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

Advances in Mn-Based MOFs and Their Derivatives for High-Performance Supercapacitor

As the most widely used metal material in supercapacitors, manganese (Mn)-based materials possess the merits of high theoretical capacitance, stable structure as well as environmental friendliness. However, due to poor conductivity and easy accumulation, the practical capacitance of Mn-based materials is far lower than that of theoretical value. Therefore, accurate structural adjustment and controllable strategies are urgently needed to optimize the electrochemical properties of Mn-based materials. Metal-organic frameworks (MOFs) are porous materials with high specific surface area (SSA), tunable pore size, and controllable structure. These features make them attractive as precursors or scaffold for the synthesis of metal-based materials and composites, which are important for electrochemical energy storage applications. Therefore, a timely and comprehensive review on the classification, design, preparation and application of Mn-based MOFs and their derivatives for supercapacitors has been given in this paper. The recent advancement of Mn-based MOFs and their derivatives applied in supercapacitor electrodes are particularly highlighted. Finally, the challenges faced by Mn-MOFs and their derivatives for supercapacitors are summarized, and strategies to further improve their performance are proposed. The aspiration is that this review will serve as a beneficial compass, guiding the logical creation of Mn-based MOFs and their derivatives in the future.

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.

Rich-grain-boundary Ni-Co-Se nanowire arrays for fast charge storage in alkaline electrolyte

In this work, the one-dimensional (1D) Ni-Co-Se nanowire arrays with rich grain-boundaries were prepared through the solvothermal method and gas-phase selenizaiton. The results showed that the structure and crystallization of the Ni-Co-Se nanowire arrays could be modulated through the optimization of selenizaiton time. The optimal Ni-Co-Se electrode sample displayed an area specific capacitance of 242.6μAh cm-2at 30 mA cm-2with a current retention rate of 68.34%. The assembled Ni-Co-Se/Active carbon (AC) electrode-based asymmetric supercapacitor (ASC) showed the area specific capacitances of 329.2μAh cm-2and 225.8μAh cm-2at 3 mA cm-2and 30 mA cm-2, respectively. A 73.33% retention rate of capacitance was observed after 8000 charge/discharge cycles. Besides, the further fabricated all-solid ASC delivered the power densities of 342.94 W kg-1and 3441.33 W kg-1at the energy densities of 37.62 Wh kg-1and 25.81 Wh kg-1, respectively. Those results suggested the potentials of the obtained Ni-Co-Se nanowire arrays as electrode material for the high-performance pseudocapacitors.

Carbon-Encased Mixed-Metal Selenide Rooted with Carbon Nanotubes for High-Performance Hybrid Supercapacitors

Transition metal-based compounds with high theoretical capacitance and low cost represent one class of promising electrode materials for high-performance supercapacitors. However, their low intrinsic electrical conductivity impedes their capacitive effect and further limits their practical application. Rational regulation of their composition and structure is, therefore, necessary to achieve a high electrode performance. Herein, a well-designed carbon-encased mixed-metal selenide rooted with carbon nanotubes (Ni-Co-Se@C-CNT) was derived from nickel–cobalt bimetallic organic frameworks. Due to the unique porous structure, the synergistic effect of bimetal selenides and the in situ growth of carbon nanotubes, the composite exhibits good electrical conductivity, high structural stability and abundant redox active sites. Benefitting from these merits, the Ni-Co-Se@C-CNT exhibited a high specific capacity of 554.1 C g−1 (1108.2 F g−1) at 1 A g−1 and a superior cycling performance, i.e., 96.4% of the initial capacity was retained after 5000 cycles at 10 A g−1. Furthermore, a hybrid supercapacitor assembled with Ni-Co-Se@C-CNT cathode and activated carbon (AC) anode shows a superior energy density of 38.2 Wh kg−1 at 1602.1 W kg−1.

Selenization governs the intrinsic activity of copper-cobalt complexes for enhanced non-radical Fenton-like oxidation toward organic contaminants

Non-radical oxidation pathways in the Fenton-like process have a superior catalytic activity for the selective degradation of organic contaminants under complicated water matrices. Whereas the synthesis of high-performance catalysts and research on reaction mechanisms are unsatisfactory. Herein, it was the first report on copper-cobalt selenide (CuCoSe) that was well-prepared to activate hydrogen peroxide (H₂O₂) for non-radical species generation. The optimized CuCoSe+H₂O₂ system achieved excellent removal of chlortetracycline (CTC) in 10 min at neutral pH along with pleasing reusability and stability. Moreover, it exhibited great anti-interference capacity to inorganic anions and natural organic matters even in actual applications. Multi-surveys verified that singlet oxygen (¹O₂) was the dominant active species in this reaction and electron transfer on the surface-bound of CuCoSe and H₂O₂ likewise played an important role in direct CTC oxidation. Where the synergetic metals of Cu and Co accounted for the active sites, and the introduced Se atoms accelerated the circulation efficiency of Co³⁺/Co²⁺, Cu²⁺/Cu⁺ and Cu²⁺/Co²⁺. Simultaneously, the produced Se/O vacancies further facilitated electron mediation to enhance non-radical behaviors. With the aid of intermediate identification and theoretical calculation, the degradation pathways of CTC were proposed. And the predicted ecotoxicity indicated a decrease in underlying environmental risk.

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.

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.

Constructing Heterostructured Bimetallic Selenides on an N-Doped Carbon Nanoframework as Anodes for Ultrastable Na-Ion Batteries

Transition-metal selenides have been recognized as a class of promising anode materials for sodium-ion batteries (SIBs) on account of their high capacity. Nevertheless, the sluggish conversion kinetics and rapid capacity decay caused by insufficient conductivity and volume change restrain their applications. Herein, hollow heterostructured bimetallic selenides embedded in an N-doped carbon nanoframework (H-CoSe₂/ZnSe@NC) were prepared via a facile template-engaged method. Benefiting from the rich defect at the phase boundary of the CoSe₂/ZnSe heterostructure, pre-reserved cavity, and enhanced structure rigidity, the abovementioned issues are resolved at once, and the accelerated charge transportation kinetics traced by spectroscopy techniques and theoretical calculations certify the interface effect in the capacity release. In addition, ex situ X-ray photoelectron spectroscopy, X-ray diffraction, and high-resolution transmission electron microscopy all confirm the high-reversible electrochemical conversion mechanism in H-CoSe₂/ZnSe@NC. Together with a reasonable structural architecture and the highly reversible conversion reaction, H-CoSe₂/ZnSe@NC displays a prominent rate capacity (244.8 mA h g^-1 at 10 A g^-1) as well as an ultralong lifespan (10,000 cycles at 10 A g^-1), highlighting the significance of structure control in fabricating high-performance anodes for SIBs.

Influence of Transition Metals (Cu and Co) on the Carbon-Coated Nickel Sulfide Used as Positive Electrode Material in Hybrid Supercapacitor Device

Herein, a facile, environment-friendly and cost-effective approach was followed for the preparation of metal sulfide-based supercapacitor electrodes. The effect of transition metal interrogation on the morphology and electrochemical performance of carbon-coated nickel sulfide composite electrode was investigated. Physicochemical characterization showed that the enhancement in electrical conductivity and electrochemical reaction sites with the introduction of copper (Cu) and cobalt (Co) was due to the variation in morphology. Fast ionic transformation and improvement in the number of redox active sites might improve the supercapacitor performance. The electrochemical experiment showed that the NCoSC electrode exhibited the highest capacitance value of ~760 F g−1 at 2 A g−1 current density as compared to the NCuSC and NSC electrodes. Therefore, a hybrid supercapacitor (HSC) device was fabricated by using NCoSC as the positive electrode and thermally reduced graphene oxide (TRGO) as the negative electrode. The fabricated device demonstrated maximum energy density of ~38.8 Wh Kg−1 and power density of 9.8 kW Kg−1. The HSC device also showed ~89.5% retention in specific capacitance after 10,000 charge–discharge cycles at 12 A g−1 current density. So, the tuning of electronic and physical properties by the introduction of Cu and Co on nickel sulfide improved the supercapacitor performance.

Metal-organic-framework derived hollow manganese nickel selenide spheres confined with nanosheets on nickel foam for hybrid supercapacitors

Metal-organic framework (MOF) derived nanoarchitectures have special features, such as high surface area (SA), abundant active sites, exclusive porous networks, and remarkable supercapacitive performance when compared to traditional nanoarchitectures. Herein, we propose a viable strategy for the synthesis of hollow manganese nickel selenide spheres comprising nanosheets supported on the nickel foam (denoted as MNSe@NF) from the MOF. The MNSe nanostructures can demonstrate enriched active sites, and shorten the ion-electron diffusion pathways. When the MNSe@NF electrode is used as a cathode electrode for a hybrid supercapacitor, the electrode reflected impressive supercapacitive properties with a high capacity of 325.6 mA h g-1 (1172.16 C g-1) at 2 A g-1, an exceptional rate performance of 86.6% at 60 A g-1, and remarkable longevity (3.2% capacity decline after 15 000 cycles). Also, the assembled MNSe@NF∥AC@NF hybrid supercapacitors employing activated carbon on the nickel foam (AC@NF, anode electrode) and MNSe@NF (cathode electrode) revealed an impressive energy density of 66.1 W h kg-1 at 858.45 W kg-1 and an excellent durability of 94.1% after 15 000 cycles.

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.