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Summary: The significant influences of the external stress in the electrochemical performances of the supercapacitors require the optimization of the electrode materials with reasonable morphology. In this work, activated carbon spheres (ACSs) of different sizes are prepared from hydrothermal processing of glucose aqueous solution, pre‐carbonization, and KOH activation. The energy storage performance of ACS‐based supercapacitors (SCs) under compression is analyzed. Increasing the compressive stress from 1 MPa to 8 MPa promotes the specific capacitance of the ACS‐based SCs, which achieves 374 F/g at 0.5 A/g for the ACSs with the smallest diameter of 1.48 μm. Applying higher compressive stress also reduces IR drop and the self‐discharge rate. The compression is found to have more significant positive effects on the electrochemical properties of the ACSs with larger sizes. The understanding of the morphological effect of the electrode materials on the electrochemical properties under compressive stress can help design and select appropriate electrode materials for supercapacitors applied under certain stresses. [ABSTRACT FROM AUTHOR]

Summary: In this work, oxygen‐doped activated carbons (ACs) are derived from glucose by hydrothermal synthesis (HTS) and a two‐step consecutive activation/treatment. The first KOH activation leads to the formation of well‐developed hierarchical porous structure. The second H2O‐steam treatment controls the fraction of oxygen contents ranging from 3.35 to 10.43 at% by regulating the treatment time and temperature. We propose a reaction for the oxygen reduction during the H2O‐steam treatment, of which the resultant reaction rate increases with the increase of the treatment temperature. The nominal activation energy for the reaction is 18.79 kJ/mol. The symmetric supercapacitors with the ACs of the highest oxygen content exhibit the best electrochemical performances of an optimum specific capacitance of 240.49 F/g in the electrolyte of 1 M H2SO4. However, the symmetric supercapacitors with the ACs of the lowest oxygen content exhibit the best electrochemical performances of an optimum specific capacitance of 171.81 F/g in the organic electrolyte of 1 M Et4BF4 in AN. [ABSTRACT FROM AUTHOR]

• High-performance N/O-co-doped activated carbons (ACs) are prepared with glucose as precursor and egg solution as nitrogen source. • Excellent electrochemical properties of N/O-co-doped ACs are achieved with optimum specific capacitance of 417 F/g. • Effects of heteroatoms on electrochemical properties of ACs are analyzed by comparing the single O-doped to the N/O-co-doped ACs. Single O-doped and N/O co-doped activated carbons (ACs) are prepared via hydrothermal synthesis (HTS) and a subsequent KOH activation with glucose as precursor and egg solution as nitrogen source. Controlling the activation temperature and mass ratio of activation agent KOH to HTS product (biochar), we tailor the surface area, porous structure as well as the amounts of heteroatoms of the prepared ACs. Using 6 M KOH solution as electrolyte, the electrochemical properties of all the prepared ACs are analyzed. For the same activation parameters, the single O-doped ACs exhibit very similar porous structure and possess a higher heteroatom amount than the N/O co-doped ACs. The N/O co-doped ACs exhibit superior capacitive behavior to the corresponding single O-doped ACs and achieve a specific capacitance of 417 F/g at a current density of 0.5 A/g and 334 F/g at 20 A/g. This work demonstrates a cheap and green route to produce high-performance ACs and helps to have a deeper understanding of the effects of the heteroatoms on the electrochemical properties of ACs. [Display omitted]. [ABSTRACT FROM AUTHOR]