Ni-Co Selenide Nanosheet/3D Graphene/Nickel Foam Binder-Free Electrode for High-Performance Supercapacitor

Revolutionizing energy storage with advanced reduced graphene oxide-wrapped MnSe@CoSe@FeSe2 nanowires

Thanks to their good redox activity properties and exceptional conductivity, metal selenides (MSs) have attracted great attention as prospective positive electrodes for hybrid supercapacitors. However, they demonstrate low-rate capacities and poor endurance. Nanomaterials fabricated from MSs and reduced graphene oxide (rGO) with a porous skeleton can effectively mitigate the above-mentioned problems. Herein, porous MnSe@CoSe@FeSe2 nanowires wrapped with rGO on nickel foam (NF@MCFS-rGO) are manufactured as a binder-free electrode for a hybrid supercapacitor. The obtained NF@MCFS-rGO, acting as a positive electrode, has distinct advantages such as (1) the porous nanowires are helpful for fast electrolyte penetration, (2) the conductivity of the MCFS is further improved when combined with rGO, and (3) wrapping MCFS within the rGO endows the nanomaterial with much better structural durability. Capitalizing on the high conductivity of the rGO and the porous morphology, the fabricated NF@MCFS-rGO manifests impressive characteristics with a capacitance of 1830 F g-1 at 1 A g-1 and only 6.75% capacitance loss within 10 000 cycles. By matching NF@MCFS-rGO with activated carbon (AC), the fabricated apparatus (AC\\NF@MCFS-rGO) reveals an energy density (ED) of 64.6 W h kg-1 and a long lastingness of 90.55% after 10 000 cycles.

A self-sacrificing template strategy: In-situ construction of bimetallic MOF-derived self-supported CuCoSe nanosheet arrays for high-performance supercapacitors

Transition metal selenides (TMSs) are viewed as a prospective high-capacity electrode material for asymmetric supercapacitors (ASCs). However, the inability to expose sufficient active sites due to the limitation of the area involved in the electrochemical reaction severely limits their inherent supercapacitive properties. Herein, a self-sacrificing template strategy is developed to prepare self-supported CuCoSe (CuCoSe@rGO-NF) nanosheet arrays by in situ construction of copper-cobalt bimetallic organic framework (CuCo-MOF) on rGO-modified nickel foam (rGO-NF) and rational design of Se2- exchange process. Nanosheet arrays with high specific surface area are considered to be ideal platforms for accelerating electrolyte penetration and exposing rich electrochemical active sites. As a result, the CuCoSe@rGO-NF electrode delivers a high specific capacitance of 1521.6 F/g at 1 A/g, good rate performance and an excellent capacitance retention of 99.5% after 6000 cycles. The assembled ASC device has a high energy density of 19.8 Wh kg-1 at 750 W kg-1 and an ideal capacitance retention of 86.2% after 6000 cycles. This proposed strategy offers a viable strategy for designing and constructing electrode materials with superior energy storage performance.

Sea urchin-like CoNi2S4materials derived from nickel hexamyanocobaltate for high-performance asymmetric hybrid supercapacitor

In this work, a mild chemical precipitation method and simple hydrothermal treatment of the nickel hexamyanocobaltate precursor strategy are developed to prepare a sea urchin-like CoNi₂S₄compound with remarkable specific capacity and excellent cycling stability. The prepared CoNi₂S₄has an outstanding specific capacity of 149.1 mA h g^-1at 1 A g^-1and an initial capacity of 83.1% after 3000 cycles at 10 A g^-1. Moreover, the porous carbon nanospheres (PCNs) with exhibit cycling stability (94.7% of initial specific capacity after 10 000 cycles at 10 A g^-1) are selected as negative electrode to match CoNi₂S₄positive electrode for assembly of CoNi₂S₄//PCNs asymmetric supercapacitor (ASC). Satisfactorily, the as-assembled CoNi₂S₄//PCNs ASC exhibits an impressive energy density of 41.6 Wh kg^-1at 797 W kg^-1, as well as the suitable capacity retention of 82.8% after 10 000 cycles. The superior properties of the device demonstrated that the as-prepared material is potential energy storage material.

Advances and challenges in metal selenides enabled by nanostructures for electrochemical energy storage applications

The development of nanomaterials and their related electrochemical energy storage (EES) devices can provide solutions for improving the performance and development of existing EES systems owing to their high electronic conductivity and ion transport and abundant embeddable sites. Recent progress has demonstrated that metal selenides are attracting increasing attention in the field of EES because of their unique structures, high theoretical capacities, rich element resources, and high conductivity. However, there are still many challenges in their application in EES, and thus the use of nanoscale metal selenide materials in commercial devices is limited. In this review, we summarize recent advances in the nanostructured design of metal selenides (e.g., zero-, one-, two-, and three-dimensional, and self-supported structures) and present their advantages in terms of EES performance. Moreover, some remarks on the potential challenges and research prospects of nanostructured metal selenides in the field of EES are presented.

Recent Advancements in Chalcogenides for Electrochemical Energy Storage Applications

Energy storage has become increasingly important as a study area in recent decades. A growing number of academics are focusing their attention on developing and researching innovative materials for use in energy storage systems to promote sustainable development goals. This is due to the finite supply of traditional energy sources, such as oil, coal, and natural gas, and escalating regional tensions. Because of these issues, sustainable renewable energy sources have been touted as an alternative to nonrenewable fuels. Deployment of renewable energy sources requires efficient and reliable energy storage devices due to their intermittent nature. High-performance electrochemical energy storage technologies with high power and energy densities are heralded to be the next-generation storage devices. Transition metal chalcogenides (TMCs) have sparked interest among electrode materials because of their intriguing electrochemical properties. Researchers have revealed a variety of modifications to improve their electrochemical performance in energy storage. However, a stronger link between the type of change and the resulting electrochemical performance is still desired. This review examines the synthesis of chalcogenides for electrochemical energy storage devices, their limitations, and the importance of the modification method, followed by a detailed discussion of several modification procedures and how they have helped to improve their electrochemical performance. We also discussed chalcogenides and their composites in batteries and supercapacitors applications. Furthermore, this review discusses the subject’s current challenges as well as potential future opportunities.

Electrodeposition of CoxNiVyOz Ternary Nanopetals on Bare and rGO-Coated Nickel Foam for High-Performance Supercapacitor Application

We report a simple strategy to grow a novel cobalt nickel vanadium oxide (CoxNiVyOz) nanocomposite on bare and reduced-graphene-oxide (rGO)-coated nickel foam (Ni foam) substrates. In this way, the synthesized graphene oxide is coated on Ni foam, and reduced electrochemically with a negative voltage to prepare a more conductive rGO-coated Ni foam substrate. The fabricated electrodes were characterized with a field-emission scanning electron microscope (FESEM), energy-dispersive X-ray spectra (EDX), X-ray photoelectron spectra (XPS), and Fourier-transform infrared (FTIR) spectra. The electrochemical performance of these CoxNiVyOz-based electrode materials deposited on rGO-coated Ni foam substrate exhibited superior specific capacitance 701.08 F/g, which is more than twice that of a sample coated on bare Ni foam (300.31 F/g) under the same experimental conditions at current density 2 A/g. Our work highlights the effect of covering the Ni foam surface with a rGO film to expedite the specific capacity of the supercapacitors. Despite the slightly decreased stability of a CoxNiVyOz-based electrode coated on a Ni foam@rGO substrate, the facile synthesis, large specific capacitance, and preservation of 92% of the initial capacitance, even after running 5500 cyclic voltammetric (CV) scans, indicate that the CoxNiVyOz-based electrode is a promising candidate for high-performance energy-storage devices.

In-situ construction of heterostructure (Ni, Co)Se2 nanoarrays derived from cone-like ZIF-L for high-performance hybrid supercapacitors

The construction of heterostructure could enhance the electron transfer efficiency and increase the number of active sites, which can further develop high-performance electrode materials of supercapacitors. Herein, (Ni, Co)Se₂ nanorod arrays were prepared based on the NiCo-LDH derived from a conical ZIF-L. Significantly, the single nanorod is composed of interconnected NiSe₂ and CoSe₂ nanoparticles, the heterostructure can expose higher conductivity, more sufficient redox reaction active sites and larger specific surface area. The as-obtained CF@(Ni, Co)Se₂ achieved a high specific capacity of 188.8 mAh g^-1 at the current density of 1.0 A g^-1 and an outstanding cycling stability with a high capacity retention of 90% after 8000 cycles. Finally, an hybrid supercapacitor device composed of activated carbon (AC) as negative electrode and CF@(Ni, Co)Se₂ as positive electrode was designed, which revealed an ideal voltage window of 0-1.6 V and exhibited a great energy density of 36.02 Wh kg^-1 at the power density of 800 W kg^-1, such surpassing energy storage characteristics evidently testify that (Ni, Co)Se₂ nanorod arrays can be as the potential electrode material to promote the development of high-performance supercapacitors.

Zn-doped NiSe2@Ni(OH)2 nanocomposites as binder-free electrodes for asymmetric supercapacitors with impressive performance

The low stability and poor activities of transition metal selenides (TMSs) in alkaline electrolyte limit their application in supercapacitors. Metal doping and hybridization of various electroactive materials with different properties are utilized to enhance the electrochemical performance of TMSs by optimizing their electronic structure and providing rich electrochemical active sites. Herein, we report a simple two-step hydrothermal method for the growth of Zn-doped NiSe2 and Ni(OH)2 nanocomposites on Ni foam [Zn-NiSe2/Ni(OH)2]. The resulting material delivers high specific capacity (1525.8 C g-1/564.7 mA h g-1 at 6 A g-1 and 1220 C g-1 at 10 A g-1) in a three-electrode system. A Zn-NiSe2/Ni(OH)2//porous carbon (PC) aqueous asymmetric supercapacitor (ASC) was built by utilizing Zn-NiSe2/Ni(OH)2 as the positive electrode and PC as the negative electrode. This Zn-NiSe2/Ni(OH)2//PC ASC shows an energy density of 75.8 W h kg-1 at a power density of 916.1 W kg-1 and achieves a specific capacity retention of 100% after 25 000 cycles at 10 A g-1. These results reveal that the Zn doping and the hybridization of NiSe2 with Ni(OH)2 can obtain impressive electrochemical properties in ASCs.

Synthesis of bimetallic nickel cobalt selenide particles for high-performance hybrid supercapacitors

Supercapacitors are known as promising excellent electrochemical energy storage devices because of their attractive features, including quick charge and discharge, high power density, low cost and high security. In this work, a series of litchi-like Ni-Co selenide particles were synthesized via a simple solvothermal method, and the Ni-Co compositions were carefully optimized to tune the charge storage performance, charge storage kinetics, and conductivity for battery-like supercapacitors. Interestingly, the optimal sample Ni0.95Co2.05Se4 exhibits a high capacity of 1038.75 F g-1 at 1 A g-1 and superior rate performance (retains 97.8% of the original capacity at 4 A g-1). Moreover, an asymmetric supercapacitor device was assembled based on the Ni0.95Co2.05Se4 cathode and activated carbon anode. The device of Ni0.95Co2.05Se4//active carbon (AC) reveals a peak energy density of 37.22 W h kg-1, and the corresponding peak power density reaches 800.90 W kg-1. This work provides a facile and effective way to synthesize transition metal selenides as high-performance supercapacitor electrode materials.

Scalable CNTs/NiCoSe2 Hybrid Films for Flexible All-Solid-State Asymmetric Supercapacitors

The rapidly developing wearable flexible electronics makes the development of high-performance flexible energy storage devices, such as all-solid-state supercapacitors (SCs), particularly important. Herein, we report the fabrication of CNTs/NiCoSe₂ hybrid films on carbon cloth (CC) through a facile co-electrodeposition method based on flexible electrodes for all-solid-state SCs. The NiCoSe₂ sheets grown on CNTs uniformly with a diameter of 50-100 nm act as the active materials. The CNTs in the hybrid films act as the scaffold to offer more deposition sites for NiCoSe₂ and provide a conductive network to facilitate the transfer of electrons. Moreover, the one-step electrodeposition process avoids the usage of any organic binders. Benefiting from the high intrinsic reactivity and unique 3D architecture, the obtained CNTs/NiCoSe₂ electrode delivers high specific capacity (218.1 mA h g^-1) and satisfactory durability (over 5000 cycles). Remarkably, the CNTs/NiCoSe₂//AC flexible all-solid-state (FASS) ASC provides remarkable energy density (112.2 W h kg^-1) within 0-1.7 V and maintains 98.1% of its initial capacity after 10,000 cycles. In addition, this flexible ASC device could be fabricated at a large scale (5 × 6 cm²), and the LED arrays (>3.7 V) can be easily lighted up by three ASCs in series, showing its potential practical application.

Synergetic Advantages of Atomically Coupled 2D Inorganic and Graphene Nanosheets as Versatile Building Blocks for Diverse Functional Nanohybrids

2D nanostructured materials, including inorganic and graphene nanosheets, have evoked plenty of scientific research activity due to their intriguing properties and excellent functionalities. The complementary advantages and common 2D crystal shapes of inorganic and graphene nanosheets render their homogenous mixtures powerful building blocks for novel high-performance functional hybrid materials. The nanometer-level thickness of 2D inorganic/graphene nanosheets allows the achievement of unusually strong electronic couplings between sheets, leading to a remarkable improvement in preexisting functionalities and the creation of unexpected properties. The synergetic merits of atomically coupled 2D inorganic-graphene nanosheets are presented here in the exploration of novel heterogeneous functional materials, with an emphasis on their critical roles as hybridization building blocks, interstratified sheets, additives, substrates, and deposited monolayers. The great flexibility and controllability of the elemental compositions, defect structures, and surface natures of inorganic-graphene nanosheets provide valuable opportunities for exploring high-performance nanohybrids applicable as electrodes for supercapacitors and rechargeable batteries, electrocatalysts, photocatalysts, and water purification agents, to give some examples. An outlook on future research perspectives for the exploitation of emerging 2D nanosheet-based hybrid materials is also presented along with novel synthetic strategies to maximize the synergetic advantage of atomically mixed 2D inorganic-graphene nanosheets.

The implementation of graphene-based aerogel in the field of supercapacitor

Graphene and graphene-based hybrid materials have emerged as an outstanding supercapacitor electrode material primarily because of their excellent surface area, high electrical conductivity, and improved thermal, mechanical, electrochemical cycling stabilities. Graphene alone exhibits electric double layer capacitance (EDLC) with low energy density and high power density. The use of aerogels in a supercapacitor is a pragmatic approach due to its extraordinary properties like ultra-lightweight, high porosity and specific surface area. The aerogels encompass a high volume of pores which leads to easy soak by the electrolyte and fast charge-discharge process. Graphene aerogels assembled into three-dimensional (3D) architecture prevent there stacking of graphene sheets and maintain the high surface area and hence excellent cycling stability and rate capacitance. However, the energy density of graphene aerogels is limited due to EDLC type of charge storage mechanism. Consequently, 3D graphene aerogel coupled with pseudocapacitive materials such as transition metal oxides, metal hydroxides, conducting polymers, nitrides, chalcogenides show an efficient energy density and power density performance due to the presence of both types of charge storage mechanisms. This laconic review focuses on the design and development of graphene-based aerogel in the field of the supercapacitor. This review is an erudite article about methods, technology and electrochemical properties of graphene aerogel.

Heterogeneous assembly of Ni-Co layered double hydroxide/sulfonated graphene nanosheet composites as battery-type materials for hybrid supercapacitors

Graphene-based hybrid composites as positive electrodes have aroused great interest in the field of hybrid supercapacitors. However, the charge storage capability of hybrid composites suffers from the scarce interaction between their end members to some extent. Herein, a hybrid composite with electrostatic interaction was obtained by employing a heterogeneous assembly strategy of Ni-Co layered double hydroxide (LDH) and sulfonated graphene nanosheets (SGN). Depending on the substitution of the negatively charged SGN for the interlayer nitrate anions compensating for the positively charged LDH host slabs, the abundance of Ni³⁺ on the surface of the hybrid composite could be increased to intensify the electrostatic interaction within hybrid composites. As expected, the effective coupling of LDH with SGN ensured the uniform incorporation of heterogeneous components. The unique structure of the hybrid composite accelerated electron transfer and ion diffusion processes during electrochemical reactions, which is beneficial to improve the electrochemical performance of battery-type electrodes. Further evaluation showed that the specific capacity of the LDH/SGN hybrid composite is 1177 C g^-1 (2354 F g^-1) at 1 A g^-1. Additionally, the LDH/SGN//AC hybrid supercapacitor achieved an energy density of 43 W h kg^-1 at 800 W kg^-1 and still retained 94% of its initial specific capacitance over 10 000 cycles. The boosting effect of the electrostatic interaction within the hybrid composite on electrochemical properties offers a novel pathway for the development of supercapacitors.

The electrochemical kinetics of cerium selenide nano-pebbles: the design of a device-grade symmetric configured wide-potential flexible solid-state supercapacitor

Next-generation portable flexible electronic appliances require liquid-free energy storage supercapacitor devices to eliminate leakage and to support mechanical bending that is compatible with roll-to-roll technologies. Hence, a state-of-the-art process is presented to design a solid-state, wide-potential and flexible supercapacitor through the use of nano-pebbles of cerium selenide via a simple successive ionic layer adsorption and reaction (SILAR) method that could allow an industry scalable route. We strongly believe that this is the first approach amongst physical and chemical routes not only for synthesizing cerium selenide in thin-film form but also using it for device-grade supercapacitor applications. The designed solid-state symmetric supercapacitor assembled from cerium selenide electrodes sandwiched by PVA-LiClO₄ gel electrolyte attains a wide potential window of 1.8 V with capacitance of 48.8 F g^-1 at 2 mV s^-1 and reveals excellent power density of 4.89 kW kg^-1 at an energy density of 11.63 W h kg^-1. The formed device is capable of 87% capacitive retention even at a mechanical bending angle of 175°. Lighting up a strip of 21 parallel connected red LEDs clearly demonstrates the practical use of the designed symmetric solid-state supercapacitor, aiming towards the commercialization of the product in the future.

A high-energy-density supercapacitor with multi-shelled nickel-manganese selenide hollow spheres as cathode and double-shell nickel-iron selenide hollow spheres as anode electrodes

Thanks to the attractive structural characteristics and unique physicochemical properties, mixed metal selenides (MMSes) can be considered as encouraging electrode materials for energy storage devices. Herein, a straightforward and efficient approach is used to construct multi-shelled nickel-manganese selenide hollow spheres (MSNMSeHSs) as cathode and double-shell nickel-iron selenide hollow spheres (DSNFSeHSs) as anode electrode materials by tuning shell numbers for supercapacitors. The as-designed MSNMSeHS electrode can deliver a splendid capacity of ∼339.2 mA h g-1/1221.1 C g-1, impressive rate performances of 78.8%, and considerable longevity of 95.7%. The considerable performance is also observed for the DSNFSeHS electrode with a capacity of 258.4 mA h g-1/930.25 C g-1, rate performance of 75.5%, and longevity of 90.9%. An efficient asymmetric apparatus (MSNMSeHS||DSNFSeHS) fabricated by these two electrodes depicts the excellent electrochemical features (energy density of ≈112.6 W h kg-1 at 900.8 W kg-1) with desirable longevity of ≈94.4%.

Nanostructure Nickel-Based Selenides as Cathode Materials for Hybrid Battery-Supercapacitors

Supercapacitors (SCs) have attracted many attentions and already became part of some high-power derived devices such as Tesla's electric cars because of their higher power density. Among all types of electrical energy storage devices, battery-supercapacitors are the most promising for superior performance characteristics, including short charging time, high power density, safety, easy fabrication procedures, and long operational life. An SC usually consists of two foremost components, namely electrode materials, and electrolyte. The selection of appropriate electrode materials with rational nanostructured designs have resulted in improved electrochemical properties for high performance and has reduced the cost of SCs. In this review, we mainly spotlight the nickel-based selenides nanostructured which applied as high-performance cathode materials for SCs. Different nickel-based selenides materials are highlighted in various categories, such as nickel-cobalt-based bimetallic chalcogenides and nickel-M based selenides. Also, we mentioned material modification for this material type. Finally, the designing strategy and future improvements on nickel-based selenides materials for the application of SCs are also discussed.

The synergistic effect of carbon nanotubes and graphitic carbon nitride on the enhanced supercapacitor performance of cobalt diselenide-based composites

Carbon nanotubes and g-C₃N₄ synergistically optimize the electrical conductivity and spatial structure of CoSe₂, thus improving the performance of supercapacitors.

One-Dimensional NiSe-Se Hollow Nanotubular Architecture as a Binder-Free Cathode with Enhanced Redox Reactions for High-Performance Hybrid Supercapacitors

Selenium-enriched nickel selenide (NiSe-Se) nanotubes supported on highly conductive nickel foam (NiSe-Se@Ni foam) were synthesized using chemical bath deposition with the aid of lithium chloride as a shape-directing agent. The uniformly grown NiSe-Se@Ni foam, with its large number of electroactive sites, facilitated rapid diffusion and charge transport. The NiSe-Se@Ni foam electrode exhibited a superior specific capacitance value of 2447.46 F g^-1 at a current density value of 1 A g^-1 in 1 M aqueous KOH electrolyte. Furthermore, a high-energy-density pouch-type hybrid supercapacitor (HSC) device was fabricated using the proposed NiSe-Se@Ni foam as the positive electrode, activated carbon on Ni foam as the negative electrode, and a filter paper separator soaked in 1 M KOH electrolyte solution. The HSC delivered a specific capacitance of 84.10 F g^-1 at a current density of 4 mA cm^-2 with an energy density of 29.90 W h kg^-1 at a power density of 594.46 W kg^-1 for an extended operating voltage window of 1.6 V. In addition, the HSC exhibited excellent cycling stability with a capacitance retention of 95.09% after 10,000 cycles, highlighting its excellent potential for use in the hands-on applications. The real-life practicality of the HSC was tested by using it to power a red light-emitting diode.

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.

One-step electrodeposited 3D porous NiCoSe2 nanosheet array for high-performance asymmetric supercapacitors

3D porous nanosheet arrays are desirable structures for supercapacitors due to their large surface and fast transportation for ions and electrons. However, their synthesis usually involves two or more steps, which is not only time-consuming but also makes the in situ growth more difficult to achieve. In this work, 3D porous NiCoSe₂ nanosheet array were in situ synthesized on Ni foam by one-step electrodeposition, and then employed as a supercapacitor electrode for the first time. The electrodeposited NiCoSe₂ electrode displays a high specific capacity of 520 C g^-1 at 1 A g^-1 and good rate capability of 53.7% with a 30-fold increase to 30 A g^-1. In addition, an asymmetric supercapacitor (ASC) device was assembled with NiCoSe₂ and activated carbon as the binder-free positive and negative electrode, respectively. The ASC exhibits a high specific energy of 44.4 Wh kg^-1 at a specific power of 776.7 W kg^-1, and outstanding cycling stability of 133% after 10000 cycles. Most importantly, the energy storage mechanism of NiCoSe₂ was proposed. This is mainly due to the significantly increased electroactive surface area and superior electron transfer properties of NiCoSe₂, which can compensate for the capacity decay of NiCoSe₂ induced by Se and Co loss after cycling.

A bifunctional nanoporous Ni-Co-Se electrocatalyst with a superaerophobic surface for water and hydrazine oxidation

The sluggish kinetics of the oxygen evolution reaction (OER) has severely hindered the energetic convenience of water splitting. Thus, developing a highly efficient catalyst for the OER and replacing the OER with hydrazine oxidation (HzOR) are effective strategies for water electrolysis to achieve sustainable hydrogen production. Herein, bifunctional nanosheet arrays Ni0.6Co0.4Se with a porous structure were fabricated on Ni foam (NF) by the bubble dynamic template method during electrodeposition. Compared with CoSe2 and NiSe2, Ni0.6Co0.4Se exhibits excellent electrocatalytic performance for both the OER and HzOR. A low overpotential of only 249 mV is required to drive 10 mA cm-2, and a retention rate of nearly 100% after 24 h at 10 mA cm-2 is observed for Ni0.6Co0.4Se towards the OER. By substituting the OER by HzOR, an extremely high current density of 300 mA cm-2 at 0.4 V vs. RHE and a retention rate of 86.8% at 200 mA cm-2 after 12 h can be achieved. Interestingly, the mechanistic reason for the enhanced catalytic ability of Ni0.6Co0.4Se was studied, which is associated with the synergistic effects of Ni and Co, large ECSA, high electrical conductivity and most importantly the superaerophobic nature induced by the porous structure of Ni0.6Co0.4Se. The non-noble metal bifunctional electrocatalyst demonstrates a promising potential for application in both the OER and HzOR.

Selenium-rich nickel cobalt bimetallic selenides with core-shell architecture enable superior hybrid energy storage devices

The continuous exploration of advanced electrode materials is of remarkable significance to revolutionize next-generation high-performance energy storage devices towards a green future. Benefiting from their electrochemically active sites and abundant redox centers, bimetallic selenides with desirable nanostructures recently have emerged as promising electrode alternatives for battery-supercapacitor hybrid (BSH) devices which demonstrate enormous potential in bridging the gap between electrochemical properties with high power densities (supercapacitors) and energy densities (batteries). Herein, employing the hydrothermal approach with solid Ni-Co spheres as precursors followed by the selenization process, selenide-rich bimetallic selenide spheres with a core-shell nanostructure were rationally designed and synthesized for use as the cathode electrode in superior BSH devices. The as-obtained (NiCo)₉Se₈/(NiCo)_0.85Se (Ni-Co-Se) exhibits a high specific capacity of 164.44 mA h g^-1 at a current density of 1 A g^-1 with 85.72% capacity retention even after 5000 cycles at a current density of as high as 8 A g^-1, suggesting its great promise in practical applications for BSH devices. By integrating activated carbon as the anode with the as-obtained bimetallic selenides as the cathode, an alkaline aqueous BSH device is fabricated and delivers a high energy density of 37.54 W h kg^-1 at a high power density of 842.7 W kg^-1. It is found that the excellent electrochemical performances can be ascribed to facile ion and electron transport pathways, high electrical conductivity and reliable structural robustness of the prepared selenides. Moreover, the synthetic strategy presented in this paper opens up an avenue to guide the synthesis of various anion doped bimetallic compounds towards high-performance energy conversion and storage devices.

Porous Ultrathin NiSe Nanosheet Networks on Nickel Foam for High-Performance Hybrid Supercapacitors

Transition metal selenides (TMSs) with excellent electrochemical activity and high intrinsic electrical conductivity have attracted considerable attention owing to their potential use in energy storage devices. However, the low energy densities of the reported TMSs, which originate from the small active surface area and poor electrolyte ion mobility, substantially restrict their application potential. In this work, porous ultrathin nickel selenide nanosheet networks (NiSe NNs) on nickel foam are fabricated by using a novel, facile method, that is, selenylation/pickling of the pre-formed manganese-doped α-Ni(OH)₂ . Removal of Mn resulted in NNs with a highly porous structure. The 3D framework of the NNs and the inherent nature of the NiSe affords high ion mobility, abundant accessible activated sites, vigorous electrochemical activity, and low resistance. One of the highest specific capacities of TMSs ever reported, that is, 443 mA h g^-1 (807 μAh cm^-2 ) at 3.0 A g^-1 , is achieved with the NNs as electrodes. The assembled NiSe NNs//porous carbon hybrid supercapacitor delivers a high energy density of 66.6 Wh kg^-1 at a power density of 425 W kg^-1 , with excellent cycling stability. This work provides a new strategy for the production of novel electrode materials that can be applied in high-performance hybrid supercapacitors, and a fresh pathway towards commercial applications of hybrid supercapacitors based on TMS electrodes.

Facile Synthesis of Yolk-Shelled CuCo2Se4 Microspheres as a Novel Electrode Material for Supercapacitor Application

Recently, metal selenides have attracted much attention in the energy storage applications. This attention is due to the outstanding properties of metal selenides (lower cost, lower electronegativity, and environmental friendliness) compared to metal sulfides and oxides. In this work, novel yolk-shelled CuCo₂Se₄ (YS-CCS) microspheres are synthesized by a facile two-step hydrothermal method and used as an electrode material for high-performance supercapacitors (SCs) in alkaline media. The proposed YS-CCS electrode shows remarkable electrochemical performance, including fast kinetics, high reversibility, low internal resistance (0.45 Ω), excellent specific capacitance (512 F g^-1 at a current density of 1A g^-1), high rate capability (70.8% after increasing the current density six times), and good cycling stability (about 83.7% of the initial retention after 6000 successive charge-discharge cycles). Furthermore, an asymmetric supercapacitor (ASC) is assembled by using the YS-CCS (as a cathode electrode material) and active carbon (as an anode electrode material). The assembled device delivers a maximum energy density of 9.45 W h kg^-1 and a power density up to 850 W kg^-1 in a wide potential window of 1.70 V. Meanwhile, the ASC device exhibits superb rate capability (∼84.67%) after increasing the current density five times and very good capacitance retention (∼88%) after 6000 cycles.

A binder-free Ni2P2O7/Co2P2O7 nanograss array as an efficient cathode for supercapacitors

Binder-free Ni₂P₂O₇/Co₂P₂O₇ cathode of nanograss morphology, delivered an energy and power density of 33.2 W h kg⁻¹ and 257.8 W kg⁻¹ respectively. Through power law, the contribution of each type of mechanism in charge storage process was calculated.

In situ growth of urchin-like cobalt–chromium phosphide on 3D graphene foam for efficient overall water splitting

The CoCr-P@3DGF composite shows excellent activity and durability for overall water splitting due to Cr-doping and the 3DGF substrate.

A facile method to synthesize CoV2O6 as a high-performance supercapacitor cathode

Transition metal oxides can easily lose electrons and thus possess multiple accessible valences. Especially, if two different transition metals are combined, better capacity and cycling stability are achieved. In this study, a binary transition metal oxide, CoV₂O₆, was synthesized via a facile co-precipitation process for use as a supercapacitor cathode; the as-synthesized CoV₂O₆ exhibited high-capacity (306.6 F g⁻¹, 1 A g⁻¹ and 219.2 F g⁻¹, 20 A g⁻¹) and stable cycling stability, retaining 83.3% of its initial specific capacitance after 20 000 cycles. We believe that this facile synthesis process presents an effective method and a new opportunity for promoting the application of electrode materials based on binary transition metal oxides in supercapacitors.

A facile chemical co-precipitation process to synthesize CoV₂O₆, which exhibits high capacity and cycling stability (83.3% after 20 000 cycles).