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.

Bimetallic Synergies Help the Application of Sodium Vanadyl Phosphate in Aqueous Sodium-Ion Batteries.

Aqueous sodium-ion batteries (ASIB) offer many potential applications in large-scale power grids since they are inexpensive, safe, and environmentally friendly. Sodium superionic conductors (NASICON), especially carbon-coated Na3 V2 (PO4 )3 (NVP), have attracted much attention due to the full use of their high ion migration speed. However, the poor cycle lifespan and capacity retention of NVP hinder its application in ASIB. Herein, a novel bimetal-doped Na3 V1.3 Fe0.5 W0.2 (PO4 )3 (NV1.3 Fe0.5 W0.2 P) cathode is designed and synthesized to achieve outstanding cycling stability (95 % of initial capacity at 50th cycle). The electrochemical behavior and charge storage mechanism of NV1.3 Fe0.5 W0.2 P are systematically investigated by various in situ and ex situ characterizations. The Fe and W codoping could stabilize the NASICON framework to suppress the proton attack on the Na site in the aqueous electrolyte, thus resulting in excellent cycling stability. DFT calculations show that bimetallic doping increases the structural stability of NVP. Moreover, an ASIB fabricated using a NV1.3 Fe0.5 W0.2 P cathode and a NaTi2 (PO4 )3 anode delivers 64 mAh g-1 at room temperature, 95 % capacity retention after 50 cycles (1 A g-1 ).

Unravelling capacity fading mechanisms in sodium vanadyl phosphate for aqueous sodium-ion batteries.

Na3V2(PO4)3 (NVP), which is known as a sodium superionic conductor (NASICON), has been successfully developed as an excellent cathode material for sodium-ion batteries (SIBs). However, the capacity of NVP quickly fades when used in an aqueous electrolyte. Herein, the charge storage and capacity attenuation mechanisms of carbon-coated NVP (NVP@C) were carefully investigated by systematic material characterization and density functional theory (DFT) calculations. According to the results, protons in the aqueous electrolyte diffuse into the surface of NVP@C to occupy the sodium site and attack the nearby phosphates during the charge-discharge cycles, leading to the deformation and breakage of the POV bond. The distorted phosphates on the surface of NVP@C gradually dissolve into the electrolyte, causing a decrease in capacity. To stabilize the phosphates on the surface of NVP, DFT calculations suggest that iron doping of NVP can effectively relieve the deformation of the POV bond and suppress the capacity decay. The as-prepared Na3V1.5Fe0.5(PO4)3@C (NV1.5Fe0.5P@C) has a capacity retention of 95% in the first ten cycles, while NVP@C retains only 55% of the initial capacity in the same number of cycles.

Designing a carbon nanofiber-encapsulated iron carbide anode and nickel-cobalt sulfide-decorated carbon nanofiber cathode for high-performance supercapacitors.

To meet the crucial demand for high-performance supercapacitors, much effort has been devoted to exploring electrode materials with nanostructures and electroactive chemical compositions. Herein, iron carbide nanoparticles are encapsulated into carbon nanofibers (Fe3C@CNF-650) through electrospinning and annealing methods. Nickel-cobalt sulfide nanoparticles are hydrothermally grown on electrospun carbon nanofibers (CNF@NiCoS-650). The Faradaic electrochemical reactions of transition metal compounds improve the specific capacitance of the developed electrode. Meanwhile, the electrically conductive framework of carbon nanofibers facilitates Faradic charge transport. In detail, the Fe3C@CNF-650 anode and CNF@NiCoS-650 cathode achieve specific capacitances of 1551 and 205 F g-1, respectively, at a current density of 1 A g-1. A hybrid supercapacitor that is fabricated from the Fe3C@CNF-650 anode and CNF@NiCoS-650 cathode delivers an energy density of 43.2 Wh kg-1 at a power density of 800 W kg-1. The designed nanostructures are promising for practical supercapacitor applications.

Nitrogen- and oxygen-doped carbon with abundant micropores derived from biomass waste for all-solid-state flexible supercapacitors.

Fabrication of porous activated carbon derived from biomass waste with high surface area, specific porosity, and excellent electroactivity has attracted much more attention in the energy conversion and storage field. Herein, mango seed waste is utilized as a precursor to synthesize nitrogen (N) and oxygen (O) co-doped porous carbon by high-temperature carbonization coupling with subsequent KOH activation. The more KOH activator was fed in the high-temperature activation process, the larger surface area, higher micropore ratio, and lower N and O doping content of the activated carbon was obtained. The optimized mango seed-derived activated carbon (MSAC) exhibits high surface area (1815 m2 g-1), micropore ratio (94%), doping content of nitrogen (1.71 at.%), and oxygen (10.93 at.%), which delivers an ultrahigh specific capacitance of 402F g-1 at 1 A g-1 and retains 102.4% of initial capacitance after 5000 cycles. The supercapacitor performance of MSAC was also investigated in 6 M KOH, 1 M [BMIM]BF4/AN, and PVA/KOH electrolytes in detail, respectively. A flexible all-solid-state asymmetric supercapacitor (FSAS) fabricated by MSAC anode, CoNiAl layered double hydroxides cathode, and PVA/KOH electrolyte achieves a high energy density of 33.65 Wh kg-1 at a power density of 187.5 W kg-1 and retains 80% of initial capacitance after 10,000 cycles. The low cost, facile synthetic process, and excellent electrochemical performance of MSAC electrode material provide a cheap and accessible strategy to obtain porous carbon material for energy conversion and storage systems.