Evaluation of Synthetic Conditions for H3PO4 Chemically Activated Rice Husk and Preparation of Honeycomb Monoliths

Activated carbons in this work were prepared from rice husk by phosphoric acid activation followed by alkaline desilication. Pseudo-random selection of 16 rice husk samples was subjected to carbonization at the following conditions: 0.5 to 2 h of activation time, 300-600 ºС and Н3РО4/precursor (wt/wt) impregnation ratio of 0.5 to 2. Concentration of NaOH desilication solution varied from 0.5 to 2M. It was found that out of the four factors impregnation ratio is clearly the strongest and at the impregnation ratio of 2 for 1 h at 500 °C N2 BET-surface area reaches 1690 m2/g (SBET (Ar)=2492 m2/g) while pore volume becomes 1.95 cm3/g. Elemental analysis showed highest carbon content for this sample (87.96%). All samples have insignificant amount of Si and traces of metals, but considerable amount of phosphorus. Blocks of honeycomb structure prepared from Ca-montmorillonite and desilicated carbonized rice husk (impregnation ratio is 1.5, 1 h at 600 ºC) have BET-surface area obtained by thermal desorption of argon up to 856 m2/g

Temperature Dependent Characteristics of Activated Carbons from Walnut Shells for Improved Supercapacitor Performance

Activated carbons (ACs) have been prepared from chemical treatment of walnut shells (WS) precursor at various temperatures (400‒800 °C) by using phosphoric acid (H3PO4) as activating agent. Influence of activation temperature on the porosity development and capacitive properties of resulting carbons was investigated. Thermal post-treatment of carbons previously activated at moderate temperature, e.g. 400 °C allowed further structural and porosity modification. Then, these carbons were investigated by scanning electron microscopy, Raman spectroscopy, energydispersive X-ray spectroscopy, electrochemical techniques and low temperature nitrogen adsorption exhibiting high BET specific surface area of approximately 2100 m2 g-1 and a total pore volume up to 1.3 cm3 g-1. Carbon material obtained through activation by H3PO4 at 400 °C and post-treated at 800 °C was used to make electrodes which were implemented to realize AC/AC capacitor using 1 mol L-1 Li2SO4. The electrochemical capacitor demonstrated high capacitance of 123 F g-1 per mass of one electrode, reduced cell resistance and stable capacitance for 5000 galvanostatic charge/discharge cycles at 1.0 A g-1