Enke Feng

A redox mediator doped gel polymer as an electrolyte and separator for a high performance solid state supercapacitor

A stable and effective redox-mediator gel electrolyte has been prepared by doping indigo carmine (IC) into a polyvinyl alcohol sulfuric acid polymer system (PVA–H2SO4), and a high performance solid state supercapacitor is fabricated by utilizing activated carbon as electrodes and the prepared gel polymer (PVA–H2SO4–IC) as an electrolyte and separator. The PVA–H2SO4–IC gel polymer has excellent bending, compressing and stretching mechanical properties. As expected, the ionic conductivity of the gel polymer electrolyte increased by 188% up to 20.27 mS cm−1 while introducing IC as the redox mediator in the PVA–H2SO4 gel electrolyte. Simultaneously, specific capacitance is increased by 112.2% (382 F g−1) and energy density (13.26 W h kg−1) is also increased. Furthermore, the fabricated device shows superior charge–discharge stability. After 3000 cycles, its capacitive retention ratio is still as high as 80.3%. This result may be due to the fact that the IC can act as a plasticizer and redox mediator, and the supercapacitor combines the double-layer characteristic of carbon-based supercapacitors and the faradaic reaction characteristic of batteries energy-storage processes.

Preparation and properties of organic–inorganic composite superabsorbent based on xanthan gum and loess

A new, low-cost, and eco-friendly organic-inorganic composite superabsorbent was successfully synthesized in aqueous solution by polymerization xanthan gum (XG), neutralized acrylic acid (AA) and loess using ammonium persulfate (APS) as initiator and N,N-methylenebisacrylamide (MBA) as crosslinker. Structure and morphological characterizations of the composite superabsorbent were investigated by Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The loess content, pH values, surfactants, salts and temperature which could affect the swelling and water-retention capabilities of the composite superabsorbent were investigated. The composite superabsorbent exhibits excellent water absorbency (610 g/g in distilled water), pH-stability (pH 5-10), and higher swelling capacity in anionic surfactant solution; on the other hand, the composite superabsorbent can be used for removing multivalent metal ions.

Eco-friendly superabsorbent composite based on sodium alginate and organo-loess with high swelling properties

A novel superabsorbent composite with high swelling properties was synthesized by the grafted co-polymerization of partially neutralized acrylic acid (AA) onto a sodium alginate (NaAlg) backbone in the presence of organo-loess. The FTIR spectra, XRD patterns and SEM micrographs prove that the AA monomers were grafted onto the NaAlg backbone, and the organo-loess dispersed into the polymer matrix that improved the porous structure, which was verified by element mapping. TGA and DSC results indicate that the incorporation of loess enhances the thermal stability of the superabsorbent. Swelling results confirm that proper amount of organo-loess in the superabsorbent can enhance the swelling capability and salt-resistant performance. The maximum equilibrium water absorbency of the superabsorbent composite incorporated with 10 wt% organo-loess in distilled water and 0.9 wt% NaCl aqueous solution were 656 g g−1 and 69 g g−1, respectively. Furthermore, the superabsorbent composite exhibited good buffer ability to external pH in the range from 4 to 10 and water retention ability. According to the performance of the eco-friendly superabsorbent composite, it can be used as a promising candidate for applications in various fields.

Porous carbon derived from sorghum stalk for symmetric supercapacitors

Sorghum stalk based porous carbons (SSCs) have been synthesized through a simple carbonization method at 800 °C used sorghum stalk as carbon precursor and ZnCl2 as activating agent. The morphology and structure of the SSCs are investigated by scanning electron microscopy, transmission electron microscopy, nitrogen adsorption–desorption, Raman spectra and X-ray diffraction. Undergoes activation at optimal amount of zinc chloride (sorghum stalks to ZnCl2 is 1 : 1), the resulting samples, labeled as SSC1.0 has a porous texture with high specific surface area and efficient ion diffusion channels (1354.7 m2 g−1 specific surface areas and 0.765 cm3 g−1 pore volumes), and the sample also has superhydrophilicity characterized by water contact angles. As supercapacitor electrode, it can deliver 216.5 F g−1 specific capacitance at 0.5 A g−1, 75% capacitance retention even at 8 A g−1 in 2 mol L−1 KOH aqueous electrolyte and excellent cyclic stability with 92% capacitance retention after 5000 cycles at 5 A g−1. Moreover, the assembled SSC1.0//SSC1.0 symmetric cell has wide voltage range of 1.8 V, and high energy density in 0.5 mol L−1 Na2SO4 aqueous electrolyte.

Effectiveness of an Eco-friendly Polymer Composite Sand-Fixing Agent on Sand Fixation

A novel and eco-friendly xanthan gum-g-poly(acrylic acid)/laterite (XG-g-PAA/laterite) organic-inorganic composite polymer used as chemical sand-fixing agent (CSFA) was successfully prepared by grafted copolymerization of natural XG, partially neutralized acrylic acid (NaA), and laterite in solution. FTIR spectra confirmed that NaA had been grafted onto XG chains, and the –OH groups of laterite participated in polymerization reaction. The influence of the content of CSFA on sand-fixing effect was investigated, and the results of the aging test indicated that the CSFA had remarkable water resistance, heat resistance, anti-freeze-thaw, and anti-ultraviolet aging performances, which could meet the requirement of application in the harsh desert environment. Moreover, it also showed excellent water-retaining and anti-evaporation properties.

Superior performance of an active electrolyte enhanced supercapacitor based on a toughened porous network gel polymer

A primary challenge of gel electrolytes in the development of flexible and wearable devices is their weak mechanical strength and poor electrochemical performances. Here, we prepare a novel PVA (polyvinyl alcohol)–H2SO4–BAAS (bromamine acid sodium) gel polymer with a porous network structure as both electrolyte and separator, which achieves excellent mechanical strength, maintains a high ionic conductivity of 21.4 mS cm−1 and provides a reversible redox reaction for enhanced supercapacitor performance. Surprisingly, the operating voltage of the present active electrolyte enhanced supercapacitor (AEESC) is up to 1.5 V, which is much larger than that of the previously reported active electrolyte based supercapacitors (about 1.0 V). Furthermore, the AEESC exhibits a maximum specific capacitance of 390 F g−1 at a current density of 0.8 A g−1, a remarkably high energy density of 30.5 W h kg−1 at a power density of 600 W kg−1 and good cycling stability. Additionally, such a device displays only a small capacitance loss when the gel polymer is under a large tensile strain of 100% or under a high pressure of 2000 kPa. Meanwhile, the capacitance of the device was maintained very well after 500 complete bending cycles, indicating that the robust gel polymer endows the fabricated AEESC with good flexibility and electrochemical stability.

Sponge integrated highly compressible all-solid-state supercapacitor with superior performance

Compressible supercapacitors are novel energy-storage devices that can be used in elastic electronics; however, the performance of the supercapacitor depends mainly on its electrode materials and configuration. Herein, free-standing three-dimensional hierarchical porous polypyrrole (PPy) wrapped nitrogen-containing polyaniline based carbon nanospheres (NPACNS) are prepared and coated on the skeleton of sponge composite electrodes (PPy/NPACNS/sponge) via dipping and drying and chemical oxidation polymerization methods. Furthermore, an integrated highly compressible all-solid-state supercapacitor is fabricated using PPy/NPACNS/sponge as the electrode and polyvinyl alcohol (PVA)/LiClO4 gel as the electrolyte, which demonstrates an outstanding electrochemical performance of 95 F g−1 (2.8 F cm−3) specific capacitance, 3.3 W h kg−1 (0.1 mW h cm−3) energy density and 93% capacitance retention after 1000 cycles. Surprisingly, the electrochemical performance of the as-fabricated device remains nearly unchanged when it is compressed under 50% strain, and its specific capacitance and compressibility are well maintained after 400 repeated compressing-releasing cycles. More importantly, due to its solid-state and integrated configuration, several compressible supercapacitors can be conveniently interconnected together in series on one chip to power electronics. This device will pave the way for advanced supercapacitor applications in compressible energy storage devices that are compatible with compression-tolerant electronics.

Polyaniline-based carbon nanospheres and redox mediator doped robust gel films lead to high performance foldable solid-state supercapacitors

A novel and high-performance foldable solid-state supercapacitor has been developed based on nitrogen-containing polyaniline-based carbon nanosphere (C-PANI) coated carbon cloth electrodes and the AQSA-Na (anthraquinone-2-sulfonic acid sodium salt) redox mediator doped PVA (polyvinyl alcohol)–H2SO4 robust gel film electrolyte. The foldable solid-state supercapacitor demonstrates outstanding electrochemical performance such as a large specific capacitance of 430 F g−1 at a current density of 0.8 A g−1, a remarkably high energy density of 33.4 W h kg−1 at a power density of 600 W kg−1 and excellent cycling stability with 90% specific capacitance retention after 1000 cycles. Simultaneously, the high flexibility of the as-fabricated solid-state supercapacitor enabled it to work under both normal and folding conditions, and the device could be folded/unfolded repeatedly up to 500 times with only a small capacitance loss of 9%. These results indicate that the as-fabricated solid-state supercapacitor is suitable for highly fold-tolerant high-energy-density energy storage device applications. More importantly, owing to the solid-state and integrated configuration, several supercapacitors can be conveniently interconnected together in series or parallel to improve the output potential or current.

Toughened redox-active hydrogel as flexible electrolyte and separator applying supercapacitors with superior performance

Gel electrolytes with a reasonable ionic conductivity and high mechanical strength have drawn great interest for applications in flexible and wearable devices. However, the demand for gel electrolytes that combine high mechanical strength and excellent electrochemical performances remains a challenge. Here, a novel redox-active gel electrolyte was prepared by adding AQQS (1-anthraquinone sulfonic acid sodium) to a PVA (polyvinyl alcohol)–H2SO4 system using a simple solution-mixing/casting method, which possesses not only excellent mechanical strength but also a high ionic conductivity of 28.5 mS cm−1. Surprisingly, the as-fabricated supercapacitor can be operated at a wide voltage range of 0–1.4 V, which is much larger than that of the previously reported active electrolyte based supercapacitors (about 1.0 V). Furthermore, the supercapacitor exhibits superior electrochemical performance such as a maximum specific capacitance of 448 F g−1 at a current density of 0.5 A g−1, a high specific energy of 30.5 W h kg−1 at a specific power of 350 W kg−1 and good cycling stability with 91% specific capacitance retention after 1000 cycles. Additionally, such a device displays remarkably stable capacitive performance with the gel electrolyte even under a large tensile strain of 100%, a high pressure of 2000 kPa or fold states. The results doubtlessly demonstrate that the toughened redox-active gel polymer is a promising electrolyte candidate for developing high energy density flexible energy storage devices.

Preparation and properties of an organic–inorganic composite superabsorbent based on attapulgite

A novel, low-cost, and eco-friendly organic–inorganic composite superabsorbent is successfully prepared in aqueous solution by graft copolymerization of partially neutralized acrylic acid (AA), polyvinyl alcohol (PVA), and attapulgite (APT) using ammonium persulfate (APS) as an initiator and N,N-methylenebisacrylamide (MBA) as a crosslinker. The structure and morphology of the composite superabsorbent are characterized by means of Fourier transform infrared, X-ray diffraction, field-emission scanning electron microscopy, and transmission electron microscopy. The effects of APT content which can affect the water absorbency and the pH, ionic surfactants and different saline solution which can affect swelling capabilities of the composite superabsorbent are also investigated. The results show the composite superabsorbent give the best absorption up to 680 g/g and 53 g/g in distilled water and 0.9 wt% NaCl solution, high water absorbency over a wide pH range of 4–10, high swelling capacity in anionic surfactant than that of cationic solution, which makes it promising for potential applications in modern agriculture and horticulture. On the other hand, the composite superabsorbent can be used for removing multivalent metal ions.