Homologous NiCoP/CoP hetero-nanosheets supported on N-doped carbon nanotubes for high-rate hybrid supercapacitors

Rational Construction of a 3D Self-Supported Electrode Based on ZIF-67 and Amorphous NiCoP for an Enhanced Oxygen Evolution Reaction

The development of efficient and Earth-abundant electrocatalysts for the oxygen evolution reaction (OER) is an urgent requirement in the field of electrochemical water splitting. The electrocatalytic performance of the OER can be greatly enhanced by the synergistic combination of zeolite imidazolate frameworks (ZIFs) and transition-metal phosphides, both of which individually exhibit promising capabilities in this regard. In this study, a novel amorphous NiCoP deposited on ZIF-67 sheets supported on Ni foam (labeled as NiCoP/ZIF-67/NF) as an OER electrocatalytic material was successfully synthesized using a simple, secure, and time-efficient two-step strategy. The experimental results demonstrate that NiCoP/ZIF-67/NF possesses a large active surface area with abundant active sites. Also, the synergistic effect and interaction between NiCoP and ZIF-67, as well as between Ni and Co within NiCoP, effectively enhance its electrochemical performance under alkaline conditions. Consequently, NiCoP/ZIF-67/NF exhibits outstanding catalytic activity for OER with an overpotential (η) of 175 mV at a current density of 10 mA cm-2 and a long-term stability over 40 h at 20 mA cm-2 in a 1.0 M KOH electrolyte. The corresponding analyses suggest that the real active sites responsible for the OER are identified as NiOOH and CoOOH species within the structure of NiCoP/ZIF-67/NF. Additionally, the catalytic function and stability of ZIF-67 toward the OER under alkaline conditions were also briefly discussed. This work provides a novel catalytic material for the OER along with a facile strategy to fabricate superior, efficient, and noble metal-free catalysts suitable for energy-related applications.

Regulation of Electronic Structures of the Urchin-Like NiCoP/CoP Nanocatalysts for Fast Hydrogen Evolution

The exploration of stable, efficient, and low-cost catalysts toward ammonia borane hydrolysis is of vital significance for the practical implementation of this hydrogen production technology. Integrating interface engineering and nano-architecture engineering is a favorable strategy to elevate catalytic performance, as it can modify the electronic structure and provide sufficient active sites simultaneously. In this work, urchin-like NiCoP/CoP heterostructures are prepared via a three-step hydrothermal-oxidation-phosphorization synthesis route. It is demonstrated that the original Ni/Co molar ratio and the amount of phosphorus are crucial for adjusting the morphology, enhancing the exposed surface area, facilitating charge transfer, and modulating the adsorption and activation of H2O molecules. Consequently, the optimal Ni1Co2P heterostructure displays remarkable catalytic properties in the hydrolysis of ammonia borane with a turnover frequency (TOF) value of 30.3 molH2 ⋅ min-1 ⋅ molmetal -1, a low apparent activation energy of 25.89 kJ ⋅ mol-1, and good stability. Furthermore, by combining infrared spectroscopy and isotope kinetics experiments, a possible mechanism for the hydrolysis of ammonia borane was proposed.

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.

Hierarchical Cube-in-Cube Cobalt-Molybdenum Phosphide Hollow Nanoboxes Derived from the MOF Template Strategy for High-Performance Supercapacitors

The design of hierarchical hollow nanostructures with complex shell architectures is an attractive and effective way to obtain a desirable electrode material for energy storage application. Herein, we report an effective metal-organic framework (MOF) template-engaged method to synthesize novel double-shelled hollow nanoboxes, in terms of chemical composition and structure complexity, for supercapacitor application. Starting from cobalt-based zeolitic imidazolate framework (ZIF-67(Co)) nanoboxes as the removal template, we developed a rational preparation approach to synthesize cobalt-molybdenum-phosphide (CoMoP) double-shelled hollow nanoboxes (donated as CoMoP-DSHNBs) through (i) ion-exchange reaction, (ii) template etching, and (iii) phosphorization treatment, respectively. Notably, despite the previously reported works, the phosphorization was simply done using the facile solvothermal method, without employing annealing and high-temperature conditions, which can be considered as one of the merits of the current work. CoMoP-DSHNBs showed excellent electrochemical properties owing to their unique morphology, high surface area, and optimal elemental composition. In a three-electrode system, the target material showed a superior specific capacity of 1204 F g^-1 at 1 A g^-1 with a remarkable cycle stability of 87% after 20000 cycles. The hybrid device formed of activated carbon (AC) as the negative electrode and CoMoP-DSHNBs as the positive electrode exhibited a high specific energy density of 49.99 W h kg^-1 and a maximum power density of 7539.41 W kg^-1 with a great cycling stability of 84.5% after 20,000 cycles.

Activation-Assisted High-Concentration Phosphorus-Doping to Enhance the Electrochemical Performance of Cobalt Carbonate Hydroxide Hydrate

P-doping into metal oxides has been demonstrated as a valid avenue to ameliorate electrochemical performance because it can tune the electronic structures and increase the active sites for an electrochemical reaction. However, it usually results in a low P-doping concentration via the commonly used gas phosphorization method. In this work, an activation-assisted P-doping strategy was explored to significantly raise the P-doping concentration in cobalt carbonate hydroxide hydrate (CCHH). The activation treatment increased active sites for electrochemical reaction and endowed the sample with a high P content in the subsequent gas phosphorization process, thereby greatly enhancing the conductivity of the sample. Therefore, the final CCHH-A-P electrode exhibited a high capacitance of 6.62 F cm^-2 at 5 mA cm^-2 and good cyclic stability. In addition, the CCHH-A-P//CC ASC with CCHH-A-P as the positive electrode and carbon cloth as the negative electrode provided a high energy density of 0.25 mWh cm^-2 at 4 mW cm^-2 as well as excellent cycling performance with capacitance retention of 91.2% after 20,000 cycles. Our work shows an effective strategy to acquire Co-based materials with high-concentration P-doping that holds great potential in boosting the electrochemical performance of electrode materials via P-doping technology.

Graphene frameworks-confined synthesis of 2D-layered NiCoP for the electrochemical sensing of H2O2 at lower overpotential

A new 2D-layered nickel cobalt phosphide nanosheet confined by 3D graphene frameworks (denoted as NiCoP/GFs) is in situ controllably synthesized as a highly efficient and durable electrocatalyst, which is obtained from the transformation of corresponding NiCo layer double hydroxides and GFs. Hydrogen peroxide (H₂O₂) is selected as a demonstration to study the electrochemical sensing performance of the NiCoP/GFs. Benefiting from 2D morphology of NiCoP and network structure of GFs, NiCoP/GFs exhibits remarkable electroactivity toward H₂O₂ at a relatively low overpotential of approximately - 0.3 V (vs sat. Ag/AgCl) in 0.01 M phosphate-buffered saline solution (PBS, pH = 7.4). The NiCoP/GFs-based H₂O₂ electrochemical sensor achieves a high sensitivity of ∼4398 μA mM^-1 cm^-2, a low detection limit of 0.028 ± 0.006 μM, and desirable selectivity. In addition, the sensor can sensitively detect H₂O₂ from living cancer cells. This study not merely broadens the synthesis methods of transition metal phosphide-based nanocrystals but the NiCoP/GFs also has broad prospects in diverse electrochemistry fields. We have reported a controllable synthesis of 2D nickel cobalt phosphide nanosheet confined by graphene frameworks (denoted as NiCoP/GFs) as a greatly efficient and durable electrocatalyst. The NiCoP/GFs exhibits remarkable electroactivity toward detection of H₂O₂ at a relatively low overpotential of approximately -0.3 V. Density functional theory (DFT) calculations further prove that regulation of the electronic structure of NiCoP by GFs lowers the adsorption free energy of *OOH intermediates, and thus contributes to the greatly improved the electrocatalytic performance of NiCoP/GFs toward H₂O₂ reduction. The developed NiCoP/GFs can be applied as excellent electrode materials for efficient electrochemical sensing of H₂O₂.

Hierarchical core-shell-structured bimetallic nickel-cobalt phosphide nanoarrays coated with nickel sulfide for high-performance hybrid supercapacitors

High-performance supercapacitors have attracted considerable interests due to their high-power density, fast charge/discharge process and long cycle life. However, the wide application of supercapacitors is limited by their low energy density. Herein, the hierarchical core-shell structured NiCoP@NiS nanoarrays have been successfully synthesized by using the vertically grown nickel-cobalt bimetallic phosphide (NiCoP) nanowire as the core and the nickel sulfide (NiS) by electrodeposition as the shell. As the "super channel" for electron transfer, the NiCoP core is coupled with the NiS shell to promote rapid diffusion of electrons and improve cycle stability of the electrode. Consequently, the optimized NiCoP@NiS nanoarrays display an extremely good specific capacitance (2128F g^-1 at 1 A g^-1) and a superior long cycle life (the capacitance retention of 90.36 % after 10,000 cycles). A hybrid supercapacitor (HSC) has been assembled using the NiCoP@NiS as the positive and the activated carbon (AC) as the negative, which displays a superior energy density of 30.47 Wh kg^-1 at a remarkable power energy of 800 W kg^-1. This study shows that the prepared hierarchical core-shell structured nanoarrays have great prospects as a novel electrode material in energy storage.

Facile and Controllable Synthesis of CuS@Ni-Co Layered Double Hydroxide Nanocages for Hybrid Supercapacitors

The synthesis of battery-type electrode materials with hollow nanostructures for high-performance hybrid supercapacitors (HSCs) remains challenging. In this study, hollow CuS@Ni-Co layered double hydroxide (CuS-LDH) composites with distinguished compositions and structures are successfully synthesized by co-precipitation and the subsequent etching/ion-exchange reaction. CuS-LDH-10 with uniformly dispersed CuS prepared with the addition of 10 mg of CuS shows a unique hollow polyhedral structure constituted by loose nanosphere units, and these nanospheres are composed of interlaced fine nanosheets. The composite prepared with 30 mg of CuS addition (CuS-LDH-30) is composed of a hollow cubic morphology with vertically aligned nanosheets on the CuS shell. The CuS-LDH-10 and CuS-LDH-30 electrodes exhibit high specific capacity (765.1 and 659.6 C g^-1 at 1 A g^-1, respectively) and superior cycling performance. Additionally, the fabricated HSC delivers a prominent energy density of 52.7 Wh kg^-1 at 804.5 W kg^-1 and superior cycling performance of 87.9% capacity retention after 5000 cycles. Such work offers a practical and effortless route for synthesizing unique metal sulfide/hydroxide composite electrode materials with hollow structures for high-performance HSCs.

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.

Freestanding 3D Metallic Micromesh for High-Performance Flexible Transparent Solid-State Zinc Batteries

Flexible transparent energy supplies are extremely essential to the fast-growing flexible electronic systems. However, the general developed flexible transparent energy storage devices are severely limited by the challenges of low energy density, safety issues, and/or poor compatibility. In this work, a freestanding 3D hierarchical metallic micromesh with remarkble optoelectronic properties (T = 89.59% and R_s = 0.23 Ω sq^-1 ) and super-flexibility is designed and manufactured for flexible transparent alkaline zinc batteries. The 3D Ni micromesh supported Cu(OH)₂ @NiCo bimetallic hydroxide flexible transparent electrode (3D NM@Cu(OH)₂ @NiCo BH) is obtained by a combination of photolithography, chemical etching, and electrodeposition. The negative electrode is constructed by electrodeposition of electrochemically active zinc on the surface of Ni@Cu micromesh (Ni@Cu@Zn MM). The metallic micromesh with 3D hierarchical nanoarchitecture can not only ensure low sheet resistance, but also realize high mass loading of active materials and short electron/ion transmission path, which can guarantee high energy density and high-rate capability of the transparent devices. The flexible transparent 3D NM@Cu(OH)₂ @NiCo BH electrode realizes a specific capacity of 66.03 μAh cm^-2 at 1 mA cm^-2 with a transmittance of 63%. Furthermore, the assembled solid-state NiCo-Zn alkaline battery exhibits a desirable energy density/power density of 35.89 μWh cm^-2 /2000.26 μW cm^-2 with a transmittance of 54.34%.

The Preparation and Electrochemical Pseudocapacitive Performance of Mutual Nickel Phosphide Heterostructures

Transition metal phosphide composite materials have become an excellent choice for use in supercapacitor electrodes due to their excellent conductivity and good catalytic activity. In our study, a series of nickel phosphide heterostructure composites was prepared using a temperature-programmed phosphating method, and their electrochemical performance was tested in 2 mol L−1 KOH electrolyte. Because the interface effect can increase the catalytic active sites and improve the ion transmission, the prepared Ni2P/Ni3P/Ni (Ni/P = 7:3) had a specific capacity of 321 mAh g−1 under 1 A g−1 and the prepared Ni2P/Ni5P4 (Ni/P = 5:4) had a specific capacity of 218 mAh g−1 under 1 A g−1. After the current density was increased from 0.5 A g−1 to 5 A g−1, 76% of the specific capacity was maintained. After 7000 cycles, the capacity retention rate was above 82%. Due to the phase recombination effect, the electrochemical performance of Ni2P/Ni3P/Ni and Ni2P/Ni5P4 was much better than that of single-phase N2P. After assembling the prepared composite and activated carbon into a supercapacitor, the Ni2P/Ni3P/Ni//AC had an energy density of 22 W h kg−1 and a power density of 800 W kg−1 and the Ni2P/Ni5P4//AC had an energy density of 27 W h kg−1 and a power density of 800 W kg−1.

Co2P decorated Co3O4 nanocomposites supported on carbon cloth with enhanced electrochemical performance for asymmetric supercapacitors

An effective strategy is demonstrated to promote electrochemical performance by the combination of Co3O4 with Co2P to form a composite electrode.

Nano-dendrite structured cobalt phosphide based hybrid supercapacitor with high energy storage and cycling stability

The supercapacitors possessing high energy storage and long serving period have strategic significance to solve the energy crisis issues. Herein, fluffy nano-dendrite structured cobalt phosphide (CoP) is grown on carbon cloth through simple hydrothermal and electrodeposition treatments (CoP/C-HE). Benefit from its excellent electrical conductivity and special structure, CoP/C-HE manifests a high specific capacity of 461.4 C g^-1at 1 A g^-1. Meanwhile, the capacity retention remains 92.8% over 10 000 cycles at 5 A g^-1, proving the superior cycling stability. The phase conversion of Co₂P during the activation process also contributes to the improved performance. The assembled two-electrode asymmetric supercapacitor demonstrates excellent performance in terms of energy density (42.4 W h kg^-1at a power density of 800.0 W kg^-1) and cycling stability (86.3% retention over 5000 cycles at 5 A g^-1), which is superior to many reported cobalt-based supercapacitors. Our work promotes the potential of transition metal phosphides for the applications in supercapacitors.

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.

Realizing high-performance and low-cost lithium-ion capacitor by regulating kinetic matching between ternary nickel cobalt phosphate microspheres anode with ultralong-life and super-rate performance and watermelon peel biomass-derived carbon cathode

Lithium-ion capacitors (LICs) are emerging as one of the most advanced energy storage devices by combining the virtues of both supercapacitors (SCs) and lithium-ion batteries (LIBs). However, the kinetic and capacity mismatch between anode and cathode is the main obstacle to wide applications of LICs. Therefore, the effective strategy of constructing a high-performance LIC is to improve the rate and cycle performance of the anode and the specific capacity of the cathode. Herein, the nickel cobalt phosphate (NiCoP) microspheres anode is demonstrated with robust structural integrity, high electrical conductivity, and fast kinetic feature. Simultaneously, the watermelon-peel biomass-derived carbon (WPBC) cathode is demonstrated a sustainable synthesis strategy with high specific capacity. As expected, the NiCoP exhibits high specific capacities (567 mAh g^-1 at 0.1 A g^-1), superior rate performance (300 mAh g^-1 at 1A g^-1), and excellent cycle stability (58 mAh g^-1 at 5 A g^-1 after 15,000 cycles). The WPBC possesses a high specific surface area (SSA) of 3303.6 m² g^-1 and a high specific capacity of 226 mAh g^-1 at 0.1 A g^-1. Encouragingly, the NiCoP//WPBC-6 LIC device can deliver high energy density (ED) of 127.4 ± 3.3 and 67 ± 3.8Wh kg^-1 at power density (PD) of 190 and 18240 W kg^-1 (76.4% capacity retention after 7000 cycles), respectively.

Fabrication of Nanoflower-like MCoP (M = Fe and Ni) Composites for High-Performance Supercapacitors

Elaborating the development of functional materials with excellent performance for supercapacitors is important in energy storage devices. In the present study, nanoflower-like MCoP (M = Ni and Fe) composites were successfully fabricated on Ni foam (denoted as NF@MCoP) by a cost-effective hydrothermal and low-temperature phosphating method. Simultaneously, the unique three-dimensional structure, nanoflower morphology, and the conductive substrate provide a favorable large electroactive area, shorter electron transfer distance, and rapid electron conductivity. The as-synthesized nanoflower-like MCoP composites exhibit outstanding energy density, power density, and long-term cycling stability. These results show that the developed electrode materials with excellent performance have great application prospects in the field of supercapacitor applications.

Recent Developments of Transition Metal Compounds-Carbon Hybrid Electrodes for High Energy/Power Supercapacitors

Due to their rapid power delivery, fast charging, and long cycle life, supercapacitors have become an important energy storage technology recently. However, to meet the continuously increasing demands in the fields of portable electronics, transportation, and future robotic technologies, supercapacitors with higher energy densities without sacrificing high power densities and cycle stabilities are still challenged. Transition metal compounds (TMCs) possessing high theoretical capacitance are always used as electrode materials to improve the energy densities of supercapacitors. However, the power densities and cycle lives of such TMCs-based electrodes are still inferior due to their low intrinsic conductivity and large volume expansion during the charge/discharge process, which greatly impede their large-scale applications. Most recently, the ideal integrating of TMCs and conductive carbon skeletons is considered as an effective solution to solve the above challenges. Herein, we summarize the recent developments of TMCs/carbon hybrid electrodes which exhibit both high energy/power densities from the aspects of structural design strategies, including conductive carbon skeleton, interface engineering, and electronic structure. Furthermore, the remaining challenges and future perspectives are also highlighted so as to provide strategies for the high energy/power TMCs/carbon-based supercapacitors.

Crystal Phase-Controlled Synthesis of the CoP@Co2P Heterostructure with 3D Nanowire Networks for High-Performance Li-Ion Capacitor Applications

The paramount focus in the construction of lithium-ion capacitors (LICs) is the development of anode materials with high reversible capacity and fast kinetics to overcome the mismatch of kinetics and capacity between the anode and cathode. Herein, a strategy is presented for the controllable synthesis of cobalt-based phosphides with various morphologies by adjusting the time of the phosphidation process, including 3D hierarchical needle-stacked diabolo-shaped CoP nanorods, 3D hierarchical stick-stacked diabolo-shaped Co₂P nanorods, and 3D hierarchical heterostructure CoP@Co₂P nanorods. 3D hierarchical nanostructures and a highly conductive project to accommodate volume changes are rational designs to achieve a robust construction, effective electron-ion transportation, and rapid kinetics characteristics, thus leading to excellent cycling stability and rate performance. Owing to these merits, the 3D hierarchical CoP, Co₂P, and CoP@Co₂P nanorods demonstrate prominent specific capacities of 573, 609, and 621 mA h g^-1 at 0.1 A g^-1 over 300 cycles, respectively. In addition, a high-performance CoP@Co₂P//AC LIC is successfully constructed, which can achieve high energy densities of 166.2 and 36 W h kg^-1 at power densities of 175 and 17524 W kg^-1 (83.7% capacity retention after 12000 cycles). Therefore, the controllable synthesis of various simultaneously constructed crystalline phases and morphologies can be used to fabricate other advanced energy storage devices.

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%.

Direct Growth of Oxygen Vacancy-Enriched Co3O4 Nanosheets on Carbon Nanotubes for High-Performance Supercapacitors

Ultrathin Co₃O₄ nanosheets (NSs) with abundant oxygen vacancies on conductive carbon nanotube (CNT) nanocomposites (termed as Co₃O₄-NSs/CNTs) are easily achieved by an effective NaBH₄-assisted cyanogel hydrolysis strategy under ambient conditions. The specific capacitance of Co₃O₄-NSs/CNTs with 5% CNT mass can reach 1280.4 F g^-1 at 1 A g^-1 and retain 112.5% even after 10 000 cycles, demonstrating very high electrochemical capability and stability. When assembled in the two-electrode Co₃O₄-NSs/CNTs-5%//reduced graphene oxide (rGO) system, a maximum specific energy density of 37.2 Wh kg^-1 (160.2 W kg^-1) is obtained at room temperature. Ultrathin structure of nanosheets, abundant oxygen vacancies, and the synergistic effect between Co₃O₄-NSs and CNTs are crucial factors for excellent electrochemical performance. Specifically, these characteristics favor rapid electron transfer, complete exposure of the active interface, and sufficient adsorption/desorption of electrolyte ions within the active material. This work gives insights into the efficient construction of two-dimensional hybrid electrodes with high performance for the new-generation energy storage system.

Overview of transition metal-based composite materials for supercapacitor electrodes

Supercapacitors (SCs) can bridge the gap between batteries and conventional capacitors, playing a critical role as an efficient electrochemical storage device in intermittent renewable energy sources. Transition metal-based electrode materials have been investigated extensively as a class of electrode materials for SC application, but they have some limitations due to the sluggish ion/electron diffusion and inferior electronic conductivity, restricting their electrochemical performances towards energy storage. Developing advanced transition metal-based electrode materials is crucial for high energy density along with high specific power and fast charging/discharging rates towards high performance SCs. In this review, we highlight the state-of-the-art of transition metal-based electrode materials (transition metal oxides and their composites, transition metal sulfides and their composites, and transition metal phosphides and their composites), focusing on specific morphologies, components, and power characteristics. We also provide future prospects for transition metal-based electrode materials for SCs and hope this review will shed light on the achievement of higher performance and hold great promise in vast applications for future energy storage and conversion.

Novel Skutterudite CoP3 -Based Asymmetric Supercapacitor with Super High Energy Density

Skutterudite CoP₃ holds a unique structural formation that exhibits much better electronic properties for obtaining high energy density supercapacitors. Herein, novel skutterudite Ni-CoP₃ nanosheets are constructed by etching and coprecipitating at room temperature and subsequent low-temperature phosphorization reaction. Benefiting from the enhanced electrical conductivity and more electroactive sites brought about by adjusting the electronic structure with Ni incorporating the Ni-CoP₃ electrode with a battery-type demonstrates an ultrahigh specific capacity of 0.7 mA h cm^-2 and exceptional cycling stability. The asymmetric supercapacitor (ASC) device fabricated by employing Ni-CoP₃ and activated carbon (AC) as positive and negative electrodes, resepectively, exhibits a remarkable high energy density of 89.6 Wh kg^-1 at 796 W kg^-1 and excellent stability of 93% after 10 000 cycles, due to the skutterudite structure. The skutterudite Ni-CoP₃ shows a great potential to be an excellent next-generation electrode candidate for supercapacitors and other energy storage devices.

Nitrogen-doped carbon integrated nickel–cobalt metal phosphide marigold flowers as a high capacity electrode for hybrid supercapacitors

The fabrication of advanced MOF-derived multicomponent NiCoP/NC marigold flowers electrode for high-performance hybrid supercapacitors.

A rational design of nanoporous Cu–Co–Ni–P nanotube arrays and CoFe2Se4 nanosheet arrays for flexible solid-state asymmetric devices

A facile method was developed to synthesize nanoporous Cu–Co–Ni–P nanotube arrays and hierarchical CoFe₂Se₄ nanosheet arrays for a flexible asymmetric device.