Fast Ion Diffusion Research Articles

Constructing titanium carbide MXene/reduced graphene oxide superlattice heterostructure via electrostatic self-assembly for high-performance capacitive deionization

Capacitive deionization has attracted wide concern on accountof its high energy efficiency, low manufacturing cost and environmental friendliness. Nevertheless, the development of capacitive deionization is still impeded because of the scarcity of suitable electrode materials with superior performance. Herein, we successfully prepared the two-dimensional (2D) titanium carbide (Ti3C2Tx) MXene/ reduced graphene oxide (rGO) superlattice heterostructure by a facile electrostatic self-assembly strategy and systematically investigated its performance as capacitive deionized electrode materials. The unique 2D/2D superlattice heterostructure not only effectively alleviates the self-stacking problem of Ti3C2Tx MXene nanosheets, but also endows the heterostructure with superior conductivity and fast ion diffusion rate. As a result, the MXene/rGO superlattice heterostructure exhibits an outstanding salt (Na+) adsorption capacity (48 mg g−1) at 1.2 V significantly superior to pristine Ti3C2Tx MXene nanosheets, along with outstanding long-term cycling performance. Furthermore, the mechanism involved was elucidated through comprehensive characterizations. Therefore, this study offers a new pathway for designing high-performance electrode materials for capacitive deionization.

Carbon-coated monoclinic NbOPO4 with polyanionic framework for rechargeable aqueous lithium-ion batteries beyond 2 V

The choice of anode materials for high-voltage aqueous batteries beyond 1.5 V is still far from satisfactory, due to the narrow electrochemical stability window of aqueous electrolytes. With the inherent advantages of low working voltage and fast ionic diffusion, niobium phosphates with polyanionic framework groups built of NbO6 octahedra and PO4 tetrahedra are very promising anode materials for high-voltage aqueous batteries. Herein, carbon-coated NbOPO4 (NPO/C) materials with monoclinic structure has been prepared by the solid-state reaction & chemical vapor deposition method. Between -1.34 V and 0.6 V vs. standard hydrogen electrode, it could deliver a specific capacity of 116 mAh/g with a high coulombic efficiency of 92.0% at a low current rate of 0.33C in aqueous electrolytes based on methylsulfonylmethane, LiClO4 and H2O (DES). The diffusion-controlled process dominates the electrochemical reaction of NPO/C. Upon the reversible insertion/extraction of lithium ion into/from NPO/C, it maintains the monoclinic structure with a small lattice expansion, which is a characteristic of zero-strain effect. Finally, the full cell based on NPO/C anode, LiMn2O4 cathode and DES electrolytes with a high specific energy 101.6 Wh/kg and a high voltage output beyond 2 V has been validated. It also shows excellent cycling performance with the capacity retention of 94.3% after 1000 times at 2C rate, which suggests that monoclinic β-NbOPO4 can be used as a promising electrode material for aqueous lithium-ion batteries with high voltage output for energy storage in the future.

Metal-N/P coordination assisted construction of robust heterointerface for stable and superior-rate electrodes in battery-type supercapacitors

Holding ultralong cycle life and superior rate capability with high specific capacity is an inevitable requirement for the practical applications of transition metal compounds battery-type supercapacitor electrode materials. In this paper, a novel class of transition metal phosphide (TMP) nanostructures evenly bonded on N/P co-doped graphene nanotubes (N/P-GNTs@b-TMP) is firstly built via one-step in-situ growth procedure. The N, P elements as substitutions of C in GNTs skeleton introduce rich electronic centers, further change the surface electronic structures of the skeleton, inducing the TMPs to anchor the surface of N/P-GNTs through metal-N and metal-P bonds, which is demonstrated by the characterizations and Density functional theory (DFT) calculation. The unique chemical bonding can not only reinforce the integration of the hybrid electrode materials during durable cycling, but also generate the typical internal electric field and greatly reduce the free energy of the reaction system, endowing a superior rate capacity and easy redox process relating to high specific capacity. Moreover, ex-situ impedance and capacitive/diffusion control analysis suggest the fast ions diffusion behavior and reaction kinetics. Benefiting from the unique architecture, the achieved N/P-GNTs@b-NiCoP positive electrode possesses high specific capacity of 250 mAh g−1 (1800 F g−1) at 2 A g−1 and 166 mAh g−1 (1200 F g−1) at 50 A g−1. Meanwhile, the N/P-GNTs@b-Fe2NiP and N/P-GNTs@b-FeCoP negative electrodes constructed by the same approach can also own a high specific capacity of 151.9, 159.7 mAh g−1 (547, 575 F g−1) at 1A g−1 and 63.6, 73.6 mAh g−1 (229, 265 F g−1) at 50 A g−1, respectively. More significantly, they all can present ∼90% capacity retention after 75000 cycles, which can be comparable to all of the reported transition metal compound electrodes even commercial carbonaceous materials. In addition, an asymmetric supercapacitor (ASC) using the achieved N/P-GNTs@b-NiCoP as electrode expresses a remarkable energy density of 77.8 Wh kg−1 and cycling stability. This work provides an innovative structural design strategy for obtaining battery-type supercapacitor electrode materials with commercial application prospects.

Anisotropic lithium-ion migration and electro-chemo-mechanical coupling in Sb2Se3 single crystals

Harvesting the promising high energy density of advanced electrode materials in lithium-ion batteries is critically dependent on a mechanistic understanding on how the materials function and degrade along with the battery cycling. Here, we tracked phase transformations during (de)lithiation of Sb2Se3 single crystals using in situ high-resolution transmission electron microscopy (HRTEM) technique, and revealed electro-chemo-mechanical evolution at the reaction interface. The effect of this electro-chemo-mechanical coupling has a complicated interplay on the lithiation kinetics and causes various types of defects at the reaction front, including dislocation dipoles, antiphase boundaries, and cracks. In return, the formed cracks and related defects build a path for fast diffusion of lithium ions and trigger a highly anisotropic lithiation at the twisted reaction front, giving rise to the formation of presumably “dead” Sb2Se3 nanodomains in amorphous LixSb2Se3. The detailed mechanistic understanding may facilitate the rational design of high-capacity electrode materials for battery applications.

Hydrochloric Acid-Assisted Synthesis of Highly Dispersed MoS2 Nanoflowers as the Cathode Material for Mg-Li Batteries

The layered material MoS2 has significant potential as a cathode material for hybrid Mg2+/Li+ batteries (MLIBs) due to its fast two-dimensional ion diffusion channel. However, the low capacity and poor cycling stability limit the practical application of MoS2. Herein, highly dispersed MoS2 nanoflowers with a large Brunauer–Emmett–Teller (BET) area of 118.25 m2 g–1 and a large lattice spacing of 0.65 nm are synthesized by a one-step hydrothermal method. The obtained MoS2 nanoflowers deliver a remarkable reversible capacity of 321 mA h g–1 at 0.1 A g–1. Notably, it displays an impressive cycling stability with a reversible capacity of 103 mA h g–1 over 600 consecutive cycles at 1 A g–1. The favorable electrochemical properties of the MoS2 are attributed to the large BET area and increased lattice spacing that are more conducive to the full contact between the electrolyte and the material, thus promoting the diffusion of ions and improving the reaction kinetics. The results of the present study offer an idea to prepare highly dispersed MoS2 with enhanced capacity and durability.

Defect-engineered metal-organic framework with enhanced photoreduction activity toward uranium extraction from seawater

Photoreduction conversion of soluble U(VI) to insoluble U(IV) is considered a promising strategy for uranium capture from radioactive wastewater and seawater. Metal-organic frameworks (MOFs) are emerging as potential photocatalysts due to their inherent large surface areas, tunable cavities, and tailorable photo response. Herein, the electronic structure of UiO-66-NH2 (Zr-MOF) is modulated by missing-linker defects and node metal substitution, allowing for the reduced energy needed to transfer the excited linker’s electrons to the node’s unoccupied d orbitals, which contributes to enhanced photocatalytic uranium extraction capacity. Moreover, the missing-linker defects create more open frameworks, which facilitate fast diffusion of uranyl ions (UO22+) into inner pores and hence increase utilization of the hidden adsorption binding sites. Consequently, light-irradiated Zr/Ti-MOF-25 delivers a high uranium sorption capacity (8.66 ± 0.29 mg-U/g-Ads) with excellent antimicrobial ability in natural seawater. Creation of defects in MOFs opens novel opportunities for enhancing uranium capture through combined complexation and photoreduction.

Electrochemical activity of triple-layered boron-containing carbon nanofibers with hollow channels in supercapacitors

Triple-layered boron-containing carbon nanofibers (CNFs) with hollow channels (PPMPB) are fabricated via step-by-step electrospinning for high-performance freestanding supercapacitors. Polyacrylonitrile (PAN)-based CNFs in the first layer are chosen as the support layer material because of their excellent chemical stability and electrospinnability. The well-developed hollow channels provided fast ion diffusion in the second layer of PAN/poly(methyl methacrylate) (PMMA)-based CNFs. The surface boron functional groups constituting the third layer contribute to the pseudo-capacitance. The symmetric supercapacitor of the PPMPB electrodes delivers a maximum specific capacitance of 180 Fg−1 at 1 mAcm−2, a high energy density of 22.38 Whkg−1 at a power density of 400 Wkg−1, and an excellent retention rate of 96% after 10,000 cycles in aqueous solution. The excellent electrochemical performance is attributed to the unique sandwich nanostructure with a three-layer structure, in which the factors representing the electrochemical properties of each layer do not interfere with each other. Therefore, a moderate amount of boron and the high surface area of the triple-layer structured PPMPB can be fully utilized as an excellent conductive network and electroactive sites, which is expected in a high-performance supercapacitor electrode.

Influence of heat-treatment temperature on the improvement of the electrochemical performance of CoMoO4 nanomaterials for hybrid supercapacitor application

The rational design and construction of nanostructured materials have a great impact on the development of high-performance advanced electrode materials, which has attracted extensive attention to improve reliable and efficient energy storage devices. Herein, we report vertically aligned CoMoO4 nanoflakes with interconnected network-like porous structures as Faradic battery-type electrode materials for the advancement of supercapacitors (SCs). The nanoarchitecture CoMoO4 electrode materials were effectively fabricated through simple hydrothermal method and subsequent heat-treatment under different temperatures. Further, the effect of heat-treatment on the electrodes materials’ structural, morphological, and electrochemical properties were investigated by utilizing various characterization techniques. The unique nanoarchitecture of the 400 °C heat-treated CoMoO4 (CMO1) endows a facile pathway for the fast diffusion of the electrolyte ions and mass transfer reaction. Interestingly, the CMO1 (400 °C) electrode exhibits the specific capacity of 499 C g−1, which is higher than those of the CMO2 (500 °C) of 385 C g−1 and CMO3 (600 °C) of 260 C g−1, respectively. Furthermore, the hybrid supercapacitor (HSC) tailored with CMO1 as a positrode and activated carbon as a negatrode delivers a high specific capacitance of 102 F g−1 with excellent energy and power densities of 31.61 W h kg−1 and 19.29 kW kg−1, respectively.

Tailoring surface capacitance of Ti3C2Tx-PANI@CNTs nanoarchitecture for tunable energy storage and high-performance micro-supercapacitor

Transition metal carbide or nitride (MXenes), as a novel family of two-dimensional materials, exhibit huge potential for electrochemical energy storage thanks to their excellent electrical conductivity, fast ion diffusion rate, high electrochemical activity and good hydrophilicity. However, the electrochemical properties of MXenes tend to be deteriorated due to the self-restacking phenomenon. Herein, by self-assembly, a unique three-dimensional (3D) Ti3C2Tx-PANI@CNTs (TPCs) nanoarchitecture was constructed. Through optimizing structures, the surface capacitance of TPCs can be tailored to tune energy storage. The optimal specific capacitance up to 431.9 F/g was achieved under 1 A/g. Further, the TPCs nanoarchitectures were prepared into self-standing films with excellent mechanical properties and micro-supercapacitors (MSCs) in various shapes were manufactured based on the film. The MSCs demonstrate competitive energy storage capacities, obtaining an areal capacitance of 78.2 mF/cm2 and energy density of up to 2.72 μWh/cm2, still maintain excellent performance under harsh bending. The strategy for constructing 3D nanoarchitectures and further manufacturing MSCs can inspire the design of novel electrode materials and devices to advance the development in the field of energy storage.

In-situ construction of extra ion-store sites and fast ion-diffusion channels for lithium-rich manganese-based oxides cathode

Lithium-rich manganese-based oxides (LRMO) are very promising cathode materials for next-generation high-energy-density Li-ion batteries, but their application is hindered by the inherent low initial Coulombic efficiency (ICE) (<80%), poor cycling stability, and rate performance. Herein, we solve these bottlenecks via in-situ constructing a P2-type Na0.66MnO2 phase on the surface of LRMO particles (LRMO/P2) using a two-step coprecipitation and one-step co-firing strategy. The P2-type Na0.66MnO2 phase offers extra ion-store sites for LRMO particles to offset the irreversible capacity loss in the first cycle, which improves the ICE to above 92%. It can also provide a fast ion-diffusion channel with a low Li-ion diffusion energy barrier, which effectively raises the discharge capacity. The developed LRMO/P2 cathode delivers a high reversible capacity of 243 mAh·g−1 at 1 C with a retention of 80% after 240 cycles. This works gives new insights into developing high-performance cathode materials for high-energy-density batteries.

In-situ formation of Li0.5Mn0.5O coating layer through defect controlling for high performance Li-rich manganese-based cathode material

Li-rich layered oxide of Li1.2Mn0.6Ni0.2O2 (LMNO) with a considerable specific capacity and higher voltage is regarded as a kind of promising cathode material. However, it suffers from transition metal ion dissolution and oxygen escape that leads to rapid capacity decay. In addition, the poor lithium-ion diffusion kinetics gives rise to unsatisfied rate performance. Herein, a stable layer of Li0.5Mn0.5O (LMO) out of LMNO is in-situ constructed through acetic passivation and following calcination process. The generated defect structure in the composite material exhibits fast ion diffusion kinetics and the produced LMO layer can stabilize the substructure, resulting in elevated cycling stability and rate performance. In specific, the LMNO@LMO material exhibits a high initial coulombic efficiency of 80.3% and remarkable capacity retention of 80.7% after 200 cycles at 1 C. Besides, the composite material reveals prominent rate performance that delivers discharge capacities of 158 and 131 mAh g−1 at 5 and 10 C, respectively. At last, this study presents a new approach to optimizing the Li-rich cathode materials.

Uncovering the hydride ion diffusion pathway in barium hydride via neutron spectroscopy

Solid state materials possessing the ability for fast ionic diffusion of hydrogen have immense appeal for a wide range of energy-related applications. Ionic hydrogen transport research is dominated by proton conductors, but recently a few examples of hydride ion conductors have been observed as well. Barium hydride, BaH2, undergoes a structural phase transition around 775 K that leads to an order of magnitude increase in the ionic conductivity. This material provides a prototypical system to understand hydride ion diffusion and how the altered structure produced by the phase transition can have an enormous impact on the diffusion. We employ quasielastic and inelastic neutron scattering to probe the atomic scale diffusion mechanism and vibrational dynamics of hydride ions in both the low- and high-temperature phases. Jump lengths, residence times, diffusion coefficients, and activation energies are extracted and compared to the crystal structure to uncover the diffusion pathways. We find that the hydrogen jump distances, residence times, and energy barriers become reduced following the phase transition, allowing for the efficient conduction of hydride ions through a series of hydrogen jumps of length L = 3.1 Å.

Controllable and Scale-Up Synthesis of Nickel-Cobalt Boride@Borate/RGO Nanoflakes via Reactive Impingement Mixing: A High-Performance Supercapacitor Electrode and Electrocatalyst.

Large-scale synthesis of graphene-based nanomaterials in stirred tank reactor (STR) often results in serious agglomeration because of the poor control during micromixing process. In this work, reactive impingement mixing is conducted in a two-stage impinging jet microreactor (TS-IJMR) for the controllable and scale-up synthesis of nickel-cobalt boride@borate core-shell nanostructures on RGO flakes (NCBO/RGO). Benefiting from the good process control and improved micromixing efficiency of TS-IJMR, NCBO/RGO nanosheet provides a large BET surface area, abundant of suitable mesopores (2–5 nm), fast ion diffusion, and facile electron transfer within the whole electrode. Therefore, NCBO/RGO electrode exhibits a high specific capacitance of 2383 F g−1 at 1 A g−1, and still retains 1650 F g−1 when the current density is increased to 20 A g−1, much higher than those of nickel boride@borate/RGO (NBO/RGO) and cobalt boride@borate/RGO (CBO/RGO) synthesized in TS-IJMR, as well as NCBO/RGO-S synthesized in STR. In addition, an asymmetric supercapacitor (NCBO/RGO//AC) is constructed with NCBO/RGO and activated carbon (AC), which displays a high energy density of 53.3 W h kg−1 and long cyclic lifespan with 91.8% capacitance retention after 5000 charge-discharge cycles. Finally, NCBO/RGO is used as OER electrocatalyst to possess a low overpotential of 309 mV at a current density of 10 mA cm−2 and delivers a good long-term durability for 10 h. This study opens up the potential of controllable and scale-up synthesis of NCBO/RGO nanosheets for high-performance supercapacitor electrode materials and OER catalysts.

Resolving the Seeming Contradiction between the Superior Rate Capability of Prussian Blue Analogues and the Extremely Slow Ionic Diffusion.

The superior rate capabilities of metal ion battery materials based on Prussian blue analogues (PBAs) are almost exclusively ascribed to the extremely fast solid-state ionic diffusion, which is possible due to structural voids and spacious three-dimensional channels in PBA structures. We performed a detailed electroanalytical study of alkali ion diffusivities in nanosized cation-rich and cation-poor PBAs obtained as particles or electrodeposited films in both aqueous and non-aqueous media, which resulted in a solid conclusion about the exceptionally slow ionic transport. We show that the impressive rate capability of PBA materials is determined solely by the small size of the primary particles of PBAs, while the apparent diffusion coefficients are 3-5 orders of magnitude lower than those reported in earlier studies. Our finding calls for a reconsideration of the apparent facility of ionic transport in PBA materials and deeper analysis of the charge carrier-host interactions in PBAs.

Creating Unidirectional Fast Ion Diffusion Channels in G/NiS2 -MoS2 Heterostructures for High-Performance Sodium-Ion Batteries.

Exploring novel electrode composites and their unique interface physics plays a significant role in tuning electrochemical properties for boosting the performance of sodium-ion batteries (SIBs). Herein, mixed-dimensional G/NiS2 -MoS2 heterostructures are synthesized in a low-cost meteorological vulcanization process. The stable graphene supporting layer and nanowire heterostructure guarantee an outstanding structural stability to tolerate certain volume changes during the charge/discharge process. The rational construction of NiS2 -MoS2 heterostructures induces abundant interfaces and unique ion diffusion channels, which render fast electrochemical kinetics and superior reversible capacities for high-performance SIBs. Interestingly, theoretical studies reveal that the anisotropic diffusion barriers create unidirectional "high-speed" channels, which can lead to ordered and fast Na+ insertion/extraction in designed heterostructures. G/NiS2 -MoS2 anode exhibits a high capacity of 509.6mAhg-1 after 500 cycles and a coulombic efficiency >99% at 0.5Ag-1 , which also displays excellent cycling performance with the capacity of 383.8mAhg-1 after the 1000 cycles at 5Ag-1 . Furthermore, full cells are constructed exhibiting ahigh capacity of 70mAhg-1 at 0.1Ag-1 after 150 cycles and applied to light LEDs. This study provides a feasible strategy of constructing mixed-dimensional heterostructures for SIBs with excellent performance and a long service lifetime.

Flexible aqueous asymmetric capacitor with SiC-decorated boron-doped graphene cathode and core–shell SiC@graphene anode

• Core-shell SiC@graphene (Gr) nanoparticles were synthesized as an anode material. • B-doped graphene (BGr) nanosheets embedded with SiC nanoparticles were synthesized. • SiC-BGr electrocatalyzed the NiOOH/NiO redox reaction to improve pseudocapacitance. • SiC-BGr cathode showed the maximum specific capacitance of 1803 mF cm −2 at 4 mA cm −2 . • Aqueous SiC-BGr//SiC@Gr capacitor showed high working voltage and stability. Flexible aqueous pseudocapacitors have the advantages of high specific capacitance, high safety, low cost, and fast ion diffusion. However, the development of such devices is a challenge because of the low stability of the active material and the high interface resistance of the current collector-active material. In this study, we used silicon carbide (SiC)-boron-doped graphene (BGr) nanosheets and core–shell SiC@Gr nanoparticles as the cathode and anode, respectively, and constructed a flexible aqueous asymmetric capacitor (ASC) with a 3 M NaOH/carboxymethyl cellulose hydrogel as the electrolyte. In an aqueous NaOH solution, the optimized SiC-BGr cathode showed a specific capacitance of 1384.3 mF cm −2 (461.4 F g −1 ) at the current density of 3 mA cm −2 (1 A g −1 ), and the core–shell SiC@Gr anode showed a wide potential window of −1.0–0 V. The as-assembled ASC device had a high working voltage of 1.4 V, delivered an excellent capacitance of 337.1 mF cm −2 , and retained 86% of its initial capacitance after 10 000 cycles. Furthermore, the ASC also showed high energy density (57.3 μWh cm −2 ), high power density (6536.9 μW cm −2 ), high bending stability, and applicability at a low temperature of −20 °C. Thus, the preparation of novel SiC-Gr materials can promote the development of flexible aqueous capacitors with high working voltage and good temperature adaptability for application in the field of wearable electronic devices with safety, strong environmental adaptability, and reliable performance.

Cation-induced Ti3C2Tx MXene hydrogel for capacitive energy storage

To date, Ti3C2Tx MXene has been a promising candidate for energy storage field, however the construction of 3D MXene hydrogel with their inherent hydrophilicity and high conductivity remains a challenge. Herein, a series of Ti3C2Tx MXene hydrogel was fabricated successfully via a facile and fast cation-induced strategy. Typically, the formation of hydrogel is stem from the quick cross-linking of Ti3C2Tx nanosheets, accompanying with the intercalation of high-concentration cation between the layers. Characterization analyses have demonstrated that the cation-induced Ti3C2Tx hydrogel possesses 3D porous structure and controllable basal spacing, which could synergistically facilitate fast diffusion of electrolyte ions and accessibility of electrochemical active sites. Density functional theory (DFT) calculation shows that larger hydrated radii and more intercalated cation are favorable for the expansion of basal spacing thermodynamically. As a result, the excellent capacitance and high rate-capability are both realized in cation-induced Ti3C2Tx hydrogels. Especially, as-synthesized Al-Ti3C2Tx hydrogel delivery a remarkable capacitance of 675F/g at 1 A/g, along with a specific energy density of 46 Wh/kg when the power density is 349 h/kg, which is superior to the previous reported Ti3C2Tx electrodes. Besides, the well-designed H-Ti3C2Tx hydrogel still achieves 206F/g capacitance when the scan rate is up to 1 V/s, and it could withstand 5000 cycles with only 8% loss of capacitance. This work not only illuminates a straightforward way to construct high-performance MXene electrode for capacitive energy storage, but also provides a new guideline over the manipulation of interlayer spacing and morphology of 2D colloid materials.

Integration of a low-tortuous electrode and an in-situ-polymerized electrolyte for all-solid-state lithium-metal batteries

All-solid-state lithium batteries have attracted great attention because of their high safety, considerable energy density, and long lifespan. However, poor interfacial contact between the electrolyte and electrode has hindered its development. Here, we design the integration of a low-tortuous electrode and an in-situ-polymerized electrolyte for all-solid-state lithium-metal batteries. Vertically aligned channels are produced in electrode materials using the ice-templating method, and then a solid polymer electrolyte is penetrated into aligned porous channels of the electrodes by in situ UV-curing polymerization. The lithium metal cells using the electrode and electrolyte integration exhibit excellent discharge specific capacity and cycle stability at room temperature. This superior electrochemical performance is because of the good electrode/electrolyte interfacial contact and fast ion-diffusion kinetics in the electrode. This work provides a simple, efficient, and practical strategy to fabricate high-energy-density solid-state batteries.

Poly(Anthraquinonyl Sulfide)/CNT Composites as High-Rate-Performance Cathodes for Nonaqueous Rechargeable Calcium-Ion Batteries.

Calcium‐ion batteries (CIBs) are considered as promising alternatives in large‐scale energy storage due to their divalent electron redox properties, low cost, and high volumetric/gravimetric capacity. However, the high charge density of Ca2+ contributes to strong electrostatic interaction between divalent Ca2+ and hosting lattice, leading to sluggish kinetics and poor rate performance. Here, in situ formed poly(anthraquinonyl sulfide) (PAQS)@CNT composite is reported as nonaqueous calcium‐ion battery cathode. The enolization redox chemistry of organics has fast redox kinetics, and the introduction of carbon nanotube (CNT) accelerates electron transportation, which contributes to fast ionic diffusion. As the conductivity of the PAQS is enhanced by the increasing content of CNT, the voltage gap is significantly reduced. The PAQS@CNT electrode exhibits specific capacity (116 mAh g−1 at 0.05 A g−1), high rate capacity (60 mAh g−1 at 4 A g−1), and an initial capacity of 82 mAh g−1 at 1 A g−1 (83% capacity retention after 500 cycles). The electrochemical mechanism is proved to be that the PAQS undergoes reduction reaction of their carbonyl bond during discharge and becomes coordinated by Ca2+ and Ca(TFSI)+ species. Computational simulation also suggests that the construction of Ca2+ and Ca(TFSI)+ co‐intercalation in the PAQS is the most reasonable pathway.

Binder-Free Porous 3D-ZnO Hexagonal-Cubes for Electrochemical Energy Storage Applications.

Considerable efforts are underway to rationally design and synthesize novel electrode materials for high-performance supercapacitors (SCs). However, the creation of suitable materials with high capacitance remains a big challenge for energy storage devices. Herein, unique three-dimensional (3D) ZnO hexagonal cubes on carbon cloth (ZnO@CC) were synthesized by invoking a facile and economical hydrothermal method. The mesoporous ZnO@CC electrode, by virtue of its high surface area, offers rich electroactive sites for the fast diffusion of electrolyte ions, resulting in the enhancement of the SC’s performance. The ZnO@CC electrode demonstrated a high specific capacitance of 352.5 and 250 F g−1 at 2 and 20 A g−1, respectively. The ZnO@CC electrode revealed a decent stability of 84% over 5000 cycles at 20 A g−1 and an outstanding rate-capability of 71% at a 10-fold high current density with respect to 2 A g−1. Thus, the ZnO@CC electrode demonstrated improved electrochemical performance, signifying that ZnO as is promising candidate for SCs applications.