Preparation of Nitrogen and Sulfur Co‐doped and Interconnected Hierarchical Porous Biochar by Pyrolysis of Mantis Shrimp in CO 2 Atmosphere for Symmetric Supercapacitors

Biomass-Derived Carbon Materials for Electrochemical Energy Storage

The environmental impact from the waste disposal has been widely concerned around the world. The conversion of wastes to useful resources is important for the sustainable society. As a typical family of wastes, biomass materials basically composed of collagen, protein and lignin are considered as useful resources for recycle and reuse. In recent years, the development of carbon material derived from biomasses, such as plants, crops, animals and their application in electrochemical energy storage have attracted extensive attention. Through the selection of the appropriate biomass, the optimization of the activation method and the control of the pyrolysis temperatures, carbon materials with desired features, such as high-specific surface area, variable porous framework, and controllable heteroatom-doping have been fabricated. Herein, this review summarized the preparation methods, morphologies, heteroatoms doping in the plant/animal-derived carbonaceous materials, and their application as electrode materials for secondary batteries and supercapacitors, and as electrode support for lithium-sulfur batteries. The challenges and prospects for the controllable synthesis and large-scale application of biomass-derived carbonaceous materials have also been outlooked.

N,S-codoped biochar outperformed N-doped biochar on co-activation of H2O2 with trace dissolved Fe(Ⅲ) for enhanced oxidation of organic pollutants

Co-activation of H2O2 with biochar and iron sources together provides an attractive strategy for efficient removal of refractory pollutants, because it can solve the problems of slow Fe(Ⅱ) regeneration in Fenton/Fenton-like processes and of low •OH yield in biochar-activated process. In this study, a wood-derived biochar (WB) was modified by heteroatom doping for the objective of enhancing its reactivity toward co-activation of H2O2. The performance of the co-activated system using doped biochars and trace dissolved Fe(Ⅲ) on oxidation of organic pollutants was evaluated for the first time. The characterizations using X-ray photoelectron spectroscopy (XPS), Raman spectra and electrochemical analyses indicate that heteroatom doping introduced more defects in biochar and improved its electron transfer capacity. The oxidation experiments show that heteroatom doping improved the performance of biochar in the co-activated process, in which the N,S-codoped biochar (NSB) outperformed the N-doped biochar (NB) on oxidation of pollutants. The reaction rate constant (kobs) for oxidation of sulfadiazine in NSB + Fe + H2O2 is 2.25 times that in NB + Fe + H2O2, and is 72.9 times that in the Fenton-like process without biochar, respectively. The mechanism investigations indicate that heteroatom doping enhanced biochar's reactivity on catalyzing the decomposition of H2O2 and on reduction of Fe(Ⅲ) due to the improved electron transfer/donation capacity. In comparison with N-doping, N,S-codoping provided additional electron donor (thiophenic C-S-C) for faster regeneration of Fe(Ⅱ) with less amount of doping reagent used. Furthermore, co-activation with NSB maintained to be efficient at a milder acidic pH than Fenton/Fenton-like processes, and can be used for oxidation of different pollutants and in real water. Therefore, this research provides a novel, sustainable and cost-efficient method for oxidation of refractory pollutants.

N/O Co-doped hierarchical nanoporous biochar derived from waste polypropylene nonwoven for high-performance supercapacitors

How to efficiently treat municipal solid waste (MSW) has become one of the critical solutions in response to the call for "carbon neutrality". Here, the waste polypropylene nonwoven fabric of waste diapers was converted into hierarchical nanoporous biochar (HPBC) through pre-carbonization and activation processes as an ideal precursor for supercapacitors (SCs) with excellent performance. The prepared HPBC-750-4 with an ultrahigh specific surface area (3838.04 m2 g-1) and abundant heteroatomic oxygen (13.25%) and nitrogen (1.16%) codoped porous biochar structure. Given its structural advantages, HPBC-750-4 achieved a specific capacitance of 340.9 F g-1 at a current density of 1 A g-1 in a three-electrode system. Its capacitance retention rate was above 99.2% after 10 000 cycles at a current density of 10 A g-1, which indicated an excellent rate capability and long-term cycling stability. Furthermore, the HPBC-750-4//HPBC-750-4 symmetric SC exhibited a superb energy density of 10.02 W h kg-1 with a power density of 96.15 W kg-1 in a 6 M KOH electrolyte. This work not only demonstrates the enormous potential of waste polypropylene nonwoven fabric in the SC industry but also provides an economically feasible means of managing MSW.

Lignin-Based/Polypyrrole Carbon Nanofiber Electrode With Enhanced Electrochemical Properties by Electrospun Method

Tailoring the structure and properties of lignin is an important step toward electrochemical applications. In this study, lignin/polypyrrole (PPy) composite electrode films with microporous and mesoporous structures were designed effectively by electrostatic spinning, carbonization, and in situ polymerization methods. The lignin can not only reduce the cost of carbon fiber but also increase the specific surface area of composite films due to the removal of carbonyl and phenolic functional groups of lignin during carbonization. Besides, the compact three-dimensional (3D) conductive network structures were constructed with PPy particles densely coated on the lignin nanofibers, which was helpful to improve the conductivity and fast electron transfer during the charging and discharging processes. The synthesized lignin carbon fibers/PPy anode materials had good electrochemical performance in 1 M H2SO4 electrolyte. The results showed that, at a current density of 1 A g−1, the lignin carbon nanofibers/PPy (LCNFs/PPy) had a larger specific capacitance of 213.7 F g−1 than carbon nanofibers (CNFs), lignin carbon nanofibers (LCNFs), and lignin/PPy fiber (LPAN/PPy). In addition, the specific surface area of LCNFs/PPy reached 872.60 m2 g−1 and the average pore size decreased to 2.50 nm after being coated by PPy. Therefore, the independent non-binder and self-supporting conductive film is expected to be a promising electrode material for supercapacitors with high performance.