Nitrogen-Doped Hierarchical Porous Carbon Framework Derived from Waste Pig Nails for High-Performance Supercapacitors

Three-Dimensional Hierarchical Porous Carbons Derived from Betelnut Shells for Supercapacitor Electrodes

Electrochemical energy storage (EES) systems are attracting research attention as an alternative to fossil fuels. Advances in the design and composition of energy storage materials are particularly significant. Biomass waste-derived porous carbons are particularly suitable for use in EES systems as they are capable of tuning pore networks from hierarchical porous structures with high specific surface areas. These materials are also more sustainable and environmentally friendly and less toxic and corrosive than other energy storage materials. In this study, we report the creation of a three-dimensional hierarchical porous carbon material derived from betelnut shells. The synthesized three-dimensional (3D) hierarchical porous carbon electrode showed a specific capacitance of 290 F g-1 using 1 M KOH as an electrolyte at a current density of 1 A g-1 in three-electrode systems. Moreover, it offered a high charge/discharge stability of 94% over 5000 charge-discharge cycles at a current density of 5 A g-1. Two-electrode symmetric systems show a specific capacitance of 148 F g-1, good cyclic stability of 90. 8% for 5000 charge-discharge cycles, and high energy density of 41 Wh Kg-1 at the power density of 483 W Kg-1 in aqueous electrolyte.

Nitrogen-Doped Hierarchical Meso/Microporous Carbon from Bamboo Fungus for Symmetric Supercapacitor Applications

We report the synthesis of nitrogen-doped hierarchical meso/microporous carbon using renewable biomass bamboo fungus as precursor via two-step pyrolysis processes. It is found that the developed porous carbon (NHPC-800) features honeycomb-like cellular framework with well-developed porosity, huge specific surface area (1708 m² g⁻¹), appropriate nitrogen-doping level (3.2 at.%) and high mesopore percentage (25.5%), which are responsible for its remarkable supercapacitive performances. Electrochemical tests suggest that the NHPC-800 electrode offers the largest specific capacitance of 228 F g⁻¹, asplendid rate capability and stable electrochemical behaviors in a traditional three-electrode system. Additionally, asymmetric supercapacitor device is built based on this product as well. An individual as-assembled supercapacitor of NHPC-800//NHPC-800 delivers the maximum energy density of 4.3 Wh kg⁻¹; retains the majority of capacitanceat large current densities; and shows terrific cycling durability with negligible capacitance drop after long-term charge/discharge for beyond 10,000 cycles even at a high current density of 10 A g⁻¹. These excellent supercapacitive properties of NHPC-800 in both three- and two-electrode setups outperform those of lots of biomass-derived porous carbons and thus make it a perspective candidate for producing cost-effective and high-performance supercapacitors

Hierarchical Porous Carbon Derived from Sichuan Pepper for High-Performance Symmetric Supercapacitor with Decent Rate Capability and Cycling Stability

Hierarchical micro-mesoporous carbon (denoted as HPC-2 in this study) was synthesized by pre-carbonization of biomass Sichuan pepper followed by KOH activation. It possessed well-developed porosity with the specific surface area of 1823.1 m² g⁻¹ and pore volume of 0.906 cm³ g⁻¹, and exhibited impressive supercapacitive behaviors. For example, the largest specific capacitance of HPC-2 was tested to be ca. 171 F g⁻¹ in a three-electrode setup with outstanding rate capability and stable electrochemical property, whose capacitance retention was near 100% after cycling at rather a high current density of 40 A g⁻¹ for up to 10,000 cycles. Furthermore, a two-electrode symmetric supercapacitor cell of HPC-2//HPC-2 was constructed, which delivered the maximum specific capacitance and energy density of ca. 30 F g⁻¹ and 4.2 Wh kg⁻¹, respectively, had prominent rate performance and cycling stability with negligible capacitance decay after repetitive charge/discharge at a high current density of 10 A g⁻¹ for over 10,000 cycles. Such electrochemical properties of HPC-2 in both three- and two-electrode systems are superior or comparable to those of a great number of porous biomass carbon reported previously, hence making it a promising candidate for the development of high-performance energy storage devices.

Preparation of chrome-tanned leather shaving-based hierarchical porous carbon and its capacitance properties

Based on the complexes formed by the original Cr(iii) in chrome-tanned leather shavings and the carboxyl groups in collagen as raw materials, a chromium oxide-carbon composite material was formed by the high-temperature carbonization of chromium-tanned leather shavings, followed by the leaching of chrome oxide and activation by KOH. By this method, the hierarchical porous carbon with a high surface area doped with oxygen and nitrogen was prepared. The forming process of the hierarchical porous structure is discussed in detail. Through adjusting the mass ratio of KOH to carbon during the activation process, with a mass ratio of 2, the chromium-tanned leather shavings-based hierarchical porous carbon (called CTSHPC-2) was prepared with an optimal specific surface area (3211 m² g⁻¹) and a large volume ratio of mesopores to macropores (61.9%) as well as abundant oxygen (13.92 at%) and nitrogen (3.58 at%) functional groups. The results showed that CTSHPC-2 obtained a high specific capacitance of 335.5 F g⁻¹ at a current density of 0.5 A g⁻¹. In addition, it had higher rate performance, low resistance, and better cycle stability. Even when the current density is 10 A g⁻¹ over 5000 cycles, the specific capacity retention rate is 93.5%. Therefore, CTSHPC-2 is a promising electrode material for supercapacitors.

A chromium oxide-carbon composite material was formed by the high-temperature carbonization of chromium-tanned leather shavings, followed by the leaching of chrome oxide and activation by KOH.

Sustainable Utilization of Biomass Refinery Wastes for Accessing Activated Carbons and Supercapacitor Electrode Materials

Biomass processing wastes (humins) are anticipated to become a large-tonnage solid waste in the near future, owing to the accelerated development of renewable technologies based on utilization of carbohydrates. In this work, the utility of humins as a feedstock for the production of activated carbon by various methods (pyrolysis, physical and chemical activation, or combined approaches) was evaluated. The obtained activated carbons were tested as potential electrode materials for supercapacitor applications and demonstrated combined micro- and mesoporous structures with a good capacitance of 370 F g^-1 (at a current density of 0.5 A g^-1 ) and good cycling stability with a capacitance retention of 92 % after 10 000 charge/discharge cycles (at 10 A g^-1 in 6 m aqueous KOH electrolyte). The applicability of the developed activated carbon for practical usage as a supercapacitor electrode material was demonstrated by its successful utilization in symmetric two-electrode cells and by powering electric devices. These findings provide a new approach to deal with the problem of sustainable wastes utilization and to advance challenging energy storage applications.