Nanoflakes of Ni-Co LDH and Bi2O3 Assembled in 3D Carbon Fiber Network for High-Performance Aqueous Rechargeable Ni/Bi Battery

Hierarchical bismuthyl bromide microspheres assembled by laminas as efficient negative material for aqueous alkali battery

Bismuth (Bi) based compounds are promising negative materials in aqueous alkali batteries (AABs) for the 3-electron redox chemistry of Bi element within low potentials, the exploration of new Bi-based negative materials is still a meaningful work in this field. Herein, a hierarchical bismuthyl bromide (BiOBr) microspheres material assembled by laminas was prepared via solvothermal reaction and attempted as negative battery material for AAB. The pronounced redox reactions of Bi species in low potential enable high battery capacity, and the porous texture with high hydrophilicity facilitates diffusion of OH- and participation in faradaic reactions. When used as negative battery electrode, the BiOBr could offer decent specific capacity (Cs, 190 mAh g-1 at 1 A g-1), rate capability (Cs remained to 163 mAh g-1 at 8 A g-1) and cycleability (85% Cs retention after 1000 charge-discharge cycles). The AAB based on BiOBr negative electrode could export an energy density (Ecell) of 61.5 Wh kg-1 at power density (Pcell) of 558 W kg-1 and good cycleability. The current work showcases valuable application expansion of a traditional BiOBr photocatalyst in battery typed charge storage.

Carbon-Hybridized Hydroxides for Energy Conversion and Storage: Interface Chemistry and Manufacturing

Carbon-hybridized hydroxides (CHHs) have been intensively investigated for uses in the energy conversion/storage fields. Nevertheless, the intrinsic structure-activity relationships between carbon and hydroxides within CHHs are still blurry, which hinders the fine modulation of CHHs in terms of practical applications to some degree. This review aims to figure out the intrinsic role of carbon materials in CHHs with a focus on the interface chemistry and the engineering strategy in-between two components. The fundamental effects of the carbon materials in enhancing the charge/mass transfer kinetics are first analyzed, particularly the extra electron pathways for fast charge transfer and the anchoring sites for boosting the mass transfer. Subsequently, the surface-guided/confined effects of carbon materials in CHHs to modify the morphology and tailor the hydroxides, and functional heterojunction for regulating the inner electronic structure are decoupled. The methods to efficiently construct a stable yet robust solid-solid heterointerface are summarized, including oxygen functional groups engrafting, topological defective sites construction and heteroatom incorporation to activate the inert carbon surface. The smart CHHs in some typical energy applications are demonstrated. Additionally, the methodologies that can reveal the hybridization electron configuration between two components are summed up. At last, the perspective and challenges faced by the CHHs for energy-related applications are outlined.

Iron-selenide-based titanium dioxide nanocomposites as a novel electrode material for asymmetric supercapacitors operating at 2.3 V

This study portrays a facile wet-chemical synthesis of FeSe2/TiO2 nanocomposites for the first time for advanced asymmetric supercapacitor (SC) energy storage applications. Two different composites were prepared with varying ratios of TiO2 (90 and 60%, symbolized as KT-1 and KT-2) and their electrochemical properties were investigated to obtain an optimized performance. The electrochemical properties showed excellent energy storage performance owing to faradaic redox reactions from Fe2+/Fe3+ while TiO2 due to Ti3+/Ti4+ with high reversibility. Three-electrode designs in aqueous solutions showed a superlative capacitive performance, with KT-2 performing better (high capacitance and fastest charge kinetics). The superior capacitive performance drew our attention to further employing the KT-2 as a positive electrode to fabricate an asymmetric faradaic SC (KT-2//AC), exceeding exceptional energy storage performance after applying a wider voltage of 2.3 V in an aqueous solution. The constructed KT-2/AC faradaic SCs significantly improved electrochemical parameters such as capacitance of 95 F g-1, specific energy (69.79 Wh kg-1), and specific power delivery of 11529 W kg-1. Additionally, extremely outstanding durability was maintained after long-term cycling and rate performance. These fascinating findings manifest the promising feature of iron-based selenide nanocomposites, which can be effective electrode materials for next-generation high-performance SCs.

High-performance aqueous rechargeable nickel//bismuth batteries with Bi2MoO6@rGO and Co0.5Ni0.5MoO4@rGO as electrode materials

Aqueous rechargeable nickel–bismuth batteries have surfaced as a prospective energy storage and conversion system because of their merits of good safety, high power density, and low cost.

Hierarchical Heterostructure Engineering of Layered Double Hydroxides on Nickel Sulfides Heteronanowire Arrays as Efficient Cathode for Alkaline Aqueous Zinc Batteries

Aqueous alkaline rechargeable nickel-zinc (Ni-Zn) batteries possess great potential for large-scale energy storage systems because of their high output voltage, cheap cost, and intrinsic safety. However, the practical applicability of Ni-Zn batteries has been limited by traditional Ni-based cathodes with low capacity and poor cycle stability. Rational design of electrode structure and composition is highly desired but still significantly challenging. Herein, uniform self-supported hierarchical heterostructure composites interacting NiCo-layered double hydroxide with 1D nickel sulfides heteronanowire rooted on Ni foam (NF\Ni₃ S₂ /NiS@NiCo-LDH) are successfully developed by a hydrothermal sulfurization-electrodeposition process. The self-supported 3D hierarchical heterostructured composites nanoarray provides abundant reactive sites, rapid ion diffusion channels, and fast electron transfer routes, as well as strong structural stability. More significantly, the strong interfacial charge transfer between Ni₃ S₂ /NiS heteronanowire and NiCo-LDH effectively modifies the electronic structure of the composites and thereby improving the reaction kinetics. Consequently, the NF\Ni₃ S₂ /NiS@NiCo-LDH electrode presents a superior capacity of 434.5 mAh g^-1 (1.73 mAh cm^-2 ) at 3 mA cm^-2 . In addition, the fabricated NF\Ni₃ S₂ /NiS@NiCo-LDH//Zn battery can offer a maximal energy density and power density as large as 556.3 Wh kg^-1 and 26.3 kW kg^-1 , respectively, as well as an exceptional cycling performance.

Highly stable, stretchable, and versatile electrodes by coupling of NiCoS nanosheets with metallic networks for flexible electronics

The rapid development of portable electronics has contributed to an urgent demand for versatile and flexible electrodes of wearable energy storage devices and pressure sensors. We fabricate a stretchable electrode by coupling the nickel-cobalt sulfide (NiCoS) nanosheet layer with Ag@NiCo nanowire (NW) networks. NiCoS wrinkled nanostructure, highly conductive networks, and intense interactions between substrate/networks and active materials/networks endow the electrodes with excellent energy storage capacity, superior electrochemical/mechanical stability, and good conductivity. A high-performance asymmetric supercapacitor is developed using the composite electrode. It operates in a wide potential window of 1.4 V and achieves a maximum energy density of 40.0 W h kg^-1 at a power density of 1.1 kW kg^-1; it also exhibits excellent mechanical flexibility and good waterproof performance. Moreover, a sandwiched capacitive pressure sensor constructed using the same electrodes has a wide sensing range (up to 260 kPa), low detection limit (∼47 mN), fast response (∼66 ms), and excellent mechanical stability (10 000 cycles). This study demonstrates that the appropriate design of the functional electrode facilitates the construction of various high-performance devices, denoting the versatility of our electrodes in the development of wearable electronics.

Bismuth Nanoparticles Encapsulated in Nitrogen-Rich Porous Carbon Nanofibers as a High-Performance Anode for Aqueous Alkaline Rechargeable Batteries

The aqueous alkaline rechargeable batteries (AARBs) have an attractive potential for electrochemical energy storage devices. In view of the advantages of high theoretical capacity and desirable negative operating window, bismuth (Bi) has been deemed as a hopeful anode material for AARBs. Unfortunately, intensive reported works of Bi anode are still confronted with limited capacity and poor cycling stability. Herein, the designed electrodes of different size Bi nanoparticles embedded in porous carbon nanofibers with a contrasting nitrogen doping content are obtained by electrospinning and thermal treatment processes. The effect of the N dopant in carbon shell is demonstrated on the Bi core, which is in favor of enhancing the capacity of Bi anodes. More importantly, the core structure with highly dispersed ultrasmall Bi nanoparticles (<20 nm) in carbon matrix plays a crucial role in long-term durability. Accordingly, the optimized polydisperse ultrasmall Bi nanoparticles confined in N-rich porous carbon nanofibers electrode (Bi@NPCF) presents an admirable capacity of 196.1 mAh g^-1 at 3 A g^-1 and outstanding durable lifespan (retain 116.95% after 10 000 cycles). In addition, the fabricated Bi@NPCF//NiCo₂ O₄ battery exhibits an exceptional energy and power density with durable stability (95.9% after 5000 cycles).

Oxygen-vacancy abundant alpha bismuth oxide with enhanced cycle stability for high-energy hybrid supercapacitor electrodes

Bi₂O₃ is an outstanding electrode material due to its high theoretical specific capacity. Hence, the synthesis of δ-Bi₂O₃ materials with high oxygen-vacancy contents could improve their electrochemical performances but causes easy conversion to α-Bi₂O₃ with low oxygen-vacancy contents, leading to poor cycling stability and limited practical applications. To overcome these problems, an effective strategy for constructing high oxygen vacancies α-Bi₂O₃ on activated carbon fiber paper (ACFP) is developed in this study. To this end, ACFP/Bi(OH)₃ is first synthesized by the solvothermal method and then converted to ACFP/α-Bi₂O₃ by in situ electrochemical activation. The proposed innovative electrochemical method quickly and easily introduces oxygen vacancies while preserving the three-dimensional structure, thereby promoting the charge transfer and ions diffusion in ACFP/α-Bi₂O₃. Consequently, the specific capacity of ACFP/α-Bi₂O₃ reaches 906C g^-1 at 1 A g^-1, and the capacity retention remains above 70% after 3000 cycles, a value higher than that of δ-Bi₂O₃ (45%). Furthermore, the hybrid supercapacitor device assembled by ACFP/α-Bi₂O₃ delivers a maximum energy density of 114.9 Wh kg^-1 at 900 W kg^-1 and outstanding cycle stability with 73.56 % retention after 5500 cycles. In sum, the proposed ACFP/α-Bi₂O₃ with high performance and good stability looks promising for use as bismuth-based anode materials in supercapacitors and aqueous batteries.

Mechanism orienting structure construction of electrodes for aqueous electrochemical energy storage systems: a review

Aqueous electrochemical energy storage systems (AEESS) are considered as the most promising energy storage devices for large-scale energy storage. AEESSs, including batteries and supercapacitors, have received extensive attention due to their low cost, eco-friendliness, and high safety. However, the insufficient energy densities of the state-of-the-art AEESSs limit their practical applications which are mainly dominated by the electrochemical performances of individual electrode materials. Understanding the underlying relationship between structures, reaction mechanisms, and performances can further lead to the design and optimization of structures of the electrodes instructively, thereby harvesting favorable performances. This review classified the intrinsic logic of structure-mechanism-performance by taking some prevailing mechanisms with some classical structures of materials as examples. Moreover, some problem-oriented structural engineering strategies are proposed aiming to optimize their performance. Finally, comprehensive structural design engineering and some suggestions for fine modifications of electrode materials at the atomic and molecular levels are proposed to combine the advantages of supercapacitor- and battery-type materials for designing excellent electrode materials for AEESSs.

Extending effective microwave absorbing bandwidth of CoNi bimetallic alloy derived from binary hydroxides

Effectively broadening microwave absorbing frequency of pure magnetic substances remains a huge challenge. Herein, micro-perspective structures can be controlled through a calcination route. Satisfactorily, the composites prepared at the calcination temperature of 900 °C exhibit excellent microwave attenuation performance with a broad working frequency and appropriate paraffin filling ratio. Remarkably, the composites can reach an extremely high reflection loss (RL) value of - 49.79 dB, and the extended effective working frequency range (RL < - 10 dB) of 6.84 GHz can also be obtained. Superb magnetic loss, admirable dielectric loss, sufficient dipole polarization, as well as superior impedance matching should be band together for obtaining ideal microwave absorbers. The CoNi hydroxides derived bimatallic alloy composites were fabricated via a cost-effective and facile synthesis process, and this work aroused inspirations of designing high-performance microwave absorbers for mataining the sustainable development.

Tuning wall thickness of TiO2 microtubes for an enhanced photocatalytic activity with thickness-dependent charge separation efficiency

TiO₂ microtubes with tunable wall thickness have been synthesized by a one-step electrospinning method linked with a calcination process. The wall thickness of TiO₂ microtubes can be easily tuned by altering the dosage of liquid paraffin. The influence of the thickness on the light-harvesting ability and separation efficiency of the photogenerated carriers was studied using ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy, photoluminescence emission spectroscopy, and photocurrent density measurements. Results show that TiO₂ microtubes with an appropriate thickness exhibit enhanced light scattering effect, UV-vis light-harvesting ability, charge separation efficiency, and photocatalytic performance. The degradation rates of rhodamine B and 2,4-dinitrophenol by using TiO₂ microtubes synthesized at a dosage of 0.14 g/mL liquid paraffin are 99.9% within 60 min and 97.8% within 40 min, respectively, which are higher than most of the reported values. All these results suggest that our work provides an ideal strategy for adjusting the wall thickness of TiO₂ microtubes and new approach to enhance the photocatalytic performance of TiO₂.

Transformation of 2D Planes into 3D Soft and Flexible Structures with Embedded Electrical Functionality

Three-dimensional (3D) structures composed of flexible and soft materials have been in demand for implantable biomedical devices. However, the fabrication of 3D structures using microelectromechanical system (MEMS) techniques has limitations in terms of the materials and the scale of the structures. Here, a technique to selectively bond polydimethylsiloxane (PDMS) and parylene-C by plasma treatment is reported, with which two-dimensional structures that are fabricated using MEMS techniques are turned into 3D structures by the inflation of selectively non-bonded patterns. The bonding strength and the bonding mechanism were analyzed by mechanical tests and chemical analyses, respectively. We fabricated soft and flexible 3D structures with various patterns and dimensions, even with embedded electrical functions, including light emitting diodes and electrocorticogram electrodes. Based on these results, the flexible, soft, and MEMS-capable 3D structures that are obtained by the developed selective bonding technique are promising for applications in a wide range of biomedical applications.

(Ni,Co)Se2 /NiCo-LDH Core/Shell Structural Electrode with the Cactus-Like (Ni,Co)Se2 Core for Asymmetric Supercapacitors

Supercapacitors (SCs) have been widely studied as a class of promising energy-storage systems for powering next-generation E-vehicles and wearable electronics. Fabricating hybrid-types of electrode materials and designing smart nanoarchitectures are effective approaches to developing high-performance SCs. Herein, first, a Ni-Co selenide material (Ni,Co)Se₂ with special cactus-like structure as the core, to scaffold the NiCo-layered double hydroxides (LDHs) shell, is designed and fabricated. The cactus-like structural (Ni,Co)Se₂ core, as a highly conductive and robust support, promotes the electron transport as well as hinders the agglomeration of LDHs. The synergistic contributions from the two types of active materials together with the superior properties of the cactus-like nanostructure enable the (Ni,Co)Se₂ /NiCo-LDH hybrid electrode to exhibit a high capacity of ≈170 mA h g^-1 (≈1224 F g^-1 ), good rate performance, and long durability. The as-assembled (Ni,Co)Se₂ /NiCo-LDH//PC (porous carbon) asymmetric supercapacitor (ASC) with an operating voltage of 1.65 V delivers a high energy density of 39 W h kg^-1 at a power density of 1650 W kg^-1 . Therefore, the cactus-like core/shell structure offers an effective pathway to engineer advanced electrodes. The assembled flexible ASC is demonstrated to effectively power electronic devices.

Construction of MOF-derived hollow Ni-Zn-Co-S nanosword arrays as binder-free electrodes for asymmetric supercapacitors with high energy density

Mixed transition metal sulfides with hollow structures hold great promise for energy-related applications. However, most of them are in the powder form, which should be mixed with unwanted polymer binders and conductive agents. In this study, a facile two-step strategy has been developed to grow mesoporous and hollow Ni-Zn-Co-S nanosword arrays (NSAs) on a nickel foam (NF) substrate with robust adhesion, which involves the hydrothermal growth of bimetallic Zn-Co-ZIF NSAs on NF and subsequent transformation into hollow Ni-Zn-Co-S NSAs through the sulfurization process. Benefiting from the unique structural and compositional advantages as well as directly grown conductive substrate, the Ni-Zn-Co-S-0.33 NSAs/NF electrode exhibits the best electrochemical performance when investigated as a binder-free electrode for supercapacitors. Impressively, the Ni-Zn-Co-S-0.33 NSAs/NF electrode delivers a high areal capacity of 1.11 mA h cm^-2 at the current density of 10 mA cm^-2, and the corresponding specific capacity is as high as 358.1 mA h g^-1. Moreover, an asymmetric supercapacitor (ASC) device based on the Ni-Zn-Co-S-0.33 NSAs/NF as the positive electrode and Bi₂O₃/NF as the negative electrode has been successfully fabricated, and can deliver a high energy density of 91.7 W h kg^-1 at a power density of 458 W kg^-1 and maintain the energy density of 66.9 W h kg^-1 at a high power density of 6696 W kg^-1. The electrochemical results suggest that the hollow Ni-Zn-Co-S NSAs would possess great potential for applications in high-performance supercapacitors.

In Situ Activation of 3D Porous Bi/Carbon Architectures: Toward High-Energy and Stable Nickel-Bismuth Batteries

To achieve high-energy and stable aqueous rechargeable batteries, state-of-the art of anode materials are needed. Bismuth (Bi) has recently emerged as an attractive anode material due to its highly reversible redox reaction and suitable negative operating working window. However, the capacity and durability of currently reported Bi anodes are still far from satisfactory. Here, an in situ activation strategy is reported to prepare a 3D porous high-density Bi nanoparticles/carbon architecture (P-Bi-C) as an efficient anode for nickel-bismuth batteries. Taking advantages of the fast channels for charge transfer and ion diffusion, enhanced wettability, and accessible surface area, the highly loaded P-Bi-C electrode delivers a remarkable capacity of 2.11 mA h cm^-2 as well as high rate capability (1.19 mA h cm^-2 at 120 mA cm^-2 ). To highlight, a robust aqueous rechargeable Ni//Bi battery based on the P-Bi-C anode is first constructed, achieving decent capacity (141 mA h g^-1 ), impressive durability (94% capacity retention after 5000 cycles), and admirable energy density (16.9 mW h cm^-3 ). This work paves the way for designing superfast nickel-bismuth batteries with high energy and long-life and may inspire new development for aqueous rechargeable batteries.

A flexible rechargeable quasi-solid-state Ni–Fe battery based on surface engineering exhibits high energy and long durability

With the rapid development of portable and wearable electronics, energy storage devices featuring high energy and power densities, long-cycle lifetime, environment friendliness, safe operation, lightweight, ultrathin thickness and flexibilityl have become increasingly important.