Zn-Co phosphide porous nanosheets derived from metal-organic-frameworks as battery-type positive electrodes for high-performance alkaline supercapacitors

High-mass-loading cobalt iron phosphide@nickel vanadium layered double hydroxide heterogeneous nanosheet arrays for hybrid supercapacitors

Designing multidimensional heterostructures on flexible substrates is an efficient approach to resolve the low energy density of supercapacitors. Herein, a three-dimensional (3D) porous cobalt iron phosphide (CoFeP)@nickel vanadium-layered double hydroxide (NiV-LDH) heterostructure has been prepared anchored on carbon cloth (CC) substrate. In this nanoarchitecture, NiV-LDH nanosheets are densely wrapped on the surface of CoFeP nanosheets, which forms a hierarchically porous framework with an enlarged surface area and accessible pore channels. Benefiting from the strong interaction and synergistic effect between CoFeP and NiV-LDH, the well-defined heterostructure can realize simultaneously rich redox active sites, rapid reaction dynamics, and good structural stability. Thus, the binder-free CoFeP@NiV-LDH electrode with a high mass loading of 6.47 mg cm-2 displays a significantly increased specific capacity of 903.1C g-1 (2.35C cm-2) at 1 A g-1 and enhanced rate capability when compared to pristine CoFeP and NiV-LDH. Additionally, the assembled hybrid supercapacitor (HSC) yields an energy density of 77.9 Wh kg-1/0.98 Wh cm-2 and excellent long-term stability. This research proposes a rational route for designing heterogeneous micro-/nanoarchitectures with commercial-level mass loading for the practical application of high-energy-density supercapacitors.

Phosphorization Engineering on a MOF-Derived Metal Phosphide Heterostructure (Cu/Cu3P@NC) as an Electrode for Enhanced Supercapacitor Performance

A highly conductive and rationally constructed metal-organic framework (MOF)-derived metal phosphide with a carbonaceous nanostructure is a meticulous architecture toward the development of electrode materials for energy storage devices. Herein, we report a facile strategy to design and construct a new three-dimensional (3D) Cu-MOF via a solvent diffusion method at ambient temperature, which was authenticated by a single-crystal X-ray diffraction study, revealing a novel topology of (2,4,7)-connected three-nodal net named smm4. Nevertheless, the poor conductivity of pristine MOFs is a major bottleneck hindering their capacitance. To overcome this, we demonstrated an MOF-derived Cu3P/Cu@NC heterostructure via low-temperature phosphorization of Cu-MOF. The electronic and ionic diffusion kinetics in Cu3P/Cu@NC were improved due to the synergistic effects of the heterostructure. The as-prepared Cu3P/Cu@NC heterostructure electrode delivers a specific capacity of 540 C g-1 at 1 A g-1 with outstanding rate performance (190 C g-1 at 20 A g-1) and cycle stability (91% capacity retention after 10,000 cycles). Moreover, the assembled asymmetric solid-state supercapacitor (ASC) achieved a high energy density/power density of 45.5 Wh kg-1/7.98 kW kg-1 with a wide operating voltage (1.6 V). Long-term stable capacity retention (87.2%) was accomplished after 5000 cycles. These robust electrochemical performances suggest that the Cu3P/Cu@NC heterostructure is a suitable electrode material for supercapacitor applications.

Bi Nanosheets on Porous Carbon Cloth Composites for Ultrastable Flexible Nickel-Bismuth Batteries

The use of bismuth (Bi) as an anode material in nickel-metal batteries has gained significant attention due to its highly reversible redox reaction and suitable operating conditions. However, the cycling stability and flexibility of nickel-bismuth (Ni//Bi) batteries need to be further improved. This paper employs a facile electrodeposition technique to prepare Bi nanosheets uniformly grown on a porous carbon cloth (PCC), denoted as Bi-PCC electrodes. The Bi-PCC electrode portrays a specific surface area and good wettability that enable fast charge transfer and ion transport channels. Consequently, the Bi-PCC electrode demonstrates a high specific capacity of up to 297.1 mAh g^-1 at 2 A g^-1, with a capacity retention of up to 71.5% at 2-40 A g^-1 and an impressive capacity retention of 79.9% after 1000 cycles at 2-40 A g^-1. More importantly, the flexible rechargeable Ni//Bi battery (denoted as Ni(OH)₂-PCC//Bi-PCC) with Bi-PCC as the anode and Ni(OH)₂-PCC as the cathode has excellent electrochemical performance. The Ni(OH)₂-PCC//Bi-PCC battery boasts a remarkable capacity retention of 93.6% after 3000 cycles at 10 A g^-1. Further, the cell presents a maximum energy density of 73.1 Wh kg^-1 and an impressive power density of 11.9 kW kg^-1.

Principles of Design and Synthesis of Metal Derivatives from MOFs

Materials derived from metal-organic frameworks (MOFs) have demonstrated exceptional structural variety and complexity and can be synthesized using low-cost scalable methods. Although the inherent instability and low electrical conductivity of MOFs are largely responsible for their low uptake for catalysis and energy storage, a superior alternative is MOF-derived metal-based derivatives (MDs) as these can retain the complex nanostructures of MOFs while exhibiting stability and electrical conductivities of several orders of magnitude higher. The present work comprehensively reviews MDs in terms of synthesis and their nanostructural design, including oxides, sulfides, phosphides, nitrides, carbides, transition metals, and other minor species. The focal point of the approach is the identification and rationalization of the design parameters that lead to the generation of optimal compositions, structures, nanostructures, and resultant performance parameters. The aim of this approach is to provide an inclusive platform for the strategies to design and process these materials for specific applications. This work is complemented by detailed figures that both summarize the design and processing approaches that have been reported and indicate potential trajectories for development. The work is also supported by comprehensive and up-to-date tabular coverage of the reported studies.

Multimetallic transition metal phosphide nanostructures for supercapacitors and electrochemical water splitting

Transition metal phosphides (TMPs) have recently emerged as an important class of functional materials and been demonstrated to be outstanding supercapacitor electrode materials and catalysts for electrochemical water splitting. While extensive investigations have been devoted to monometallic TMPs, multimetallic TMPs have lately proved to show enhanced electrochemical performance compared to their monometallic counterparts, thanks to the synergistic effect between different transition metal species. This topical review summarizes recent advance in the synthesis of new multimetallic TMP nanostructures, with particular focus on their applications in supercapacitors and electrochemical water splitting. Both experimental reports and theoretical understanding of the synergy between transition metal species are comprehensively reviewed, and perspectives of future research on TMP-based materials for these specific applications are outlined.

Uniform Bi-Bi2O3 nanoparticles/reduced graphene oxide composites for high-performance aqueous alkaline batteries

Aqueous alkaline batteries (AABs) with the merits of both high energy density and power density have emerged as one of the most promising candidates for the new generation of energy storage devices, while their practical applications are still limited by the lack of high-performance electrode materials, especially for the anode materials. Herein, metallic bismuth-bismuth oxide nanoparticles (Bi-Bi₂O₃), with numerous heterogeneous interfaces, are successfully anchored and uniformly distributed on reduced graphene oxide (rGO) sheets. When Bi-Bi₂O₃/rGO-20 electrode is used as the anode material for an AAB, it shows a high specific capacity of 288.0 mA h g^-1 (1036.9 F g^-1) at 1 A g^-1 and good rate capability (74.7% of capacity retention ratio at 20 A g^-1). Additionally, in order to match well with a Bi-Bi₂O₃/rGO-20 anode, CoVS_x thin sheets decorated with Ni-Co layered double hydroxide sheets (NiCo-LDH) were successfully constructed via a facile multistep hydrothermal method and a subsequent electrodeposition process. The resulting cathode exhibits a high specific capacity of 306.0 mA h g^-1 (2448 F g^-1) at 1 A g^-1. The assembled CoVS_x@NiCo-LDH//Bi-Bi₂O₃/rGO-20 AAB delivers an outstanding energy density of 106.1 Wh kg^-1 at a power density of 789.6 W kg^-1. Besides, the as-synthesized Bi-based electrode is also used in aqueous Zn alkaline batteries to further extend its application and the assembled Bi-Bi₂O₃/rGO-20//Zn batteries possess an ultralong flat discharge plateau and exhibit a specific capacity of 250.6 mA h g^-1 at 1 A g^-1. The results demonstrate that the as-assembled AAB has huge potential for practical applications and provides an inspiration for the next-generation energy storage devices.

Iron decorated ultrathin cobaltous hydroxide nanoflakes with impressive electrochemical reactivity for aqueous Zn batteries

The main bottlenecks of current Co-based cathodes are their relatively low capacity and inferior reversibility. Here, we report Fe decorated cobaltous hydroxide (FCO) nanoflakes with vastly improved capacity and cycling stability via an efficient surface activation approach, which function as an advanced cathode for Co-Zn batteries. In comparison with the pristine cobaltous hydroxide (CO), the FCO sample owns higher electrochemical reactivity and a larger electrochemical surface area, endowing it with impressive electrochemical properties.

Toward Enhanced Electrochemical Performance by Investigation of the Electrochemical Reconstruction Mechanism in Co2V2O7 Hexagonal Nanosheets for Hybrid Supercapacitors

As for hybrid supercapacitors, it is important to enhance the long cycling performance and high specific capacitance. In this paper, cobalt vanadate (Co₂V₂O₇) hexagonal nanosheets on nickel foam are manufactured by a facile hydrothermal method and then transformed into numerous smaller size interconnected hierarchical nanosheets without any shape change via electrochemical reconstruction. Benefiting from the favorable architecture of hierarchical nanosheets via electrochemical reconstruction, the Co₂V₂O₇ hexagonal nanosheet electrode exhibits a remarkable long cycling performance with 272% specific capacitance retention after 100,000 cycles at a current density of 5 A g^-1 and then displays an increasing specific capacitance of 1834 F g^-1 (tested at 1 A g^-1). Furthermore, an aqueous hybrid supercapacitor device based on the Co₂V₂O₇ hexagonal nanosheet electrode exhibits a high energy density of 35.2 Wh kg^-1 at a power density of 1.01 kW kg^-1 and an excellent cyclic stability with 71.4% capacitance retention after 10,000 cycles at 5 A g^-1. These results offer a practicable pathway for enhancing the electrochemical properties of other metal oxides through electrochemical reconstruction.

High-capacity CoP-Mn3P nanoclusters heterostructures derived by Co2MnO4 as advanced electrodes for supercapacitors

Although transition metal oxides (TMOs) have attracted enormous attention owing to their high performance in supercapacitors, it still remains challenging issues in terms of the poor electrical conductivity, sluggish redox kinetics and insufficient electrochemical active sites. Herein, the high-capacity CoP-Mn₃P nanoclusters featuring the heterogeneous interfaces have been successfully synthesized through hydrothermal method followed by annealing. The heterojunction formed between CoP and Mn₃P redistributes the charge at the interface between them, generating the built-in electric field to accelerate electron transfer, and thus the conductivity of the electrode is enhanced. Moreover, the unique morphology of nanoclusters composed of flake structures is beneficial to provide more electrochemical active sites. Consequently, the resultant CoP-Mn₃P nanoclusters electrode delivers an exceptional gravimetric specific capacity (2714 F g^-1 at 1 A g^-1) as well as a long cycle lifespan (83.1% of capacitance retention after 10,000 cycles). An asymmetric supercapacitor (ASC) device assembling with employing CoP/Mn₃P electrode presents an ultrahigh energy density value of 46.4 Wh kg^-1 at a power density of 800.0 W kg^-1 and a super capacitance retention of 86.2% after 30,000 cycles. This work paves an effective way for the investigation on the charge transfer kinetics of electrode materials.

High-performance quasi-solid-state flexible supercapacitors based on a flower-like NiCo metal–organic framework

NiCo metal–organic framework (MOF) electrodes were prepared by a simple hydrothermal method. The flower-like NiCo MOF electrode exhibited an exciting potential window of 1.2 V and an excellent specific capacitance of 927.1 F g⁻¹ at 1 A g⁻¹. The flower-like NiCo MOF//activated carbon (AC) device delivered a high energy density of 28.5 W hkg⁻¹ at a power density of 400.5 W kg⁻¹ and good cycle stability (95.4% after 5000 cycles at 10 A g⁻¹). Based on the flower-like NiCo MOF electrode, the asymmetric quasi-solid-state flexible supercapacitor (AFSC) was prepared and exhibited good capacitance retention after bending (79% after 100 bends and 64.4% after 200 bends). Furthermore, two AFSCs in series successfully lit up ten parallel red LED lights, showing great application potential in flexible and wearable energy storage devices.

The flower-like NiCo MOF prepared by a hydrothermal has a specific capacitance of 927.1 F g⁻¹ at 1 A g⁻¹ and a capacitance retention of 69.7% from 1 A g⁻¹ to 10 A g⁻¹, showing excellent electrochemical performance.

Rational synthesis of CoFeP@nickel-manganese sulfide core-shell nanoarrays for hybrid supercapacitors

Transition metal phosphide electrodes, particularly those with unique morphologies and micro-/nanostructures, have demonstrated desirable capabilities for hybrid supercapacitor applications by virtue of their superior electrical conductivity and high electrochemical activity. Here, three-dimensional hierarchical CoFeP@nickel-manganese sulfide nanoarrays were in situ constructed on a flexible carbon cloth via a hydrothermal method, a phosphorization process, followed by an electrodeposition approach. In this smart nanoarchitecture, CoFeP nanorods grown on carbon cloth act as the conductive core for rapid electron transfer, while the nickel-manganese sulfide nanosheets decorated on the surface of CoFeP serve as the shell for efficient ion diffusion, forming a stable core-shell heterostructure with enhanced electrical conductivity. Benefiting from the synergy of the two components and the generation of a heterointerface with a modified electronic structure, The CoFeP@nickel-manganese sulfide electrodes deliver a high capacity of 260.7 mA h g^-1 at 1 A g^-1, excellent rate capability, and good cycling stability. More importantly, an aqueous hybrid supercapacitor based on CoFeP@nickel-manganese sulfide as a positive electrode and a lotus pollen-derived hierarchical porous carbon as a negative electrode is constructed to display a maximum energy density of 60.1 W h kg^-1 at 371.8 W kg^-1 and a good cycling stability of 85.7% capacitance retention after 10 000 cycles.