3D-engineered WO3 microspheres assembled by 2D nanosheets with superior sodium storage capacity.

Because of the inadequate sodium storage capacity of graphite, the exploration of high-performance SIB anodes is a crucial step forward. Herein, we report the hydrothermally synthesized self-assembled interconnected nanosheets of WO3 microspheres possessing admirable sodium storage in terms of cycling stability and acceptable rate capability. Benefitting from the interconnected nature of the nanosheets with a hollow interior, the WO3 microspheres exhibited a high sodiation capacity of 431 mA h g-1 at 100 mA g-1 and an excellent rate performance of 60 mA h g-1 at 500 mA g-1 with an impressive coulombic efficiency of around 99%. Importantly, even after continuous cycling with increasing current densities, a specific capacity as high as 220 mA h g-1 could be recovered at a current density of 50 mA g-1, suggesting excellent sodium storage reversibility.

Experimental and theoretical insights into the supercapacitive performance of interconnected WS2 nanosheets.

Transition metal dichalcogenides (TMDs) are fascinating and prodigious considerations in the electrochemical energy storage sector because of their two dimensional chemistry as well as heterogeneous characteristics. Herein, we synthesized interconnected WS2 nanosheets by a hydrothermal method followed by sulphuration at 850 °C in an argon atmosphere. The ultrathin WS2 nanosheet array is endowed with an excellent specific capacitance of 74 F g-1 at the current density of 3 A g-1 up 7000 cycles. Moreover, a symmetric supercapacitor was fabricated using WS2 nanosheets, which provided the admirable high specific capacity of 6.3 F g-1 at 0.05 A g-1 with the energy and power density of 5.6 × 102 mW h kg-1 and 3.6 × 10 5 mW kg-1, respectively. Density functional theory (DFT) simulations revealed the presence of populated energy states near the Fermi level resulting in a high quantum capacitance value, which supports the experimentally achieved high capacitance value. The attained results recommend interconnected WS2 nanosheets as a novel, robust, and low-cost electrode material for supercapacitor energy storage devices.

Exchanging Anion in CuCo-Carbonate Double Hydroxide for Faradaic Supercapacitors: A Case Study.

A systematic synthetic method involving the anion exchange process was designed and developed to fabricate the superior functioning three-dimensional (3-D) urchin-architectured copper cobalt oxide (CuCo2O4; CCO) and copper cobalt sulfide (CuCo2S4; CCS) electrode materials from copper-cobalt carbonate double hydroxide [(CuCo)2(CO3)(OH)2; CCH]. The effective tuning of chemical, crystalline, and morphological properties was achieved during the derivatization process of CCH, based on the anion exchange effect and phase transformation without altering the 3-D spatial assembly. Benefiting from morphological and structural advantages, CCO and CCS exhibited superior electrochemical activity with capacity values of 1508 and 2502 C g-1 at 10 A g-1 to CCH (1182 C g-1 at 10 A g-1). The thermal treatment of CCH has generated a highly porous nature in nanospikes of 3-D urchin CCO structures, which purveys betterment in electrochemical phenomena than pristine smooth-surfaced CCH. Meanwhile, the sulfurization reaction induced the anion effect to a greater extent in the CCS morphology, resulting in hierarchical 3-D urchins formed by 1-D nanospikes constituting coaxially swirled 2-D nanosheets with high exposure of active sites, specific surface areas, and 3-D electron/ion transportation channels. The asymmetric supercapacitor was constructed with a superior CCS electrode as a cathode and an activated carbon electrode as an anode, showing a high specific capacity of 287.35 C g-1 at 7 A g-1 and durability for 5000 cycles with 94.2% retention at a high current density of 30 A g-1. The ultrahigh energy and power density of 135.3 W h kg-1 (10 A g-1) and 44.35 kW kg-1 (30 A g-1) were harvested during the PC device performance. Our finding proposes an idea about the importance of anions and phase transformation as a versatile tool for engineering high-functioning electrode materials and their endeavor toward overwhelming the major demerit of SCs by aggrandizing the energy density value and rate performance.

Carbon spheres decorated-graphene oxide framework as an excellent active material for redox flow battery and supercapacitors.

Composite of dextrose-derived oxygen-rich carbon spheres and graphene oxide, synthesised using a cost-effective and easy hydrothermal process, was used as an active material in two of the trending and promising energy storage devices. The surface morphology and properties of the composite were studied using scanning electron microscope, X-ray diffractometer, energy dispersive X-ray analysis, elemental mapping and Raman spectra. To analyse the electrochemical behaviour of the material, several electrochemical techniques such as cyclic voltammetry (CV), chronopotentiometry, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarisation study were used. The reversibility of Fe2+/Fe3+ redox species and resistance offered by electrolyte towards the modified electrode were studied using CV, EIS and Tafel studies. Further evaluation of efficacy of the active material towards the iron redox flow battery (IRFB) of 132 cm2 area was analysed by performing charge discharge studies at varied current densities. Substantial increase in the electrochemical performance of the IRFB with a coulombic efficiency (CE) 93% along with the good life cycle stability up to 25 cycles was observed. The composite was also used as a superior electrode material for supercapacitor application resulting in significant enhancement in the electrochemical performance with specific capacitance of 610 F g-1 and CE of 83% with 93% retention up to 1600 cycles.

Design of P-Doped Mesoporous Carbon Nitrides as High-Performance Anode Materials for Li-Ion Battery.

Herein, we demonstrate a simple and unique strategy for the preparation of P-doped into the substructure of mesoporous carbon nitride materials (P-MCN-1) with ordered porous structures as a high-energy and high-power Li-ion battery (LIB) anode. The P-MCN-1 as an anode in LIB delivers a high reversible discharge capacity of 963 mAh g-1 even after 1000 cycles at a current density of 1 A g-1, which is much higher than that of other counterparts comprising s-triazine (C3H3N3, g-C3N4), pristine MCN-1, and B-containing MCN-1 (B-MCN-1) subunits or carbon allotropes like CNT and graphene (rGO) materials. The P-MCN-1 electrode also exhibits exceptional rate capability even at high current densities of 5, 10, and 20 A g-1 delivering 685, 539, and 274 mAh g-1, respectively, after 2500 cycles. The high electrical conductivity and Li-ion diffusivity (D), estimated from electrochemical impedance spectra (EIS), very well support the extraordinary electrochemical performance of the P-MCN-1. Higher formation energy, lower bandgap value, and high Li-ion adsorption ability predicted by first principle calculations of P-MCN-1 are in good agreement with experimentally observed high lithium storage, stable cycle life, high power capability, and minimal irreversible capacity (IRC) loss. To the best of our knowledge, it is an entirely new material with the combination of ordered mesostructures with P codoping in carbon nitride substructure which offers superior performance for LIB, and hence we believe that this work will create new momentum for the design and development of clean energy storage devices.

Self-Supported 3 D Ultrathin Cobalt-Nickel-Boron Nanoflakes as an Efficient Electrocatalyst for the Oxygen Evolution Reaction.

The development of highly active and efficient nonprecious-metal electrocatalysts for the oxygen evolution reaction is important for the design of renewable energy production and storage devices. In this work, highly dense, ultrathin Co-Ni boride nanoflakes supported on a 3 D CoNi skeleton are fabricated in situ by a simple one-step, high-temperature, solid-state boronation process. As a result of the induced high electroactive surface area and low charge transfer resistance, CoNiB-700 exhibits high catalytic activity at an overpotential of 262 (η10 ) and 284 mV (η20 ) to deliver current densities of 10 and 20 mA cm-2 , respectively, with a Tafel slope of 58 mV dec-1 in an alkaline medium towards the oxygen evolution reaction. DFT calculations show that the Ni-regulated Co-B compound has a lower rate-determining energy barrier for the *OOH intermediate than the mono-Co-B compound, which facilitates the production of more active catalytic sites for an accelerated surface charge-transfer process for the oxygen evolution reaction.

Hybrid Ni3S2-MoS2 nanowire arrays as a pH-universal catalyst for accelerating the hydrogen evolution reaction.

Hybrid Ni3S2-MoS2 NWAs/NF, hybrid Ni3S2-MoS2 nanowire arrays in situ grown on Ni foam via a two-step hydrothermal method, can achieve cathodic current densities of 10 mA cm-2 and 100 mA cm-2 at overpotentials of 99 mV and 260 mV in 1.0 M KOH and 111 mV and 194 mV in 0.5 M H2SO4, respectively. It still needs an overpotential of 103 mV at 10 mA cm-2 in 0.1 M PBS. This work opens a new avenue for designing heterogeneous active electrocatalysts for energy conversion and storage.

Hierarchically designed SiOx/SiOy bilayer nanomembranes as stable anodes for lithium ion batteries.

Hierarchically designed SiOx /SiOy rolled-up bilayer nanomembranes are used as anodes for lithium-ion batteries. The functionalities of the SiO(x,y) layers can be engineered by simply controlling the oxygen content, resulting in anodes that exhibit a reversible capacity of about 1300 mA h g(-1) with an excellent stability of over 100 cycles, as well as a good rate capability.

Nickel foam supported mesoporous MnO2 nanosheet arrays with superior lithium storage performance.

Mesoporous MnO2 nanosheet arrays have been directly grown on nickel foam current collectors and exhibited a reversible capacity as high as 1690 mA h g(-1) even after one hundred cycles at 100 mA g(-1). They also reveal good rate capability and excellent cycling stability.