Morphological modulation of NiCo2Se4 nanotubes through hydrothermal selenization for asymmetric supercapacitor

Boosting the capacitive property of binary metal tellurium of MnCoTe/NiFeTe yarn coils-like through surface engineering for high-performance supercapacitors

Improving the performance of electrode materials based on transition metals can significantly push advancements in energy storage devices. In this work, we offer a novel in situ tellurization approach to synthesize brand-new decorated yarn-coils MnCoTe/NiFeTe on a NiF (labeled MCTe/NFTe@NiF) which makes them attractive candidates for electrode materials in hybrid supercapacitors. At first, two consecutive hydrothermal methods were used to create electrode materials MnCo-LDH and MnCo-LDH/NiFe-LDH on nickel foam, respectively. In the following, electrode material MnCo-LDH/NiFe-LDH was subjected to a tellurization process to create MnCoTe/NiFeTe nanostructures. The direct growth strategy of electrode materials on a conductive substrate (NiF) effectively eliminates the need for polymer binder or conductive materials, thereby facilitating the redox process. The MnCoTe/NiFeTe@NiF electrode benefits from the synergistic effects of conductive tellurium and yarn coils-like morphology, resulting in faster electron/ion transport, increased efficiency, and superior electrochemical performance. The MCTe/NFTe@NiF electrode reveals highly desirable electrochemical characteristics, including a specific capacity of 223.36 mA h/g at 1 A/g, and reliable longevity surpassing 10,000 GCD cycles, with maintaining 73.18 % of its initial specific capacity at 30 A/g. We have prepared a hybrid supercapacitor (labeled MCTe/NFTe@NiF(+)//AC@NiF(-)), which utilizes the positive MCTe/NFTe@NiF and the negative AC@NiF electrodes. This hybrid supercapacitor indicated an excellent energy density of 51.55 Wh/kg, a power density of 799.98 W/kg, and showed substantial longevity (92.33 % after 10,000 GCD cycles).

Vacancy Engineering of Selenium-Vacant NiCo2Se4 with Enhanced Electrochemical Performance for Supercapacitor

Vacancy engineering effectively modulates the electronic properties of electrode materials, thereby improving their electrochemical performance. In this study, we prepared selenium-deficient NiCo2Se4 (Sev-NCS) using ethylene glycol as a reducing agent in NaOH alkaline environment, and investigated its potential as an electrode material for supercapacitors. Both theoretical and experimental results confirmed that the introduction of vacancies altered the morphology and electronic structure of NiCo2Se4, which in turn synergistically improved the conductivity and the diffusion capability of electrolyte ions. The optimized Sev-NCS electrode achieved an excellent specific capacitance of 2962.7 F g-1 at a current density of 1 A g-1 and superior cycling stability with a capacitance retention of 89.5% even after 10,000 cycles. Furthermore, an asymmetric device composed of the optimized Sev-NCS electrode as the positive electrode and activated carbon as the negative electrode achieved an energy density of 55.6 Wh kg-1 at a power density of 800 W kg-1. Therefore, this work offers novel insights into the role of vacancy engineering in improving the performance of transition metal compound-based electrode materials for supercapacitor.

Revealing the Effect of Anion Regulation in NiCo2X4 (X = O, S, Se, Te) on Photoassisted Methanol Electrocatalytic Oxidation

Designing nonprecious metal anode catalysts for photoassisted direct methanol fuel cells (PDMFCs) remains a challenge. As a semiconductor catalyst with a spinel structure, NiCo2O4 has good methanol catalytic oxidation activity and photocatalytic activity, making it a highly promising anode non-noble metal catalyst for PDMFCs. However, compared with the noble metal catalyst, the photoelectrocatalytic activity remained to be improved. In this report, an anion regulation strategy was adopted to improve the photoassisted methanol electrocatalytic activity. Using a CoNi-Aspartic (CoNi-Asp) nanorod as the precursor, the anion-regulated NiCo2X4 (X = O, S, Se, Te) was prepared by oxidation, sulfuration, selenization, and telluridation reactions. The regulation of anions and their effects on the electronic structure, intermediate product, and photoelectric catalytic performance of NiCo2X4 (X= O, S, Se, Te) was systematically discussed. Photoelectrochemical characterization and adsorption energy of •OH revealing the volcano-like correlation between the anion in NiCo2X4 (X = O, S, Se, Te) and their photoelectrocatalytic performance. The narrowest band gap (2.239 eV), the highest •OH adsorption energy (-3.32 eV), and the highest ratio of Co3+/Co2+ (2.19) ensure the best photoelectric catalytic performance of NiCo2S4, under the visible light irradiation, the photoresponse current density was 1.9 A g-1, the current density at 0.6 V was up to 21.9 A g-1. After 9 h of stability testing, the current retention rate was 80%. This report sheds an idea for the rational design of non-noble anode catalysts for PDMFCs.

All-Solid-State Supercapacitors Based on Cobalt Magnesium Telluride Microtubes Decorated with Tellurium Nanotubes

Magnesium (Mg) has received very little exploration on its importance in the realm of battery-type energy storage technologies. They are abundantly present in seawater, and if successfully extracted and utilized in energy storage systems, it could lead to the long-term advancement of human civilization. Here, we fabricated an all-solid-state supercapacitor (ASSSC) using tellurium nanotubes decorated cobalt magnesium telluride microtubes (Te NTs@CoMgTe MTs) clad on nickel foam (NF). Owing to the unique mixed phase hierarchical structure, Te NTs@CoMgTe MTs showcases some advancement in energy storage performance. When tested in a three-electrode system, multiphasic hybrid of elemental Te and metal tellurides, Te NTs@CoMgTe MTs outperforms the monometallic telluride owing to the strong synergistic interaction effect triggered from conductive three components and delivers a long-life span performance up to 15,000 cycles. The fabricated Te NT@CoMgTe MT//AC solid-state device exhibits a maximum areal capacity of 59.2 μAh cm-2 (56.3 mAh g-1) at a current density of 6 mA cm-2 with a maximum energy density of 42.2 Wh kg-1 (46.5 μWh cm-2) at a power density of 6857.1 W kg-1 (7574.6 μW cm-2). The performance of the device is rigid even at different bending angles (0 to 180°) which validates the extensibility of the process for future applications.

Hierarchical Mn3O4/NiSe2-MnSe2: A Versatile Electrode Material for High-Performance All-Solid-State Hybrid Pseudocapacitors with Supreme Working Durability

As highly efficient electrochemical energy storage devices are in indispensable demand for numerous modern-day technologies, herein sluggish precipitation followed by an anion exchange procedure has been developed to synthesize an oxide-selenide mixed phase (Mn3O4/NiSe2-MnSe2) novel electrode material with high surface area and porosity for high-performance all-solid-state hybrid pseudocapacitors (ASSHPC). Mn3O4/NiSe2-MnSe2 shows a rich Tyndall effect (in H2O) and possesses randomly arranged low-dimensional crystallites of nearly similar size and uniform shape. The electrochemical analyses of Mn3O4/NiSe2-MnSe2 corroborate good electrochemical reversibility during charge transfer, superior pseudocapacitive charge-storage efficiency, and very low charge transfer and series resistance, ion-diffusion resistance, and relaxation time, which endorse the quick pseudocapacitive response of the material. The Mn3O4/NiSe2-MnSe2||N-rGO ASSHPC device demonstrates excellent charge-storage physiognomies suggestive of rich electrochemical and electromicrostructural compatibility between the electrode materials in the fabricated assembly. The Mn3O4/NiSe2-MnSe2||N-rGO ASSHPC device delivers high mass and area specific capacitance/capacity, very low charge-transfer resistance (∼0.74 Ω), total series resistance (∼0.76 Ω), diffusion resistance, and a relaxation time constant, which endorse the quick pseudocapacitive response of the device. The device delivers higher energy and power density (∼34 W h kg-1 at ∼2994 W kg-1), rate efficiency (∼17 W h kg-1 at ∼11,995 W kg-1), and cyclic performance (∼97.2% specific capacity/capacitance retention after 9500 continuous GCD cycles). The superior Ragone and cyclic efficiencies of the ASSHPC device are ascribed to the multiple redox-active Ni and Mn ions which lead to the supplemented number of redox reactions; "electroactive-ion buffering pool"-like physiognomics of Mn3O4/NiSe2-MnSe2, which facilitate the electrolyte ion dissemination to the electroactive sites even at high rate redox condition; and ideal electro-microstructural compatibility between the electrode materials, which leads to assisted charge transfer and absolute ion dissemination during the charge-storage process.

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.

Electrodeposition Synthesis of Coral-like MnCo Selenide Binder-Free Electrodes for Aqueous Asymmetric Supercapacitors

Bimetallic selenide compounds show great potential as supercapacitor electrode materials in energy storage and conversion applications. In this work, a coral-like MnCo selenide was grown on nickel foam using a facile electrodeposition method to prepare binder-free supercapacitor electrodes. The heating temperature was varied to tune the morphology and crystal phase of these electrodes. Excellent electrochemical performance was achieved due to the unique coral-like, dendritic- dispersed structure and a bimetallic synergistic effect, including high specific capacitance (509 C g-1 at 1 A g-1) and outstanding cycling stability (94.3% capacity retention after 5000 cycles). Furthermore, an asymmetric supercapacitor assembled with MnCo selenide as the anode and active carbon as the cathode achieved a high specific energy of 46.2 Wh kg-1 at 800 W kg-1. The work demonstrates that the prepared coral-like MnCo selenide is a highly promising energy storage material.

Multifunctional metal selenide-based materials synthesized via a one-pot solvothermal approach for electrochemical energy storage and conversion applications

Highly-efficient electroactive materials with distinctive electrochemical features, along with suitable strategies to prepare hetero-nanoarchitectures incorporating two or more transition metal selenides, are currently required to increase charge storage ability. Herein, a one-pot solvothermal approach is used to develop iron-nickel selenide spring-lawn-like architectures (FeNiSe SLAs) on nickel (Ni) foam. The porous Ni foam scaffold not only enables the uniform growth of FeNiSe SLAs but also serves as an Ni source. The effect of reaction time on their morphological and electrochemical properties is investigated. The FeNiSe-15 h electrode shows high areal capacity (493.2 μA h cm-2) and superior cycling constancy. The as-assembled aqueous hybrid cell (AHC) demonstrates high areal capacity and a decent rate capability of 59.4% (50 mA cm-2). The AHC exhibits good energy and power densities, along with excellent cycling stability. Furthermore, to confirm its practicability, the AHC is employed to drive portable electronic appliances by charging it with wind energy. The electrocatalytic activity of FeNiSe-based materials to complete the oxygen evolution reaction (OER) is explored. Among them, the FeNiSe-15 h catalyst shows good OER performance at a current density of 50 mA cm-2. This general synthesis approach may initiate a strategy of advanced metal selenide-based materials for multifunctional applications.

Experimental and Theoretical Insights of Anion Regulation in MOF-Derived Ni-Co-Based Nanosheets for Supercapacitors and Anion Exchange Membrane Water Electrolyzers

The anionic components have a significant role in regulating the electrochemical properties of mixed transition-metal (MTM)-based materials. However, the relationship between the anionic components and their inherent electrochemical properties in MTM-based materials is still unclear. Herein, we report the anion-dependent supercapacitive and oxygen evolution reaction (OER) properties of in situ grown binary Ni-Co-selenide (Se)/sulfide (S)/phosphide (P) nanosheet arrays (NAs) over nickel foam starting from MOF-derived Ni-Co layered double hydroxide precursors. Among them, the Ni-Co-Se NAs exhibited the best specific capacity (289.6 mA h g^-1 at 4 mA cm^-2). Furthermore, a hybrid device constructed with Ni-Co-Se NAs delivered an excellent energy density (74 W h kg^-1 at 525 W kg^-1) and an ultra-high power density (10 832 W kg^-1 at 46 W h kg^-1) with outstanding durability (∼94%) for 10 000 cycles. Meanwhile, the Ni-Co-Se NAs showed superior electrocatalytic OER outputs with the lowest overpotential (235 mV at 10 mA cm^-2) and Tafel slope. In addition, Ni-Co-Se NAs outperformed IrO₂ as an anode in an anion exchange membrane water electrolyzer at a high current density (>1.0 A cm^-2) and exhibited a stable performance up to 48 h with a 99% Faraday efficiency. Theoretical analyses validate that the Se promotes OH adsorption and improves the electrochemical activity of the Ni-Co-Se through a strong electronic redistribution/hybridization with an active metal center due to its valence 4p and inner 3d orbital participations. This study will provide in-depth knowledge of bifunctional activities in MTM-based materials with different anionic substitutions.

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.

Bimetallic CoSe2/FeSe2 hollow nanocuboids assembled by nanoparticles as a positive electrode material for a high-performance hybrid supercapacitor

Design and fabrication of impressive and novel electrode materials for energy storage devices, especially supercapacitors, are of great importance. Herein, bimetallic CoSe₂/FeSe₂ hollow nanocuboid nanostructures derived from Co/Fe-Prussian Blue analogues (denoted as CoSe₂/FeSe₂ HNCs) are successfully designed and fabricated as a remarkable positive electrode material for high-performance supercapacitors. The bimetallic CoSe₂/FeSe₂ HNC nanostructures can have increased active sites and short electron-ion diffusion pathways. Bimetallic CoSe₂/FeSe₂ HNCs@NiF as a positive electrode showed efficient supercapacitive properties with a great specific capacity of 332.75 mA h g^-1 (1197.90 C g^-1) at 1 A g^-1, retaining 80.61% of its initial capacity at 20 A g^-1, considerable longevity (91.47% of its initial capacity after 10 000 cycles) and an excellent coulombic efficiency of 98.49%. Also, the designed and fabricated CoSe₂/FeSe₂ HNCs@NiF||AC@NiF hybrid supercapacitor device using bimetallic CoSe₂/FeSe₂ HNCs@NiF (positive electrode) and activated carbon@NiF (AC, negative electrode) exhibited an efficient energy density of 63.62 W h kg^-1 and a superior durability of 91.14% after 10 000 cycles.

Self-Activated Formation of Hierarchical Co3 O4 Nanoflakes with High Valence-State Conversion Capability for Ultrahigh-Capacity Zn-Co Batteries

Cobalt-based materials are attracting increasing interest in alkaline Zn batteries due to the high theoretical capacity. However, the practical utilization is restricted by the poor microstructure and insufficient valence-state conversion. Herein, a self-activated formation of hierarchical Co₃ O₄ nanoflakes with high valence-state conversion capability is designed. This electrode not only exhibits the optimized microstructure with large reaction surfaces, but also shows excellent valence-state conversion capability. Consequently, this battery delivers an ultrahigh capacity of 481.4 mAh g^-1 and an energy density of 818.3 Wh kg^-1 based on the active material, which shines among reported Co-based materials. Besides, the capacity can retain 41.9% with even 20× current density increases, and it can operate with a capacity decay of 20% after the 1000th cycle. This strategy greatly enhances the performance and durability of integrated air electrodes, raising the attention of boundary design for other electrochemical energy conversion and storage devices.

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.

Self-templating Scheme for the Synthesis of NiCo2Se4 and BiSe Hollow Microspheres for High-energy Density Asymmetric Supercapacitors

Porous hollow structure of the electrode materials can enlarge the surface area in contact with the electrolyte, accelerating the transport of ions and electrons during redox reaction to enhance electrochemical...

Mixed Cu2 Se Hexagonal Nanosheets@Co3 Se4 Nanospheres for High-Performance Asymmetric Supercapacitors

Rational designing and constructing multiphase hybrid electrode materials is an effective method to compensate for the performance defects of the single component. Based on this strategy, Cu₂ Se hexagonal nanosheets@Co₃ Se₄ nanospheres mixed structures have been fabricated by a facile two-step hydrothermal method. Under the synergistic effect of the high ionic conductivity of Cu₂ Se and the remarkable cycling stability of Co₃ Se₄ , Cu₂ Se@Co₃ Se₄ can exhibit outstanding electrochemical performance as a novel electrode material. The as-prepared Cu₂ Se@Co₃ Se₄ electrode displays high specific capacitance of 1005 F g^-1 at 1 A g^-1 with enhanced rate capability (56 % capacitance retention at 10 A g^-1 ), and ultralong lifespan (94.2 % after 10 000 cycles at 20 A g^-1 ). An asymmetric supercapacitor is assembled applying the Cu₂ Se@Co₃ Se₄ as anode and graphene as cathode, which delivers a wide work potential window of 1.6 V, high energy density (30.9 Wh kg^-1 at 0.74 kW kg^-1 ), high power density (21.0 Wh kg^-1 at 7.50 kW kg^-1 ), and excellent cycling stability (85.8 % after 10 000 cycles at 10 A g^-1 ).

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.

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.

Rod-like nickel doped Co3Se4/reduced graphene oxide hybrids as efficient electrocatalysts for oxygen evolution reactions

In the oxygen evolution reaction (OER), highly active catalysts are essential for reducing the overpotential and improving the slow kinetics of the process. Cobalt selenide (Co₃Se₄) has always been considered as a promising electrocatalyst for the OER due to the well-suited electronic configuration of the Co ions in it. However, poor exposure of the active sites and low electron conductivity are still its biggest problems. In this study, we report an efficient Ni-doped rod-like Co₃Se₄ hybridized with reduced graphene oxide (Ni-Co₃Se₄/rGO) as an OER electrocatalyst. The Ni doping regulates the electronic structure of Co₃Se₄ and significantly reduces the overpotential of Co₃Se₄ toward the OER under alkaline conditions. Simultaneously, hybridization of the reduced graphene oxide (rGO) enhances the conductivity which leads to the improvement in OER activity. The Ni-Co₃Se₄/rGO catalyst shows a lower overpotential (284 mV at 10 mA cm^-2) as well as a Tafel slope (71 mV dec^-1), which outperformed the benchmark of commercial RuO₂. Moreover, Ni-Co₃Se₄/rGO also shows high stability and long-term durability.