Storage Kinetics Research Articles

Cobalt-Nickel Layered Double Hydroxides on Electrospun MXene for Superior Asymmetric Supercapacitor Electrodes.

Flexible electrodes for energy storage and conversion require a micro-nanomorphology and stable structure. Herein, MXene fibers (MX-CNF) are fabricated by electrospinning, and Co-MOF nanoarrays are prepared on the fibers to form Co-MOF@MX-CNF. Hydrolysis and etching of Co-MOF@MX-CNF in the Ni2+ solution produce cobalt-nickel layered double hydroxide (CoNi-LDH). The CoNi-LDH nanoarrays on the MX-CNF substrate have a large specific surface area and abundant electrochemical active sites, thus ensuring effective exposure of the CoNi-LDH active materials to the electrolyte and efficient pseudocapacitive energy storage and fast reversible redox kinetics for enhanced charging-discharging characteristics. The CoNi-LDH@MX-CNF electrode exhibits a discharge capacity of 996 F g-1 at a current density of 1 A g-1 as well as 78.62% capacitance retention after 3,000 cycles at 10 A g-1. The asymmetric supercapacitor (ASC) comprising the CoNi-LDH@MX-CNF positive electrode and negative activated carbon electrode shows an energy density of 48.4 Wh kg-1 at a power density of 499 W kg-1 and a capacity retention of 78.9% after 3,000 cycles at a current density of 10 A g-1. Density-functional theory calculations reveal the charge density difference and partial density of states of CoNi-LDH@MX-CNF confirming the large potential of the CoNi-LDH@MX-CNF electrode in energy storage applications.

Effect of Ti0.9Zr0.1Mn1.5V0.3 alloy catalyst on hydrogen storage kinetics and cycling stability of magnesium hydride

As a high-capacity hydrogen storage material, MgH2 still has the problem of high operating temperature and slow reaction kinetics. In this work, an TiMn2-based Laves phase alloy (Ti0.9Zr0.1Mn1.5V0.3, denoted as Ti–Mn) was first synthesized by arc melting and then employed to regulate the hydrogen storage properties of MgH2, with the carbon nanotubes (CNTs) as an aid agent to facilitate the hydrogen diffusion and heat transfer. It was shown that the introduction of Ti–Mn/CNTs can remarkably improve the hydrogen storage properties of MgH2. The MgH2 + 10 wt% Ti–Mn + 1 wt% CNTs composite has an initial dehydrogenation temperature of 195 °C and can absorb hydrogen at room temperature. As for the kinetics, it can release 6.1 wt% H2 in 5 min at 300 °C, and absorb 4.8 wt% H2 in 10 min at 150 °C. It still has a reversible capacity of 6.2 wt% after 100 cycles. Combination of Ti–Mn alloy and CNTs is more effective than Ti–Mn alloy or CNTs alone for regulating MgH2. Ti–Mn/CNTs does not alter the overall thermodynamics of MgH2. However, local destabilization of Mg–H bonds induced by the MgH2/Ti–Mn interfaces was observed experimentally and confirmed theoretically, which partially contributes to the enhanced hydrogen storage of MgH2. In addition, the active transition metals contained in the alloy was believed to accelerate the hydrogen dissociation and delivery during the hydrogen storage process. This work not only achieves the synergistic improvement of hydrogen storage of MgH2 by combination of Ti–Mn alloy and CNTs, but also presents the local destabilization mechanism to explain the improved hydrogen storage of MgH2 by Ti–Mn alloy experimentally and theoretically.

An electron/ion pathway reconstruction strategy enabling fast aqueous Zn2+ storage

Aqueous Zn-ion batteries (ZIBs) are considered ideal alternatives for scalable energy storage due to their reliable safety, affordable cost, and sustainability. However, the further development of ZIBs is limited by the design of the cathode, especially with the kinetic coupling of electron transfer and ion diffusion. Here, we develop an electron/ion pathway reconstruction strategy to enhance the kinetics of Zn storage by designing a composite of reduced graphene oxide-wrapped polyaniline/vanadium oxide superlattices. The superlattice structure of V–O layers stacked with polyaniline enables rapid Zn2+ diffusion due to the enlarged interlayer spacing and redistributed electron structure. Meanwhile, the lamellar superlattices wrapped with rGO optimize the electron transfer pathway and enhance mechanical stability. Therefore, the synergistic optimization between ion migration inside superlattices and charge transport in bulk materials achieves double acceleration for Zn2+ storage kinetics, showing superior rate capability (≥100 mAh/g at 20 A/g) and cycling durability. Moreover, the electrochemical mechanism investigation shows that the as-obtained composite cathode presents highly reversible Zn diffusion behavior and good structural stability through a series of in-situ spectroscopic characterizations. It is hoped that this electron/ion pathway reconstruction strategy can provide a new perspective for the development of high-performance cathodes for aqueous batteries.

Mo-doped NiCo-LDH nanoflower derived from ZIF-67 nanosheet arrays for high-performance supercapacitors

Layered double hydroxides (LDHs) have gained utmost concern as anode materials for supercapacitors considering their high theoretical specific capacitances, short ion channels and good electrochemical properties. However, their practical application is hindered by low conductivity and limited performance in terms of charge storage. In this study, the researcher successfully synthesized Mo-doped NiCo-LDH nanoflower structures through a straightforward hydrothermal reaction and calcination utilizing lamellar ZIF-67 as a precursor. By adjusting the Mo doping concentration, the researcher was able to maintain the unique multilevel nanoflower-like structure of NiCo-LDH. Furthermore, the inclusion of Mo as a dopant introduced an amorphous phase and effectively modulated the electronic structure of NiCo-LDH, resulting in accelerating charge storage kinetics and reduced volume change. The 0.075 Mo-doped NiCo-LDH exhibited a specific capacitance of 1368.4C g−1 at 1 A g−1, with the capacity retention of 88.4 % at 10 A g−1. Additionally, the assembled asymmetric supercapacitor constructed with 0.075 Mo-doped NiCo-LDH@C//RGO achieved an energy density of 52.2 Wh kg−1 with a power density of 799.3 W kg−1. This study provides valuable insights into the rational doping of Mo elements for the controlled synthesis of supercapacitor electrode materials.

Hydrogen storage thermodynamics and kinetics of as-cast Ce–Mg–Ni-based alloy

Hydrogen storage thermodynamics and kinetics of as-cast Ce–Mg–Ni-based alloy

2D heterostructural Mn2O3 quantum dots embedded N-doped carbon nanosheets with strongly stable interface enabling high-performance sodium-ion hybrid capacitors

The ingenious architectural structural engineering is extensively identified as a cogent means for facilitating the electrochemical properties of conversion-type anode materials for sodium-ion storage. Herein, a delicate, scalable and controllable solvent-free strategy is proposed to synthesize ultrafine Mn2O3 quantum dots embedded into N-doped carbon to generate two-dimensional (2D) composites (MNC) with robust interfacial heterostructural interactions for high sodium ion storage and fast reaction kinetics, which averts the use of solvents and environmental pollution, greatly reduces time and production costs. The introduction of metallic Mn species simultaneously achieves the construction of ultrafine Mn2O3 quantum dots and strong interfacial heterostructural COMn bonds between metal species and 2D N-doped carbon matrix. The synergistic effect of the formation of oxide quantum dots, the combination of 2D N-doped carbon and the construction of robust interfacial interactions provides the stable electrode structure, fast reaction kinetics and high electrochemical storage capability of anode materials. Hence, MNC composites in SIBs convey remarkable reversible rate capability. Its superior capacity reaches 215 mAh g−1 for 50 cycles at 0.2 A g−1 and 155 mAh g−1 for 1000 cycles at a high current density of 5 A g−1, which shows good long-term stability. The assembled sodium-ion hybrid capacitors (SIHCs) device delivers outstanding energy density of 138 Wh kg−1 at a power density of 126 W kg−1 and 98% capacity retention after 2000 cycles at 2 A g−1, and tremendous capability for practical applications (69 LEDs can be easily lighted). This work not merely offers guidance for the rational interfacial engineering design of high-capacity Mn-based electrode materials in a feasible and scalable solvent-free tactics for Na+ storage, but also broadens the routes for projecting a better electrode material for other battery systems.

Electrochemical investigation of β-MnO2 octahedral microparticles decorated micro-sized silicon

Charge storage study using β-MnO2 octahedrons has not been studied due to its relatively lower capacitive property. This work presents the charge storage capacity of truncated β-MnO2 octahedral microparticles decorated onto micro-sized silicon (mSi) prepared by simple cost-effective and environment-friendly hydrothermal method. The designed truncated MnO2 octahedrons- mSi observed through SEM, when structurally characterized using XRD and Raman spectroscopy revealed the β phase of MnO2. The 3-electrode cell-based charge storage study demonstrated a specific capacitance of 353 F g−1 at 5 mV s−1 with an equivalent series resistance (ESR) of 10.29 ohms. The CV curves revealed a pseudocapacitive charge storage behavior with reversible Faradaic reactions and confirmed through charge storage kinetics evaluation using power law. An attractive energy density of 97.75 Wh kg−1 and 1700 W kg−1 power density was displayed by the electrode at 1.7 A g−1 current density which is comparable to existing literature in the field. This study not only opens the possibility of exploring the practical applicability of the enhanced charge storage capability using the proposed design but also stimulates further research on doped β-MnO2 with suitable conductive material to reduce ESR. In addition, the role of mSi can be further explored to provide enhanced energy storage applications.

Solvothermal Synthesis and Pyrolysis Toward Heteroatom-Doped Carbon Microspheres for Zinc-Ion Hybrid Capacitors.

Heteroatom-doped porous carbon materials have investigated to promote the energy density of zinc-ion hybrid capacitors (ZICs). Yet, the quest for high-performance carbon materials or cathodes brings to light the question of which dopants facilitate fast energy storage kinetics and various types of pseudocapacitive reactions. Investigation of carbon materials with precise quantitative dopants as the key variable represents an effective appropriate approach to comprehending the intricate role of dopants in energy storage areas. Here, a straightforward solvothermal strategy is demonstrated for a variety of pristine and iron-incorporated polymer microspheres, used as precursors for durable spherical carbons intended for cathode applications in ZICs. The strategy effectively governs the incorporation of dopants within the carbon materials, whilewhile maintaining consistent morphology, microtexture, and pore structure across different carbon variations. The synergistic effect of various dopants enhance the pseudocapacitance and facilitate the ion storage process. In consequence, the optimal cathode delivers considerable capacity (178.8mAhg-1 at 0.5Ag-1), good energy density (120.2Whkg-1 at 336Wkg-1), and excellent cycling stability (101.5% capacity retention at 35000 cycles). The demonstration showcases a viable method for crafting carbon materials with precise dopants to accommodate the zinc anode, thus enabling high-capacity and high-energy ZICs.

A Universal Cross-Synthetic Strategy for Sub-10nm Metal-Based Composites with Excellent Ion Storage Kinetics.

The sub-10nm metal-based nanomaterials (SMNs) show great potential for the electrochemical energy storage field. However, their ion storage capacity and stability suffer from severe agglomeration and interface problems. Herein, a universal strategy is reported to synthesize a wide range of SMNs (e.g., metal, nitride, oxide, and sulfides) embedded in free-standing carbon foam (SMN/FC-F) composite electrodes by crossing the interfacial confinement of NaCl self-assembly with the thermal-mechanical coupling of powder metallurgy. The pressure-enhanced NaCl self-assembly interfacial confinement is greatly beneficial to preventing SMN agglomeration and promoting SMNs embedded in FC-F which originate from the welding of carbon nanosheets. They are confirmed via a series of advanced characterizations including X-ray photoelectron spectroscopy, and spherical aberration-corrected scanning transmission electron microscopy, with theoretical computations. Benefiting from the unique structure, SMNs/FC-F delivers ultrafast and stable ion-storage kinetics. As a proof-of-concept demonstration, the MoS2 /FC-F shows excellent ion storage kinetics and superior long-term cycling performance for ion storage (e.g., Na3 V2 (PO4 )2 O2 F/C//MoS2 /FC-F sodium-ion batteries exhibit a high reversible capacity of 185mAhg-1 at 0.5Ag-1 with a decay rate of 0.05% per cycle.). This work provides a new opportunity to design and fabricate promising SMN-based free-standing working electrodes for electrochemical energy storage and conversion applications.

Effect of rapid thermal annealing on the charge storage kinetics of conductive N-doped SnO2 thin film anodes for Li-ion batteries

This study focuses on the fabrication of a flexible thin film electrode composed of N-doped tin oxide (SnO2: N). The fabrication process involves sputtering SnO2 onto a Cu foil sheet using radio frequency (RF) magnetron sputtering, conducted under an N2 atmosphere. The deposited thin films are subsequently exposed to annealing treatment using rapid thermal annealing (RTA) at temperatures ranging from 200 to 400 °C. The primary objective of this study is to get an understanding of the effects of N-doping, annealing temperature on the growth of SnO2: N. as well as the influence of film thickness on the crystallographic state. We evaluate their thin-film anode performance for lithium-ion batteries (LIBs). The specific capacity of the as-deposited SnO2 thin films standing at 859 mAh g−1 when measured at 1 mA g−1. This enhanced capacity is attributed to the limited crystal growth in ultrathin SnO2, a factor that effectively combats electrode degradation while simultaneously improving the lithium-ion diffusion coefficient and electron kinetics of the electrode. However, the SnO2: N film that undergoes annealing at 400 °C demonstrates remarkable cyclic retention, reaching 82 %. This improvement is due to the enhanced electrical conductivity resulting from annealing, which prevents the aggregation of tin (Sn) and effectively accommodates the volume changes that occur in prolonged cycles. Additionally, this synchronized approach involving sputtering and RTA is proving to be a simple, efficient, and scalable method. It holds the potential to emerge as a valuable strategy to produce anode materials for lithium-ion batteries.

Unveiling the Double‐Edged Behavior of Controlled Selenium Substitution in Cobalt Sulfide for Balanced Na‐Storage Capacity and Rate Capability

AbstractTransition metal sulfide‐based anodes usually suffer from huge volumetric change and sluggish reaction kinetics, hindering their application for long‐term and high‐power/energy sodium‐ion batteries. Herein, a new design of CoS2‐xSex (0≤x≤2) nanocrystals with highly controllable selenium substitution and S, Se‐codoped graphene immobilization (CoS2‐xSex@SG) is proposed to tune the reaction kinetics and structural stability. The nanocrystal‐on‐graphene structure and robust C─S &C─Se bonding rivets between CoS2‐xSex and SG greatly improve the structural stability of the CoS2‐xSex@SG. Electrochemical performance, kinetic analysis, and theoretical calculation reveal that Se substitution plays a double‐edged role in sodium storage: the increase of Se substitution content enhances the Na+ diffusion kinetics but decreases the Na‐storage capacity. When the Se substitution content is 0.4, the CoS1.6Se0.4@SG electrode demonstrates the best performance: high initial Coulombic efficiency (95.5%), ultrahigh rate capability (412.8 mAh g−1 at 30 A g−1), and ultra‐stable cycling performance (97.6% capacity retention after 1000 cycles). In situ/ex situ measurements further unveil that the conversion reaction between Co0 and Na2S/Na2Se generates the micro‐scaled CoSe2–CoS2 heterostructure, synergistically improving the Na‐storage active sites and reaction kinetics. This work provides a controllable anion substitution strategy to balance the Na+ storage active sites and kinetics with potential applications for high‐power/energy sodium‐ion batteries.

Stable multi-electron reaction stimulated by W doping VS4 for enhancing magnesium storage performance

Rechargeable magnesium batteries (RMBs) hold promise for offering higher volumetric energy density and safety features, attracting increasing research interest as the next post lithium-ion batteries. Developing high performance cathode material by inducing multi-electron reaction process as well as maintaining structural stability is the key to the development and application of RMBs. Herein, multi-electron reaction occurred in VS4 by simple W doping strategy. W doping induces valence of partial V as V2+ and V3+ in VS4 structure, and then stimulates electrochemical reaction involving multi-electrons in 0.5% W-V-S. The flower-like microsphere morphology as well as rich S vacancies is also modulated by W doping to neutralize structure change in such multi-electron reaction process. The fabricated 0.5% W-V-S delivers higher specific capacity (149.3 mA h g−1 at 50 mA g−1, which is 1.6 times higher than that of VS4), superior rate capability (76 mA h g−1 at 1000 mA g−1), and stable cycling performance (1500 cycles with capacity retention ratio of 93.8%). Besides that, pesudocapaticance-like contribution analysis as well as galvanostatic intermittent titration technique (GITT) further confirms the enhanced Mg2+ storage kinetics during such multi-electron involved electrochemical reaction process. Such discovery provides new insights into the designing of multi-electron reaction process in cathode as well as neutralizing structural change during such reaction for realizing superior electrochemical performance in energy storage devices.

High pseudocapacitance electrode enabled by heterovalent doping and surface coating for rapid charge storage

With admirable energy storage kinetics and high capacitance, pseudocapacitive electrodes have been regarded as promising candidates to replace active carbon materials for next-generation supercapacitors. Unfortunately, these materials usually present lower capacitance compared to the Ni/Co-based battery-type materials, and insufficient cycling lifespans due to repeat surface redox reactions. Here, we employ Fe doping and surface coating to construct a high-capacitance robust pseudocapacitive WO3-based electrode (10-Fe-WO3/PANI). Heterovalent doping breaks the octahedral symmetry of WO3 and effectively boosts the reversible capacitance of WO3 due to Jahn-Teller distortion, creating abundant active sites for energy storage. Polyaniline (PANI) coating enhances the structural durability and ion diffusion kinetics of WO3 in the acid electrolyte, promoting long-term cycling performance. As expected, the optimized electrode can deliver a high specific capacitance of 4006 mF cm−2 at 5 mA cm−2, which is about five-fold higher than that of a pure WO3 electrode (733.7 mF cm−2) and can steadily work for 10,000 cycles without apparent capacitance decay. The full device using polypyrrole (PPy) as the cathode exhibits intriguing energy/power density and cycling lifespans, demonstrating the application potential of this material. This work may enlighten the development of cationic doping and advanced pseudocapacitive materials design in electrochemical energy storage fields.

Unveiling the impact of reaction temperature on hydrothermally synthesized nickel phosphate hydrate for supercapacitors

Transition metal phosphates have engrossed a hefty amount of interest in the field of energy storage owing to their fascinating characteristics. Herein, this study reports nickel phosphate hydrate (NP) deposited on nickel foam using a facile hydrothermal method. The X-ray diffraction (XRD) technique confirms the formation of NP on the nickel foam having a monoclinic structure and an “I2/m” space group. The scanning electron microscopy (SEM) studies revealed a stacked micro-sheet-like structure. The electrochemical measurements were examined under a potential window of −0.2 to 0.55 V Vs SCE in a 1 M KOH electrolyte delivering a maximum areal capacitance of 6333.33 mF cm−2 at a current density of 10 mA cm−2. The synthesized electrodes’ charge storage kinetics were diffusion-driven. Moreover, the electrode produced an energy density of 316.67 µWh cm−2 along with an impressive cyclic retention of ∼89 % over 1000 charge–discharge cycles. A hybrid supercapacitor device was fabricated with N5//AC as the electrodes shows 94.44 % of its initial capacitance retention after 5000 cycles.

Effect of the addition of 1.5 wt.% of mischmetal in the ZK60 alloy processed by Friction Stir Process (FSP) followed by filing on the H-absorption/desorption kinetics

This work investigates the application of Friction Stir Process (FSP) to the ZK60 alloy enhanced with 1.5 % mischmetal (ZK60–1.5 wt% Mm) combined with manual filing to achieve significant improvement in the hydrogen storage properties of this alloy. Addition of 1.5 wt% Mm to the ZK60 alloy yields a matrix with high thermal stability, attributable to the formation of high melting point intermetallic phases. Post FSP, the ZK60–1.5 wt% Mm material shows a refined, pulverized, and recrystallized structure. Such a structure allows the acquisition of filings with nanometric particle sizes and even more pulverized intermetallic phases post-FSP. This synergistic approach produces a significantly homogeneous microstructure morphology, facilitating the study of the catalytic role Mm plays in the hydrogen storage kinetics of the ZK60 alloy at 350 °C. Currently, among all Severe Plastic Deformation (SPD) techniques, only FSP followed by manual filing has demonstrated a capacity to provide a nanometric, homogeneous microstructure that significantly enhances hydrogen storage kinetics and cycling properties. Additionally, the combination of FSP and manual filing is an industrialization process that can be easily implemented, offering reliability, controllability, and cost-effectiveness compared with alternative methods like High-energy Ball Milling (HEBM). Experimental kinetic data for (de)hydrogenation reactions were analyzed using the Luus-Jaakola optimization method, underscoring the potential applicability of the FSP-manual filing route for hydrogenation temperatures <350 °C.

Defect-induced electron rich nanodomains in CoSe0.5S1.5/GA realize fast ion migration kinetics as sodium-ion capacitor anode

Optimizing charge migration and alleviating volume expansion in anode materials are the key to improve the electrochemical performance for sodium-ion storage devices. Herein, a hierarchical porous conducting matrix confining defect-rich selenium doped cobalt dichalcogenide (CoSe0.5S1.5/GA) is constructed as a promising SICs anode based on the guidance of theoretical calculation analysis. The increased defect concentration significantly enhanced the disorder degree of the compound and presented electron aggregation around the S atoms, which effectively modulated the electronic structure, further enabling high rate and ultra-capacity sodium storage. Moreover, strong interfacial coupling could construct spatial constraint to alleviate volume expansion as well as maintain electrode integrity and stability. The CoSe0.5S1.5/GA electrode can deliver a high capacity of 310.1 mA h g−1 after 2000 cycles at 1 A g−1, and the CoSe0.5S1.5/GA//AC sodium ion capacitor can exhibit an outstanding energy density of 237.5 W h kg−1. A series of characterization and theoretical calculation convincingly reveal that the defect moieties can regulate the Na+ storage and diffusion kinetics, which prove that our defect manufacture coupling with space-confined strategy can provide deep insights into the development of high-performance Na+ storage devices.

Storage and degradation kinetics of physicochemical and bioactive attributes in microalgal-derived fucoxanthin-rich microcapsules

Microencapsulation can improve carotenoid stability by slowing down degradation. Studies on the production and processing effects of microencapsulated carotenoids were reported in the past however long-term storage studies on fucoxanthin stability remains limited. This study investigated the effects of an eighteen-week storage period across four conditions on fucoxanthin derived from the diatom, Chaetoceros calcitrans. The fucoxanthin powders were prepared using two microencapsulation methods i.e., freeze drying and spray drying. Briefly, the microcapsules produced were stored in amber bottles under room temperature (25 °C) or refrigerated (4 °C) in the dark or in the presence of light. Samples were collected every two weeks where the physicochemical characteristics, carotenoid stability and antioxidant activity were evaluated. It was found that the freeze-dried microcapsule stored in 4 °C showed significantly (p < 0.05) better carotenoid retainment (7.5 times more) and antioxidant outcomes (3.5 times higher), as compared to the spray-dried microcapsule stored in 25 °C light. All microcapsules were found to be mainly comprised of the carotenoids fucaxanthin, dehydro fucoxanthin acetate, capsanthone, antheraxanthin, and celaxanthin. The major carotenoid identified was fucoxanthin where correlation studies showed it was responsible for the antioxidant activities and stability of the produced microcapsules. Overall, both freeze-dried and spray-dried fucoxanthin microcapsules followed a first-order kinetic degradation reaction and the recommended storage condition for fucoxanthin microcapsules was ranked as follows 4 °C (dark) > 25 °C (dark) > 40 °C (dark) > 25 °C (light). This finding offer useful insights into optimizing fucoxanthin microencapsulation methods, maintaining product quality during storage and distribution, and ensuring compliance with quality standards of fucoxanthin-based products available to consumers across the production and distribution chain.

4,4′-Biphenyldicarboxylic acid as an anode for sodium-ion batteries: Different electrochemical behaviors in ester and ether-based electrolytes

Organic electrode materials have been regarded as sustainable alternatives for sodium-ion batteries (SIBs) due to their high theoretical specific capacity, large reserves and wide sources from biomass. However, the variety of presently reported organic electrode materials is very limited and their essential electrochemical sodium storage behaviors also deserve further investigating. In this paper, we explore the electrochemical sodium storage behavior of a conjugated aromatic acid (4,4′-biphenyldicarboxylic acid, H2bpdc) in esters and ethers-based electrolytes. The results illustrate that in esters-based electrolytes, H2bpdc just shows limited capacity and poor electrochemical sodium storage kinetics. By contrast, in ethers-based electrolytes, H2bpdc experiences a process similar to conversion type mechanism from pristine acid to sodium salt, displaying fast kinetics and delivers a high reversible capacity of 280 mA h g−1. This research would provide basic and novel insights to the electrochemical sodium storage behaviors of promising organic electrode materials and accelerate the new materials exploration process for SIBs.

An in-situ self-etching enabled high-power electrode for aqueous zinc-ion batteries

Sluggish storage kinetics is considered as the main bottleneck of cathode materials for fast-charging aqueous zinc-ion batteries (AZIBs). In this report, we propose a novel in-situ self-etching strategy to unlock the Palm tree-like vanadium oxide/carbon nanofiber membrane (P-VO/C) as a robust free-standing electrode. Comprehensive investigations including the finite element simulation, in-situ X-ray diffraction, and in-situ electrochemical impedance spectroscopy disclosed it an electrochemically induced phase transformation mechanism from VO to layered ZnxV2O5⋅nH2O, as well as superior storage kinetics with ultrahigh pseudocapacitive contribution. As demonstrated, such electrode can remain a specific capacity of 285 mA h g−1 after 100 cycles at 1 A g−1, 144.4 mA h g−1 after 1500 cycles at 30 A g−1, and even 97 mA h g−1 after 3000 cycles at 60 A g−1, respectively. Unexpectedly, an impressive power density of 78.9 kW kg−1 at the super-high current density of 100 A g−1 also can be achieved. Such design concept of in-situ self-etching free-standing electrode can provide a brand-new insight into extending the pseudocapacitive storage limit, so as to promote the development of high-power energy storage devices including but not limited to AZIBs.

Superior hydrogen storage kinetics of MgH2 by in-situ generated α-Fe from the Fe-zeolitic imidazolate framework

While MgH2 is one of the promising hydrogen storage materials, its poor de/hydrogenation kinetics have hindered its potential applications. Here, we report that kinetic and cycle properties can be improved using Fe-doped zeolitic imidazolate framework (Fe-ZIF) as the catalysts. The synthesized MgH2@5 wt.% Fe-ZIF can absorb 5.0 wt.% hydrogen in 1 min at 200 °C and desorb 5.0 wt.% hydrogen within 16 min at 300 °C. No clear degradation of catalytic effects was observed over 30 cycles. Structural analysis revealed that the Fe-ZIF gradually decomposed into α-Fe, which strongly interacts with MgH2, realizing much higher catalytic activity and stability. Furthermore, the Fe-ZIF is characterized by a simple process and low cost nature, posing the metal-ZIF composite as a promising platform to disperse nano-catalysts in Mg-based hydrogen storage materials.