High‐performance activated carbons for supercapacitor: Effects of porous structures, heteroatom doping, and morphology

Abstract

In this work, we prepare a series of activated carbons (ACs) of different morphologies, porous structures, and oxygen contents from glucose with hydrothermal synthesis (HTS) followed by a one-step (H 2 O-steam or KOH) or two-step (H 2 O-steam-KOH or KOH-H 2 O-steam) activation. The largest surface area of the prepared ACs is more than 3400 m 2 /g, and the corresponding mesopore volume is 1.21 cm 3 /g. The fraction of oxygen in the ACs varies in a range of 3.94 to 9.9 at%. The electrochemical performance of the symmetric supercapacitor cells (SCs) made from the as-prepared ACs is characterized in different aqueous electrolytes. The optimum capacitance of the SCs is 421 F/g at 0.5 A/g and 304 F/g at 10 A/g. The oxygen-enriched functional groups have limited contribution to the energy storage for the SCs with neutral electrolyte and profound effects on the increase of the energy storage for the SCs with strong acidic and alkaline electrolytes. The processing routes developed in this work likely open an avenue to tailor the structures and oxygen-enriched functional groups of ACs.

Controllable adjustment of oxygen contents in activated carbons and oxygen effect on electrochemical performances in supercapacitors

“…Additional pseudo‐capacitance from reversible faradic reactions may be introduced with the O‐functional groups, which refurnish the total capacitance. Th trend presented in Figure 10 is consistent with the report that O‐enriched surface‐functional groups improve the wettability of inorganic electrolyte solutions on the AC surface, and the interaction between electrolyte ions and electrode and acidic environment benefits the development of pseudo‐capacitance 41 …”

“…Oxygen is widely present in the precursors of ACs, including saccharides, 36 biomass, 37,38 and food/industrial wastes, 39,40 and can be easily introduced into ACs during the formation processes, such as oxidation, carbonization, and activation. 41 Other heteroatoms are generally limited in the precursors 42,43 and can be significantly reduced during the common physical/chemical activation processes. Adding an additional agent or using different techniques are generally needed in order to introduce reasonable amounts of other heteroatoms, 44,45 leading to the increases in chemical pollution and industrial cost.…”

“…Oxygen is widely present in the precursors of ACs, including saccharides, 36 biomass, 37,38 and food/industrial wastes, 39,40 and can be easily introduced into ACs during the formation processes, such as oxidation, carbonization, and activation 41 . Other heteroatoms are generally limited in the precursors 42,43 and can be significantly reduced during the common physical/chemical activation processes.…”

“…The KOH activation leads to the formation of well‐developed hierarchical porous structure, which is beneficial for the energy storage especially for organic electrolytes 46 and for the stabilization of the physical/chemical properties of the hydrothermally synthesized carbon spheres. Using the KOH, activation can furnish the oxygen content in porous carbon spheres 41 . The main purpose of the H 2 O‐steam treatment is to tailor the oxygen contents in the ACs by regulating the experimental parameters, which significant influence the electrochemical performances of the ACs.…”

Facile 3D Nitrogen‐Doped Hierarchical Porous Carbon for High‐Performance Supercapacitors

“…For instance, the presence of surface functional groups can enhance the wettability of electrodes and may also result in a pseudocapacitive feature. [ 36 ] Therefore, X‐Ray photoelectron spectroscopy (XPS) was performed to the nitrogen content of ANPC, and the results are presented in Figure 5 c. The nitrogen content of the four types of N‐doped porous carbon structures decreases in the following order ANPC‐5 > ANPC‐4 > ANPC‐3 > ANPC‐2.…”