Outstanding long-term cycling stability of a sulfur-doped graphene electrode for supercapacitors obtained by post-tailoring the chemical states of doped-sulfur

Abstract For further enhancing the supercapacitive performances of carbon materials, heteroatoms-doping has proved to be one of the most promising approaches. Up to now, most of the researches focus on the effects of the dopant type and the doping amount. However, it is presently not understood how affects the capacitive performances if the chemical states of the heteroatom doped in carbon materials are further tailored. In this paper, we report for the first time the effect of post-tailoring the chemical states of doped‑sulfur on the supercapacitive performances of a sulfur-doped graphene. In our post-tailoring strategy, the S-doping is firstly realized by thermally treating the H2SO4-GIC compound, and then the chemical states of doped-S are post-tailored by the subsequent Hummers' oxidation. Our work has demonstrated that a unique oxidized-S species ( C S(O)x C ), which is transformed from the thiophene-S species by the Hummers' oxidation, has superior contribution to the supercapacitive performances (e.g., specific capacitance, rate performance and long-term cycling stability). Interestingly, the S-doped graphene sample, which contains the highest content of the unique oxidized-S species, exhibits an outstanding long-term cycling stability, its capacitance retention being up to 100.8% after 10,000 consecutive cycling test, far higher than those previously report for the heteroatom-doped carbon materials. The present work suggests that post-tailoring the chemical states of the doped-heteroatoms can be considered as an effective strategy to obtain the optimal electrochemical performances for the heteroatoms-doped carbon materials.