B, O and N Codoped Biomass-Derived Hierarchical Porous Carbon for High-Performance Electrochemical Energy Storage

Multi-heteroatom-doped porous carbon with high surface adsorption energy of potassium derived from biomass waste for high-performance supercapacitors

Sustainable and renewable biomass-derived porous carbon (BPC) have garnered considerable attention owing to their low cost, high specific surface area, and outstanding electrochemical performance. However, the subpar energy density severely restricts the applications of BPC in high-energy-density devices. Herein, a high-surface-area porous carbon with multiple heteroatoms doping was derived from rapeseed meals by hydrothermal carbonization and high-temperature activation. The rapeseed meal-derived activated carbon (RMAC) exhibits a remarkable surface area of 3291 m2 g-1 and is doped with nitrogen (1.05 at.%), oxygen (7.4 at.%), phosphorus (0.31 at.%), and sulfur, resulting in an impressive specific capacitance of 416 F g-1 at 1 A g-1. Furthermore, even after 10,000 cycles, the optimized RMAC-800 electrode maintains 92 % of its initial capacitance, attesting to its exceptional performance. Through comprehensive density functional theory (DFT) calculations, the elements O, N, P, and S can significantly enhance the electron negativity and density, improving the adsorption and diffusion of K+ to attain a high capacitance. To assess the RMAC-800's practical performance, an asymmetric supercapacitor with 1 M [BMIM]BF4/AN electrolyte was produced that delivered a high energy density of 195.94 Wh kg-1 at a power density of 1125 W kg-1. Thus, we propose an eco-friendly strategy for producing BPC materials with outstanding electrochemical performance for supercapacitors.

Hierarchical Porous Heteroatoms-Co-Doped Activated Carbon Synthesized from Coconut Shell and Its Application for Supercapacitors

Coconut husk biomass waste was used as the carbon precursor to develop a simple and economical process for the preparation of hierarchical porous activated carbon, and the electrochemical properties of the electrode material were explored. The important process variables of carbonization, the weight ratios of the coconut shell/KOH, the amount of source dopant, and the carbonization temperature were investigated in order to reveal the influence of the as-obtained microporous/mesoporous/macroporous hierarchical porous carbon materials on the powder properties. Using a BET specific surface area analyzer, Raman analysis, XPS and SEM, surface morphology, pore distribution and specific surface area of the hierarchical porous carbon materials are discussed. The results show that the as-prepared N-, S- and O-heteroatom-co-doped activated carbon electrode was manufactured at 700 °C for electrochemical characteristics. The electrochemical behavior has the characteristics of pseudo-capacitance, and could reach 186 F g^-1 at 1 A g^-1 when measured by the galvanostatic charge-discharge (GCD) test. After 7000 cycles of the charge-discharge test, the initial capacitance value retention rate was 95.6%. It is predicted that capacitor materials made when using coconut shell as a carbon source will have better energy storage performance than traditional carbon supercapacitors.

Nanoporous Carbon from Oil Palm Leaves via Hydrothermal Carbonization-Combined KOH Activation for Paraquat Removal

In this study, nano-porous carbon was completely obtained from oil palm leaves (OPL) by hydrothermal pretreatment with chemical activation, using potassium hydroxide (KOH) as an activating agent. Potassium hydroxide was varied, with different ratios of 1:0.25, 1:1, and 1:4 (C: KOH; w/w) during activation. The physical morphology of nano-porous carbon has a spongy, sponge-like structure indicating an increase in specific surface area and porosity with the increasing amount of KOH activating agent. The highest specific surface area of OPL nano-porous carbon is approximately 1685 m²·g^-1, with a total pore volume of 0.907 cm³·g^-1. Moreover, the OPL nano-porous carbon significantly showed a mesoporous structure designed specifically to remove water pollutants. The adsorptive behavior of OPL nano-porous carbon was quantified by using paraquat as the target pollutant. The equilibrium analyzes were explained by the Langmuir model isotherm and pseudo-second-order kinetics. The maximum efficiency of paraquat removal in wastewater was 79%, at a paraquat concentration of 400 mg·L^-1, for 10 min in the adsorption experiment. The results of this work demonstrated the practical application of nano-porous carbon derived from oil palm leaves as an alternative adsorbent for removing paraquat and other organic matter in wastewater.