Highly stretchable,ionic conductive and self-recoverable zwitterionic polyelectrolyte-based hydrogels by introducing multiple supramolecular sacrificial bonds in double network

Zwitterionic hydrogels have been explored for applications in electrochemical devices very recently due to their high water retention ability and interesting electrochemical properties. The use of zwitterionic hydrogels in devices requires them tough and recoverable or healable from fatigue damage. Herein, a double network zwitterionic hydrogel contains a reversible noncovalent interaction crosslinked polyvinyl alcohol (PVA) first network, together with a covalent/noncovalent hybrid crosslinked acrylamide and sulfobetaine methacrylate copolymer (P(AM-co-SBMA)) second network, was fabricated by a simple two-steps methods of copolymerization and freezing/thawing. The reversible hydrogen bonds, crystalline domain, and electrostatic interactions in the double networks work as sacrificial bonds to dissipate energy and toughen the materials when hydrogel deforms. The broken bonds can reform upon unloading endowing the recovery of hydrogels' properties with the assistance of the elastic covalent network. The optimal hydrogels are highly stretchable (fracture strain 970%), tough (fracture toughness 693 kJ m⁻³), rapidly recoverable (65% toughness recovery and 75% stiffness recovery after resting 5 min at room temperature) and with widely tunable mechanical properties by multibond crosslinking. Meanwhile, the zwitterionic counterions of SBMA moieties endow the tough and recoverable hydrogels extremely high intrinsic ionic conductivities (7.49 S m⁻¹) at room temperature. This work not only provides a simple strategy for fabricating tough and recoverable zwitterionic hydrogels but also demonstrates multifunctional properties of the zwitterionic hydrogels, which possess a great potential to fulfill flexible devices applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47783.     

Ultratough and recoverable ionogels based on multiple interpolymer hydrogen bonding as durable electrolytes for flexible solid-state supercapacitor

The emerging application of ionogels in flexible devices require it enough durable under repeated mechanical deformation while maintaining their superior electrochemical properties. In this work, ultratough and recoverable ionogels, where ionic liquids are confined in chemically and interpolymer hydrogen-bonding hybrid crosslinked network, were fabricated by in situ copolymerization of acrylic acid and 1-vinylimidazole monomer within 1-buty-3-methylimidazolium chloride ionic liquid. The reversible hydrogen bonds between imidazole and carboxylic acid groups of polymer chains in the network work as reversible “sacrificial bonds” to toughen ionogel, which makes the ionogels tough (tensile strength 1.62 MPa, toughness 8.7 MJ m⁻³), stretchable (elongation at break 1090%), and recoverable (91% recovery resting for 30 min, at 534 kPa stress and 500% strain). Moreover, the hydrogen-bonded ionogels exhibit high ionic conductivity of 2.3 S m⁻¹ at 80°C to 3.2 S m⁻¹ at 150°C. Furthermore, the ionogel-based flexible electrical double-layer capacitor can be operated up to 1.5 V with a capacitance of 341.47 F g⁻¹ at 0.5 A·g⁻¹ and exhibits excellent capacitance retention after 1000 cycles as well as superior electrochemical performance over a wide range of temperature. This work provides new insights into the synthesis of tough and recoverable ionogels for high-performance flexible supercapacitors.     

Janus POSS-based hydrogel electrolytes with highly stretchable and low-temperature resistant performances for all-in-one supercapacitors

Conductive hydrogels can be utilized in the field of flexible supercapacitors due to their stretchable properties and high ionic conductivity. However, many of the conductive hydrogels lose their stretchability and conductivity at subzero temperatures. Herein, a novel Janus POSS-based hydrogel electrolyte that shows excellent flexibility and ionic conductivity at low temperatures is designed and prepared by the copolymerization of acrylamide and a water-soluble Janus-type polyhedral oligomeric silsesquioxane (AS-POSS) containing sodium sulfonate groups and double bonding groups. The sodium sulfonate groups of AS-POSS and LiCl endow the hydrogel electrolyte with excellent anti-freezing ability. Simultaneously, the double bonding groups of AS-POSS enable a successful POSS crosslinking in the polymer network, resulting in a highly stretchable hydrogel electrolyte (1445%) with high ionic conductivity (0.067 S cm⁻¹) at −20°C. Thereafter, the all-in-one flexible supercapacitor is prepared by in-situ polymerization of aniline. Based on the exceptional anti-freezing properties of the Janus POSS-based hydrogel electrolyte, the all-in-one supercapacitor exhibits stable electrochemical performance (>90% capacitance retained under deformation at −20°C) and excellent cycling stability (only 19.7% capacitance decay over 2000 charge/discharge cycles at −20°C) at low temperatures. The Janus POSS-based hydrogel electrolyte is expected to be a promising gel electrolyte for an all-in-one supercapacitor that resists freezing.     

Behaviors of polyelectrolyte AAm/AMPS/bentonite composite hydrogels in uptake of uranyl ions from aqueous solutions

Uranyl ion (UO₂²⁺) sorption properties of polyelectrolyte composite hydrogels made by the polymerization of acrylamide (AAm) with 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPS) and clay such as bentonite (Bent) were investigated as a function of composition to find materials with swelling and uranyl ion sorption properties. Highly swollen AAm/AMPS hydrogels and AAm/AMPS/Bent composite hydrogels were prepared by free radical solution polymerization in aqueous solutions of AAm with AMPS as co‐monomer and two multifunctional crosslinkers such as ethylene glycol dimethacrylate (EGDMA) and 1,4 butanediol dimethacrylate (BDMA). Swelling experiments were performed in water at 25°C, gravimetrically. The influence of AMPS content in hydrogels was examined. Uranyl ion adsorption from aqueous solutions was studied by batch sorption technique at 25°C. The effect of uranyl ion concentration and mass of AMPS on the uranyl ion adsorption were examined. Finally, adsorption capacity (the amount of sorbed uranyl ion per gram of dry hydrogel) (q) was calculated to be 0.67 × 10⁻³–2.11 × 10⁻³ mol uranyl ion per gram for the hydrogels. Removal effiency of uranyl ions (RE%) was changed range 9.05–29.92%. The values of partition ratio (K_d) of uranyl ions was calculated to be 0.10–0.43 for AAm/AMPS hydrogels and AAm/AMPS/Bent composite hydrogels, respectively. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Design of highly stretchable deep eutectic solvent-based ionic gel electrolyte with high ionic conductivity by the addition of zwitterion ion dissociators for flexible supercapacitor

Nonvolatile deep eutectic solvent (DES) electrolytes with good electrochemical stability have recently emerged as promising electrolytes for energy storage devices. In this report, for the first time a polymerized zwitterionic molecule was introduced and a series of hybrid cross-linked zwitterion-containing copolymer DES gels are synthesized via UV initiated free-radical copolymerization of acrylic acid (AA), sulfobetaine vinylimidazole (VIPS) and poly(ethylene glycol) diacrylate (PEGDA) monomers, in situ within DES, which is prepared from 1:2 M ratio of choline chloride and ethylene glycol. Systematically varying the AA:VIPS molar ratio and copolymer contents within the copolymer network enables one to widely tune the mechanical properties and ionic conductivity of the poly(AA-co-VIPS) DES gels. The tensile strength of P(AA-co-VIPS) DES gels significantly increased from 28 kPa to 176 kPa with fracture strain from 720% to 1370%, while the ionic conductivity of copolymer DES gels remains high from 2.7 to 4.1 mS cm⁻¹ with the increase of copolymer content from 25 wt % to 45 wt%. A copolymer DES gel not only enables a supercapacitor deliver high capacitance of 71.52 F g⁻¹ at 0.5 A g⁻¹, and retains ∼97% of its capacitance after 2000 cycles, but also achieves outstanding capacitive performance over wide temperature range.     

Ultrastretchable,Super Tough,and Rapidly Recoverable Nanocomposite Double‐Network Hydrogels by Dual Physically Hydrogen Bond and Vinyl‐Functionalized Silica Nanoparticles Macro‐Crosslinking

It remains a challenge to develop tough hydrogels with recoverable or healable properties after damage. Herein, a new nanocomposite double‐network hydrogel (NC‐DN) consisting of first agar network and a homogeneous vinyl‐functionalized silica nanoparticles (VSNPs) macro‐crosslinked polyacrylamide (PAM) second network is reported. VSNPs are prepared via sol‐gel process using vinyltriethoxysilane as a silicon source. Then, Agar/PAM‐SiO₂ NC‐DN hydrogels are fabricated by dual physically hydrogen bonds and VSNPs macro‐crosslinking. Under deformation, the reversible hydrogen bonds in agar network and PAM nanocomposite network successively break to dissipate energy and then recombine to recover the network, while VSNPs in the second network could effectively transfer stress to the network chains grafted on their surfaces and maintain the gel network. As a result, the optimal NC‐DN hydrogels exhibit ultrastretchable (fracture strain 7822%), super tough (fracture toughness 18.22 MJ m^‐3, tensile strength 431 kPa), rapidly recoverable (≈92% toughness recovery after 5 min resting at room temperature), and self‐healable (can be stretched to 1331% after healing) properties. The newly designed Agar/PAM‐SiO₂ NC‐DN hydrogels with tunable network structure and mechanical properties by multi‐bond crosslinking provide a new avenue to better understand the fundamental structure‐property relationship of DN hydrogels and broaden the current hydrogel research and applications.     

Behaviors of Chemically Crosslinked CAAMPS Hydrogels in Uptake of Uranyl Ions from Aqueous Solutions

Uranyl ion adsorption from aqueous solutions has been investigated by chemically crosslinked (C) polyelectrolyte acrylamide/2-acrylamido-2-methyl-1-propanesulfonic acid (CAAMPS) hydrogels. CAAMPS hydrogels with various compositions were prepared from ternary mixtures of acrylamide (A), 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), and water by free radical polymerization in an aqueous solution using multifunctional crosslinkers such as ethylene glycol dimethacrylate (EGDMA) and 1,4 butanediol dimethacrylate (BDMA). The swelling equilibrium of polyelectrolyte copolymer gels containing of CAAMPS hydrogels has been studied as a function of copolymer composition. Swelling experiments were performed in water at 25°C, gravimetrically. The influence of AMPS content in hydrogels was examined. The weight-swelling ratio of CAAMPS hydrogels was increased up to 127.03 (for 300 mg AMPS and crosslinked by EGDMA) and 93.32 (for 300 mg AMPS and crosslinked by BDMA), while acrylamide hydrogels swelled up to 10.27 (crosslinked by EGDMA) and 10.06 (crosslinked by BDMA). Uranyl ion adsorption from aqueous solutions was studied by batch sorption technique at 25°C. The effect of uranyl ion concentration and mass of AMPS on the uranyl ion adsorption were examined. In the experiments of the sorption, L type sorption in the Giles classification system was found. Finally, the amount of sorbed uranyl ion per gram of dry hydrogel (q) was calculated to be 0.67 × 10^?3–2.11 × 10^?3 mol uranyl ion per gram for CAAMPS hydrogels. Removal effiency of uranyl ions (RE%) was changed range 9.05–29.92%. The values of partition ratio, (K _d ) of uranyl ions was calculated to be 0.10–0.43 for CAAMPS hydrogels.     

Removal of hazardous by radiation‐synthesized copolymer hydrogels based on 2‐acrylamido‐2‐methylpropanesulfonic acid and 2‐dimethyaminoethyl methacrylate monomers

Superabsorbent copolymer hydrogels were prepared by gamma irradiation of aqueous solutions of 2‐acrylamido‐2‐methylpropanesulfonic acid (AMPS) and 2‐dimethyaminoethyl methacrylate (DEMA) monomers mixtures. The thermal stability of hydrogels was evaluated by thermogravimetric analysis. The ability to adsorb Cu²⁺ ions and dyes by the prepared hydrogels from aqueous solutions was investigated. The swelling study, in water, showed that the hydrogels based on pure AMPS monomer and AMPS/DEMA copolymers reached the equilibrium state after 6 h. However, the hydrogel based on pure AMPS monomer showed higher swelling than the copolymer hydrogels based on AMPS/DEMA. It was found that the copolymer hydrogels based on different compositions showed affinity to absorb Cu²⁺ metal ions as well as basic and acid dyes; however, this affinity was found to decrease with increasing the ratio of DEMA in the initial feeding solutions. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Dual-responsive shape memory hydrogels with self-healing and dual-responsive swelling behaviors

Shape memory hydrogels (SMHs) can fix the hydrogels in a provisional shape and restore the initial shape under external stimulation. Herein, a dual-responsive shape memory hydrogel with dual-responsive swelling and self-healing properties is presented in this work. The SMHs were fabricated by one-step emulsion copolymerization of acrylic acid (AAc), acrylamide (AAm) and stearyl methacrylate (SMA). Sodium alginate (SA) was introduced as an interpenetrating polymer in the network. With ionic cross-linking between -COO⁻ and Fe³⁺ or saline-reinforced hydrophobic association, the hydrogels can be fixed in a provisional shape, which can be restored by immersing the hydrogels in vitamin C solution or pure water, respectively. When the as-prepared hydrogels were immersed in FeCl₃ solutions, additional ionic cross-linking between Fe³⁺ and -COO⁻ could be formed, thus constructing the dual physically cross-linked (DPC) network, which endows the hydrogels with excellent fracture stress (2.6 MPa) and toughness (5.47 MJ/m³). Besides, the reversible physical cross-linkings endowed the hydrogel with outstanding self-healing capability. Furthermore, the pH and saline responsive swelling properties of the SMHs are additional fantastic properties. Therefore, we believe that this simple strategy provides a great opportunity for the preparation of SMHs with multiple intellectual performances.     

N/S-Dual doped MnO modified spore-based ellipsoidal porous carbons for supercapacitors

Owing to the significance and requirement of renewable energy resources, in this study, ellipsoidal porous carbons with yolk-shell structures assembled using MnO and Ganoderma lucidum spores are fabricated for application prospects in energy storage systems; they exhibit excellent ion transfer capability. However, the surface of carbon nanomaterials is naturally hydrophobic, resulting in a lower energy density. Herein, heteroatom doping and O₂/Ar plasma surface treatment are utilized to obtain high specific capacitance and fast charging. Surface functionalization increases the surface roughness and oxygen-containing functional groups of the material. The specific capacitance of the best sample MnO/GSC-O–NS–10 was 568.9 F g⁻¹ when the current density was 0.5 A g⁻¹. The performance test was carried out for 10000 cycles at a current density of 10 A g⁻¹ and the capacitance retention rate was 75.11%. The assembled two-electrode capacitor exhibited a specific capacitance of 240.4 F g⁻¹ and an energy density of 33.4 Wh kg⁻¹ at a power density of 407 W kg ⁻¹. These findings provide sufficient theoretical guidance for the development of high-performance supercapacitors.     

Tough and recoverable triple‐network hydrogels based on multiple pairs of toughing mechanisms with excellent ionic conductivity as stable strain sensors

The emerging applications of hydrogels in flexible devices require it possess multifunctional properties including stable mechanical and functions under various deformations or external environments. Herein, a multifunctional polyvinyl alcohol/M‐alginate/PAM hydrogel with very excellent mechanical properties and sensing functions was fabricated by introducing multiple pairs of toughing mechanisms into triple network (TN). The multiple supramolecular physical networks work as sacrificial networks to toughen the materials when hydrogel deforms. The broken bonds can reform upon unloading endowing the recovery of hydrogels' properties and functions with the assistance of the elastic covalent network. The optimal TN hydrogels are extremely tough (a fracture strength of 512 kPa, a fracture toughness of 3 MJ/m³) and recoverable from fatigue damage (~77% toughness recovery after 5 min resting at room temperature). The presence of abundant ionic species endows the tough and recoverable TN hydrogels high ionic conductivity and high sensitivity as strain sensors. Moreover, such TN hydrogels with multi‐bond crosslinking in three networks can potentially guarantee stable mechanical and sensor functions under various deformations or external environments compared to the DN candidates. This work provides a simple strategy for fabricating multifunctional hydrogels with high stability to fulfill its flexible devices applications. POLYM. ENG. SCI., 59:1657–1666 2019. © 2019 Society of Plastics Engineers     

Charge density dependence of elastic modulus of strong polyelectrolyte hydrogels

The mechanical behavior of a series of strong polyelectrolyte hydrogels based on acrylamide and 2-acrylamido-2-methylpropane sulfonic acid sodium salt (AMPS) was investigated. The hydrogels were prepared at a fixed crosslinker ratio and monomer concentration, but at various charge densities, i.e. AMPS contents between 0 and 100 mol%. The elastic modulus of the hydrogels after their preparation first increases with increasing charge density but then decreases continuously. Investigation of the swollen state properties of the hydrogels shows existence of a large number of ionic groups inside the gel that are ineffective in gel swelling. The results indicate two opposite effects of charged groups on the elastic modulus of the hydrogels: formation of multiplets acting as additional crosslinks in the gel increases the elastic modulus of ionic hydrogels, whereas the effect of the electrostatic interaction of charged groups on elastic free energy decreases the modulus.     

All-gel-state supercapacitors of polypyrrole reinforced with graphene nanoplatelets

The development of supramolecular structures (conducting hydrogels) obtained from the charge–charge interaction of sodium dodecyl sulfate micelles and oppositely charged polypyrrole chains represents an important step to obtain self-supported and flexible electrodes for supercapacitors. Herein, the energy density of polypyrrole hydrogel-based supercapacitors is enhanced by the incorporation of graphene nanoplatelets that introduced the electrical double capacitance contribution to the overall response. The electrochemical performance of synthesized electrodes was optimized from the relative variation in the concentration of supramolecular arrangements (micelles of sodium dodecyl sulfate), pyrrole, and graphene nanoplatelets. As result, higher capacitive retention is observed for modified electrodes (with the incorporation of graphene) – in order of 90% after 1000 cycles of use, preserving the high conductivity and intrinsic mechanical properties (flexibility and stretchability) reaching an areal capacitance of 210.7 mFcm⁻².     

Encapsulation and delivery of protein from within poly(sulfobetaine) hydrogel beads

Advancement of therapeutic protein therapies can be hindered by their poor stability and short in vivo half-life. There is emerging evidence that biocompatible zwitterionic materials can prevent nonspecific interactions within proteins systems that contribute to protein instability. Here, zwitterionic hydrogel beads are synthesized from poly(sulfobetaine methyl methacrylate), pSB, using an inverse emulsion, free radical polymerization reaction technique. The transport properties within the zwitterionic hydrogels were characterized using ¹H NMR diffusometry. Equilibrium water content as high as 0.90 was measured for the synthesized hydrogels. Our study revealed that the pSB hydrogels are nontoxic, ion responsive, and their swelling is temperature dependent. The zwitterionic hydrogel beads were capable of undergoing lyophilization without aggregation. Hydrogel beads were loaded with a model protein, bovine serum albumin (BSA), using a postfabrication loading technique. The protein loading was studied using confocal laser microscopy, indicating homogenous protein dispersion of up to 40 μg BSA/mg hydrogel within the beads. Furthermore, the release rate of the protein from the synthesized hydrogel was studied at different crosslinker to monomer ratios. The protein encapsulated within the zwitterionic hydrogel had slower rates of thermal aggregation compared to nonencapsulated protein in solution. Furthermore, the protein-loaded inside the zwitterionic hydrogel better maintained its bioactivity.     

Porous carbon nanosheet with high surface area derived from waste poly(ethylene terephthalate) for supercapacitor applications

Converting waste plastics into valuable carbon materials has obtained increasing attention. In addition, carbon materials have shown to be the ideal electrode materials for double-layer supercapacitors owing to their large specific surface area, high electrical conductivity, and stable physicochemical properties. Herein, an easily operated approach is established to efficiently convert waste poly(ethylene terephthalate) beverage bottles into porous carbon nanosheet (PCNS) through the combined processes of catalytic carbonization and KOH activation. PCNS features an ultrahigh specific surface area (2236 m² g⁻¹), hierarchically porous architecture, and a large pore volume (3.0 cm³ g⁻¹). Such excellent physicochemical properties conjointly contribute to the outstanding supercapacitive performance: 169 F g⁻¹ (6 M KOH) and 135 F g⁻¹ (1 M Na₂SO₄). Furthermore, PCNS shows a high capacitance of 121 F g⁻¹ and a corresponding energy density of 30.6 Wh kg⁻¹ at 0.2 A g⁻¹ in the electrolyte of 1 M TEATFB/PC. When the current density increases to 10 A g⁻¹, the capacitance remains at 95 F g⁻¹, indicating the extraordinary rate capability. This work not only proposes a facile approach to synthesize PCNS for supercapacitors, but also puts forward a potential sustainable way to recycle waste plastics and further hopefully mitigates the waste plastics-related environmental issues. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48338.     

Modified carrageenan. 4. Synthesis and swelling behavior of crosslinked κC‐g‐AMPS superabsorbent hydrogel with antisalt and pH‐responsiveness properties

To synthesize a novel biopolymer‐based superabsorbent hydrogel, 2‐acrylamido‐2‐methylpropanesulfonic acid (AMPS) was grafted onto kappa‐carrageenan (κC) backbones. The graft copolymerization reaction was carried out in a homogeneous medium and in the presence of ammonium persulfate (APS) as an initiator, N,N,N′,N′‐tetramethyl ethylenediamine (TMEDA) as an accelerator, and N,N′‐methylene bisacrylamide (MBA) as a crosslinker. A proposed mechanism for κC‐g‐AMPS formation was suggested and the hydrogel structure was confirmed using FTIR spectroscopy. The affecting variables on swelling capacity, i.e., the initiator, the crosslinker, and the monomer concentration, as well as reaction temperature, were systematically optimized. The swelling measurements of the hydrogels were conducted in aqueous solutions of LiCl, NaCl, KCl, MgCl₂, CaCl₂, SrCl₂, BaCl₂, and AlCl₃. Due to the high swelling capacity in salt solutions, the hydrogels may be referred to as antisalt superabsorbents. The swelling of superabsorbing hydrogels was measured in solutions with pH ranging 1 to 13. The κC‐g‐AMPS hydrogel exhibited a pH‐responsiveness character so that a swelling–deswelling pulsatile behavior was recorded at pH 2 and 8. The overall activation energy for the graft copolymerization reaction was found to be 14.6 kJ/mol. The swelling kinetics of the hydrogels was preliminarily investigated as well. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 255–263, 2005     

A high-performance supercapacitor electrode based on freestanding N-doped Ti3C2Tx film

Two-dimensional transition metal carbide (MXene) is a promising electrode material for supercapacitors because of its excellent electrochemical properties. Here, we report a controllable and facile strategy to prepare a freestanding and flexible N-doped Ti₃C₂T_x (N–Ti₃C₂T_x) film electrode with a hydrothermal method using hydrazine hydrate (N₂H₄∙H₂O) as a nitrogen source. At a scan rate of 2 mV s⁻¹, the N–Ti₃C₂T_x film electrode exhibits a high specific capacitance of 340 F g⁻¹ and no capacitance degradation after 10,000 cycles in 1 M H₂SO₄ electrolyte. These results show that the N–Ti₃C₂T_x film could be used as an outstanding electrode material for high-performance supercapacitors. The operation of hydrazine treatment provides a more practical and convenient experimental method for N-doping.     

Polymeric absorbent for water sorption based on chemically crosslinked poly (acrylamide/2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt) hydrogels

Summary Swelling equilibrium of polyelectrolyte copolymer gels containing of acrylamide (AAm) and 2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt (AMPS) have been studied as a function of copolymer composition. AAm/AMPS hydrogels were prepared by free radical solution polymerization in aqueous solution of AAm with AMPS as anionic comonomer and two multifunctional crosslinkers such as ethylene glycol dimethacrylate (EGDMA) and trimethylolpropane triacrylate (TMPTA). Swelling experiments were performed in water at 25 °C, gravimetrically. The influence of AMPS content in hydrogels was examined. Swelling of AAm/AMPS hydrogels was increased up to 1018% (for containing 2% AMPS and crosslinked by EGDMA) 15246% (for containing 8% AMPS and crosslinked by TMPTA), while AAm hydrogels swelled up to 804% (crosslinked by TMPTA)–770% (crosslinked by EGDMA). The values of equilibrium water content of the hydrogels are 0.8851–0.9935. Diffusion behavior was investigated. Water diffusion into hydrogels was found to be non-Fickian in character.     

Facile synthesis of NiMn2O4 nanosheet arrays grown on nickel foam as novel electrode materials for high-performance supercapacitors

Nanostructured spinel NiMn₂O₄ arrays have been fabricated by a facile hydrothermal approach and further investigated as binder-free electrode for high-performance supercapacitors. Compared with Mn₃O₄, NiMn₂O₄ exhibited higher specific capacitances (662.5 F g⁻¹ and 370.5 F g⁻¹ in different electrolytes at the current density of 1 A g⁻¹) and excellent cycling stability (~96% capacitance retention after 1000 cycles) in a three-electrode system. Such a novel microstructure grown directly on the conductive substrate provided sufficient active sites for redox reaction resulting in their enhanced electrochemical behaviors. Their improved performances suggested that ultrathin sheet-like NiMn₂O₄ arrays on Ni foam substrate were a promising electrode material for supercapacitors.     

Perovskite oxide and polyazulene–based heterostructure for high–performance supercapacitors

Several types of electrode materials have been developed for high–performance supercapacitors. Most of the relevant studies have focused on the discovery of new atomic structures and paid limited attention to the effect of heterostructures in supercapacitor electrodes, which has long hindered the fundamental understanding of the use of hybrid materials in supercapacitors. In this study, a novel heterostructure based on perovskite oxide (LaNiO₃) nanosheets and polyazulene was synthesized. The as–prepared heterostructure–based supercapacitor exhibited a specific capacitance of up to 464 F g⁻¹ at a high current density of 2 A g⁻¹ in 1–ethyl–3–methylimidazolium tetrafluoroborate. In a symmetric supercapacitor, this heterostructure delivered an energy density of up to 56.4 Wh kg⁻¹ at a power density of 1100 W kg⁻¹. Both LaNiO₃ and polyazulene contributed pseudocapacitance and dominated the performance. Unexpectedly, electric double–layer capacitance was found to contribute in this system. Density functional theory calculations indicated that the advantage of the high electrical conductivity of the heterostructure benefited the supercapacitor operation. Electrochemical quartz crystal microbalance analysis revealed that the fast ion flux and adsorption boosted performance. The high intrinsic electrical conductivity and improved stability make this heterostructure a promising electrode material candidate for supercapacitors.