Abstract
Activated carbons prepared from rice husk by chemical activation with dual activation agents, KOH and NaOH, have been studied and characterized by BET, SEM, EDX, FTIR, Boehm titration, Raman, and TGA. It was found that the KOH/NaOH impregnation ratio plays an important role on textural properties of AC. At the same amount of total alkali hydroxide, the KOH/NaOH ratio higher than 1.33 resulted in larger specific surface area (2990∼3043 m2·g−1), microporous surface area (2747∼2831 m2·g−1), and higher micropore volume (1.4250∼1.4316 cm3·g−1). The as-prepared samples exist in the form of spherical-shaped particles with the size ranging from 20 to 60 nm and contain numerous surface functional groups. The as-prepared activated carbons were then assessed as an electrode material of supercapacitor operating in the 0.5 M K2SO4 electrolyte in potential windows of −1.0∼0.0 V. The highest capacitance obtained was 205 F·g−1 at the scan rate of 2 mV·s−1 and 225 F·g−1 at a current density of 0.2 A·g−1. At the scan rate as high as 50 mV·s−1, all the as-prepared activated carbons in this study have the specific capacitance greater than 100 F·g−1.
Highlights
It is well known that activated carbon (AC) is a material with a porous structure and high specific surface area and is widely used as an adsorbent in water/air treatment, catalyst supporter, or electrical energy/gas storage material
In the chemical activation process, the chars are impregnated in activation agents such as potassium hydroxide (KOH), sodium hydroxide (NaOH), zinc chloride (ZnCl2), and phosphoric acid (H3PO4) followed by activation at temperature in the range between 600 and 900°C under nitrogen flow. e characteristics of the resulting AC are very sensitive to preparing conditions, especially types of activating agents. e activated carbons prepared from lapsi seed (Nepal) are highly porous when activated by KOH or CaCl2 than nonactivating agent pyrolyzed char; on the other hand, the activated carbons impregnated with MgCl2, FeCl3, and H2SO4 do not show porous structure [1]
Enteromorpha prolifera (China) based activated carbon activated by KOH resulted in higher surface area and larger total pore volume than that activated by H4P2O7 [3]; tomato paste processing industry waste (Turkey) established highest surface area that was activated by KOH, much larger than by K2CO3 or HCl [4]
Summary
It is well known that activated carbon (AC) is a material with a porous structure and high specific surface area and is widely used as an adsorbent in water/air treatment, catalyst supporter, or electrical energy/gas storage material. In the chemical activation process, the chars (carbonized materials) are impregnated in activation agents such as potassium hydroxide (KOH), sodium hydroxide (NaOH), zinc chloride (ZnCl2), and phosphoric acid (H3PO4) followed by activation at temperature in the range between 600 and 900°C under nitrogen flow. E KOH ACs had higher micropore volumes, whereas NaOH ACs had relatively higher densities [6] Another difference between the activation process by KOH and NaOH is that KOH can be used effectively with any types of materials while NaOH only with disorder materials. E main objective of this work is to prepare AC from rice husk with high porosity and large specific surface area using dual activating agent (KOH and NaOH) and investigate the effect of the NaOH/KOH ratio on the specific surface area, pore structure, morphology, and thermal stability of the AC samples. The obtained materials were characterized and evaluated for potential application as supercapacitor electrode materials
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