Ionic self-assembled organogel polyelectrolytes for energy storage applications

High performance organogel polyelectrolytes were synthesized by super acid catalyst step-growth polycondensation of isatin and the non-activated multiring aromatic p-terphenyl. Subsequently, a chemical modification reaction was carried out to obtained quaternary ammonium functionalized polyelectrolytes through a nucleophilic substitution reaction with (3-bromopropyl)trimethylammonium bromide and potassium carbonate at room temperature. Different functionalization degrees were obtained by controlling the molar ratio of the polymer and the modification agent. The organogel polyelectrolytes were formed due to the high phase segregation and self-assembling observed owing to the amphiphilic character of the material (hydrophobic backbone and hydrophilic fragment grafted). The organogel polyelectrolytes were used to fabricate supercapacitors using two commercial graphite electrodes. These polyelectrolytes displayed good ionic conductivity without the use of another doping agent such as salts, acids or ionic liquids. In this work, a strong correlation of functionalization degree and ionic conductivity of the polyelectrolytes and capacitance of the supercapacitors was observed. The ionic conductivity of the polyelectrolytes reached 0.46 mS cm⁻¹ for the 100% functionalization degree, meanwhile the polyelectrolyte with the 10% functionalization degree shows 0.036 mS cm⁻¹. Li-doped polyelectrolytes showed higher ionic conductivity due the presence of extra ionic charges (2.26 and 0.2 mS cm⁻¹ for the polyelectrolytes with the 100% and 10% of functionalization degree, respectively). The principal novelty of this work lies in the possibility of modulating the ionic conductivity of organogels and the capacitance of supercapacitors by chemical modifications. The capacitance of the supercapacitors was 1.17 mF cm⁻² for the 100% functionalized polyelectrolyte and is higher in comparison with the polyelectrolyte with 10% functionalization degree (0.68 mF cm⁻²) measured at a discharge current of 52 μA cm⁻² by galvanostatic charge discharge technique. Additionally, when lithium salt (lithium triflate) was added, the polyelectrolytes retained a gel consistency, increasing the ionic conductivity and capacitance. For the doped polyelectrolytes, the areal capacitance reaches 1.37 mF cm⁻² for the 100% functionalization degree polyelectrolyte with lithium triflate. These organogel polyelectrolytes open the possibility to design flexible and all solid-state supercapacitors without the risk of leakage.

High performance organogel polyelectrolytes were synthesized by super acid catalyst step-growth polycondensation of isatin and the non-activated multiring aromatic p-terphenyl.     

High ionic conduction,toughness and self-healing poly(ionic liquid)-based electrolytes enabled by synergy between flexible units and counteranions

Polymer electrolytes offer great potential for emerging wearable electronics. However, the development of a polymer electrolyte that has high ionic conductivity, stretchability and security simultaneously is still a considerable challenge. Herein, we reported an effective approach for fabricating high-performance poly(ionic liquids) (PILs) copolymer (denoted as PIL-BA) electrolytes by the interaction between flexible units (butyl acrylate) and counteranions. The introduction of butyl acrylate units and bis(trifluoromethane-sulfonyl)imide (TFSI⁻) counteranions can significantly enhance the mobility of polymer chains, resulting in the effective improvement of ion transport, toughness and self-healability. As a result, the PIL-BA copolymer-based electrolytes containing TFSI⁻ counterions achieved the highest ionic conductivity of 2.71 ± 0.17 mS cm⁻¹, 1129% of that of a PIL homopolymer electrolyte containing Cl⁻ counterions. Moreover, the PIL-BA copolymer-based electrolytes also exhibit ultrahigh tensile strain of 1762% and good self-healable capability. Such multifunctional polymer electrolytes can potentially be applied for safe and stable wearable electronics.

Polymer electrolytes offer great potential for emerging wearable electronics.     

Solvent extraction of rare earths elements from nitrate media in DMDOHEMA/ionic liquid systems: performance and mechanism studies

Extraction of La(iii), Eu(iii) and Fe(iii) was compared in n-dodecane and two ionic liquids (ILs) (1-ethyl-1-butylpiperidinium bis (trifluoromethylsulfonyl)imide [EBPip⁺] [NTf₂⁻] and 1-ethyl-1-octylpiperidinium bis (trifluoromethylsulfonyl)imide [EOPip⁺] [NTf₂⁻]). Using the extractant N,N′-dimethyl-N,N′-dioctylhexylethoxymalonamide (DMDOHEMA), the effect of pH was investigated in detail to recover extraction mechanisms. The use of ILs as the organic solvent instead of n-dodecane, greatly enhances extraction efficiency, and an ionic liquid with a shorter alkyl chain [EBPip⁺] [NTf₂⁻] provides higher extraction than [EOPip⁺] [NTf₂⁻]. The mechanistic study points out that for low nitric acid concentrations ([HNO₃] ≤ 0.01 M), metal is extracted via a cation of the ionic liquids, while for higher nitric acid concentrations ([HNO₃] ≥ 1.0 M), extraction occurs through pure solvation mechanism of DMDOHEMA as in conventional diluents. This latter case is of high interest for applications, as higher extraction can be obtained without any loss of ILs by ion exchange mechanisms.

Extraction of La(iii), Eu(iii) and Fe(iii) was compared in n-dodecane and in two ionic liquids (ILs) [EBPip⁺] [NTf₂⁻] and [EOPip⁺] [NTf₂⁻]. Extraction mechanisms have been investigated as a function of pH.     

The synergistic effect of the PEO–PVA–PESf composite polymer electrolyte for all-solid-state lithium-ion batteries

Blending with poly(vinyl alcohol) (PVA) and poly(oxyphenylene sulfone) (PESf) has been investigated to improve the properties of a polymer electrolyte based on a poly(ethylene oxide) (PEO) matrix. The composite electrolyte shows a high ionic conductivity of 0.83 × 10⁻³ S cm⁻¹ at 60 °C due to the significant inhibition of crystallization caused by the synergistic effects of PVA and PESf. The symmetrical cell Li/CPE/Li is continuously operated for at least 200 hours at a current density of 0.1 mA cm⁻² without the enhancement in the polarization potential. In addition, the all-solid-state LiFePO₄/CPE/Li cells exhibit small hysteresis potential (about 0.10 V), good cycle stability and excellent reversible capacity (126 mA h g⁻¹ after 100 cycles).

PVA and PESf have synergistic effects for CPE, resulting in a wider electrochemical window, higher ionic conductivity and better cyclic performance.     

Preparation and characterization of nanofibrous cellulose as solid polymer electrolyte for lithium-ion battery applications

A novel bacterial cellulose (BC)-based nanofiber material has been utilized as an ionic template for the battery system solid polymer electrolyte (SPE). The effect of drying techniques such as oven and freeze-drying on the gel-like material indicate differences in both visual and porous structures. The morphological structure of BC after oven and freeze-drying observed by field-emission scanning electron microscopy indicates that a more compact porous structure is found in freeze-dried BC than oven-dried BC. After the BC-based nanofiber immersion process into lithium hexafluorophosphate solution (1.0 M), the porous structure becomes a host for Li-ions, demonstrated by significant interactions between Li-ions from the salt and the C O groups of freeze-dried BC as shown in the infrared spectra. X-ray diffraction analysis of freeze-dried BC after immersion in electrolyte solution shows a lower degree of crystallinity, thus allowing an increase in Li-ion movement. As a result, freeze-dried BC has a better ionic conductivity of 2.71 × 10⁻² S cm⁻¹ than oven-dried BC, 6.00 × 10⁻³ S cm⁻¹. Freeze-dried BC as SPE also shows a larger electrochemical stability window around 3.5 V, reversible oxidation/reduction peaks at 3.29/3.64 V, and an initial capacity of 18 mAHr g⁻¹ at 0.2C. The high tensile strength of the freeze-dried BC membrane of 334 MPa with thermal stability up to 250 °C indicates the potential usage of freeze-dried BC as flexible SPE to dampen ionic leakage transfer.

Nanofibrous cellulose as solid polymer electrolyte for lithium-ion battery applications.     

Rechargeable aluminum batteries: effects of cations in ionic liquid electrolytes

Room temperature ionic liquids (RTILs) are solvent-free liquids comprised of densely packed cations and anions. The low vapor pressure and low flammability make ILs interesting for electrolytes in batteries. In this work, a new class of ionic liquids were formed for rechargeable aluminum/graphite battery electrolytes by mixing 1-methyl-1-propylpyrrolidinium chloride (Py13Cl) with various ratios of aluminum chloride (AlCl₃) (AlCl₃/Py13Cl molar ratio = 1.4 to 1.7). Fundamental properties of the ionic liquids, including density, viscosity, conductivity, anion concentrations and electrolyte ion percent were investigated and compared with the previously investigated 1-ethyl-3-methylimidazolium chloride (EMIC-AlCl₃) ionic liquids. The results showed that the Py13Cl–AlCl₃ ionic liquid exhibited lower density, higher viscosity and lower conductivity than its EMIC-AlCl₃ counterpart. We devised a Raman scattering spectroscopy method probing ILs over a Si substrate, and by using the Si Raman scattering peak for normalization, we quantified speciation including AlCl₄⁻, Al₂Cl₇⁻, and larger AlCl₃ related species with the general formula (AlCl₃)_n in different IL electrolytes. We found that larger (AlCl₃)_n species existed only in the Py13Cl–AlCl₃ system. We propose that the larger cationic size of Py13⁺ (142 ų) versus EMI⁺ (118 ų) dictated the differences in the chemical and physical properties of the two ionic liquids. Both ionic liquids were used as electrolytes for aluminum–graphite batteries, with the performances of batteries compared. The chloroaluminate anion-graphite charging capacity and cycling stability of the two batteries were similar. The Py13Cl–AlCl₃ based battery showed a slightly larger overpotential than EMIC-AlCl₃, leading to lower energy efficiency resulting from higher viscosity and lower conductivity. The results here provide fundamental insights into ionic liquid electrolyte design for optimal battery performance.

Room temperature ionic liquids (RTILs) are solvent-free liquids comprised of densely packed cations and anions. Properties of Py13Cl–AlCl₃ ILs were studied and compared with EMIC-AlCl₃ ILs for use as electrolyte in Al–graphite battery.     

Rechargeable Zn2+/Al3+ dual-ion electrochromic device with long life time utilizing dimethyl sulfoxide (DMSO)-nanocluster modified hydrogel electrolytes

Despite recent advances in hydrogel electrolytes for flexible electrochemical energy storage, ion conductors still exhibit some major shortcomings including low ionic conductivity and short lifetimes. As such, for applications in electrochromic batteries, a transparent, highly conductive electrolyte based on a dimethyl-sulfoxide (DMSO) modified polyacrylamide (PAM) hydrogel is being developed and implemented in a dual-ion Zn²⁺/Al³⁺ electrochromic device consisting of a Zn anode and WO₃ cathode. Gelation in a DMSO : H₂O mixed solvent leads to highly increased electrolyte retention in the hydrogel and prolonged life time for ionic conduction. The hydrogel-based electrochromic device offers a specific charge capacity of 16.9 μAh cm⁻² at a high current density of 200 μA cm⁻² while retaining 100% coulombic efficiency over 200 charge–discharge cycles. While the DMSO-modified electrolyte shows ionic conductivities up to 27 mS cm⁻¹ at room temperature, the formation of DMSO : H₂O nanoclusters enables ionic conduction even at temperatures as low as −15 °C and retention of ionic conduction over more than 4 weeks. Furthermore, the electrochromic WO₃ cathode gives the device a controllable absorption with up to 80% change in transparency. Based on low-cost, earth abundant materials like W (tungsten), Zn (zinc) and Al (aluminum) and a scalable fabrication process, the introduced hydrogel-based electrochromic device shows great potential for next-generation flexible and wearable energy storage systems.

A novel electrochromic energy storage device based on a long-lifetime DMSO-modified hydrogel electrolyte.     

Novel polymeric acidic ionic liquids as green catalysts for the preparation of polyoxymethylene dimethyl ethers from the acetalation of methylal with trioxane

A series of micro–mesoporous polymeric acidic ionic liquids (PAILs) have been successfully synthesized and subsequently characterized using Fourier transform-infrared spectroscopy, N₂ adsorption–desorption isotherms, scanning electron microscopy and thermogravimetry. Furthermore, the catalytic performance of the synthesized PAILs was investigated for the acetalation of methylal (DMM₁) with 1,3,5-trioxane (TOX), micro–mesoporous PAILs copolymerized by divinylbenzene with cations and anions exhibited moderate to excellent catalytic activities for the acetalation. In particular, VIMBs–AMPs–DVB, with higher specific surface area (25.51 m² g⁻¹) and total pore volume (0.15 cm³ g⁻¹) displayed an elevated conversion of formaldehyde (82.2%) and selectivity for polyoxymethylene dimethyl ethers (CH₃O(CH₂O)_nCH₃; PODE_n or DMM_n) n = 3–8 (52.6%) at 130 °C, 3.0 MPa for 8 h. Moreover, the influence of various reaction parameters was investigated by employing VIMBs–AMPs–DVB as the catalyst and it demonstrated high thermal stability and easy recovery.

Polyoxymethylene dimethyl ethers were successfully synthesized from acetalation under the catalysis of novel polymeric acidic ionic liquids (PAILs). PAILs copolymerized by divinylbenzene with ILs displayed exceptional catalytic efficiencies.     

Novel poly(epichlorohydrin)-based matrix for monolithic ionogel electrolyte membrane with high lithium storage performances

Based on gelling matrices and ionic liquids (ILs), monolithic ionogel electrolyte membranes (MIEMs) have become a research focus. However, further application is limited by lack of functional matrices. Herein, we proposed the introduction of an ionized polymer, i.e., polyether polymer with side-chain ionic groups obtained via the reaction of quaternary ammonium with uncrystallizable poly (epichlorohydrin) (PECH), as the matrix into the gels to balance the mechanical properties and the ionic conductivity. In combination with lithium bis-(fluorosulfonyl) imide (LiFSI) and 1-ethyl-3-methylimidazolium bis-(fluorosulfonyl)-imide (EMImFSI) via a solvent casting technique, a flexible MIEM was successfully prepared. The as-obtained MIEM exhibited good thermal stability (up to about 250 °C) and a high ionic conductivity of 1.21 mS cm⁻¹ at 20 °C. Moreover, Li|LiFePO₄ coin cells using this MIEM delivered high capacity (150.0 mA h g⁻¹ at 0.2C) with good cycling stability, and an excellent C-rate response. This work discloses a novel and paramount route to exploit PECH-based MIEMs for Li storage, as well as energy storage systems beyond Li.

Novel monolithic ionogel electrolyte membrane based on uncrystallizable poly (epichlorohydrin) is prepared, with high thermal stability and high lithium storage.     

Enhanced ionic conductivity in halloysite nanotube-poly(vinylidene fluoride) electrolytes for solid-state lithium-ion batteries

Solid composite electrolytes have gained increased attention, thanks to the improved safety, the prolonged service life, and the effective suppression on the lithium dendrites. However, a low ionic conductivity (<10⁻⁵ S cm⁻¹) of solid composite electrolytes at room temperature needs to be greatly enhanced. In this work, we employ natural halloysite nanotubes (HNTs) and poly(vinylidene fluoride) (PVDF) to fabricate composite polymer electrolytes (CPEs). CPE-5 (HNTs 5 wt%) shows an ionic conductivity of ∼3.5 × 10⁻⁴ S cm⁻¹, which is ∼10 times higher than the CPE-0 (without the addition of HNTs) at 30 °C. The greatly increased ionic conductivity is attributed to the negatively-charged outer surface and a high specific surface area of HNTs, which facilitates the migration of Li⁺ in PVDF. To make a further illustration, a solid-state lithium-ion battery with CPE-5 electrolyte, LiMn₂O₄ cathode and Li metal anode was fabricated. An initial discharge capacity of ∼71.9 mA h g⁻¹ at 30 °C in 1C is obtained, and after 250 cycles, the capacity of 73.5 mA h g⁻¹ is still maintained. This study suggests that a composite polymer electrolyte with high conductivity can be realized by introducing natural HNTs, and can be potentially applied in solid-state lithium-ion batteries.

The special structure of HNTs and the further formation of amorphous PVDF contribute to the enhancement of the Li⁺ transfer.     

A study on the preparation of polycation gel polymer electrolyte for supercapacitors

The polycation gel polymer electrolyte (PGPE) is a promising electrolyte material for supercapacitors due to its high ionic conductivity and great flexibility. Herein, we report a novel flexible PGPE film, which is prepared by thermal copolymerization. The superiority of PGPE is attributed to the existence of charged groups in the polymer skeleton. Consequently, the crystallinity of the polymer is effectively reduced, and the migration of the lithium ion is evidently promoted. Moreover, the liquid retention capacity of the film is improved, which enhances its ionic conductivity as well. The reported PGPE exhibits a high ionic conductivity of 57.6 mS cm⁻¹ at 25 °C and a potential window of 0–1.2 V. The symmetrical PGPE supercapacitor (AC/AC) shows 95.21% mass-specific capacitance retention after 5000 cycles at 2 A g⁻¹ with a maximum energy density of 12.8 W h kg⁻¹ and a maximum power density of 5.475 kW kg⁻¹. This study confirms the exciting potential of PGPE for high performance supercapacitors.

The polycation gel polymer electrolyte (PGPE) is a promising electrolyte material for supercapacitors due to its high ionic conductivity and great flexibility.     

Poly(ethylene glycol)-functionalized 3D covalent organic frameworks as solid-state polyelectrolytes

Existing lithium-ion-conducting covalent organic frameworks (COFs) are mainly two-dimensional, in which the one-dimensional channels are difficult to completely and uniformly stack in the same direction, particularly in the case of powdered COFs, resulting in the hindrance of ion transport at the grain boundary or at the interface of the powder contact. In this contribution, poly(ethylene glycol) (PEG)-functionalized three-dimensional COFs with 3D channels were successfully constructed for ion conduction in different directions, which is conducive to reducing the grain boundary and interface contact resistance. Combined with the coupling behaviour between the PEG chain segments and Li-ions, the 3D COF incorporated with LiTFSI achieves a high ionic conductivity of 3.6 × 10⁻⁴ S cm⁻¹ at 260 °C. The maximum operating temperature is higher than the boiling point of commercial organic electrolytes, indicating the excellent security of PEG-based COFs as Li-ion polyelectrolytes at high temperature.

Poly(ethylene glycol)-functionalized three-dimensional COFs with 3D channels were successfully constructed for ion conduction in different directions, which achieves a high ionic conductivity of 3.6 × 10⁻⁴ S cm⁻¹ at 260 °C.

Lithium-ion batteries (LIBs) are an indispensable energy storage system in contemporary society,^1–3 but most of them use liquid electrolytes, posing the risk of flammability, particularly in large-scale applications.^4,5 Solid electrolytes have been explored as ideal substitutes,^6–12 which commonly encompass ether polymeric- or ceramic-based electrolytes. Nonetheless, ceramic electrolytes still encounter large obstacles, such as instability, poor processability, and non-negligible grain boundary resistance.^8,13,14 Polymer electrolytes have higher stability and lower interfacial resistance, and are considered to be more promising polyelectrolyte materials. In particular, poly(ethylene glycol) (PEG)-based polymers, which are constructed by grafting PEG onto polymer chains, possess considerable ionic conductivity. However, they undergo a solid-to-liquid translation process with increasing temperature,¹⁵ which can easily cause a short circuit between the cathode and anode from the electrolyte draining, leading to acute safety risks. It is also laborious to expound the structure–property relationship between the ion-conducting pathways and ion conduction due to the structurally disordered character of PEG-based electrolytes.¹⁶Covalent organic frameworks (COFs) are a novel class of Li-ion conducting materials, which can acquire superior chemical, thermal and electrochemical stability through certain organic bonds or robust π–π stacking.^17–22 Compatible COFs can not only provide precisely tuned spatial pores for ion transport but also provide insight into the conduction mechanisms based on the long-range order.^23–26 The existing COF-based electrolytes are mainly divided into three categories: (i) COFs with non-electric neutral skeletons (Li-ion as the equilibrium cation), which need an external organic solvent to support ion transport, posing similar safety problems as organic liquid electrolytes;^27,28 (ii) COFs doped with PEG and lithium salt, in which the physically adsorbed PEG has a leakage risk;¹⁵ and (iii) PEG-functionalized COFs, of which the powder has anisotropy, resulting in disappointing ionic conductivity.^29–31 To the best of our knowledge, most of the existing Li-ion-conducting COFs are two dimensional, in which the one-dimensional channels can hardly be completely and uniformly stacked in the same direction, especially in the case of the powder-form COFs, which will lead to blockage of ion transport at the grain boundary or at the interface of the powder contact.In view of this, we have developed a self-assembly strategy to construct a PEG-functionalized three-dimensional COF, which has more ion transport paths in different directions that are beneficial to reducing the grain boundary and interface contact resistance experienced in the bulk condition. Distinct from amorphous bulk PEG, the grafted PEG constructs clear Li⁺-conducting routes in crystalline frameworks, which is beneficial to understanding the relationship between structure and ionic conduction. PEG with small molecular weight exhibits a liquid state at room temperature, but the hybrid materials consisting of short-chain PEG and COFs macroscopically present a solid state due to the confinement of the rigid skeleton of the COFs. The highest operating temperature can reach 260 °C along with a remarkable ionic conductivity of 3.6 × 10⁻⁴ S cm⁻¹. This temperature is higher than the boiling point of commercial organic electrolytes such as propylene carbonate (242 °C), diethyl carbonate (127 °C) and dimethyl carbonate (91 °C), indicating the excellent security of PEG-based COFs as Li-ion electrolytes.In this work, three types of PEG-functionalized COFs were synthesized under solvothermal conditions by the condensation of tetrakis(4-aminophenyl)methane with three aldehyde monomers with different lengths of PEG chains (Fig. 1a). The corresponding three-dimensional COFs, denoted as 3D-COF-PEG2, 3D-COF-PEG3 and 3D-COF-PEG6 hereafter, were produced as microcrystalline powders insoluble in common organic solvents. 3D-COF-PEG2-Li, 3D-COF-PEG3-Li and 3D-COF-PEG6-Li were prepared by introducing LiTFSI into the COFs.Open in a separate windowFig. 1(a) A bottom-up strategy for the synthesis of COFs. (b) Observed PXRD patterns of 3D-COF-PEG2: experimental PXRD pattern (black line), Pawley-refined pattern (red line), calculated pattern (blue line), and their difference (green line). (c) dia topology structure of 3D-COF-PEG2.The crystallinity of the COFs was evaluated by PXRD, and due to the structural consistency of these samples, 3D-COF-PEG2 was taken out to build in Materials Studio. The PXRD pattern of 3D-COF-PEG2 with its simulated value is illustrated in Fig. 1b, showing that it possessed a dia topology with 5-fold interpenetration, and it could be observed that the obvious peaks at 4.24° along with few weaker peaks at 6.13° and 8.63° corresponded to the (220), (040) and (440) planes with the FDDD (70) space group. The negligible values of R_wp = 2.78% and R_p = 2.11% imply that the Pawley refinement of the 3D-COF-PE2 pattern coincides with the experimental pattern. There are no diffraction peaks after modification with LiTFSI (Fig. S1, ESI^†), which is due to the disordered LiTFSI and ion-coupled PEG chains in the channel. The three-dimensional compounds are connected by imine bonds, and the structures are shown in Fig. 1c.For the isomorphic compounds, the PXRD of the three samples are consistent (Fig. 2a). Their morphology reveals uneven spherical and elliptical shapes, as seen in the SEM images (Fig. 3). It could be seen that the maximum nitrogen adsorption values are 133, 102 and 101 cm³ g⁻¹ for 3D-COF-PEG2, 3D-COF-Open in a separate windowFig. 2(a) PXRD patterns, (b) N₂ adsorption, (c) TG plots and (d) DSC curves of 3D-COF-PEG2, 3D-COF-PEG3 and 3D-COF-PEG6. (e) IR plots of 3D-COF-PEG6 and 3D-COF-PEG6-Li. (f) ⁷Li solid NMR for LiTFSI, 3D-COF-PEG2-Li, 3D-COF-PEG3-Li and 3D-COF-PEG6-Li.Open in a separate windowFig. 3(a–c) SEM patterns of 3D-COF-PEG2, 3D-COF-PEG3 and 3D-COF-PEG6, respectively. (d–f) SEM patterns of 3D-COF-PEG2-Li, 3D-COF-PEG3-Li and 3D-COF-PEG6-Li, respectively.PEG3 and 3D-COF-PEG6, respectively, proving a more crowded situation in 3D-COF-PEG6 (Fig. 2b). After introducing LiTFSI, the adsorption amounts clearly drop to 71.0, 39.8 and 79.2 cm³ g⁻¹ for 3D-COF-PEG2-Li, 3D-COF-PEG3-Li and 3D-COF-PEG6-Li, respectively (Fig. S2, ESI^†). The thermal stability and thermodynamics were also analysed. There is almost no weight loss before 400 °C for these COFs before or after introducing LiTFSI, demonstrating their remarkable thermal stability (Fig. 2c and S3, ESI^†). As seen in Fig. 2d, three COFs exhibit an endothermic peak at −11 °C in the measured temperature region, showing a segment movement behaviour, which is conducive to ionic conduction (Fig. S4, ESI^†). From the IR plots (Fig. 2e), it can be seen that there is a single v_as(COC) peak at 1103 cm⁻¹ for 3D-COF-PEG6, but it splits into two peaks for 3D-COF-PEG6-Li at 1109 cm⁻¹ and 1093 cm⁻¹ (Fig. 2e). This is similar to the other samples, implying an interaction between Li⁺ and the PEG chains (Fig. S5, ESI^†). The ⁷Li NMR peaks are located at −946 Hz, −1106 Hz, −1126 Hz and −1074 Hz for bulk LiTFSI, 3D-COF-PEG2-Li, 3D-COF-PEG3-Li and 3D-COF-PEG6-Li, respectively, showing a unique chemical state of the Li-ions in the COFs (Fig. 2f).The ionic conductivity (σ) was calculated from the Nyquist plots versus different temperatures (Fig. 4a and S6–S8, ESI^†). The σ of 3D-COF-PEG2-Li is 8.5 × 10⁻⁹ S cm⁻¹ at 100 °C, 1.2 × 10⁻⁶ S cm⁻¹ at 180 °C and 1.2 × 10⁻⁵ S cm⁻¹ at 260 °C. 3D-COF-PEG3-Li exhibits higher ionic conductivity values of 3.4 × 10⁻⁸ S cm⁻¹ at 100 °C, 4.5 × 10⁻⁶ S cm⁻¹ at 180 °C, and 5.3 × 10⁻⁴ S cm⁻¹ at 260 °C. The ionic conductivity of 3D-COF-PEG6-Li is the highest, at 3.7 × 10⁻⁶ S cm⁻¹ at 100 °C, 7.0 × 10⁻⁵ S cm⁻¹ at 180 °C, and 3.6 × 10⁻⁴ S cm⁻¹ at 260 °C (Fig. 4b). Obviously, with an increase in the length of the PEG chain, the ionic conductivity climbs as well, because of which the longer PEG chain offers more coupling sites for lithium ions to facilitate the ionic conduction. Furthermore, the highest operating temperature (260 °C) is higher than the boiling point of commercial organic electrolytes such as propylene carbonate (242 °C), diethyl carbonate (127 °C), and dimethyl carbonate (91 °C), indicating the excellent safety of PEG-based COFs as Li-ion electrolytes. The long-term ionic conduction durability measurement of 3D-COF-PEG6-Li was also carried out at 200 °C for 42 h (Fig. 4c). It affords stable conductivity above ∼10⁻⁴ S cm⁻¹, demonstrating its prominent ionic conductivity retention. The activity energy value (E_a) is calculated to be around 0.49 eV for 3D-COF-PEG6-Li, which is smaller than those of 3D-COF-PEG2-Li and 3D-COF-PEG3-Li (0.78 eV and 0.79 eV, respectively) (Fig. 4d and S9, ESI^†), showing the lower Li⁺ conducting energy barrier in COF-PEG-B6-Li. With longer PEG chains, the coupling behaviour between ether bonds and lithium ions will be more frequent, which is one important cause of the decreased Li⁺ conduction barrier. As illustrated in Fig. 4e, the Li⁺ transference number is around 0.22 for COF-PEG-B6-Li at 100 °C, which is comparable to that of PEG-based polymer electrolytes. COFs introduced with LiTFSI also show high electrochemical stability, and they are all stable when the voltage is lower than 4 V, suggesting their compatibility with high voltage cathodes (Fig. 4e and S10, ESI^†).Open in a separate windowFig. 4(a) Nyquist plots of 3D-COF-PEG6-Li at 260 °C. (b) Ionic conductivity of 3D-COF-PEG2-Li, 3D-COF-PEG3-Li and 3D-COF-PEG6-Li versus temperature from 100 °C to 260 °C. (c) Long-term ionic conducting durability test of 3D-COF-PEG6-Li at 200 °C. (d) Calculation of activation energy for 3D-COF-PEG2-Li, 3D-COF-PEG3-Li and 3D-COF-PEG6-Li. (e) Li⁺ transference number measurement of 3D-COF-PEG6-Li at 100 °C. (f) Linear sweep voltammograms (LSV) of 3D-COF-PEG6-Li at 100 °C.     

Glyme–Li salt equimolar molten solvates with iodide/triiodide redox anions

Room-temperature-fused Li salt solvates that exhibit ionic liquid-like behaviour can be formed using particular combinations of multidentate glymes and lithium salts bearing weakly coordinating anions, and are now deemed a subset of ionic liquids, viz. solvate ionic liquids (SILs). Herein, we report redox-active glyme–Li salt molten solvates consisting of tetraethyleneglycol ethylmethyl ether (G4Et) and lithium iodide/triiodide, [Li(G4Et)]I and [Li(G4Et)]I₃. The coordination structure of the complex ions and the thermal, transport, and electrochemical properties of these molten Li salt solvates were investigated to diagnose whether they can be categorized as SILs. [Li(G4Et)]⁺ and I₃⁻ were found to remain stable as discrete ions and exist as well-dissociated forms in the liquid state, indicating that [Li(G4Et)]I₃ can be classified as a good SIL. This study also clarified that the I⁻ and I₃⁻ counter anions exhibit an electrochemical redox reaction in the highly concentrated molten Li salt solvates. The redox-active molten Li solvates were further studied as a highly concentrated catholyte for use in rechargeable semi-liquid lithium batteries. Although the cell constructed using [Li(G4Et)]I₃ failed to charge after the initial discharge step, the cell containing [Li(G4Et)]I demonstrates reversible charge–discharge behaviour with a high volumetric energy density of 180 W h L⁻¹ based on the catholyte volume.

Redox-active glyme–Li salt equimolar molten solvates based on a I⁻/I₃⁻ couple could be employed as a highly concentrated catholyte for semi-liquid rechargeable lithium batteries.     

On-chip integration of bulk micromachined three-dimensional Si/C/CNT@TiC micro-supercapacitors for alternating current line filtering

Three-dimensional (3D) micro-supercapacitors (MSCs) with superior performances are desirable for miniaturized electronic devices. 3D interdigitated MSCs fabricated by bulk micromachining technologies have been demonstrated for silicon wafers. However, rational design and fabrication technologies of 3D architectures still need to be optimized within a limited footprint area to improve the electrochemical performances of MSCs. Herein, we report a 3D interdigitated MSC based on Si/C/CNT@TiC electrodes with high capacitive properties attributed to the excellent electronic/ionic conductivity of CNT@TiC core–shells with a high aspect ratio morphology. The symmetric MSC presents a maximum specific capacitance of 7.42 mF cm⁻² (3.71 F g⁻¹) at 5 mV s⁻¹, and shows an 8 times areal capacitance increment after material coating at each step, fully exploiting the advantage of 3D interdigits with a high aspect ratio. The all-solid-state MSC delivers a high energy density of 0.45 μW h cm⁻² (0.22 W h kg⁻¹) at a power density of 10.03 μW h cm⁻², and retains ∼98% capacity after 10 000 cycles. The MSC is further integrated on-chip in a low-pass filtering circuit, exhibiting a stable output voltage with a low ripple coefficient of 1.5%. It is believed that this work holds a great promise for metal-carbide-based 3D interdigitated MSCs for energy storage applications.

A novel fabrication strategy for the realization of a bulk micromachined 3D Si/C/CNT@TiC micro-supercapacitor is experimentally demonstrated.     

Hydrogen production rates of aluminum reacting with varying densities of supercritical water

Aluminum particles, spanning in size from 10 μm to 3 mm, were reacted with varying densities of water at 655 K. The density of the water is varied from 50 g L⁻¹ to 450 g L⁻¹ in order to understand the effect of density on both reaction rates and yields. Low-density supercritical water is associated with properties that make it an efficient oxidizer: low viscosity, high diffusion, and low relative permittivity. Despite this, it was found that the high-density (450 g L⁻¹) supercritical water was the most efficient oxidizer both in terms of reaction rate and hydrogen yield. The 10 μm powder had a peak reaction rate of approximately 675 cm_H2³ min⁻¹ g_Al⁻¹ in the high-density water, and a peak reaction rate below 250 cm_H2³ min⁻¹ g_Al⁻¹ in the low- and vapour-density water. A decline in peak reaction rate with decreasing water density was also observed for the 120 μm powder and the 3 mm slugs. These findings imply that the increased collision frequency, a property of the high-density water, outpaces reduction in the reaction enhancing properties associated with low-density supercritical water. Hydrogen yield was minimally affected by decreasing the oxidizer density from 450 g L⁻¹ to 200 g L⁻¹, but did drop off significantly in the vapour-density (50 g L⁻¹) water.

Hydrogen production rates of aluminum reacting with various densities of supercritical water are determined using a novel method. High-density supercritical water is found to be the most efficient oxidizer, in terms of both reaction rates and yields.     

Remarkable adsorptive removal of nitrogen-containing compounds from hydrotreated fuel by molecularly imprinted poly-2-(1H-imidazol-2-yl)-4-phenol nanofibers

Molecularly imprinted polymer (MIP) nanofibers were prepared by the electrospinning of poly 2-(1H-imidazol-2-yl)-4-phenol (PIMH) in the presence of various nitrogen containing compounds (N-compounds). Molecularly imprinted polymer nanofibers show selectivity for various target model nitrogen-containing compounds with adsorption capacities of 11.7 ± 0.9 mg g⁻¹, 11.9 ± 0.8 mg g⁻¹ and 11.3 ± 1.1 mg g⁻¹ for quinoline, pyrimidine and carbazole, respectively. Molecular modelling based upon density functional theory (DFT) indicated that hydrogen bond interactions may take place between the lone-pair nitrogen atom of model compounds (quinoline and pyrimidine) and the –OH and –NH groups of the PIMH nanofibers. The adsorption mode followed the Freundlich (multi-layered) adsorption isotherm, which indicated possible nitrogen–nitrogen compound interactions. Molecularly imprinted polymer nanofibers show potential for the removal of nitrogen-containing compounds in fuel.

Molecularly imprinted poly-2-(1H-imidazol-2-yl)-4-phenol nanofibers fabricated via electrospinning displayed excellent selectivity adsorption capacities nitrogen containing compounds (N-compounds) in hydro-treated fuels.     

Physicochemical characterizations of novel dicyanamide-based ionic liquids applied as electrolytes for supercapacitors

Novel ionic liquids (ILs), containing a dicyanamide anion (DCA⁻), are synthesized and applied as suitable electrolytes for electrochemical double layer capacitors (EDLCs). The prepared ILs are either composed of triethyl-propargylammonium (N_222pr⁺) or triethyl-butylammonium (N₂₂₂₄⁺) cations paired with the DCA⁻ anion. The structure of the cation influences its electrostatic interaction with the DCA⁻ anion and highly impacts the physical and electrochemical properties of the as-prepared ILs. The geometry and the length of the alkyl chain of the propargyl group in N_222pr⁺ enhance the ionic conductivity of N_222pr–DCA (11.68 mS cm⁻¹) when compared to N₂₂₂₄–DCA (5.26 mS cm⁻¹) at 298 K. It is demonstrated that the Vogel–Tammann–Fulcher model governs the variations of the transport properties investigated over the temperature range of 298–353 K. A maximum potential window of 3.29 V is obtained when N_222pr–DCA is used as electrolyte in a graphene based symmetric EDLC system. Cyclic voltammetry and galvanostatic measurements confirm that both electrolytes exhibit an ideal capacitive behavior. The highest specific energy of 55 W h kg⁻¹ is exhibited in the presence of N₂₂₂₄–DCA at a current density of 2.5 A g⁻¹.

Novel ionic liquids (ILs), containing a dicyanamide anion (DCA⁻), are synthesized and applied as suitable electrolytes for electrochemical double layer capacitors (EDLCs).     

One-pot synthesis of poly(ionic liquid)s with 1,2,3-triazolium-based backbones via clickable ionic liquid monomers

Clickable α-azide-ω-alkyne ionic liquid monomers were developed and subsequently applied to the one-pot synthesis of ionically conducting poly(ionic liquid)s with 1,2,3-triazolium-based backbones through a click chemistry strategy. This approach does not require the use of solvents, polymerisation mediators, or catalysts. The obtained poly(ionic liquid)s were characterized by NMR, differential scanning calorimetry, thermogravimetric analysis, and impedance spectroscopy analysis. Moreover, these poly(ionic liquid)s were cross-linked via N-alkylation with a dianion quarternizing agent to achieve enhanced ionic conductivity and mechanical strength. The resulting free-standing films showed a Young''s modulus up to 4.8 MPa and ionic conductivities up to 4.60 × 10⁻⁸ S cm⁻¹ at 30 °C. This facile synthetic strategy has the potential to expand the availability of poly(ionic liquid)s and promote the development of functional materials.

Clickable ionic liquid monomers realize the one-pot synthesis of ionically conducting poly(ionic liquid)s with 1,2,3-triazolium-based backbones via click chemistry.     

Magnetic solid-phase extraction of pyrethroid insecticides from tea infusions using ionic liquid-modified magnetic zeolitic imidazolate framework-8 as an adsorbent

A simple, sensitive, and reliable magnetic solid-phase extraction (SPE) method coupled with GC-MS/MS for the effective analysis of four pyrethroids from tea infusions was developed. A magnetic adsorbent, named ionic liquid-modified magnetic zeolitic imidazolate framework-8 (Fe₃O₄/ZIF-8/IL), was prepared by immobilizing an ionic liquid (IL) on the surface of Fe₃O₄/ZIF-8. The textures of Fe₃O₄/ZIF-8/IL were confirmed by material characterization, and the results suggested that the adsorbent possessed high magnetism (59.0 emu g⁻¹), an adequate Brunauer–Emmett–Teller (BET) surface area (104 m² g⁻¹), and a large pore volume (0.68 cm³ g⁻¹). To confirm the extraction performance of the prepared Fe₃O₄/ZIF-8/IL, several experimental conditions affecting the extraction efficiency were investigated. Under the optimum conditions, the limits of determination (LODs) for the four pyrethroids were in the range of 0.0065–0.1017 μg L⁻¹ (S/N = 3 : 1) with an intra-day relative standard deviation (RSD) of ≤9.70% and inter-day RSD of ≤11.95%. The linear ranges were 0.5–50 μg L⁻¹ for bifenthrin and 0.5–500 μg L⁻¹ for permethrin, cypermethrin, and flucythrinate, with determination coefficients higher than 0.999. Finally, the proposed technique was successfully applied for the determination of pyrethroids in real tea infusions. This work could be extended to other IL-modified metal–organic frameworks (MOFs) and to the development of different sample pretreatment techniques.

A MSPE-GC-MS/MS method was developed for the analysis of pyrethroids from tea infusions using Fe₃O₄/ZIF-8/IL as an adsorbent.     

Atomic force microscopy and Raman spectra profile of blood components associated with exposure to cigarette smoking

Tobacco smoke contains several compounds with oxidant and pro-oxidant properties with the capability of producing structural changes in biomolecules, as well as cell damage. This work aimed to describe and analyse the effect of tobacco smoke on human blood components, red blood cell (RBC) membrane, haemoglobin (Hb) and blood plasma by Atomic Force Microscopy (AFM) and Raman spectroscopy. Our results indicate that tobacco induced RBC membrane nano-alterations characterized by diminished RBC diameter and increased nano-vesicles formation, and RBC fragility. The Raman spectra profile suggests modifications in chemical composition specifically found in peaks 1135 cm⁻¹, 1156 cm⁻¹, 1452 cm⁻¹ and intensity relation of peaks 1195 cm⁻¹ and 1210 cm⁻¹ of blood plasma and by change of peaks 1338 cm⁻¹, 1357 cm⁻¹, 1549 cm⁻¹ and 1605 cm⁻¹ associated with the pyrrole ring of Hb. The relevance of these results lies in the identification of a profile of structural and chemical alterations that serves as a biomarker of physiological and pathological conditions in the human blood components induced by tobacco exposure using AFM and the Raman spectroscopy as tools for monitoring them.

Tobacco smoke contains several compounds with oxidant and pro-oxidant properties with the capability of producing structural changes in biomolecules, as well as cell damage.