Dual Strategies of Metal Preintercalation and In Situ Electrochemical Oxidization Operating on MXene for Enhancement of Ion/Electron Transfer and Zinc-Ion Storage Capacity in Aqueous Zinc-Ion Batteries

Ni1-x Mn x Co2O4 Nanoparticles as High-Performance Electrochemical Sensor Materials for Acetaminophen Monitoring

Ternary metal oxides, known for their superior electrical and optical properties compared to binary or conventional oxides, hold significant promise for catalysis and energy storage applications. This study investigates the electrochemical performance of Ni1-x Mn x Co2O4 nanoparticles for detecting acetaminophen in aqueous phosphate buffer solution. The cobaltite nanoparticles were obtained through a simple gel-combustion synthesis, and the sensors were characterized using cyclic voltammetry, chronoamperometry, and differential pulse voltammetry. The anodic peak currents associated with acetaminophen oxidation were assessed by varying the scan rate of current-voltage cycles. Among the sensors tested, the one fabricated with Ni0.5Mn0.5Co2O4 nanoparticles as an active material exhibited the highest sensitivity of 38.2 μA cm-2 mM-1 and a detection limit of approximately 2 μM, demonstrating its potential for sensitive and efficient acetaminophen detection. Moreover, the sensors fabricated using these ternary oxide nanostructures demonstrate a rapid chronoamperometric response time of 35.4 s and a decay lifetime of 0.31 s, highlighting the fast detection capabilities of acetaminophen. The electrochemical oxidation mechanism of acetaminophen and the charge transfer characteristics at the electrode-electrolyte interface have been discussed.

Boosting Ion Transport Kinetics in Sulfolane-Modified Aqueous Electrolytes for High-Performance Zinc-Ion Batteries with V₂C MXene Cathodes

The advancement of zinc-ion batteries (ZIBs) is propelled by their inherent safety, cost-effectiveness, and environmental sustainability. This study investigates the role of sulfolane (SL), a polar aprotic solvent with a high dielectric constant, as an electrolyte additive to enhance ion transport and electrochemical performance in V₂C MXene cathodes for high-performance ZIBs. The addition of 1% SL optimizes Zn-ion transport by increasing ionic conductivity, suppressing electrolyte decomposition, and mitigating zinc dendrite formation. Galvanostatic Intermittent Titration Technique (GITT) analysis reveals a reduction in Zn2⁺ diffusion coefficient from 1.54 × 10⁻⁷ cm2/s in 2 m ZnSO₄ to 1.07 × 10⁻⁹ cm2 s-1 in the SL-modified system, indicating a more confined Zn2⁺ transport environment. Electrochemical Impedance Spectroscopy (EIS) further demonstrates a substantial decrease in activation energy from 123.78 to 65.08 kJ mol⁻¹, signifying improved charge transfer kinetics. Ex situ XRD confirms that SL stabilizes the phase transformation of V₂C to Zn₀.₂₉V₂O₅, enhancing structural integrity. The modified system achieves an impressive specific capacity of 545 mAh g⁻¹ at 0.5 A g⁻¹ and exhibits exceptional cycling stability, retaining 91% capacity over 7000 cycles at 20 A g⁻¹. These findings underscore the potential of sulfolane as a key additive for advancing V₂C MXene-based ZIBs.

Oxygen Vacancy-Rich Cobalt-Doped MnO2 Nanorods for Zn Ion Batteries

Improving electrical conductivity and increasing the active site are important directions for improving the technology of manganese-based cathode materials for zinc ion batteries (ZIBs). In this paper, cobalt-doped and oxygen-vacancy coupled MnO2 nanorods (Vo-CMO) were prepared by defect engineering and an ion doping strategy as cathode materials for rechargeable ZIBs. Oxygen vacancies can increase the defect density of the material and provide more migration paths for zinc ions, thereby increasing the electrochemical activity and improving the specific capacity. The introduction of cobalt can adjust the electronic structure of manganese oxide, change the Fermi level of the material, and promote the generation and transmission of charge carriers, thereby increasing the charge transfer rate and increasing the conductivity of the material. The synergistic effect among them can improve the diffusion kinetics of zinc ions, thereby increasing the capacity and cycle stability of the material. The Vo-CMO has better Zn2+ storage capacity of 295.6 mAh·g-1 at 0.1 A·g-1. The reaction mechanism of Vo-CMO material was H+/Zn2+ coinsertion through galvanostatic current intermittent titration (GITT) and ex situ experiments. In addition, the Vo-CMO material assembled the flexible quasi-solid ZIB. The synergistic effect of cobalt doping and oxygen vacancy can provide a new way to develop water-based ZIBs.

In situ-Induced Crystal Facet Engineering to Enhance the Rate Performance of Zn2+ Storage

In recent years, aqueous zinc-ion batteries (ZIBs) have shown considerable promise in the energy storage sector, attributed to their inherent high safety and cost-effectiveness. Zn3V2O7(OH)2·2H2O (ZVO) has emerged as a promising candidate for Zn2+ storage in recent years, owing to its exceptional structural stability that endows it with an excellent cycle life. However, an unsatisfactory rate performance is a limiting factor for its development in ZIBs. Crystal facet engineering can be employed to rationally adjust the number of exposed diffusion channel entrances, thereby effectively enhancing the rate performance of ZIBs. Here, theoretical calculations are employed to analyze the diffusion energy barrier of Zn2+, providing guidance for selecting the optimal crystal facet. The obtained ZVO via electrochemical in situ conversion (e-ZVO) with increased exposed diffusion channel entrances of Zn2+ was proposed to enhance the rate performance. The modulation of ZVO crystal facet orientation and exposed diffusion channel entrances is achieved by manipulating the adsorption-induced surface energy of (CF3SO3)- on crystal facets. As a result, the e-ZVO achieves a high-rate performance of 57 mAh g-1 at 50 A g-1 and a capacity output of 41 mAh g-1 at 40 A g-1 even at -20 °C.

In Situ Synthesis of MoO3 by Surface Oxidation of Mo2C (MXene) for Stable Near-Surface Reactions in Aqueous Aluminum-Ion Battery

Molybdenum trioxide (MoO3) is a promising positive electrode material for aqueous aluminum-ion batteries (AAIBs) due to its high theoretical capacity. However, MoO3 faces several challenges in an aqueous electrolyte, such as easy dissolution of reaction products, volume expansion, and low conductivity, which severely limit its application in aqueous batteries. In this work, we effectively increased the overall conductivity of the electrode by in situ growing MoO3 on the Mo2C MXene layer. MXene can effectively inhibit the dissolution and structural loss of MoO3 reaction products. Additionally, the coordination effect of Mo2C and MoO3 achieves a stable near-surface reaction on the MXene laminates, resulting in the Mo2C/MoO3 composite exhibiting excellent aluminum storage properties (123.5 mAh/g after 200 cycles at 0.4 A/g). The energy storage mechanism of H+/Al3+ co-insertion/extraction was elucidated through ex situ characterization, and the promotion effect of Mo2C on MoO3 reaction kinetics was verified by density functional theory (DFT) calculations. This work provides new insights into improving the stability of AAIBs cathodes and extends the application of Mo-based MXene in aqueous batteries.

Recent Advances in Current Collectors for Aqueous Zinc-ion Batteries

Aqueous zinc-ion batteries (AZIBs) are promising options for large-scale electrical energy storage because of their safety, affordability, and environmental friendliness. As an indispensable component of AZIBs, a current collector plays a crucial role in supporting electrode materials and collecting the accumulated electrical energy. Recently, some progress has been made in the study of current collectors for AZIBs; however, only few comprehensive reviews on this topic are available. In this review, the systematic summary and discussion of research progress on current collectors for AZIBs is presented. Furthermore, the main challenges and key prospects for the future development of current collectors for AZIBs are discussed.

Recent Progress in the Applications of MXene-Based Materials in Multivalent Ion Batteries

Multivalent-ion batteries have garnered significant attention as promising alternatives to traditional lithium-ion batteries due to their higher charge density and potential for sustainable energy storage solutions. Nevertheless, the slow diffusion of multivalent ions is the primary issue with electrode materials for multivalent-ion batteries. In this review, the suitability of MXene-based materials for multivalent-ion batteries applications is explored, focusing onions such as magnesium (Mg2+), aluminum (Al3+), zinc (Zn2+), and beyond. The unique structure of MXene offers large interlayer spacing and abundant surface functional groups that facilitates efficient ion intercalation and diffusion, making it an excellent candidate for multivalent-ion batteries electrodes with excellent specific capacity and power density. The latest advancements in MXene synthesis and engineering techniques to enhance its electrochemical performance have been summarized and discussed. With the versatility of MXenes and their ability to harness diverse multivalent ions, this review underscores the promising future of MXene-based materials in revolutionizing the landscape of multivalent-ion batteries.

Effects of interlayer space engineering and surface modification on the charge storage mechanisms of MXene nanomaterials: A review on recent developments

Two-dimensional MXenes were discovered in 2011 and, because of their outstanding properties, have attracted significant attention as electrode materials for supercapacitors, rechargeable batteries, and hybrid energy storage devices. Numerous studies were dedicated to identifying feasible charge storage mechanisms in MXenes and investigating the effects of structural and superficial properties on the corresponding mechanisms. The results clarify that interlayer distance and surface termination groups in MXenes significantly determine the deliverable energy and power density in respective energy storage devices. Additionally, due to van der Waals interactions, adjacent MXene sheets tend to aggregate and restack during electrode preparation or charge and discharge cycling, reducing the MXene interlayer distance and deteriorating its energy storage ability. In this review, we first summarize the different charge storage mechanisms applicable to MXenes in different energy storage devices and describe the effect of interlayer spacing and surface termination groups. Then, different interlayer space engineering methods are reviewed in terms of materials and procedures, and their impact on the electrochemical behavior and restacking tendency of MXene is described.

A Cu/MnOx Composite with Copper-Doping-Induced Oxygen Vacancies as a Cathode for Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries are anticipated to be the next generation of important energy storage devices to replace lithium-ion batteries due to the ongoing use of lithium resources and the safety hazards associated with organic electrolytes in lithium-ion batteries. Manganese-based compounds, including MnOx materials, have prominent places among the many zinc-ion battery cathode materials. Additionally, Cu doping can cause the creation of an oxygen vacancy, which increases the material's internal electric field and enhances cycle stability. MnOx also has great cyclic stability and promotes ion transport. At a current density of 0.2 A g-1, the Cu/MnOx nanocomposite obtained a high specific capacitance of 304.4 mAh g-1. In addition, Cu/MnOx nanocomposites showed A high specific capacity of 198.9 mAh g-1 after 1000 cycles at a current density of 0.5 A g-1. Therefore, Cu/MnOx nanocomposites are expected to be a strong contender for the next generation of zinc-ion battery cathode materials in high energy density storage systems.

Electrochemically Induced Phase Transformation in Vanadium Oxide Boosts Zn-Ion Intercalation

Vanadium oxides are excellent cathode materials with large storage capacities for aqueous zinc-ion batteries, but their further development has been hampered by their low electronic conductivity and slow Zn2+ diffusion. Here, an electrochemically induced phase transformation strategy is proposed to mitigate and overcome these barriers. In situ X-ray diffraction analysis confirms the complete transformation of tunnel-like structural V6O13 into layered V5O12·6H2O during the initial electrochemical charging process. Theoretical calculations reveal that the phase transformation is crucial to reducing the Zn2+ migration energy barrier and facilitating fast charge storage kinetics. The calculated band structures indicate that the bandgap of V5O12·6H2O (0.0006 eV) is lower than that of V6O13 (0.5010 eV), which enhanced the excitation of charge carriers to the conduction band, favoring electron transfer in redox reactions. As a result, the transformed V5O12·6H2O delivers a high capacity of 609 mA h g-1 at 0.1 A g-1, superior rate performance (300 mA h g-1 at 20 A g-1), fast-charging capability (<7 min charging for 465 mA h g-1), and excellent cycling stability with a reversible capacity of 346 mA h g-1 at 5 A g-1 after 5000 cycles.

Phase-Stabilized Crystal Etching to Unlock An Oxygen-Vacancy-Rich Potassium Vanadate For Ultra-Fast Zn Storage

Despite holding the advantages of high theoretical capacity and low cost, the practical application of layered-structured potassium vanadates in zinc ion batteries (ZIBs) has been staggered by the sluggish ion diffusion, low intrinsic electronic conductivity, and unstable crystal structure. Herein, for the first time, a phase stabilized crystal etching strategy is proposed to innovate an oxygen-vacancy-rich K0.486 V2 O5 nanorod composite (Ov-KVO@rGO) as a high-performance ZIB cathode. The in situ ascorbic acid assisted crystal etching process introduces abundant oxygen-vacancies into the K0.486 V2 O5 lattices, not only elaborately expanding the lattice spacing for faster ion diffusion and more active sites due to the weakened interlayer electrostatic interaction, but also enhancing the electronic conductivity by accumulating electrons around the vacancies, which is also evidenced by density functional theory calculations. Meanwhile, the encapsulating rGO layer ably stabilizes the K0.486 V2 O5 crystal phase otherwise is hard to endure subject to such a harsh chemical etching. As a result, the optimized Ov-KVO@rGO electrode delivers record-high rate capabilities with 462 and 272.39 mAh g-1 at 0.2 and 10 A g-1 , respectively, outperforming all previously reported potassium vanadate cathodes and most other vanadium-based materials. This work highlights a significant advancement of layer-structured vanadium based-materials towards practical application in ZIBs.

High-Performance Layered CaV4O9-MXene Composite Cathodes for Aqueous Zinc Ion Batteries

Due to their reliability, affordability and high safety, rechargeable aqueous zinc ion batteries (ZIBs) have garnered a lot of attention. Nevertheless, undesirable long-term cycle performance and the inadequate energy density of cathode materials impede the development of ZIBs. Herein, we report a layered CaV₄O₉-MXene (Ti₃C₂T_x) composite assembled using CaV₄O₉ nanosheets on Ti₃C₂T_x and investigate its electrochemical performance as a new cathode for ZIBs, where CaV₄O₉ nanosheets attached on the surface of MXene and interlamination create a layered 2D structure, efficiently improving the electrical conductivity of CaV₄O₉ and avoiding the stacking of MXene nanosheets. The structure also enables fast ion and electron transport. Further discussion is conducted on the effects of adding MXene in various amounts on the morphology and electrochemical properties. The composite shows an improved reversible capacity of 274.3 mA h g^-1 at 0.1 A g^-1, superior rate capabilities at 7 A g^-1, and a high specific capacity of 107.6 mA h g^-1 can be delivered after 2000 cycles at a current density of 1 A g^-1. The improvement of the electrochemical performance is due to its unique layered structure, high electrical conductivity, and pseudo capacitance behavior.