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

Metal Selenide-Based Superstructure Nanoarrays with Ultrahigh Capacity for Alkaline Zn Batteries

Transition metal selenides (TMSs) have great potential as cathode materials for alkaline Zn batteries (AZBs) owing to their high theoretical capacity and metallic conductivity. However, achieving a high specific capacity remains a formidable challenge due to the low structural stability and sluggish reaction kinetics of single-phase TMS. Herein, a facile method for fabricating a robust CoSe2@Ni3Se4@Ni(OH)2 superstructure nanoarray (CNSNA) as an AZB cathode is presented. The sophisticated design enables structural stability and abundant active surface sites for efficient charge storage. Furthermore, the redox mediator K3[Fe(CN)6] is employed to expedite the reaction kinetics and introduce supplementary redox reactions, further enhancing the charge storage capability. Consequently, the CNSNA electrode delivers an exceptional specific capacitance (609.08 mAh g-1 at 1 A g-1), surpassing all previously reported selenide-based materials. High-rate capability (239.37 mAh g-1 at 20 A g-1) and long cycling stability have also been achieved. The comprehensive charge storage mechanism studies confirmed the structural integrity, kinetic improvement, and high reactivity of the CNSNA superstructure. Moreover, the corresponding AZB based on CNSNA demonstrates an extraordinarily high energy density of 516.58 Wh kg-1. The work offers guidance in the construction of superstructure-based TMS electrode materials, paving the way for the development of high-performance AZBs.

Morphological control and performance engineering of Co-based materials for supercapacitors

As one of the most promising energy storage devices, supercapacitors exhibit a higher power density than batteries. However, its low energy density usually requires high-performance electrode materials. Although the RuO2 material shows desirable properties, its high cost and toxicity significantly limit its application in supercapacitors. Recent developments demonstrated that Co-based materials have emerged as a promising alternative to RuO2 for supercapacitors due to their low cost, favorable redox reversibility and environmental friendliness. In this paper, the morphological control and performance engineering of Co-based materials are systematically reviewed. Firstly, the principle of supercapacitors is briefly introduced, and the characteristics and advantages of pseudocapacitors are emphasized. The special forms of cobalt-based materials are introduced, including 1D, 2D and 3D nanomaterials. After that, the ways to enhance the properties of cobalt-based materials are discussed, including adding conductive materials, constructing heterostructures and doping heteroatoms. Particularly, the influence of morphological control and modification methods on the electrochemical performances of materials is highlighted. Finally, the application prospect and development direction of Co-based materials are proposed.

Cobalt sulfide flower-like derived from metal organic frameworks on nickel foam as an electrode for fabrication of asymmetric supercapacitors

Metal-organic frameworks, as a kind of advanced nanoporous materials with metal centers and organic linkers, have been applied as promising electrode materials in energy storage devices. In this study, we are successfully prepared cobalt sulfide nanosheets (CoS) derived from the metal-organic framework on nickel foam (NF). The prepared electrodes are characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, Brunauer-Emmett-Teller and Barrett-Joyner-Halenda and electrochemical methods like voltammetry, galvanostatic charge-discharge curve and electrochemical impedance spectroscopy. The CoS/NF electrode demonstrates a high specific capacity of 377.5 mA h g-1 (1359 C g-1) at the current density of 2 A g-1, considerable rate performance and excellent durability (89.4% after 4000 cycles). A hybrid supercapacitor is assembled using CoS/NF as the positive electrode and activated carbon as the negative electrode, it shows a high energy density of 57.4 W h kg-1 at a power density of 405.2 W kg-1. The electrochemical results suggest that the CoS nanosheet arrays would possess excellent potential for applications in energy storage devices.

Interconnected CoNi-Se Hollow Flakes through Reduced Graphene Oxide Sheets as a Cathode Material for Hybrid Supercapacitors

Achieving a high energy density and long-cycle stability in energy storage devices demands competent electrochemical performance, often contingent on the innovative structural design of materials under investigation. This study explores the potential of transition metal selenide (TMSe), known for its remarkable activity, electronic conductivity, and stability in energy storage and conversion applications. The innovation lies in constructing hollow structures of binary metal selenide (CoNi-Se) at the surface of reduced graphene oxide (rGO) arranged in a three-dimensional (3D) morphology (CoNi-Se/rGO). The 3D interconnected rGO architecture works as a microcurrent collector, while porous CoNi-Se sheets originate the active redox centers. Electrochemical analysis of CoNi-Se/rGO based-electrode reveals a distinct faradic behavior, thereby resulting in a specific capacitance of 2957 F g-1 (1478.5 C g-1), surpassing the bare CoNi-Se with a value of 2149 F g-1 (1074.5 C g-1) at a current density of 1 A g-1. Both materials exhibit exceptional high-rate capabilities, retaining 83% of capacitance at 10 A g-1 compared to 1 A g-1. In a two-electrode coin cell system, the device achieves a high energy density of 73 Wh kg-1 at a power density of 1500 W kg-1, stating an impressive 90.4% capacitance retention even after enduring 20,000 cycles. This study underscores the CoNi-Se/rGO composite's promise as a superior electrode material for high-performance energy storage applications.

Binder-Free MOF-Based and MOF-Derived Nanoarrays for Flexible Electrochemical Energy Storage: Progress and Perspectives

The fast development of Internet of Things and the rapid advent of next-generation versatile wearable electronics require cost-effective and highly-efficient electroactive materials for flexible electrochemical energy storage devices. Among various electroactive materials, binder-free nanostructured arrays have attracted widespread attention. Featured with growing on a conductive and flexible substrate without using inactive and insulating binders, binder-free 3D nanoarray electrodes facilitate fast electron/ion transportation and rapid reaction kinetics with more exposed active sites, maintain structure integrity of electrodes even under bending or twisted conditions, readily release generated joule heat during charge/discharge cycles and achieve enhanced gravimetric capacity of the whole device. Binder-free metal-organic framework (MOF) nanoarrays and/or MOF-derived nanoarrays with high surface area and unique porous structure have emerged with great potential in energy storage field and been extensively exploited in recent years. In this review, common substrates used for binder-free nanoarrays are compared and discussed. Various MOF-based and MOF-derived nanoarrays, including metal oxides, sulfides, selenides, nitrides, phosphides and nitrogen-doped carbons, are surveyed and their electrochemical performance along with their applications in flexible energy storage are analyzed and overviewed. In addition, key technical issues and outlooks on future development of MOF-based and MOF-derived nanoarrays toward flexible energy storage are also offered.

Coaxial nickel cobalt selenide/nitrogen-doped carbon nanotube array as a three-dimensional self-supported electrode for electrochemical energy storage

Herein, we propose a one-step urea pyrolysis method for preparing a nitrogen-doped carbon nanotube array grown on carbon fiber paper, which is demonstrated as a three-dimensional scaffold for constructing a nickel cobalt selenide-based coaxial array structure. Thanks to the large surface area, interconnected porous structure, high mass loading, as well as fast electron/ion transport pathway of the coaxial array structure, the nickel cobalt selenide/nitrogen-doped carbon nanotube electrode exhibits over 7 times higher areal capacity than that directly grown on carbon fiber paper, and better rate capability. The cell assembled by a nickel cobalt selenide/nitrogen-doped carbon nanotube positive electrode and an iron oxyhydroxide/nitrogen-doped carbon nanotube negative electrode delivers a volumetric capacity of up to 22.5 C cm-3 (6.2 mA h cm-3) at 4 mA cm-2 and retains around 86% of the initial capacity even after 10 000 cycles at 10 mA cm-2. A volumetric energy density of up to 4.9 mW h cm-3 and a maximum power density of 208.1 mW cm-3 are achieved, and is comparable to, if not better than, those of similar energy storage devices reported previously.

Layered Double Hydroxide Nanosheets: Synthesis Strategies and Applications in the Field of Energy Conversion

In recent years, layered double hydroxides (LDH) nanosheets have garnered substantial attention as intriguing inorganic anionic layered clay materials. These nanosheets have captured the attention of researchers due to their unique physicochemical properties. This review aims to showcase the latest advancements in laboratory research concerning LDH nanosheets, with a specific emphasis on their methods of preparation. This review provides detailed insights into the factors influencing the anionic conductivity of LDH, along with delineating the applications of LDH nanosheets in the realm of energy conversion. Notably, the review highlights the crucial role of LDH nanosheets in the oxygen evolution reaction (OER), a vital process in water splitting and diverse electrochemical applications. The review emphasizes the significant potential of LDH nanosheets in enhancing supercapacitor technology, owing to their high surface area and exceptional charge storage capacity. Additionally, it elucidates the prospective application of LDH nanosheets as anion exchange membranes in anion exchange membrane fuel cells, potentially revolutionizing fuel cell performance through improved efficiency and stability facilitated by enhanced ion transport properties.

Atomic Layer Deposition-A Versatile Toolbox for Designing/Engineering Electrodes for Advanced Supercapacitors

Atomic layer deposition (ALD) has become the most widely used thin-film deposition technique in various fields due to its unique advantages, such as self-terminating growth, precise thickness control, and excellent deposition quality. In the energy storage domain, ALD has shown great potential for supercapacitors (SCs) by enabling the construction and surface engineering of novel electrode materials. This review aims to present a comprehensive outlook on the development, achievements, and design of advanced electrodes involving the application of ALD for realizing high-performance SCs to date, as organized in several sections of this paper. Specifically, this review focuses on understanding the influence of ALD parameters on the electrochemical performance and discusses the ALD of nanostructured electrochemically active electrode materials on various templates for SCs. It examines the influence of ALD parameters on electrochemical performance and highlights ALD's role in passivating electrodes and creating 3D nanoarchitectures. The relationship between synthesis procedures and SC properties is analyzed to guide future research in preparing materials for various applications. Finally, it is concluded by suggesting the directions and scope of future research and development to further leverage the unique advantages of ALD for fabricating new materials and harness the unexplored opportunities in the fabrication of advanced-generation SCs.

High-Performance Supercapacitors Using Hierarchical And Sulfur-Doped Trimetallic NiCo/NiMn Layered Double Hydroxides

A supercapacitor features high power density and long cycling life. However, its energy density is low. To ensemble a supercapacitor with high power- and energy-densities, the applied capacitor electrodes play the key roles. Herein, a high-performance capacitive electrode is designed and grown on a flexible carbon cloth (CC) substrate via a hydrothermal reaction and a subsequent ion exchange sulfuration process. It has a 3D heterostructure, consisting of sulfur-doped NiMn-layered double hydroxide (LDH) nanosheets (NMLS) and sulfur-doped NiCo-LDH nanowires (NCLS). The electrode with sheet-shaped NMLS and wire-shaped NCLS on their top (NMLS@NCLS/CC) increases the available surface area, providing more pseudocapacitive sites. It exhibits a gravimetric capacity of 555.2 C g-1 at a current density of 1 A g-1 , the retention rate of 75.1% when the current density reaches up to 20 A g-1 , as well as superior cyclic stability. The assembled asymmetric supercapacitor that is composed of a NMLS@NCLS/CC positive electrode and a sulfurized activated carbon negative electrode presents a maximum energy density of 24.2 Wh kg-1 and a maximum power density of 16000 W kg-1 . In this study, a facile strategy for designing hierarchical LDH materials is demonstrated as well as their applications in advanced energy storage systems.

Spongelike Bimetallic Selenides Derived from Prussian Blue Analogue on Layered Ni(II)-Based MOF for High-Efficiency Supercapacitors

Recently, employing metal-organic frameworks (MOFs) as precursors to prepare various metal oxides, sulfides, and selenides has drawn enormous attention in the field of energy storage. In this paper, the nanosheets of an organophosphate-based Ni-MOF were successfully synthesized and employed as the template to prepare the Prussian blue analogue (PBA) nanoslices and nanoparticles on the nanosheet (PBA/Ni-MOF-NS-x h, x h stands for the reaction time.) by an in situ etching method. After selenization by the solvothermal method, the PBA nanoslices and nanoparticles were transformed into spongelike bimetallic selenides (labeled as PBA/Ni-MOF-NS-x h-Se) decorated with some nanoparticles. All of the characterization results including PXRD, SEM, TEM, EDS, XPS, and BET demonstrated the successful transformation. Impressively, the as-synthesized PBA/Ni-MOF-NS-12 h-Se exhibited a high specific capacitance of 1897.90 F g-1 at a current density of 1 A g-1 and a superior capacitance retention rate of 73.32% as the current density increased to 20 A g-1. In addition, the asymmetric supercapacitor device, PBA/Ni-MOF-NS-12 h-Se//AC, delivered a high energy density of 30.69 W h kg-1 at 0.85 kW kg-1 and extraordinary cycling stability with an 83.00% capacitance retention rate over 5000 cycles.

Hierarchical NiCo@NiOOH@CoMoO4 Core-Shell Heterostructure on Carbon Cloth for High-Performance Asymmetric Supercapacitors

The fabrication of low-cost, effective, and highly integrated nanostructured materials through simple and reproducible methods for high-energy-density supercapacitors is highly desirable. Herein, an activated carbon cloth (ACC) is designed as the functional scaffold for supercapacitors and treated hydrothermally to deposit NiCo nanoneedles working as internal core, followed by a dip-dry coating of NiOOH nanoflakes core-shell and uniform hydrothermal deposition of CoMoO4 nanosheets serving as an external shell. The structured core-shell heterostructure ACC@NiCo@NiOOH@CoMoO4 electrode resulted in exceptional specific areal capacitance of 2920 mF cm-2 and exceptional cycling stability for 10 000 cycles. Moreover, the fabricated electrode is developed into an asymmetric supercapacitor which demonstrates excellent areal capacitance, energy density, and power density within the broad potential window of 1.7 V with a cycling life of 92.4% after 10 000 charge-discharge cycles, which reflects excellent cycle life. The distinctive core-shell structure, highly conductive substrate, and synergetic effect of coated material results in more electrochemical active sites and flanges for effective electrons and ion transportation. This unique technique provides a new perspective for cost-efficient supercapacitor applications.

Unleashing the Full Potential of Electrochromic Heterostructured Nickel-Cobalt Phosphate for Optically Active High-Performance Asymmetric Quasi-Solid-State Supercapacitor Devices

The rational design of hybrid systems that combine capacitor and battery merits is crucial to enable the fabrication of high energy and power density devices. However, the development of such systems remains a significant barrier to overcome. Herein, we report the design of a Ni-Co phosphate (Ni3-xCox(PO4)2·8H2O) nanoplatelet-based system via a facile coprecipitation method at ambient conditions. The nanoplatelets exhibit multicomponent synergy, exceptional charge storage capabilities, rich redox active sites (ameliorating the redox reaction activity), and high ionic diffusion rate/electron transfer kinetics. The designed Ni3-xCox(PO4)2·8H2O offered a respectable gravimetric specific capacity and marvelous capability rate (966 and 595 C g-1 at 1 and 15 A g-1) over the Ni3(PO4)2·8H2O (327.3 C g-1) and Co3(PO4)2·8H2O (68 C g-1) counterparts. Additionally, the nanoplatelets showed enhanced photoactive storage performance with a 9.7% increase in the recorded photocurrent density. Upon integration of Ni3-xCox(PO4)2·8H2O as a positive pole and commercial activated carbon as a negative pole, the constructed hybrid supercapacitor device with PVA@KOH quasi-gel electrolyte exhibits great energy and power densities of 77.7 Wh kg-1 and 15998.54 W kg-1 with remarkable cycling stability of 6000 charging/discharging cycles and prominent Coulombic efficiency of 100%. Interestingly, two assembled devices are capable of glowing a red LED bulb for nearly 180 s. This research paves the way to design and fabricate electroactive species via a facile approach for boosting the design of a plethora of supercapattery devices.

Fabrication of Highly Conductive Porous Fe3O4@RGO/PEDOT:PSS Composite Films via Acid Post-Treatment and Their Applications as Electrochemical Supercapacitor and Thermoelectric Material

As a remarkable multifunctional material, ferroferric oxide (Fe3O4) exhibits considerable potential for applications in many fields, such as energy storage and conversion technologies. However, the poor electronic and ionic conductivities of classical Fe3O4 restricts its application. To address this challenge, Fe3O4 nanoparticles are combined with graphene oxide (GO) via a typical hydrothermal method, followed by a conductive wrapping using poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic sulfonate) (PEDOT:PSS) for the fabrication of composite films. Upon acid treatment, a highly conductive porous Fe3O4@RGO/PEDOT:PSS hybrid is successfully constructed, and each component exerts its action that effectively facilitates the electron transfer and subsequent performance improvement. Specifically, the Fe3O4@RGO/PEDOT:PSS porous film achieves a high specific capacitance of 244.7 F g-1 at a current of 1 A g-1. Furthermore, due to the facial fabrication of the highly conductive networks, the free-standing film exhibits potential advantages in flexible thermoelectric (TE) materials. Notably, such a hybrid film shows a high electric conductivity (σ) of 507.56 S cm-1, a three times greater value than the Fe3O4@RGO component, and achieves an optimized Seebeck coefficient (S) of 13.29 μV K-1 at room temperature. This work provides a novel route for the synthesis of Fe3O4@RGO/PEDOT:PSS multifunctional films that possess promising applications in energy storage and conversion.

Dandelion-Like CuCo2O4@ NiMn LDH Core/Shell Nanoflowers for Excellent Battery-Type Supercapacitor

Dandelion-like CuCo₂O₄ nanoflowers (CCO NFs) with ultrathin NiMn layered double hydroxide (LDH) shells were fabricated via a two-step hydrothermal method. The prepared CuCo₂O₄@NiMn LDH core/shell nanoflowers (CCO@NM LDH NFs) possessed a high specific surface area (~181 m²·g^-1) with an average pore size of ~256 nm. Herein, the CCO@NM LDH NFs exhibited the typical battery-type electrode material with a specific capacity of 2156.53 F·g^-1 at a current density of 1 A·g^-1. With the increase in current density, the rate capability retention was 68.3% at a current density of 10 A·g^-1. In particular, the 94.6% capacity of CCO@NM LDH NFs remains after 2500 cycles at 5 A·g^-1. An asymmetric supercapacitor (ASC) with CCO@NM LDH NFs//activated carbon (AC) demonstrates a remarkable capacitance of 303.11 F·g^-1 at 1 A·g^-1 with excellent cycling stability. The coupling and synergistic effects of multi-valence transition metals provide a convenient channel for the electrochemical process, which is beneficial to spread widely within the realm of electrochemical energy storage.

Self-Assembly of Metal-Organic Frameworks on Graphene Oxide Nanosheets and In Situ Conversion into a Nickel Hydroxide/Graphene Oxide Battery-Type Electrode

Graphene oxide (GO) has been widely reported as a supercapacitor electrode. Especially, GO is usually utilized to composite with electrochemical active materials, such as transition-metal oxide/hydroxide/sulfide, due to its considerable conductivity and mechanical strength. However, the ideal design and treatment for compositing GO with active materials are still challenging. Herein, an Ni-metal-organic framework (MOF) was self-assembled on GO nanosheets via the solvothermal method and was subsequently etched into the Ni(OH)₂-GO composite electrode material through a gentle hydrolysis strategy. The GO support enables fast electron transport within the composite material, and the nickel hydroxide growth on GO nanosheets can prevent their aggregation, guaranteeing rapid ion migration. The improved Ni(OH)₂-GO battery-type electrode features outstanding stability (capacity retention of 108% at 8000 cycles) and a considerable specific capacity (SC) of 1007.5 C g^-1 at a current density of 0.5 A g^-1. Compared with MOF-derived Ni(OH)₂ obtained through hydrolysis, Ni(OH)₂-GO only contains 7.41% wt GO, while its SC is almost 50% higher. An asymmetric supercapacitor has an energy density of 65.22 W h kg^-1 and a power density of 395.27 W kg^-1 utilizing p-phenylenediamine-functional reduced GO as the negative electrode, and it can maintain 73.08% capacity during 8000 cycles at a current density of 5 A g^-1.

All Transition Metal Selenide Composed High-Energy Solid-State Hybrid Supercapacitor

Transition metal selenides (TMSs) have enthused snowballing research and industrial attention due to their exclusive conductivity and redox activity features, holding them as great candidates for emerging electrochemical devices. However, the real-life utility of TMSs remains challenging owing to their convoluted synthesis process. Herein, a versatile in situ approach to design nanostructured TMSs for high-energy solid-state hybrid supercapacitors (HSCs) is demonstrated. Initially, the rose-nanopetal-like NiSe@Cu₂ Se (NiCuSe) positive electrode and FeSe nanoparticles negative electrode are directly anchored on Cu foam via in situ conversion reactions. The complementary potential windows of NiCuSe and FeSe electrodes in aqueous electrolytes associated with the excellent electrical conductivity results in superior electrochemical features. The solid-state HSCs cell manages to work in a high voltage range of 0-1.6 V, delivers a high specific energy density of 87.6 Wh kg^-1 at a specific power density of 914.3 W kg^-1 and excellent cycle lifetime (91.3% over 10 000 cycles). The innovative insights and electrode design for high conductivity holds great pledge in inspiring material synthesis strategies. This work offers a feasible route to develop high-energy battery-type electrodes for next-generation hybrid energy storage systems.

Graphene Quantum Dots Pinned on Nanosheets-Assembled NiCo-LDH Hollow Micro-Tunnels: Toward High-Performance Pouch-Type Supercapacitor via the Regulated Electron Localization

A combined delicate micro-/nano-architecture and corresponding surface modification at the nanometer level can co-tailor the physicochemical properties to realize an advanced supercapacitor electrode material. Herein, nanosheets-assembled nickel-cobalt-layered double hydroxide (NiCo-LDH) hollow micro-tunnels strongly coupled with higher-Fermi-level graphene quantum dots (GQDs) are reported. The unique hollow structure endows the electrolyte accessible to more electroactive sites, while 2D nanosheets have excellent surface chemistry, which favors rapid ion/electron transfer, synergistically resulting in more super-capacitive activities. The experimental and density functional theory calculations recognize that such a precise decoration generally tunes the charge density distribution at the near-surface due to the Fermi-level difference of two components, thus regulating the electron localization, while decorating with conductive GQDs co-improves the charge mobility, affording superior capacitive response and electrode integrity. The as-acquired GQDs@LDH-2 electrode yields excellent capacitance reaching ≈1628 F g^-1 at 1 A g^-1 and durable cycling longevity (86.2% capacitive retention after 8000 cycles). When coupled with reduced graphene oxide-based negative electrode, the hybrid device unveils an impressive energy/power density (46 Wh kg^-1 / 7440 W kg^-1 ); moreover, a flexible pouch-type supercapacitor can be constructed based on this hybrid system, which holds high mechanical properties and stable energy and power output at various situations, showcasing superb application prospects.

Ternary NiCeCo-Layered Double Hydroxides Grown on CuBr2@ZIF-67 Nanowire Arrays for High-Performance Supercapacitors

Ternary layered double-hydroxide-based active compounds are regarded as ideal electrode materials for supercapacitors because of their unique structural characteristics and excellent electrochemical properties. Herein, an NiCeCo-layered double hydroxide with a core-shell structure grown on copper bromide nanowire arrays (CuBr₂@NCC-LDH/CF) has been synthesized through a hydrothermal strategy and calcination process and utilized to fabricate a binder-free electrode. Due to the unique top-tangled structure and the complex assembly of different active components, the prepared hierarchical CuBr₂@NCC-LDH/CF binder-free electrode exhibits an outstanding electrochemical performance, including a remarkable areal capacitance of 5460 mF cm^-2 at 2 mA cm^-2 and a capacitance retention of 88% at 50 mA cm^-2 as well as a low internal resistance of 0.163 Ω. Moreover, an all-solid-state asymmetric supercapacitor (ASC) installed with CuBr₂@NCC-LDH/CF and activated carbon electrodes shows a high energy density of 118 Wh kg^-1 at a power density of 1013 W kg^-1. Three assembled ASCs connected in series can operate a multifunctional display for over three and a half hours. Therefore, this innovative work provides new inspiration for the preparation of electrode materials for supercapacitors.

Electric-Field-Assisted Alkaline Hydrolysis of Metal-Organic Framework Bulk into Highly Porous Hydroxide for Energy Storage and Electrocatalysis

Metal-organic frameworks (MOFs) have attracted tremendous attention in the field of supercapacitors and electrocatalysis due to their open metal sites and high surface area. However, their inherent instability and poor electrical conductivity lead to limited electrochemical performance. Herein, we have employed a new and simple strategy for converting MOF bulk into porous Zn-Co hydroxide composites with the assistance of electric fields with different cycles. This method can alter the migration behavior of charged molecules/ions and improve the nucleation rate of hydroxide, thus adjusting the morphology of derivatives. As a supercapacitor electrode, the optimal material of Zn_0.3Co_0.7(OH)₂ with an electric-field application time of 1200 cycles shows excellent electrochemical performance with a high specific capacity of 981.2 C g^-1 at 1 A g^-1. Additionally, the fabricated asymmetric supercapacitor exhibits an energy density of 42.5 Wh kg^-1 at a power density of 750.0 W kg^-1 and a remarkable cycling stability (99% after 11,000 cycles). Simultaneously, the as-prepared Zn_0.3Co_0.7(OH)₂ with an electric-field application time of 1200 cycles delivers prominent OER performances, which can exhibit low overpotentials of 300 and 326 mV at 50 and 100 mA cm^-2, respectively, and shows a small Tafel slope of 31.5 mV dec^-1. This study represents a new strategy for the synthesis of economical and efficient electrode materials for supercapacitors and OER electrocatalysts and offers a novel way for the mild preparation of nanoderivatives from MOFs.

Three-dimensional graphene encapsulated hollow CoSe2-SnSe2nanoboxes for high performance asymmetric supercapacitors

Construction of metal selenides with a large specific surface area and a hollow structure is one of the effective methods to improve the electrochemical performance of supercapacitors. However, the nano-material easily agglomerates due to the lack of support, resulting in the loss of electrochemical performance. Herein, we successfully design a three-dimensional graphene (3DG) encapsulation-protected hollow nanoboxes (CoSe₂-SnSe₂) composite aerogel (3DG/CoSe₂-SnSe₂) via a co-precipitation method coupled with self-assembly route, followed by a high temperature selenidation strategy. The obtained aerogel possesses porous 3DG conductive network, large specific surface area and plenty of reactive active sites. It could be used as a flexible and binder-free electrode after a facile mechanical compression process, which provided a high specific capacitance of 460 F g^-1at 0.5 A g^-1, good rate capability of 212.7 F g^-1at 10 A g^-1The capacitance retention rate is 80% at 2 A g^-1after 5000 cycles due to the fast electron/ion transfer and electrolyte diffusion. With the as-prepared 3DG/CoSe₂-SnSe₂as positive electrodes and the AC (activated carbon) as negative electrodes, an asymmetric supercapacitor (3DG/CoSe₂-SnSe₂//AC) was fabricated, which delivered a high specific capacity of 38 F g^-1at 1 A g^-1and an energy density of 11.89 Wh kg^-1at 749.9 W kg^-1, as well as excellent cycle stability. This work provides a new method for preparing electrode material.

Constructing nickel cobaltate @nickel-manganese layered double hydroxide hybrid composite on carbon cloth for high-performance flexible supercapacitors

Flexible supercapacitors have received considerable interest owing to their potential application in wearable electronics. Designing subtle hybridization of active materials and constructing smart electrode architectures are effective strategies for developing high-performance flexible supercapacitors. Herein, a hierarchically hybrid electrode is engineered by integrating nanoneedle-like structural NiCo₂O₄ and NiMn layered double hydroxide (NiMn-LDH) composite on highly conductive carbon cloth (CC). This architecture can endow abundant active sites, rapid electron collection pathways and efficient ion transport channels. The resultant hybrid electrode delivers high areal capacitance of 4010.4 mF cm^-2, excellent cyclic stability and good rate performance. Furthermore, by pairing with an activated carbon (AC)/CC anode, a flexible solid-state asymmetric supercapacitor (ASC) is assembled, which exhibits the high areal energy/power density of 0.78 mWh cm^-2/40.4 mW cm^-2 and superior capacitive stability at bending deformation. Meanwhile, the assembled ASC possesses outstanding cycling stability with 97.7% capacitance retention after 10,000 cycles. This work presents the effects of rational design of hybrid electrode with high electrochemical properties and flexibility, holding great potential for flexible energy storages.

Binder-free Fe-doped NiCo2O4/Ni3S4 hollow heterostructure nanotubes for highly efficient overall water splitting

For overall water splitting, a vital challenge is to design active sites at interfaces. Heterogeneous catalysts with enhanced mass/charge transfer and accelerated adsorption of intermediates have exhibited significantly enhanced activities. Herein, a Fe-doped NiCo₂O₄/Ni₃S₄ heterogeneous electrocatalyst is synthesized for the HER and OER. On account of the synergistic effect of heterostructures, Ni-O-S presents a low overpotential of 29.1 mV (10 mA cm^-2), a relatively small Tafel slope of 53.3 mV dec^-1 for the HER, and 259 mV at a current density of 100 mA cm^-2 (33.1 mV dec^-1) for the OER. What is more, Ni-O-S acts as a binder-free bi-functional electrode in an alkaline electrolyte for overall water splitting, exhibiting a cell voltage of 1.45 V (10 mA cm^-2) with good stability. This work offers an efficient approach for designing stable and high-efficiency heterogeneous electrodes for overall water splitting.

Layered Double Hydroxide Hollowcages with Adjustable Layer Spacing for High Performance Hybrid Supercapacitor

Layered double hydroxides (LDHs) have been considered as promising electrodes for supercapacitors due to their adjustable composition, designable function and superior high theoretic capacity. However, their experimental specific capacity is significantly lower than the theoretical value due to their small interlayer spacing. Therefore, obtaining large interlayer spacing through the intercalation of large-sized anions is an important means to improve capacity performance. Herein, a metal organic framework derived cobalt-nickel layered double hydroxide hollowcage intercalated with different concentrations of 1,4-benzenedicarboxylic acid (H₂ BDC) through in-situ cationic etching and organic ligand intercalation method is designed and fabricated. The superior specific capacity and excellent rate performance are benefit from the large specific surface area of the hollow structure and increasing interlayer spacing of LDH after H₂ BDC intercalation. The sample with the largest layer spacing displays a maximum specific capacity of 229 mA h g^-1 at 1 A g^-1 . In addition, the hybrid supercapacitor assembled from the sample with the largest layer spacing and active carbon electrode has a maximum specific capacity of 158 mA h g^-1 at 1 A g^-1 ; the energy density is as high as 126.4 W h kg^-1 at 800 W kg^-1 and good cycle stability.

Interlayer Spacing Regulation of NiCo-LDH Nanosheets with Ultrahigh Specific Capacity for Battery-Type Supercapacitors

The transition metal-based layered double hydroxides (LDHs) have been extensively studied as promising functional nanomaterials owing to their excellent electrochemical activity and tunable chemical composition. In this work, using acetate anions (Ac^-) as intercalating elements, the NiCo-LDH nanosheets arraying on Ni foam with different amounts of Ac^- anion intercalation or volume of hydrothermal solution were prepared by a simple hydrothermal method. The optimized amount of Ac^- anions expanded the interlayer space of LDH nanosheets from 0.8 to 0.94 nm. An ultrahigh specific capacity of 1200 C g^-1 at 1 A g^-1 (690 C g^-1 without Ac^- anions), an outstanding rate capability of 72.5% at 30 A g^-1, and a cycle stability of 79.90% after 4500 cycles were mainly attributed to the higher interlayer spacing of Ac^- anion intercalation. The enlarged interlayer spacing was beneficial for stabilizing the α-phase of LDHs and accelerating the electron transport and electrolyte penetration in the electrochemical reaction. This work sheds light on the mechanisms of the interlayer spacing regulation of NiCo-LDH nanosheets and offers a promising strategy to synthesize functional nanomaterials with excellent electrochemical performance via integrating their unique layered structure and interlayer anion exchange characteristics.

Slight Zinc Doping by an Ultrafast Electrodeposition Process Boosts the Cycling Performance of Layered Double Hydroxides for Ultralong-Life-Span Supercapacitors

Layered double hydroxides (LDHs) have attracted much attention in supercapacitors because of the high specific surface area and theoretical capacitance. However, the bad cycling stability has always been their Achilles' heel that restrains their further application. In this paper, a small amount of unactive and single-valence element zinc, which has no contribution to the capacitance of electrodes, was first doped into NiCo-LDHs through two consecutive electrodeposition processes only within 30 min. With a polyaniline (PANI) nanolayer as the interlayer, an ultrathin NiCoZn-LDH nanoplate network was well-anchored on the carbon cloth surface. The slight Zn²⁺ doping dramatically enhanced the cycling performance of LDHs with little capacitance decay. Zn²⁺ doping enhanced the cyclic structural stability of NiCoZn-LDHs, while the PANI layer strengthened the interface interaction between LDHs and the current collector. By controlling the doping content of Zn²⁺ at 2.9%, the composite electrode achieved the best performance with a high specific capacitance of 1749 F g^-1 and an ultralong life span with 89% capacitance retention after 40,000 charge-discharge cycles. This work offers a novel strategy to fast build LDH-based supercapacitors with both high specific capacitance and cycling performance.

A high-performance asymmetric supercapacitor-based (CuCo)Se2/GA cathode and FeSe2/GA anode with enhanced kinetics matching

The performance of asymmetric supercapacitors (ASCs) is limited by the poorly matched electrochemical kinetics of available electrode materials, which generally results in reduced energy density and inadequate voltage utilization. Herein, a porous conductive graphene aerogel (GA) scaffold was decorated with copper cobalt selenide ((CuCo)Se₂) or iron selenide (FeSe₂) to construct positive and negative electrodes, respectively. The (CuCo)Se₂/GA and FeSe₂/GA electrodes exhibited high specific capacitances of 672 and 940 F g^-1, respectively, at 1 A g^-1. The capacitance contributions from the Co³⁺/Co₂⁺ and Fe³⁺/Fe²⁺ redox couple for the positive and negative electrodes were determined to elucidate the energy storage mechanism. Furthermore, the kinetics study of the two electrodes was performed, revealing b values ranging between 0.7 and 1 at various scan rates and demonstrating that the surface-controlled processes played the dominant role, leading to fast charge storage capability for both electrodes. Fabrication of an ASC device with a configuration of (CuCo)Se₂/GA//FeSe₂/GA resulted in a voltage of 1.6 V, a high energy density of 39 W h kg^-1, and a power density of 702 W kg^-1. The excellent electrochemical performances of the (CuCo)Se₂/GA and FeSe₂/GA electrodes demonstrate their potential applications in energy storage devices.

Hollow Biphase Cobalt Nickel Perselenide Spheres Derived from Metal Glycerol Alkoxides for High-Performance Hybrid Supercapacitors

Transition-metal selenides (TMSe) incorporate reversible multielectron Faradaic reactions that can deliver high specific capacitance. Unfortunately, they usually exhibit actual capacitance lower than their theoretical value and suffer from sluggish kinetics, which do not satisfy the demands of hybrid supercapacitors (HSCs), due to poor electron-transmission capability and inferior ion-transport rate. Herein, a kind of hollow biphase and bimetal cobalt nickel perselenide composed of metastable marcasite-type CoSe₂ (m-CoSe₂) and stable pyrite-type NiCoSe₄ (p-NiCoSe₄) is synthesized with metal glycerol alkoxide as precursors by regulating the Ni/Co ratios. This unique hollow biphase structure and bimetallic synergistic effect serves to boost electron-transmission capability and accelerate the ion/electron transfer rate, delivering an excellent specific capacitance of 1008 F g^-1 at 0.5 A g^-1 and a high discharge rate capability of 859 F g^-1 at 20 A g^-1. The capacitance remains around 80% of the initial capacitance after 5000 cycles. Consequently, a HSC based on the cobalt nickel perselenide cathode and a hierarchical porous carbon anode reveals a maximum energy density of 34.8 W h kg^-1 and a maximum power density of 7272 W kg^-1. This polymorphic bimetallic phase engineering provides an advanced and effective guidance for TMSe with high electrochemical properties.

Hierarchical Manganese–Iron-Layered Double Hydroxide Nanosheets for Asymmetric Supercapacitors

This work presents a synthesis of hierarchical manganese–iron-layered double hydroxide (MnFe-LDH) nanostructured electrodes using the hydrothermal synthesis route by varying the reaction time for electrochemical energy storage applications. The electrochemical behavior of the MnFe-LDH electrodes synthesized at different reaction times was analyzed in a three-electrode cell configuration using 2 M KOH electrolyte. The uniform and well-organized MnFe-LDH nanosheet electrode (MnFe-12h) showed the maximum areal capacitance of 2013 mFcm−2 at a 5 mVs−1 scan rate, and 1886 mFcm−2 at a 25 mA applied current. Furthermore, the electrochemical behavior of MnFe-12h was examined by assembling an asymmetric cell device using activated carbon (AC) as a negative electrode and MnFe-12h as a positive electrode and it was tested in a wide voltage window range of 0.0 to 1.6 V. This asymmetric cell device achieved an appropriate energy density of 44.9 µW h cm−2 (55.01 W h kg−1), with a power density of 16 mW cm−2 (5000 W kg−1) at an applied current of 10 mA, and had a long-term cycling stability (93% capacitance retention after 5000 cycles) within the 1.6 V operating voltage window.

Hierarchical NiSe2 Nanosheet Arrays as a Robust Cathode toward Superdurable and Ultrafast Ni-Zn Aqueous Batteries

Zn-based aqueous batteries are enjoying the hotspots of worldwide research as their significant merits in economic cost and safety. However, the lack of a robust cathode (positive electrode) owning excellent rate ability, high capacity, and stability challenges their practical application. Herein, we propose hierarchical NiSe₂ nanosheet arrays as a robust cathode toward high-performance Ni-Zn aqueous batteries. Attributed to in situ anion exchange and Kirkendall effects, the nanosheet arrays are hierarchically constructed by NiSe₂ nanoparticles and abundant mesopores, which fully expose the active sites and accelerate the electrode kinetics. This unique structure endows the NiSe₂ electrode with remarkable specific capacity (245.1 mAh g^-1) and extraordinary high-rate ability (maintains 58% at 72.8 A g^-1) together with 10,000 cycles without any obvious capacity degeneration. As a result, based on the total active weight, our NiSe₂//Zn battery is capable of record-high power density (91.22 kW kg^-1/639.1 mW cm^-2), imposing energy density (328.8 Wh kg^-1/2.303 mWh cm^-2), and ultralong lifespan (only 8.3% capacity loss after 10,000 cycles), surpassing most of the aqueous batteries and supercapacitors recently reported. Moreover, this NiSe₂//Zn battery is also affordable (US$40 per kWh) and safe. These results open a new avenue for developing superdurable and ultrafast high-energy Ni-Zn batteries toward affordable and practical energy storage.

A High-Energy-Density Hybrid Supercapacitor with P-Ni(OH)2 @Co(OH)2 Core-Shell Heterostructure and Fe2 O3 Nanoneedle Arrays as Advanced Integrated Electrodes

Transition metal hydro/oxides (TMH/Os) are treated as the most promising alternative supercapacitor electrodes thanks to their high theoretical capacitance due to the various oxidation states and abundant cheap resources of TMH/Os. However, the poor conductivity and logy reaction kinetics of TMH/Os severely restrict their practical application. Herein, hierarchical core-shell P-Ni(OH)₂ @Co(OH)₂ micro/nanostructures are in situ grown on conductive Ni foam (P-Ni(OH)₂ @Co(OH)₂ /NF) through a facile stepwise hydrothermal process. The unique heterostructure composed of P-Ni(OH)₂ rods and Co(OH)₂ nanoflakes boost the charge transportation and provide abundant active sites when used as the intergrated cathode for supercapacitors. It delivers an ultrahigh areal specific capacitance of 4.4 C cm^-2 at 1 mA cm^-2 and the capacitance can maintain 91% after 10 000 cycles, showing an ultralong cycle life. Additionally, a hybrid supercapacitor composed with P-Ni(OH)₂ @Co(OH)₂ /NF cathode and Fe₂ O₃ /CC anode shows a wider voltage window of 1.6 V, a remarkable energy density of 0.21 mWh cm^-2 at the power density of 0.8 mW cm^-2 , and outstanding cycling stability with about 81% capacitance retention after 5000 cycles. This innovative study not only supplies a newfashioned electronic apparatus with high-energy density and cycling stability but offers a fresh reference and enlightenment for synthesizing advanced integrated electrodes for high-performance hybrid supercapacitors.

A facile synthesis of porous bimetallic Co-Ni fluorides for high-performance asymmetric supercapacitors

Exploring specific electrode active materials with excellent kinetic properties is important for the development of high performance supercapacitors. Herein, a novel nickel-cobalt fluoride (Ni1-xCoxF2) with a porous nanoprism structure is synthesized via step-wise recrystallization and ion-exchange reactions with a morphology control agent, namely polyvinyl pyrrolidone (PVP). The synergistic effect between the bimetallic redox centers promotes the reconstruction of the electronic coordination, leading to apparent discrepancies in the microstructure and morphology of Ni1-xCoxF2 with different stoichiometric ratios of Ni/Co. The micro-porous structure also provides sufficient interfaces and active sites for efficient electrolyte penetration and ion diffusion, thus improving its electrochemical performance. Among the as-synthesized samples, Ni0.5Co0.5F2, with an Ni/Co ratio of 1 : 1, achieved the highest specific capacity of 1979.6 F g-1 at 1.0 A g-1 and a remarkable long-term cycling stability of 900 F g-1 residual after 30 000 cycles at 20 A g-1. The supercapacitor with Ni0.5Co0.5F2 and activated carbon as the positive and negative electrodes, respectively, delivers a high specific capacitance of 107.3 F g-1 at 1 A g-1, outstanding cycling stability of 90.07% capacity retention after 30 000 cycles, and a maximum energy density of 48.3 W h kg-1 at a power density of 952.9 W kg-1. A flexible asymmetric all-solid-state supercapacitor based on a PVA/KOH gel electrolyte was assembled, which delivered a specific capacitance of 41.0 F g-1 at 1 A g-1 and showed promising applications in flexible electronic devices.

Recent Progress in Two-Dimensional Layered Double Hydroxides and Their Derivatives for Supercapacitors

High-performance supercapacitors have attracted great attention due to their high power, fast charging/discharging, long lifetime, and high safety. However, the generally low energy density and overall device performance of supercapacitors limit their applications. In recent years, the design of rational electrode materials has proven to be an effective pathway to improve the capacitive performances of supercapacitors. Layered double hydroxides (LDHs), have shown great potential in new-generation supercapacitors, due to their unique two-dimensional layered structures with a high surface area and tunable composition of the host layers and intercalation species. Herein, recent progress in LDH-based, LDH-derived, and composite-type electrode materials targeted for applications in supercapacitors, by tuning the chemical/metal composition, growth morphology, architectures, and device integration, is reviewed. The complicated relationships between the composition, morphology, structure, and capacitive performance are presented. A brief projection is given for the challenges and perspectives of LDHs for energy research.

NiSe2/Ni(OH)2 Heterojunction Composite through Epitaxial-like Strategy as High-Rate Battery-Type Electrode Material

Constructing heterojunction is a promising way to improve the charge transfer efficiency and can thus promote the electrochemical properties. Herein, a facile and effective epitaxial-like growth strategy is applied to NiSe₂ nano-octahedra to fabricate the NiSe₂-(100)/Ni(OH)₂-(110) heterojunction. The heterojunction composite and Ni(OH)₂ (performing high electrochemical activity) is ideal high-rate battery-type supercapacitor electrode. The NiSe₂/Ni(OH)₂ electrode exhibits a high specific capacity of 909 C g^-1 at 1 A g^-1 and 597 C g^-1 at 20 A g^-1. The assembled asymmetric supercapacitor composed of the NiSe₂/Ni(OH)₂ cathode and p-phenylenediamine-functional reduced graphene oxide anode achieves an ultrahigh specific capacity of 303 C g^-1 at 1 A g^-1 and a superior energy density of 76.1 Wh kg^-1 at 906 W kg^-1, as well as an outstanding cycling stability of 82% retention for 8000 cycles at 10 A g^-1. To the best of our knowledge, this is the first example of NiSe₂/Ni(OH)₂ heterojunction exhibiting such remarkable supercapacitor performance. This work not only provides a promising candidate for next-generation energy storage device but also offers a possible universal strategy to fabricate metal selenides/metal hydroxides heterojunctions.

A hierarchical glucose-intercalated NiMn-G-LDH@NiCo2S4 core-shell structure as a binder-free electrode for flexible all-solid-state asymmetric supercapacitors

Flexible, lightweight, and high-energy-density asymmetric supercapacitors (ASCs) are highly attractive for portable and wearable electronics. However, the implementation of such flexible ASCs is still hampered by the low specific capacitance and sluggish reaction kinetics of the electrode materials. Herein, a hierarchical core-shell structure of hybrid glucose intercalated NiMn-LDH (NiMn-G-LDH)@NiCo2S4 hollow nanotubes is deliberately constructed on flexible carbon fiber cloth (CFC). The highly conductive hollow NiCo2S4 nanotube arrays can not only provide high-speed pathways for ion and electrolyte transfer but also regulate the growth of NiMn-G-LDH nanosheets. The expanded interlayer distance on NiMn-G-LDH nanosheets could further facilitate ion diffusion and improve the rate retention. Benefiting from the rational engineering, the flexible NiMn-G-LDH@NiCo2S4@CFC as a free-standing electrode could deliver a superior specific capacity of 1018 C g-1 at 1 A g-1, which is almost twice higher than that of pristine NiCo2S4@CFC. In addition, the as-assembled flexible all-solid-state ASC device (NiMn-G-LDH@NiCo2S4@CFC//AC) is capable of working at various bending angles and exhibits an impressive energy density of 60.3 W h kg-1 at a power density of 375 W kg-1, as well as a superior cycling stability of 86.4% after 10 000 cycles.

Toward Flexible and Wearable Embroidered Supercapacitors from Cobalt Phosphides-Decorated Conductive Fibers

Wearable supercapacitors (SCs) are gaining prominence as portable energy storage devices. To develop high-performance wearable SCs, the significant relationship among material, structure, and performance inspired us with a delicate design of the highly wearable embroidered supercapacitors made from the conductive fibers composited. By rendering the conductive interdigitally patterned embroidery as both the current collector and skeleton for the SCs, the novel pseudocapacitive material cobalt phosphides were then successfully electrodeposited, forming the first flexible and wearable in-plane embroidery SCs. The electrochemical measurements manifested that the highest specific capacitance was nearly 156.6 mF cm^-2 (65.72 F g^-1) at the current density of 0.6 mA cm^-2 (0.25 A g^-1), with a high energy density of 0.013 mWh cm^-2 (5.55 Wh kg^-1) at a power density of 0.24 mW cm^-2 (100 W kg^-1). As a demonstration, a monogrammed pattern was ingeniously designed and embroidered on the laboratory gown as the wearable in-plane SCs, which showed both decent electrochemical performance and excellent flexibility.

Chemically Bonding NiFe-LDH Nanosheets on rGO for Superior Lithium-Ion Capacitors

Layered double hydroxides (LDHs) have attracted tremendous interest for applications in energy harvest and storage. However, the aggregation of nanosheets compromises the accessible active sites and limits their electrochemical performance, especially at high rates. The present study reports the synthesis of highly dispersed NiFe-LDH nanosheets anchored on reduced graphene oxide (NiFe-LDH/rGO) composites chemically bonded via a facile one-step hydrothermal method. Defect-riched rGO provides abundant active sites for heterogeneous nucleation of NiFe-LDH nanosheets, achieving the much efficient charge transfer between rGO and NiFe-LDH as compared to physically mixed NiFe-LDH + rGO. The crystallite size can effectively reduce to 5.5 nm smaller than 15.1 nm of NiFe-LDH without rGO, beneficial to expose more active surface for fast ion diffusion and redox reactions. NiFe-LDH/rGO as an anode material in lithium-ion batteries shows superior lithium storage capacity with 1202 mAh g^-1 after 100 cycles at 100 mA g^-1 and high-rate performance with 543 mAh g^-1 even at 2000 mA g^-1. The corresponding lithium-ion capacitor with NiFe-LDH/rGO anode and mesoporous carbon microsphere cathode exhibits high energy density and power density simultaneously, with 133 Wh kg^-1 at 25 W kg^-1 and 4016 W kg^-1 at 58 Wh kg^-1, showing the great potential for high-performance hybrid energy storage systems.

Facile Fabrication of NiCoAl-Layered Metal Oxide/Graphene Nanosheets for Efficient Capacitive Deionization Defluorination

Capacitive deionization (CDI) has aroused extensive attention as a prospective technology for different ionic species removal from aqueous solutions. Traditional studies on the adsorption and desorption of fluoride from wastewater are energy-intensive and may have harmful effects on the environment. Herein, the feasibility of fluoride removal from wastewater by CDI has been investigated. NiCoAl-layered metal oxide (NiCoAl-LMO) nanosheets and reduced graphene oxide (rGO) composites (NiCoAl-LMO/rGO) were synthesized and used as CDI electrode materials for fluoride ion removal. The as-obtained NiCoAl-LMO/rGO with unique structure and high conductivity is beneficial to the adsorption of fluoride ions. In addition, the introduction of Co element in the laminate enhances the pseudocapacitive behavior of the electrode material. As expected, the CDI system with NiCoAl-LMO/rGO composites as anode and activated carbon treated by nitric acid (H-AC) as cathode exhibits outstanding defluorination performance. The maximum adsorption capacity of NiCoAl-LMO/rGO, 24.5 mg g^-1, can be reached when the initial NaF concentration is 500 mg L^-1 at 1.4 V applied voltage. The composites also show good cycle stability over 40 consecutive cycles of the CDI defluorination process. The excellent defluorination performance of NiCoAl-LMO/rGO makes it possible for its practical application in wastewater treatment.