Structure and electrochemical performance of highly porous carbons by single-step potassium humate carbonization for application in supercapacitors

Abstract

This paper presents the direct synthesis of highly porous carbons via the carbonization of potassium humate in inert atmosphere without any activation. Carbonization temperature is important for carbon structures and their electrochemical performance in electric doublelayer capacitors. The CK800 material derived from potassium humate has a high-specific surface area of 890 m 2 g -1 and an ideal average pore size of 2.56 nm. The CK800 material can also deliver a high-specific capacitance of 232 F g -1 (26.1 lF cm -2 ) at a constant charge/ discharge current of 0.5 A g -1 . This capacitance is maintained at a value of 114 F g -1 (12.8 lF cm -2 ) at 30 A g -1 . This material also has good cycle stability with over 93.5 % capacitance retention after 5000 cycles when measured in a three-electrode system using 6 M KOH as electrolyte. In this study, the CK800 material is tested in a three-electrode system using 1 M NaHCO 3 as electrolyte. Operational voltage in 1 M NaHCO 3 aqueous solution could be extended up to 1.3 V.

Potassium Humate-Derived Nitrogen-Doped Activated Carbons with Narrow Micropore Size Distribution for High-Performance Supercapacitors

“…Therefore, these samples exhibit an amorphous framework in general. 35,43 With the increase of CH 3 COOK dosage, the (002) become narrow, suggesting an increase of graphitic crystalline degree.…”

“…It is found that all process results similarly yield between 33% and 36%, comparable with that of related references. 35 Elemental analyses (Table 2) were carried out to investigate the chemical compositions of ACs. It is found that the un-activated sample (sample CK-0) demonstrates an obviously low C content of 70.09 at.% and a high O content of 9.79 at.%, which possibly results in a poor electrical conductivity.…”

“…In the low-frequency region, the Nyquist plots measured in KOH and H 2 SO 4 electrolytes are more vertical than the rest, indicating higher ion accessability onto electrode surfaces. 35 At the high-frequency region, the intercept of impedance plot with the real axis gives an estimation of the equivalent series resistance (R esr Þ, including the contact resistance of interfacial active material, electrolyte resistance and intrinsic resistance of electrode materials. 70 It is found that R esr of sample CK-2 is 0.85 , 1.24 and 3.87 in H 2 SO 4 , KOH and Na 2 SO 4 , respectively.…”

“…41,42 While in the case of HA, ACs directly carbonized by HA-K demonstrate SSAs up to 890 m 2 Á g À1 , 95 times higher than that of HA-derived AC with similar carbonization condition. 35,36 Furthermore, the average pore size (2.56 nm) of HA-K derived AC is also smaller than that of HA-derived AC (15.76 nm).…”

“…With advantages of high natural abundance, environmental friendliness and high carbon content, HA has been identi¯ed as a suitable carbon precursor of ACs. 35 By carbonizing and simultaneously activating HA, meso-/microporous, 36 oxygen-enriched, 37 hierarchical 38 ACs, have been successfully prepared, achieving high speci¯c capacitances up to 350 F Á g À1 in H 2 SO 4 electrolyte. Beside a few work employed ZnCl 2 or H 3 PO 4 as activating agent, rest of all the works employed a strongly alkaline chemical, KOH, as the activating agent.…”