Preparation of Porous Carbon from SB-HPC (Sub-Bitumious) Solution Derived from Low Quality Coal and Its Application to EDLC
Authors: Toyoda Masahiro , Ohkuma Shouta 
Published: July 2022

Introduction

Hypercol (HPC), which is ashless coal obtained from thermal extraction of coal, is soluble in organic solvents and is mainly produced by carbonization of carbon precursors prepared by the precipitation method from its solution. Porous carbon mainly with micropores can be obtained from HPC by the precipitation method. Porous carbon prepared from SB-HPC, which is an HPC derived from low-grade coal, has a high specific surface area and abundant micropores. It has been clarified that the electrode material used for EDLC is preferably a material having a high specific surface area and exhibiting electrical conductivity, and in addition, it strongly depends on its pore structure. In this study, carbon powder is prepared from the SB-HPC solution by the precipitation method, and the pore characteristics are evaluated, and the EDLC characteristics when this carbon powder is used for the electrode are evaluated.

Experimental
SB-HPC derived from low-grade coal was used as a starting material, and the HPC powder (particle size: <250 m m) was dissolved in pyridine. The obtained HPC solution was added to water to precipitate and precipitate HPC. The obtained HPC powder was insolubilized by holding it in an air atmosphere at 300 oC for 1 h, and then carbonized by holding it in a nitrogen atmosphere at 800-1000 oC for 30 min. The morphology of the prepared sample was observed using a scanning electron microscope (SEM), a nitrogen gas adsorption / desorption measuring device with surface characteristics of 77 K was used, and temperature desorption analysis (TPD) was used to quantify the surface functional groups. Was used. In addition, the specific surface area value was obtained by the s analysis method using the adsorption isotherm obtained by nitrogen adsorption / desorption measurement. The electrodes were prepared by mixing them in a weight ratio of carbon powder: acetylene black: PTFE = 8: 1: 1. The EDLC characteristics were evaluated using a triode cell, and an aqueous sulfuric acid solution was used as the electrolytic solution. Galvanostatic charge / discharge measurements were performed with a current density in the range of 50–1000 mA g-1. The capacitance at each current density was calculated in the range of 0.2 V to 0.8 V of the discharge curve obtained by the galvanostatic charge / discharge measurement. The sample code was SB- (carbonization temperature).

Results and Discussions

From the nitrogen gas adsorption / desorption isotherm of carbonized powder of SB-HPC derived from low-grade charcoal at 900 to 1300 oC, the amount of adsorption in the low relative pressure region increased as the heat treatment temperature increased. This suggests the formation of micropores. The specific surface area calculated by the α s analysis method is 900 oC at the heat treatment temperature, and the specific surface area (737 m2 g-1) is higher than that of HPC carbon powder (400 m2 g-1) derived from high-grade coal. It is inferred that the fact that the specific surface area was nearly doubled by the same heat-treatment as for high-grade coal is due to the difference in the characteristics of the starting materials. Furthermore, as the heat treatment temperature increased, the specific surface area of SB-1200 showed a maximum value of 1268 m2 g-1 and decreased after 1200 oC. In addition, the obtained capacitance was higher (284 F g-1) than the carbon powder (210 F g-1) 1) of HPC derived from high-grade coal. The discharge curve obtained from the charge / discharge curve at a current density of 50 mA g-1 for each carbon powder showed a decrease in linearity around 0.4 V to 0.8 V, and the resistance due to the oxygen-containing functional group of the carbonpowder. It was considered to be an ingredient. From the relationship between the specific surface area and the capacitance of each carbon powder, although the specific surface area increased as the heat treatment temperature increased, there was no significant difference in the capacitance and it was almost constant. Therefore, it is inferred that the contribution of capacity to the surface area is constant, there are other factors, and one is the pseudo-capacity due to the oxygen-containing functional group.