Yerba mate: From waste to activated carbon for supercapacitors

Recovery of organic materials from waste activated sludge for the rapid synthesis of N-doped hierarchical porous carbon as supercapacitor electrodes

The organic matter in waste activated sludge (WAS) is extracted via a NaOH/urea aqueous solution combined with ultrasonic treatment to obtain an organic-enriched extractant (S-NaOH/urea). N-doped hierarchical porous carbons (NPCs) are prepared by dissolving cellulose in S-NaOH/urea followed by carbonization and in situ activation. The NaOH/urea aqueous solution serves as a trifunctional medium: organic extractant for WAS, chemical activator, and nitrogen precursor during pyrolysis, significantly enhancing process efficiency while minimizing secondary reagent consumption. Structural characterization revealed that the obtained NPCs exhibit well-defined hierarchical porosity and proper heteroatom doping, endowing them with exceptional capacitive performance (390.3 F g-1 at 0.5 A g-1) and excellent cycling stability in alkaline electrolytes. Furthermore, the contributions of surface control and diffusion control from nitrogen doping were also analyzed. Additionally, the carbon materials obtained from S-NaOH/urea with wheat straw and corncob also exhibit hierarchically porous networks and favorable electrochemical properties. These findings suggested that this strategy not only provides a novel method for the resource utilization of WAS but also offers a potentially convenient synthesis route for multisource biomass-based heteroatom-doped hierarchical porous carbons.

Overview of recent developments in carbon-based nanocomposites for supercapacitor applications

Energy storage devices are recognized as environmentally friendly technologies. Supercapacitors, known for their high cycle stability, have been proposed as potential alternatives to fossil fuels. Recent studies have focused on selecting suitable electrode materials to achieve energy storage systems with high stability, high specific capacity, and biocompatibility. In particular, carbon-based electrode materials, such as graphene oxide, activated carbon, carbon nanotubes, and carbon-based quantum dots, have attracted considerable attention due to their intrinsic properties, such as high conductivity and stability. However, carbon materials alone exhibit limitations, such as low energy density and low specific capacitance. To address this limitation, the synergistic effect of carbon materials has been combined with other electroactive materials to develop electrode materials with enhanced supercapacitor properties. The present study also investigates the supercapacitor performance of carbon-based nanocomposites. It examines the effect of each carbon material (AC, CNT, GO, rGO) on improving the performance of other electroactive materials, including metal oxides, metal sulfides, MXenes, MOFs, and conductive polymers. This study provides valuable insights for further studies on carbon-based electrode materials for supercapacitor applications.

A state-of-the-art review on biomass-derived carbon materials for supercapacitor applications: From precursor selection to design optimization

Biomass-derived carbon materials have the characteristics of a wide range of precursor sources, controllable carbon nano-dimension, large specific surface area and abundant heteroatoms doping. At present, biomass-derived carbon materials have been widely used in electrochemical energy storage devices, especially the research and development of biomass-derived carbon materials for supercapacitors has become mature and in-depth. Therefore, it is of importance to summarize the advanced technologies and strategies for optimizing biomass-derived carbon materials for supercapacitors, which will effectively promote the further development of high-performance supercapacitors. In this review, the recent research progress of biomass-derived carbon materials is provided in detail, including the selection of biomass precursors, the design of carbon nano-dimension and the theory of heteroatom doping. Besides, the preparation methods of biomass-derived carbon materials and the related processes of optimizing the electrochemical performance are also summarized. This review ends with the perspectives for future research directions and challenges in the field of biomass-derived carbon materials for electrochemical applications. This review aims to provide helpful reference information for the nano-dimensional design and electrochemical performance optimization of biomass-derived carbon materials for the practical application of supercapacitors.

Use of carbon from the agricultural industry for the synthesis of catalysts destined to oxyanions removal from water

Remediation of water contaminated with oxyanions is of great importance due to the toxicity and environmental persistence of these chemical species. The present work describes the elimination of different oxyanions in water using catalysts supported on active carbon obtained from an agricultural residue (peanut shells, CPeanut) and active commercial carbon (CCom) in order to compare their structural and catalytic properties. The synthesized CPeanut and CCom were fully characterized by surface analysis, TGA, TPR, SEM-EDX, FT-IR, and TEM. It was observed that CPeanut presented similar superficial characteristics to CCom, being an adequate support to synthesize catalysts. With both carbons, catalysts based on Cu, Pd, and PdCu were prepared and evaluated in the elimination of NO3-, NO2-, and BrO3- from water using H2 as a reducing agent. The bimetallic catalysts prepared on both supports were active in the oxyanions reduction, obtaining good selectivities to the products of interest. In this sense, this work presents a potential re-use of agricultural wastes by preparing activated carbon from peanut shell residues in order to reduce the waste volume generated. In addition, the material synthetized is low cost due to its large-scale production and great availability in Argentina. The carbon obtained from the peanut shells provides a potential application in the environmental remediation of water contaminated with oxyanions.