Polyethylene-Derived Activated Carbon Materials for Commercially Available Supercapacitor in an Organic Electrolyte System

Advances in Carbon Xerogels: Structural Optimization for Enhanced EDLC Performance

This review explores the recent progress on carbon xerogels (CXs) and highlights their development and use as efficient electrodes in organic electric double-layer capacitors (EDLCs). In addition, this work examines how the adjustment of synthesis parameters, such as pH, polymerization duration, and the reactant-to-catalyst ratio, crucially affects the structure and electrochemical properties of xerogels. The adaptability of xerogels in terms of modification of their porosity and structure plays a vital role in the improvement of EDLC applications as it directly influences the interaction between electrolyte ions and the electrode surface, which is a key factor in determining EDLC performance. The review further discusses the substantial effects of chemical activation with KOH on the improvement of the porous structure and specific surface area, which leads to notable electrochemical enhancements. This structural control facilitates improvement in ion transport and storage, which are essential for efficient EDLC charge-discharge (C-D) cycles. Compared with commercial activated carbons for EDLC electrodes, CXs attract interest for their superior surface area, lower electrical resistance, and stable performance across diverse C-D rates, which underscore their promising potential in EDLC applications. This in-depth review not only summarizes the advancements in CX research but also highlights their potential to expand and improve EDLC applications and demonstrate the critical role of their tunable porosity and structure in the evolution of next-generation energy storage systems.

Application of Infrared Pyrolysis and Chemical Post-Activation in the Conversion of Polyethylene Terephthalate Waste into Porous Carbons for Water Purification

In this study, we compared the conversion of polyethylene terephthalate (PET) into porous carbons for water purification using pyrolysis and post-activation with KOH. Pyrolysis was conducted at 400-850 °C, followed by KOH activation at 850 °C for samples pyrolyzed at 400, 650, and 850 °C. Both pyrolyzed and post-activated carbons showed high specific surface areas, up to 504.2 and 617.7 m2 g-1, respectively. As the pyrolysis temperature increases, the crystallite size of the graphite phase rises simultaneously with a decrease in specific surface area. This phenomenon significantly influences the final specific surface area values of the activated samples. Despite their relatively high specific surface areas, pyrolyzed PET-derived carbons prove unsuitable as adsorbents for purifying aqueous media from methylene blue dye. A sample pyrolyzed at 650 °C, with a surface area of 504.2 m2 g-1, exhibited a maximum adsorption value of only 20.4 mg g-1. We propose that the pyrolyzed samples have a surface coating of amorphous carbon poor in oxygen groups, impeding the diffusion of dye molecules. Conversely, post-activated samples emerge as promising adsorbents, exhibiting a maximum adsorption capacity of up to 127.7 mg g-1. This suggests their potential for efficient dye removal in water purification applications.

Activated carbons derived from polyethylene terephthalate for coin-cell supercapacitor electrodes

We successfully prepared activated carbon derived from polyethylene terephthalate (PET) via carbonization and subsequent activation under various conditions and applied it as active material for supercapacitors. In the activation, we used CO2 for physical activation or KOH for chemical activation and varied the activation temperature from 600 °C to 1,000 °C. We found that CO2 activation is unsuitable because of insufficient pore formation or low activation yield. Interestingly, PET-derived activated carbon obtained using KOH (PETK) at 700 °C-900 °C exhibited higher specific surface areas than YP50f, which is a commercial activated carbon. Furthermore, some PETKs even displayed a dramatic increase in crystallinity. In particular, the PET-derived activated carbon prepared at 900 °C with KOH (PETK900) had the highest retention rate at a high charge-discharge rate and better durability after 2500 cycles than YP50f. Furthermore, employing the same process that we used with the PET chips, we successfully converted waste PET bottles into activated carbon materials. Waste PET-derived activated carbons exhibited good electrochemical performance as active material for supercapacitors. We thus found chemical activation with KOH to be an appropriate method for manufacturing PET-derived activated carbon and PETKs derived both from PET chips and waste PET have considerable potential for commercial use as active materials for supercapacitors.

Electronic Supplementary Material

Supplementary material is available for this article at 10.1007/s11814-023-1466-3 and is accessible for authorized users.

Achieving Both Ultrahigh Electrical Conductivity and Mechanical Modulus of Carbon Films: Templating-Coalescing Behavior of Single-Walled Carbon Nanotube in Polyacrylonitrile

Promoting the feasibility of carbon films as electrode applications requires sufficient performances in view of both electrical and mechanical properties. Herein, carbon films with ultrahigh electrical conductivity and mechanical modulus are prepared by high temperature carbonization of polyacrylonitrile (PAN)/single-walled carbon nanotube (SWNT) nanocomposites. Achieving both performances is ascribed to remarkable graphitic crystallinity, resulting from the sequential templating-coalescing behavior of concentrated SWNT bundles (B-CNTs). While well-dispersed SWNTs (WD-CNTs) facilitate radial templating according to their tubular geometry, flattened B-CNTs sandwiched between carbonized PAN matrices induce vertical templating, where the former and latter produce concentric and planar crystallizations of the graphitic structure, respectively. After carbonization at 2500 °C with the remaining WD-CNTs as microstructural defects, the flattened B-CNTs coalesce into graphitic crystals by zipping the surrounding matrix, resulting in high crystallinity with the crystal thicknesses of 27.4 and 39.4 nm for the (002) and (10) planes, respectively. For comparison, the graphene oxide (GO) containing carbon films produce a less-ordered graphitic phase owing to irregular templating, despite the geometrical consistency. Consequently, PAN/B-CNT carbon films exhibit exceptional electrical conductivity (40.7 × 104 S m-1 ) and mechanical modulus (38.2 ± 6.4 GPa). Thus, controlling the templating-coalescing behavior of SWNTs is the key for improving final performances of carbon films.