Enhanced Pseudo-Capacitive Contributions to High-Performance Sodium Storage in TiO2/C Nanofibers via Double Effects of Sulfur Modification

Advantageous Effects of Phase Transition-Modulated Electric Polarization of Hollow CuSx for Enhanced Electromagnetic Wave Absorption

Scrutinizing the electromagnetic wave absorption mechanism of sulfides remains a challenge due to the variability of the modulation of the crystal structure of the sulfides. To take advantage of this variability, nanosheet-assembled Cu9S5/CN composites with sulfur vacancies were prepared in this study by self-assembly synthesis and subsequent high-temperature heat treatment. Systematic studies show the phase transition-dependent induced decrease in the conductivity, the defect site-induced difference in the charge density, the weakened vacancy formation of defect polarization loss, and the influence of valence state on electric dipole polarization loss and interfacial polarization loss, making the optimization of the dielectric constant a significant positive effect on the improvement of impedance matching. This work provides a reliable example and theoretical guidance for the crystal structure design for the preparation of a new generation of efficient sulfide-based wave-absorbing materials.

Investigating composite electrode materials of metal oxides for advanced energy storage applications

Electrochemical energy systems mark a pivotal advancement in the energy sector, delivering substantial improvements over conventional systems. Yet, a major challenge remains the deficiency in storage technology to effectively retain the energy produced. Amongst these are batteries and supercapacitors, renowned for their versatility and efficiency, which depend heavily on the quality of their electrode materials. Metal oxide composites, in particular, have emerged as highly promising due to the synergistic effects that significantly enhance their functionality and efficiency beyond individual components. This review explores the application of metal oxide composites in the electrodes of batteries and SCs, focusing on various material perspectives and synthesis methodologies, including exfoliation and hydrothermal/solvothermal processes. It also examines how these methods influence device performance. Furthermore, the review confronts the challenges and charts future directions for metal oxide composite-based energy storage systems, critically evaluating aspects such as scalability of synthesis, cost-effectiveness, environmental sustainability, and integration with advanced nanomaterials and electrolytes. These factors are crucial for advancing next-generation energy storage technologies, striving to enhance performance while upholding sustainability and economic viability.

Microbial synthesis of antimony sulfide to prepare catechol and hydroquinone electrochemical sensor by pyrolysis and carbonization

The application of antimony sulfide sensors, characterized by their exceptional stability and selectivity, is of emerging interest in detection research, and the integration of graphitized carbon materials is expected to further enhance their electrochemical performance. This study represents a pioneering effort in the synthesis of carbon-doped antimony sulfide materials through the pyrolysis of the mixture of microorganisms and their synthetic antimony sulfide. The prepared materials are subsequently applied to electrochemical sensors for monitoring the highly toxic compounds catechol (CC) and hydroquinone (HQ) in the environment. Via cyclic voltammetry (CV) and impedance testing, we concluded that the pyrolytic product at 700 °C (Sb-700) demonstrated the best electrochemical properties. Differential pulse voltammetry (DPV) revealed impressive separation when utilizing Sb-700/GCE for simultaneous detection of CC and HQ, exhibiting good linearity within the concentration range of 0.1-140 μM. The achieved sensitivities of 24.62 μA μM-1 cm-2 and 22.10 μA μM-1 cm-2 surpassed those of most CC and HQ electrochemical sensors. Meanwhile, the detection limits for CC and HQ were as low as 0.18 μM and 0.16 μM (S/N = 3), respectively. Additional tests confirmed the good selectivity, reproducibility, and long-term stability of Sb-700/GCE, which was effective in detecting CC and HQ in tap water and river water, with recovery rates of 100.7%-104.5% and 96.5%-101.4%, respectively. It provides a method that combines green microbial synthesis and simple pyrolysis for the preparation of electrode materials in CC and HQ electrochemical sensors, and also offers a new perspective for the application of microbial synthesized materials.

Facile Synthesis of Band Gap-Tunable Kappa-Carrageenan-Mediated C,S-Doped TiO2 Nanoparticles for Enhanced Dye Degradation

Semiconducting nanoparticles (SNPs) have garnered significant attention for their role in photocatalysis technology, offering a cost-effective and highly efficient method for breaking down organic dyes. Of particular significance within SNP-based photocatalysis are tunable band gap TiO2 nanoparticles (NPs), which demonstrate remarkable enhancement in photocatalytic efficiency. In the present work, we introduce an approach for the synthesis of TiO2 NPs using kappa-carrageenan (κ-carrageenan), not just as a reducing and stabilizing agent but as a dopant for the resulting TiO2 NPs. During the synthesis of TiO2 NPs in the presence of sulfate-rich carrageenan, the process predominantly leaves residual sulfur and carbon. The presence of residual carbon, in conjunction with sulfur doping, as indicated by fast FTIR spectra, XPS, and EDX, leads to a significant reduction in the band gap of the resulting composite to 2.71 eV. The reduction of composite band gap yields remarkable degradation of methylene blue (99.97%) and methyl orange (97.84%). This work presents an eco-friendly and highly effective solution for the swift removal of environmentally harmful organic dyes.

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.

Facile synthesis of spongy NiCo2O4 powders for lithium-ion storage

Spongy NiCo₂O₄ powders were prepared by solution combustion synthesis (SCS) method for lithium ions storage. The effects of combustion parameters including fuel type (L-lysine, glycine, and urea) and fuel amount on the lithium storage performance of NiCo₂O₄ powders were analyzed by various characterization techniques. Single-phase NiCo₂O₄ powders with extremely porous microstructure showed a strong drop of initial specific capacity up to 350 mAhg^-1 which was recovered up to 666 mAhg^-1 following 100 charge/discharge cycles. However, the NiCo₂O₄ powders prepared by the urea and L-lysine fuels with the compacted microstructure showed the capacity loss without any recovery. The spongy NiCo₂O₄ powders showed an acceptable capability rate performance (404 mAhg^-1 @ 400 mAg^-1).

Molybdenum Oxynitride Atomic Nanoclusters Bonded in Nanosheets of N-Doped Carbon Hierarchical Microspheres for Efficient Sodium Storage

Transition metal nitrides have attracted considerable attention as great potential anode materials due to their excellent metallic conductivity and high theoretical specific capacity. However, their cycling performance is impeded by their instability caused by the reaction mechanism. Herein, we report the engineering and synthesis of a novel hybrid architecture composed of MoO_2.0N_0.5 atomic nanoclusters bonded in nanosheets of N-doped carbon hierarchical hollow microspheres (MoO_2.0N_0.5/NC) as an anode material for sodium-ion batteries. The facile self-templating strategy for the synthesis of MoO_2.0N_0.5/NC involves chemical polymerization and subsequent one-step calcination treatments. The design is beneficial to improve the electrochemical kinetics, buffer the volume variation of electrodes during cycling, and provide more interfacial active sites for sodium uptake. Due to these unique structural and compositional merits, these MoO_2.0N_0.5/NC exhibits excellent sodium storage performance in terms of superior rate capability and stable long cycle life. The work shows a feasible and effective way to design novel host candidates and solve the long-term cycling stability issues for sodium-ion batteries.

A Novel Hybrid Point Defect of Oxygen Vacancy and Phosphorus Doping in TiO2 Anode for High-Performance Sodium Ion Capacitor

Although sodium ion capacitors (SICs) are considered as one of the most promising electrochemical energy storage devices (organic electrolyte batteries, aqueous batteries and supercapacitor, etc.) due to the combined merits of battery and capacitor, the slow reaction kinetics and low specific capacity of anode materials are the main challenges. Point defects including vacancies and heteroatoms doping have been widely used to improve the kinetics behavior and capacity of anode materials. However, the interaction between vacancies and heteroatoms doping have been seldomly investigated. In this study, a hybrid point defects (HPD) engineering has been proposed to synthesize TiO₂ with both oxygen vacancies (OVs) and P-dopants (TiO₂/C-HPD). In comparison with sole OVs or P-doping treatments, the synergistic effects of HPD on its electrical conductivity and sodium storage performance have been clarified through the density functional theory calculation and sodium storage characterization. As expected, the kinetics and electronic conductivity of TiO₂/C-HPD3 are significantly improved, resulting in excellent rate performance and outstanding cycle stability. Moreover, the SICs assembled from TiO₂/C-HPD3 anode and nitrogen-doped porous carbon cathode show outstanding power/energy density, ultra-long life with good capacity retention. This work provides a novel point defect engineering perspective for the development of high-performance SICs electrode materials.

High content anion (S/Se/P) doping assisted by defect engineering with fast charge transfer kinetics for high-performance sodium ion capacitors

The rate-determining process for sodium storage in TiO₂ is greatly depending on charge transfer happening in the electrode materials owing to its inferior diffusion coefficient and electronic conductivity. Apart from reducing the diffusion distance of ion/electron, the increasement of ionic/electronic mobility in the crystal lattice is also very important for charge transport. Here, an oxygen vacancy (OV) engineering assisted in high-content anion (S/Se/P) doping strategy to enhance charge transfer kinetics for ultrafast sodium-storage performance is proposed. Theoretical calculations indicate that OV-engineering evokes spontaneous S doping into the TiO₂ phase and achieves high dopant concentration to bring about impurity state electron donor and electronic delocalization over S occupied sites, which can largely reduce the migration barrier of Na⁺. To realize the speculation, high-content anion doped anatase TiO₂/C composites (9.82 at% for S in A-TiO_2-x-S/C) are elaborately designed. The optimized A-TiO_2-x-S/C anode exhibits extraordinarily high-rate capability with 209.6 mAh g^-1 at 5000 mA g^-1. The assembled sodium ion capacitors deliver an ultrahigh energy density of 150.1 Wh kg^-1 at a power density of 150 W kg^-1 when applied as anode materials. This work provides a new strategy to realize high content anion doping concentration, and enhances the charge transfer kinetics for TiO₂, which delivers an efficient approach for the design of electrode materials with fast kinetic.

Two-Dimensional Organic/Inorganic Hybrid Nanosheet Electrodes for Enhanced Electrical Conductivity toward Stable and High-Performance Sodium-Ion Batteries

To investigate the effect of electrical conductivity on the energy-storage characteristics of anode materials in sodium-ion batteries, covalent organic nanosheets (CONs) are hybridized with highly conductive graphene nanosheets (GNs) via two different optimized synthesis routes, that is, reflux and solvothermal methods. The reflux-synthesized hybrid shows a well-overlapped 2D structure, whereas the solvothermally prepared hybrid forms a segregated phase in which the contact area between the CONs and GNs is reduced. These two hybrids synthesized by facile methods are fully characterized, and the results reveal that their energy-storage properties can be significantly improved by enhancing the electrical conductivity via the formation of a well-overlapped structure between CONs and GNs. The discharge capacity and rate capability of the reflux-synthesized hybrid was considerably larger than that of the bare CONs, highlighting that the improvement in the charge-carrier transport properties can improve the accessibility of Na ions to the surface of the hybrids. This synthetic methodology can be extended to the fabrication of high-performance anodes for Na-ion batteries.

Facile Synthesis of Graphene with Fast Ion/Electron Channels for High-Performance Symmetric Lithium-Ion Capacitors

With the battery-type anode and capacitor-type cathode, lithium-ion capacitors (LICs) are expected to exhibit both high energy and high power density but suffer from the mismatch of the electrode reaction kinetics and capacity. Herein, to alleviate the mismatch between the two electrodes and synergistically enhance the energy/power density, we design a method of microwave irradiation reduction to prepare graphene-based electrode material (MRPG/CNT) with fast ion/electron pathway. The three-dimensional structure of CNT intercalation to graphene inhibits the restacking of graphene sheets and improves the conductivity of the electrode material, resulting a rapid ion and electron diffusion channel. Due to its specific properties, MRPG/CNT materials can be used as both anode and cathode electrodes of LICs at the same time. As anode, MRPG/CNT shows a high capacity of 1200 mAh g^-1 as well as high rate performance. As cathode, MRPG/CNT displays a high capacity of 108 mAh g^-1 and the capacity retention of 100% after 8000 cycles. Coupling the prelithiated MRPG/CNT anode with MRPG/CNT cathode gives a full-graphene-based symmetric LIC, which achieves a high energy density of 232.6 Wh kg^-1 at 226.0 W kg^-1, 111.2 Wh kg^-1 at the ultrahigh power density of 45.2 kW kg^-1, and superior capacity retention of 86% after 5000 cycles. The structure design of this electrode provides a new strategy for alleviating the mismatch of LIC electrodes and constructing high-performance symmetrical LICs.

A Bifunctional-Modulated Conformal Li/Mn-Rich Layered Cathode for Fast-Charging, High Volumetric Density and Durable Li-Ion Full Cells

Lithium- and manganese-rich (LMR) layered cathode materials hold the great promise in designing the next-generation high energy density lithium ion batteries. However, due to the severe surface phase transformation and structure collapse, stabilizing LMR to suppress capacity fade has been a critical challenge. Here, a bifunctional strategy that integrates the advantages of surface modification and structural design is proposed to address the above issues. A model compound Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (MNC) with semi-hollow microsphere structure is synthesized, of which the surface is modified by surface-treated layer and graphene/carbon nanotube dual layers. The unique structure design enabled high tap density (2.1 g cm^-3) and bidirectional ion diffusion pathways. The dual surface coatings covalent bonded with MNC via C-O-M linkage greatly improves charge transfer efficiency and mitigates electrode degradation. Owing to the synergistic effect, the obtained MNC cathode is highly conformal with durable structure integrity, exhibiting high volumetric energy density (2234 Wh L^-1) and predominant capacitive behavior. The assembled full cell, with nanographite as the anode, reveals an energy density of 526.5 Wh kg^-1, good rate performance (70.3% retention at 20 C) and long cycle life (1000 cycles). The strategy presented in this work may shed light on designing other high-performance energy devices.