Preparation, characterization and application of Nanaporous activated charcoal from plant resources

Abstract

This study was undertaken to prepare Activated Carbon (AC) from an agro-waste, i.e. sawdust of Shorea robusta by chemical activation using phosphoric acid and characterized and applied this AC in energy related field. The carbonization of wood powder of Shorea robusta was carried out at 400°C in an inert atmosphere of N 2 to prepare AC, which was chemically activated with H vi

3 PO 4

and successfully tested as supercapacitor materials for the first time for its application in energy storage device. Thermogravimetric Analysis (TGA)/Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM), X-ray diffractometer (XRD), Raman spectra, Fourier Transform Infrared Spectroscopy (FTIR), Brunauer– Emmett–Teller (BET), and X-ray Photoelectron Spectroscopy (XPS) are the methods that have been utilized to characterize as prepared AC. Thermal decomposition behavior (TG curve) coupled with endothermal peak of DSC curve confirmed that 400 o C was the adequate temperature for carbonization of raw sawdust powder, since no significant weight loss occurred after 400 o C, which confirms the completion of carbonization process. FTIR spectra clearly confirmed the presence of oxygenated functional groups such as hydroxyl (-OH), aldehyde/ketone (CHO/C=O)

and ether (C-O-C), at the surface of as prepared AC. Similarly, XPS shows a broad peak at 532.6 eV for O 1s, indicating the presence of different chemical states of oxygen and the three deconvoluted peaks for oxygen at the binding energies 531 eV, 533.04 eV and 533.12 eV shows the presence of phosphatic oxygen (PO 4 3- ), hydroxyl group (-OH) and silicon dioxide (SiO 2 ) respectively. XPS spectra confirmed that as prepared activated carbon (Sa-H 3 PO 4 ) was well functionalized after H 3 PO 4 activation and consists of more acidic functional groups as aldehydes/ketones, ethers, hydroxides. This aligns with the FTIR results, where activated carbon (SaH 3 PO 4 ) showed high intensities for hydroxyl (-OH), aldehyde/ketone (-CHO/C=O) and ether (C-O-C) functional groups. XRD-pattern showed the amorphous structure of carbon having 002 and 100 plane, whereas Raman spectra clearly displayed G and D band which further confirms the amorphous nature of carbon. The G/D intensity ratio was found to be approximately 1, which indicated the presence of graphitic degree and defects in equal proportion. BET method of surface area determination showed the high specific surface area of 1270 m 2 g -1 (+ 0.57 %). Electrochemical characterization was performed in 6M aqueous KOH using Cyclic Voltammetry (CV), Galvanostatic Charge-Discharge (GCD) and Electrochemical Impendance Spectroscopy (EIS). The specific capacitance acquired from GCD at 1 A g -1 was found to be 136.3 Fg -1 (+ 0.15 %) with 0.44 Ω (+ 0.02 %) ESR. The 97 % capacitance retention was observed after 1000 cycles. The energy density of as prepared carbon electrode was found to be 3.0 (+ 0.25 %) Whkg vii

-1 at 100.5 (+ 0.20 %) Wkg -1 power density. Then the working carbon electrode was replaced by hybridcomposite-electrode

which showed the ideal capacitive behaviors having specific capacitance of 480.4 (+ 0.20 %) Fg -1 , specific energy density of 24 (+ 0.26 %) WhKg -1 at power density of 149.3 WKg -1 and low ESR value of 0.41 (+ 0.02 %) Ω. The obtained results revealed that the desirable electrochemical capacitive performances enable the hybrid composite to act as a new bio-material for high performance supercapacitors and energy storage devices. Keywords: hybrid composite, capacitive behavior, energy density, power density