g & 87.8\% at 20 A/g & 95\%-2000 & [38] \\ hollow Co\({}_{3}\)O\({}_{4}\) 3D-nanonet & 739 F/g at 1 A/g & 72\% at 15 A/g & 90.2\%-1000 & [39] \\ hollow Co\({}_{3}\)O\({}_{4}\) flowers & 210 F/g at 0.5 A/g & 86\% at 10 A/g & – & [46] \\ hollow Co\({}_{3}\)O\({}_{4}\) corals & 527 F/g at 1 A/g & 78\% at 10 A/g & 99\%-5000 & [47] \\ hollow Co\({}_{3}\)O\({}_{4}\) nanowires & 599 F/g at 2 A/g & 73\% at 40 A/g & 91\%-7500 & [48] \\ hollow Co\({}_{3}\)O\({}_{4}\) boxes & 278 F/g at 0.5 A/g & 63\% at 5 A/g & – & [49] \\ hollow Co\({}_{3}\)O\({}_{4}\) dodecahedron & 1100 F/g at 1.25 A/g & 40\% at 12.5 A/g & 95.1\%-6000 & [50] \\ Co\({}_{3}\)O\({}_{4}\) spheres & 837.7 F/g at 1 A/g & 93.6\% at 10 A/g & 87\%-2000 & [51] \\ Co\({}_{3}\)O\({}_{4}\) spheres & 261.1 F/g at 0.5 A/g & 42\% at 5 A/g & 90.2\%-2000 & [52] \\ Co\({}_{3}\)O\({}_{4}\) nanorods & 739 F/g at 5 mV/s & 52.5\% at 100 mV/s & 103\%-50000 & [53] \\ Co\({}_{3}\)O\({}_{4}\) nanowires & 977 F/g at 2 A/g & 49.5\% at 10 A/g & 90\%-2000 & [54] \\ Co\({}_{3}\)O\({}_{4}\) nanoflakes & 450 F/g at 1 A/g & 81\% at 20 A/g & 92\%-5000 & [55] \\ Mn doped Co\({}_{3}\)O\({}_{4}\) & 668.4 F/g at 1 A/g & 62\% at 10 A/g & 104\%-10000 & [34] \\ Au decorated Co\({}_{3}\)O\({}_{4}\) & 681 F/g at 0.5 A/g & 58\% at 10 A/g & 83.1\%-13000 & [42] \\ CoO/Co\({}_{3}\)O\({}_{4}\) & 451 F/g at 1 A/g & 68.3\% at 20 A/g & 108\%-5000 & [43] \\ hollow Co\({}_{3}\)O\({}_{4}\) spheres & 988 F/g at 1 A/g & 93.6\% at 20 A/g & 96.6\%-6000 & Ours \\ \hline \hline \end{tabular}
\end{table}
Table 1: Brief capacitance, rate, and cycling performance list of Co\({}_{3}\)O\({}_{4}\)-based electrode materials.  
Figure 7: Cycling performance and coulombic efficiency of the Co\({}_{3}\)O\({}_{4}\) electrode.  
1 to 20 A/g), which is very critical for commercial applications. These results indicate the exciting supercapacitor application potential of our synthesized material. Moreover, the relationship between the structure and properties is worth investigating in depth in the future.  
[PERSON] investigated the research, performed the characterizations and analyzed the data; [PERSON] and [PERSON] contributed equally to conduct the experiments and to write the manuscript; [PERSON] provided the critical feedback and designed the structure of the manuscript; [PERSON] and [PERSON] both equally supervised the experiments and refined the manuscript.  
This research was funded by the Norwegian PhD Network on Nanotechnology for Microsystems, which is sponsored by the Research Council of Norway, Division for Science, under contract no. 221860/F60. X.F. was funded by China Scholarship Council.  
Fruitful discussions with [PERSON] and [PERSON] are acknowledged.  
The authors declare no conflict of interest.