Activated Carbon Derived From Desiccated Coconut Residue As Electrode Material For Electric Doublelayer Capacitor
Studies on the preparation of activated carbon derived from agricultural waste; desiccated coconut residue (DCR); the grated coconut residue left after the extraction of milk, for electrode material in electric double layer capacitor (EDLC) were conducted. The preparation of activated carbon (AC)...
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| Summary: | Studies on the preparation of activated carbon derived from agricultural waste;
desiccated coconut residue (DCR); the grated coconut residue left after the extraction
of milk, for electrode material in electric double layer capacitor (EDLC) were
conducted. The preparation of activated carbon (AC) involves chemical activations
with sodium hydroxide (NaOH) and potassium hydroxide (KOH) to the charred DCR.
The effects of temperature and impregnation ratio on the physicochemical properties
of AC prepared were also investigated. DCR sample was first carbonized for 1 hour at
three different temperatures; 400°C, 500°C, and 600°C respectively. The resulting
chars were impregnated with NaOH and KOH at three different impregnation ratio
(IR); 1: 1,1: 2, and 1: 3 respectively followed by further activation under nitrogen
atmosphere for 1 hour at the respective carbonization temperatures. The prepared ACs
were characterized by Brunauer-Emmett-Teller (BET) surface area (SBET), bulk
density, ultimate analysis, scanning electron microscopy (SEM), and yield. Results
show both NaOH and KOH treatments resulted in different effects on the resulting
ACs particularly on SBET. NaOH derived activated carbon (NAC) was strongly
affected by IR while KOH derived activated carbon (KAC) was strongly affected by
temperature. For NAC, the SBET increased with the increased in IR while for KAC the
SBET increased with increasing temperature. The SBET of the prepared ACs was in the
order: NAC3: 500 > NAC3: 600 > NAC2: 500 > NAC2: 600 > NAC1: 500 > NAC1: 600
> NAC2: 400 > NAC3: 400 > NAC 1: 400 and KAC2: 600 > KAC3: 600 > KAC2: 500 >
KAC3: 500 > KACI: 600 > KAC 1: 500 > KAC2: 400 > KAC 1: 400 > KAC3: 400,
respectively. The highest SBET for NAC and KAC were found to be 1394.79 m2/g and
823.81 m2/g, with total pore volume (Vi) of 0.78 and 0.50 cm3/g respectively. In
general, ACs produced were microporous in characteristic and both activating agents
and temperature were found to be important factors in developing microporosity
properties of both ACs. Under SEM observation, the selected NAC and KAC had
shown a wide variety of pores with honey-comb like structure which resulted from
porosity developments. The highest SBET from both NAC and KAC were selected for
studying the AC as electrode material in EDLC. Selected ACs were further studied
under X-Ray Diffraction (XRD), Raman spectroscopy, Energy Dispersive X-Ray
(EDX), and X-ray Photoelectron Spectroscopy (XPS). Under XRD analysis, results
show both NAC and KAC were found to have turbostratic structures with amorphous
characters and disordered structures. The different values of both interlayer spacing
(d002 and d100) and microcrystallite dimensions (Lc and La) were attributed to the
activation temperature used in AC preparations. KAC was found to have higher
degree graphitization and lower degree of disordered as compared to NAC under
Raman spectroscopy analysis. Under EDX and XPS analyses, results indicate that
NAC had double amount of oxygen functional groups in comparison with KAC. For
EDLC fabrications, the EDLCs derived from NAC and KAC was characterized by
cyclic voltammetry and charge-discharge with potential window of IV using aqueous
electrolytes. Two types of current collectors were applied namely; aluminium foil and
stainless steel foil. For aluminium foil, only aqueous electrolyte of IM Na2SO4 were
used to fabricate EDLC, whereas for stainless steel foil, three types of electrolytes
were utilized; IM H2SO4, IM Na2SO4 and 6M KOH. Results showed that for IM
Na2SO4 electrolyte, both NAC and KAC showed similar trends for both types of
current collectors in which KAC had shown larger specific capacitance (SC) as
compared to NAC even though the SBET of NAC was greater than that of KAC. It was
suggested that ion sieving effects had resulted in lower specific capacitance in NAC.
Nevertheless, for IM H2SO4 and 6M KOH electrolytes, NAC had shown higher
specific capacitance than that of KAC. Factors such as surface functional groups,
molar conductivities, size of electrolyte ions have resulted in higher specific
capacitance in NAC. NAC had two times oxygen functional groups compared to KAC
which could improve the wettability of between NAC electrode surface and
electrolytes. The specific capacitance were in the order of 6M KOH > IM H2SO4 >
1M Na2SO4 for both NAC and KAC. Nevertheless, results showed that KAC had
better cycle stability than that of NAC due to higher contents of oxygen functional
groups that deteriorated the electrodes in NAC. Finally, EDLC derived from DCR was
found to exhibit excellent EDLC behaviour in terms of specific capacitance and cycle
stability. |
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