Metal-organic framework derived vanadium-doped TiO2@carbon nanotablets for high-performance sodium storage

Conformal Conversion of Polyphosphazene@Sb2MoO6 Nanowires to N/S-Doped/Carbon-Coated SbPO4/MoOx for High-performance Lithium Storage

Alloy-type antimony (Sb) and conversion-type molybdenum (Mo) anodes have attracted extensive attention in the application of lithium-ion batteries (LIBs) owing to their high theoretical capacity. In this study, Sb2MoO6 nanowires are prepared via a hydrothermal method and assessed their thermal behavior upon heat treatment, observing an intriguing transformation from nanowire to Sb2O3/MoOx nanosheets. To enhance structure stability, the Sb2MoO6 nanowires are successfully coated with a polyphosphazene layer (referred to as PZS@Sb2MoO6), which not only preserved the nanowires form but also yielded N/S co-doped carbon-coated SbPO4/MoOx (NS-C@SbPO4/MoOx) nanowires following annealing in an inert environment. This composite benefits from the stable PO4 3- anion that serve as a buffer against volume expansion and form a Li3PO4 matrix during cycling, both of which substantially bolster ion transport and cycle endurance. Doping with heteroatoms introduces numerous oxygen vacancies, augmenting the number of electrochemically active sites, and carbon integration considerably enhances the electronic conductivity of the electrode and alleviates the volume-change-induced electrode pulverization. Employed as anode materials in LIBs, the NS-C@SbPO4/MoOx electrode exhibits remarkable cycling performance (449.8 mA h g-1 at 1000 mA g-1 over 700 cycles) along with superior rate capability (394.2 mA h g-1 at 2000 mA g-1).

Encapsulation of Titanium Disulfide into MOF-Derived N,S-Doped Carbon Nanotablets Toward Suppressed Shuttle Effect and Enhanced Sodium Storage Performance

Titanium disulfide (TiS2) is a promising anode material for sodium-ion batteries due to its high theoretical capacity, but it suffers from severe volume variation and shuttle effect of the intermediate polysulfides. To overcome the drawbacks, herein the successful fabrication of TiS2@N,S-codoped C (denoted as TiS2@NSC) through a chemical vapor reaction between Ti-based metal-organic framework (NH2-MIL-125) and carbon disulfide (CS2) is demonstrated. The C─N bonds enhance the electronic/ionic conductivity of the TiS2@NSC electrode, while the C─S bonds provide extra sodium storage capacity, and both polar bonds synergistically suppress the shuttle effect of polysulfides. Consequently, the TiS2@NSC electrode demonstrates outstanding cycling stability and rate performance, delivering reversible capacities of 418/392 mAh g-1 after 1000 cycles at 2/5 A g-1. Ex situ X-ray photoelectron spectroscopy and transmission electron microscope analyses reveal that TiS2 undergoes an intercalation-conversion ion storage mechanism with the generation of metallic Ti in a deeper sodiation state, and the pristine hexagonal TiS2 is electrochemically transformed into cubic rock-salt TiS2 as a reversible phase with enhanced reaction kinetics upon sodiation/desodiation cycling. The strategy to encapsulate TiS2 in N,S-codoped porous carbon matrices efficiently realizes superior conductivity and physical/chemical confinement of the soluble polysulfides, which can be generally applied for the rational design of advanced electrodes.

Coupling ultrafine TiO2 within pyridinic-N enriched porous carbon towards high-rate and long-life sodium ion capacitors

Coupling TiO2 within N-doped porous carbon (NPC) is essential for enhancing its Na+ storage performance. However, the role of different N configurations in NPC in improving the electrochemical performance of TiO2 is currently unknown. In this study, melamine is deliberately incorporated as a pore-forming agent in the self-assembly process of metal organic framework precursors (NH2-MIL-125(Ti)). This intentional inclusion of melamine leads to the one-pot and in-situ formation of highly active edge-N, which is vital for the development of TiO2/NPC with exceptional reactivity. Electrochemical performance characterization and density functional theory (DFT) calculation indicate that the interaction between TiO2 and pyridinic-N enriched NPC can effectively narrow the bandgap of TiO2/NPC, thereby significantly improving electron/ion transfer. Additionally, the abundant mesoporous channels, high N content and oxygen vacancies also contribute to the fast reaction kinetics of TiO2/NPC. As a result, the optimized TiO2/NPC-M, with high proportion of pyridinic-N (44.1 %) and abundant mesoporous channels (97.8 %), delivers high specific capacity of 282.1 mA h-1 at 0.05 A g-1, superior rate capability of 177.3 mA h-1 at 10 A g-1, and prominent capacity retention of 89.3 % over 5000 cycles even under ultrahigh 10 A g-1. Furthermore, the TiO2/NPC-M//AC sodium ion capacitors (SIC) device achieves a high energy density of 136.7 Wh kg-1 at 200 W kg-1. This research not only offers fresh perspectives on the production of high-performance TiO2-based anodes, but also paves the way for customizing other active materials for energy storage and beyond.

Metal-Organic Framework-Based Materials for Advanced Sodium Storage: Development and Anticipation

As a pioneering battery technology, even though sodium-ion batteries (SIBs) are safe, non-flammable, and capable of exhibiting better temperature endurance performance than lithium-ion batteries (LIBs), because of lower energy density and larger ionic size, they are not amicable for large-scale applications. Generally, the electrochemical storage performance of a secondary battery can be improved by monitoring the composition and morphology of electrode materials. Because more is the intricacy of a nanostructured composite electrode material, more electrochemical storage applications would be expected. Despite the conventional methods suitable for practical production, the synthesis of metal-organic frameworks (MOFs) would offer enormous opportunities for next-generation battery applications by delicately systematizing the structure and composition at the molecular level to store sodium ions with larger sizes compared with lithium ions. Here, the review comprehensively discusses the progress of nanostructured MOFs and their derivatives applied as negative and positive electrode materials for effective sodium storage in SIBs. The commercialization goal has prompted the development of MOFs and their derivatives as electrode materials, before which the synthesis and mechanism for MOF-based SIB electrodes with improved sodium storage performance are systematically discussed. Finally, the existing challenges, possible perspectives, and future opportunities will be anticipated.

Porous carbon with the synergistic effect of cellulose fibers and MOFs as the anode for high-performance Li-ion batteries

The commercial graphene for Li ion batteries (LIBs) has high cost and low capacity. Therefore, it is necessary to develop a novel carbon anode. The cellulose nanowires (CNWs), which has advantages of low cost, high carbon content, is thought as a good carbon precursor. However, direct carbonization of CNWs leads to low surface area and less mesopores due to its easy aggregation. Herein, the metal-organic frameworks (MOFs) have been explored as templates to prepare porous carbon due to their 3D open pore structures. The porous carbon was developed with the coordination effect of CNWs and MOFs. The precursor of MOFs coordinates with the -OH and - COOH groups in the CNWs to provide stable structure. And the MOFs was grown in situ on CNWs to reduce aggregation and provide higher porosity. The results show that the porous carbon has high specific capacity and fast Li+/electronic conductivity. As anode for LIBs, it displays 698 mAh g-1 and the capacity retention is 85 % after 200 cycles. When using in the full-battery system, it exhibits energy density of 480 Wh kg-1, suggesting good application value. This work provides a low-cost method to synthesize porous carbon with fast Li+/electronic conductivity for high-performance LIBs.

Introducing Hybrid Defects of Silicon Doping and Oxygen Vacancies into MOF-Derived TiO2-X @Carbon Nanotablets Toward High-Performance Sodium-Ion Storage

Titanium dioxide (TiO2 ) is a promising anode material for sodium-ion batteries (SIBs), which suffer from the intrinsic sluggish ion transferability and poor conductivity. To overcome these drawbacks, a facile strategy is developed to synergistically engineer the lattice defects (i.e., heteroatom doping and oxygen vacancy generation) and the fine microstructure (i.e., carbon hybridization and porous structure) of TiO2 -based anode, which efficiently enhances the sodium storage performance. Herein, it is successfully realized that the Si-doping into the MIL-125 metal-organic framework structure, which can be easily converted to SiO2 /TiO2-x @C nanotablets by annealing under inert atmosphere. After NaOH etching SiO2 /TiO2-x @C which contains unbonded SiO2 and chemically bonded SiOTi, thus the lattice Si-doped TiO2-x @C (Si-TiO2-x @C) nanotablets with rich Ti3+ /oxygen vacancies and abundant inner pores are developed. When examined as an anode for SIB, the Si-TiO2-x @C exhibits a high sodium storage capacity (285 mAh g-1 at 0.2 A g-1 ), excellent long-term cycling, and high-rate performances (190 mAh g-1 at 2 A g-1 after 2500 cycles with 95.1% capacity retention). Theoretical calculations indicate that the rich Ti3+ /oxygen vacancies and Si-doping synergistically contribute to a narrowed bandgap and lower sodiation barrier, which thus lead to fast electron/ion transfer coefficients and the predominant pseudocapacitive sodium storage behavior.

Polyphosphazene-derived P/S/N-doping and carbon-coating of yolk-shelled CoMoO4 nanospheres towards enhanced pseudocapacitive lithium storage

Transition metal oxides as potentialanodes of lithium-ion batteries (LIBs) possess high theoretical capacity but suffer from large volume expansion and poor conductivity. To overcome these drawbacks, we designed and fabricated polyphosphazene-coated yolk-shelled CoMoO₄ nanospheres, in which polyphosphazene with abundant C/P/S/N species was readily converted into carbon shells and provided P/S/N dopants. This resulted in the formation of P/S/N co-doped carbon-coated yolk-shelled CoMoO₄ nanospheres (PSN-C@CoMoO₄). The PSN-C@CoMoO₄ electrode exhibits superior cycle stability of 439.2 mA h g^-1at 1000 mA g^-1after 500 cycles and rate capability of 470.1 mA h g^-1at 2000 mA g^-1. The electrochemical and structural analyses reveal that PSN-C@CoMoO₄ with yolk-shell structure, coated with carbon and doped with heteroatom not only greatly enhances the charge transfer rate and reaction kinetics, but also efficiently buffers the volume variation upon lithiation/delithiation cycling. Importantly, the use of polyphosphazene as coating/doping agent can be a general strategy for developing advanced electrode materials.

Application of Synthesized Vanadium-Titanium Oxide Nanocomposite to Eliminate Rhodamine-B Dye from Aqueous Medium

In this study, a V@TiO₂ nanocomposite is examined for its ability to eliminate carcinogenic Rhodamine (Rh-B) dye from an aqueous medium. A simple ultrasonic method was used to produce the nanosorbent. In addition, V@TiO₂ was characterized using various techniques, including XRD, HRTEM, XPS, and FTIR. Batch mode studies were used to study the removal of Rh-B dye. In the presence of pH 9, the V@TiO₂ nanocomposite was able to remove Rh-B dye to its maximum extent. A correlation regression of 0.95 indicated that the Langmuir model was a better fit for dye adsorption. Moreover, the maximum adsorption capacity of the V@TiO₂ nanocomposite was determined to be 158.8 mg/g. According to the thermodynamic parameters, dye adsorption followed a pseudo-first-order model. Based on the results of the study, a V@TiO₂ nanocomposite can be reused for dye removal using ethanol.

Enhancement of oxygen reduction reactivity on TiN by tuning the work function via metal doping

Oxide layers on conductive TiN have recently been investigated to catalyse the oxygen reduction reaction (ORR) in acidic media. The ORR reactivity, i.e., activity and selectivity, has been correlated with the surface nitrogen atoms. A new strategy, optimising the work function via the doping of foreign metals, is revealed herein to enhance the reactivity.

Bifunctional keel flower-like Ni-Co-V multicomponent oxide catalyst with enhanced electron transport for accelerating overall water splitting

Heteroatom doping is considered a typical method for improving the electrochemical properties of composites. In this work, the multi-component oxide catalyst (Ni(VO₃)₂ and Co₂V₂O₇ on Ni foam, referred to as NiCoVO_x@NF) is formed by hydrothermal doping of V element into NiCo-based precursors followed by co-oxidation. In the catalyst NiCoVO_x@NF, all three components of Ni, Co and V are particularly tightly coordinated, exhibiting an integrated structure of keel flower-like arrays. The catalyst NiCoVO_x@NF's contact surface with water is increased thanks to this unusual structure, exposing a high number of active sites. Furthermore, NiCoVO_x@NF owns efficient electronic pathways, which greatly enhances the electron transport ability. To generate a current density of 10 mA cm^-2 for hydrogen evolution reaction, just a 107 mV overpotential is required. The electrode exhibits a low overpotential of 217 mV to deliver 50 mA cm^-2 for oxygen evolution reaction. In addition, the total water splitting performance of NiCoVO_x@NF is also excellent, which could be achieved by only one 1.5 V AA battery. This study provides a feasible heteroatom doping route to design bifunctional catalysts with improved performances.

Effect of vanadium doping on the electrochemical performances of sodium titanate anode for sodium ion battery application

In this study, V⁵⁺ doped sodium titanate nanorods were successfully synthesized by a sol-gel method with different optimized vanadium concentrations. Before testing as a promising anode material for sodium ion battery (SIB) application, the samples were systematically characterized. It was clearly observed that V⁵⁺ doping significantly affects the phase formation of sodium titanate samples and leads to the alteration of the major phase of Na₂Ti₃O₇ to a single Na₂Ti₆O₁₃ phase with increasing doping concentrations. Electrochemical investigations clearly showed that the optimized 15 wt% V⁵⁺ doped sample exhibits the highest capacity of 136 mA h g^-1 at 100 mA g^-1 after 900 cycles as well as better rate capability than the undoped sample by delivering 101 mA h g^-1 capacity at a high current density of 1000 mA g^-1. It is believed that the incorporation of highly charged V⁵⁺ in sodium titanate produces oxygen vacancies along with partial reduction of Ti⁴⁺ to Ti³⁺, resulting in improved electronic conductivity. The utilization of oxygen vacancies also preserves the integrity of the electrode, giving rise to long term cycling. Thereby, V⁵⁺ doping was found to be an effective strategy to enhance the electrochemical performance of the sodium titanate anode for SIBs.