RESUMO
Transition metal sulfides (TMS) have been considered as a promising group of electrode materials for supercapacitors as a result of their strong redox activity, but high volumetric strain of the materials during electrochemical reactions causes rapid structural collapse and severe capacity loss. Herein, we have synthesized phosphorus-doped (P-doped) Ni2S3/Co3S4/ZnS battery-type nanowire/nanosheet arrays as an advanced cathode for supercapacitor through a two-step process of hydrothermal and annealing treatments. The material has a one-dimensional nanowire/two-dimensional nanosheet-like coexisting microscopic morphology, which facilitates the exposure of abundant active centers and promotes the transport and migration of ions in the electrolyte, while the doping of P significantly enhances the conductivity of the electrode material. Simultaneously, the element phosphorus with similar atomic radii and electronegativity to sulfur may act as electron donors to regulate the electron distribution, thus providing more effective electrochemically active sites. In gratitude to the synergistic effect of microstructure optimization and electronic structure regulation induced by the doing of P, the P-Ni2S3/Co3S4/ZnS nanoarrays provide a superior capacity of 2716 F g-1 at 1 A/g, while the assembled P-Ni2S3/Co3S4/ZnS//AC asymmetric supercapacitor exhibits a high energy density of 48.2 Wh kg-1 at a power density of 800 W kg-1 with the capacity retention of 89 % after 9000 cycles. This work reveals a possible method for developing high-performance transition metal sulfide-based battery-like electrode materials for supercapacitors through microstructure optimization and electronic structure regulation.
RESUMO
Layered double hydroxides (LDHs) with high theoretical capacity have broad prospectsin energy storage applications. However, their slow charge transfer kinetics and easy agglomerate hinder their applications in high-performance supercapacitors. Herein, Co2+-doped nickel aluminum layered double hydroxides (NiAl-LDH-Co2+-x, x = 0, 0.3, 0.6, 0.9, 1.2, 1.5) have been designed and prepared by a convenient hydrothermal process. The multicomponent layer structure formed by cobalt doping facilitates sufficient penetration of the electrolyte and accelerates the charge transfer kinetics. Furthermore, the more open layer spacing and electronic interactions induced by Co2+ doping are conducive to accelerating ion de-intercalation, thereby further improving the kinetic behavior of charge storage. Benefiting from the unique microstructure and Co2+ doping effect, the prepared NiAl-LDH-Co2+-0.9 provides a superior specific capacity of 985 C g-1 at 1 A g-1. In addition, the assembled hybrid supercapacitor with the NiAl-LDH-Co2+-0.9 as the positive electrode provides a remarkable energy density of 22.51 Wh kg-1 at a power density of 800 W kg-1 and exhibits an excellent cycle life with 80 % capacity retention after 20,000 cycles. This study demonstrates the great potential of efficient microstructure design and doping strategy in enhancing the charge storage of electrode materials.
RESUMO
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.
RESUMO
Metal-organic frameworks (MOFs) have attracted tremendous attention in the field of supercapacitors and electrocatalysis due to their open metal sites and high surface area. However, their inherent instability and poor electrical conductivity lead to limited electrochemical performance. Herein, we have employed a new and simple strategy for converting MOF bulk into porous Zn-Co hydroxide composites with the assistance of electric fields with different cycles. This method can alter the migration behavior of charged molecules/ions and improve the nucleation rate of hydroxide, thus adjusting the morphology of derivatives. As a supercapacitor electrode, the optimal material of Zn0.3Co0.7(OH)2 with an electric-field application time of 1200 cycles shows excellent electrochemical performance with a high specific capacity of 981.2 C g-1 at 1 A g-1. Additionally, the fabricated asymmetric supercapacitor exhibits an energy density of 42.5 Wh kg-1 at a power density of 750.0 W kg-1 and a remarkable cycling stability (99% after 11,000 cycles). Simultaneously, the as-prepared Zn0.3Co0.7(OH)2 with an electric-field application time of 1200 cycles delivers prominent OER performances, which can exhibit low overpotentials of 300 and 326 mV at 50 and 100 mA cm-2, respectively, and shows a small Tafel slope of 31.5 mV dec-1. This study represents a new strategy for the synthesis of economical and efficient electrode materials for supercapacitors and OER electrocatalysts and offers a novel way for the mild preparation of nanoderivatives from MOFs.
RESUMO
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.
RESUMO
The poor conductivity and deficient active sites of transition metal oxides lead to low energy density of supercapacitors, which limits their wide application. In this work, double transition metal oxide heterojunctions with oxygen vacancy (Vo-ZnO/CoO) nanowires are prepared by effective hydrothermal and thermal treatments. The formation of the heterojunction results in the redistribution of interface charge between ZnO and CoO, generating an internal electric field to accelerate the electron transport. Meanwhile, oxygen vacancies can enhance the redox reaction activity to further improve the electrochemical kinetics of the electrode material. Therefore, the prepared Vo-ZnO/CoO can provide a superior specific capacity of 845 C g-1 (1 A g-1). An asymmetric supercapacitor with the Vo-ZnO/CoO as positive electrode shows a higher energy density of 51.6 Wh kg-1 when the power density reaches 799.9 W kg-1. This work proposes a synergistic combination of defect and heterojunction engineering to improve the electrochemical properties of materials, providing an important guidance for material design in energy-storage field.
