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In this letter, we report on the simple process of preparing perovskite oxide SrMnO3 and the studying of the size effect on electrochemical properties for high-performance supercapacitor electrode. The high-crystalline micro-sized and nano-sized perovskite oxide SrMnO3 particles were successfully synthesized by a simple solid-state reaction, followed by a simple size reduction using high-energy ball milling. The electrochemical properties of the SrMnO3 had intriguing results on both sizes of particle, especially when comparing between before and after cycles. After a size reduction, the specific capacitance of the particles increased approximately twofold. Interestingly, the micro-sized SrMnO3 gained ∼500% its initial specific capacitance after 3000 successive cycles due to electrochemical nano-feature activation and oxygen-vacancy production, while the specific capacitance for the nano-sized SrMnO3 remained almost unchanged. Our work suggested a cost-effective and simple technique for high-performance perovskite-based supercapacitor electrodes by achieving the desired performance. [ABSTRACT FROM AUTHOR]

Nitrogen- and co-nitrogen- and sulfur-doped reduced graphene oxide (named N-rGO and N/S-rGO) was prepared by a simple hydrothermal technique using urea and thiourea as doping agents, respectively, to improve the properties of supercapacitor electrodes. Both were compared with rGO in electrochemical evaluations. The supercapacitor using N-rGO in 1 M H 2 SO 4 provided the largest specific capacitance, 99 F g−1, while those using N/S-rGO and rGO exhibited 51 and 19 F g−1 at 0.25 A g−1, respectively. Furthermore, the supercapacitors using N-rGO and N/S-rGO electrodes showed a smaller charge transfer resistance (R ct) and a lower IR -drop than those using the rGO electrode, indicating a faster charge transfer at the interface between electrode and electrolyte and higher electronic conductivity due to N or N/S heteroatom doping in the graphene oxide structure. Furthermore, the N-rGO electrode has a higher sp2 hybridization ratio and a lower I D /I G ratio than the N/S-rGO electrode. Furthermore, the lowest contact angles of the N/S-rGO electrode were found, which was attributed to better aqueous electrolyte compatibility than the N-rGO and rGO electrodes. Therefore, the higher electrical conductivity of the N-rGO electrode reveals more relevant characteristics for high-performance supercapacitors than the good wettability of the N/S-rGO electrode. • N- and N/S-doping rGO can improve the conductivity and wettability of electrodes. • N- and N/S-doped rGO demonstrates a reduction in the sp2 hybridization ratio and an increase in I D /I G. • The specific capacitance of N-rGO is greater than that of N/S-rGO and rGO. • The cycle stability of N-rGO is superior to that of N/S-rGO and rGO. [ABSTRACT FROM AUTHOR]