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Transition-metal sulfides (TMS) are generally employed as suitable materials for electrodes in supercapacitors because of their abundance of electrochemical redox active sites, good structural flexibility, and superior conductivity compared to their oxide counterparts. However, the traditional hydrothermal approach for the synthesis of TMS is characterized by time-consuming reaction times, low yield, and limited capacity, which obstruct its large-scale implementation. Herein, a facile two-step microwave-assisted hydrothermal strategy was developed for rapidly synthesizing binder-free nickel cobalt molybdenum sulfide nanosheet array electrodes on top of carbon cloth (NiCoMoS/CC). The unique 3D layered structure endows NiCoMoS/CC with many accessible electroactive sites. Consequently, the optimized Ni2Co2Mo4S/CC electrode provided a substantial specific capacity value of 177.2 mAh g–1 (1 A g–1), while maintaining a high capacity of 130.6 mAh g–1 at 10 A g–1. Moreover, a hybrid supercapacitor (HSC) was fabricated by utilizing NiCoMoS/CC to be the cathode and an anode made from rotted Cucurbita pepo -derived activated carbon, achieving an energy density (Ed) value of 39.2 Wh kg–1 with a power density (Id) value of 783 W kg–1 and retaining 70.1% of the total capacity after undergoing 1000 cycles. This work offers strategies and prospects for developing low-cost, easily prepared, and binder-free TMS electrodes with high electrochemical characteristics. [ABSTRACT FROM AUTHOR]

Transition-metal double hydroxides offer many benefits, including abundant nanostructures, low cost, easy preparation, diverse compositions, and adjustable physicochemical properties, which have a wide range of applications and are highly promising for the development of high-performance electrode materials. Herein, hydrangea-like manganese-doped nickel–cobalt double hydroxide (NiCoDH-Mn) nanostructures were prepared through a fast one-step microwave hydrothermal method within a few minutes. A thorough analysis was conducted on how the nanostructure, crystal structure, and electrochemical properties of the samples were affected by the amount of the Mn doping content. Density functional theory (DFT) calculations demonstrated that the introduction of Mn doping can generate impurity levels around the Fermi level of NiCoDH, enhancing its electrical conductivity. At a current density of 1 A g–1, the optimized NiCoDH-Mn has a remarkable specific capacity of 107.4 mA h g–1. Even when the current density increases by 15 times, it can still maintain a high specific capacity of 66.3 mA h g–1. After undergoing 1500 cycles with a current density of 5 A g–1, the electrode's capacity remains 128%. The hybrid supercapacitor consisting of the NiCoDH-Mn cathode and mango seed-derived activated carbon anode has an impressive energy density of 47.9 W h kg–1 and a power density of 850 W kg–1. Moreover, it boasts an impressive capacitance retention rate of 87.5%, even after 5000 cycles. We offer a highly effective and speedy approach to creating high-performance transition-metal hydroxides that are ideal for energy storage systems. [ABSTRACT FROM AUTHOR]

The high theoretical specific capacitance, quick redox rate, and superior electrical conductivity of transition metal sulfide materials have pushed their future use in supercapacitor electrodes to the forefront. With diethanolamine as a chelator and solvent, NiS nanoflakes were grown on electrospun carbon nanofibers (CNFs) in a one-step hydrothermal procedure. The optimized NiS/CNFs-2 electrode has a high specific capacity (133.3 mAh g–1 at 1 A g–1) and an outstanding rate performance (70.62% at 10 A g–1). Furthermore, a hybrid supercapacitor assembled using a NiS/CNFs-2 cathode and an activated carbon anode delivers an energy density of 22.35 W h kg–1 and a power density of 750.8 W kg–1. [ABSTRACT FROM AUTHOR]

Rechargeable Mg batteries, using high capacity and dendrite-free Mg metal anodes, are promising energy storage devices for large scale smart grid due to low cost and high safety. However, the performance of Mg batteries is still plagued by the slow reaction kinetics of their cathode materials. Recent discoveries demonstrate that water in cathode can significantly enhance the Mg-ion diffusion in cathode by an unknown mechanism. Here, we propose the water-activated layered-structure VOPO 4 as a novel cathode material and examine the impact of water in electrode or organic electrolyte on the thermodynamics and kinetics of Mg-ion intercalation/deintercalation in cathodes. Electrochemical measurements verify that water in both VOPO 4 lattice and organic electrolyte can largely activate VOPO 4 cathode. Thermodynamic analysis demonstrates that the water in the electrolyte will equilibrate with the structural water in VOPO 4 lattice, and the water activity in the electrolyte alerts the mechanism and kinetics for electrochemical Mg-ion intercalation in VOPO 4 . Theoretical calculations and experimental results demonstrate that water reduces both the solid-state diffusion barrier in the VOPO 4 electrode and the desolvation penalty at the interface. To achieve fast reaction kinetics, the water activity in the electrolyte should be larger than 10 -2 . The proposed activation mechanism provides guidance for screening and designing novel chemistry for high performance multivalent-ion batteries.

Oxygen is the most abundant element in the Earth's crust. The oxygen reduction reaction (ORR) is also the most important reaction in life processes and energy converting/storage systems. Developing techniques toward high-efficiency ORR remains highly desired and a challenge. Here, we report a N-doped carbon (NC) encapsulated CeO 2 /Co interfacial hollow structure (CeO 2 -Co-NC) via a generalized strategy for largely increased oxygen species adsorption and improved ORR activities. First, the metallic Co nanoparticles not only provide high conductivity but also serve as electron donors to largely create oxygen vacancies in CeO 2 . Second, the outer carbon layer can effectively protect cobalt from oxidation and dissociation in alkaline media and as well imparts its higher ORR activity. In the meanwhile, the electronic interactions between CeO 2 and Co in the CeO 2 /Co interface are unveiled theoretically by density functional theory calculations to justify the increased oxygen absorption for ORR activity improvement. The reported CeO 2 -Co-NC hollow nanospheres not only exhibit decent ORR performance with a high onset potential (922 mV vs RHE), half-wave potential (797 mV vs RHE), and small Tafel slope (60 mV dec -1 ) comparable to those of the state-of-the-art Pt/C catalysts but also possess long-term stability with a negative shift of only 7 mV of the half-wave potential after 2000 cycles and strong tolerance against methanol. This work represents a solid step toward high-efficient oxygen reduction.

Herein, MoO 2 quantum dots (QDs; <5 nm) are synthesized through a one-step solvothermal process. MoO 2 QD-bonded graphene sheets (MoO 2 -QDs@RGO) are facilely produced and can be further converted through sulfidation into MoS 2 nanoparticle-bonded graphene sheets (MoS 2 -NPs@RGO). The novel MoO 2 -QDs@RGO electrodes demonstrate exceptionally attractive lithium storage capability (e.g., 1257 mA h g -1 at 100 mA g -1 , being close to the highest values ever reported for a MoO 2 -based lithium ion battery electrode), rate capability, and cycle stability. Moreover, the MoS 2 -NPs@RGO delivered a superior capacity (1497 mA h g -1 at 100 mA g -1 ) with outstanding rate retention and cycling stability. The superior lithium storage capabilities are ascribed to the synergetic effects of the high-surface-area graphene sheets, the well-dispersed MoS 2 nanoparticles, and their strong bonding with each other, which effectively prevents aggregation of MoS 2 while the composite architecture allows fast transport of electrons and ions.

Low-cost and highly efficient bifunctional electrocatalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) are intensively investigated for overall water splitting. Herein, we combined experimental research with first-principles calculations based on density functional theory (DFT) to engineer the NiCo 2 S 4 @NiFe LDH heterostructure interface for enhancing overall water-splitting activity. The DFT calculations exhibit strong interaction and charge transfer between NiCo 2 S 4 and NiFe LDH, which change the interfacial electronic structure and surface reactivity. The calculated chemisorption free energy of hydroxide (ΔE OH ) is reduced from 1.56 eV for pure NiFe LDH to 1.03 eV for the heterostructures, indicating a dramatic improvement in OER performance, while the chemisorption free energy of hydrogen (ΔE H ) maintains almost invariable. By the use of the facile hydrothermal method, NiCo 2 S 4 nanotubes, NiFe LDH nanosheets, and NiCo 2 S 4 @NiFe LDH heterostructures are prepared on nickel foam, of which the corresponding experimental OER overpotentials are 306, 260, and 201 mV at 60 mA cm -2 , respectively. These results are good agreement with the theoretical predictions. Meanwhile, the HER performance has little improvement, with an overpotential of about 200 mV at 10 mA cm -2 . Due to the dramatic improvement in OER performance, there was an enhancement in the overall water-splitting activity of the NiCo 2 S 4 @NiFe LDH heterostructures, with a low voltage of 1.6 V.

Three dimensional (3D) hierarchical network configurations are composed of NiCo2S4 nanotube @Ni-Mn layered double hydroxide (LDH) arrays in situ grown on graphene sponge. The 3D graphene sponge with robust hierarchical porosity suitable for as a basal growth has been obtained from a colloidal dispersion of graphene oxide using a simple directional freeze-drying technique. The high conductive NiCo2S4 nanotube arrays grown on 3D graphene shows excellent pseudocapacity and good conductive support for high-performance Ni-Mn LDH. The 3D NiCo2S4@Ni-Mn LDH/GS shows a high specific capacitance (Csp) 1740 mF cm(-2) at 1 mA cm(-2), even at 10 mA cm(-2), 1267.9 mF cm(-2) maintained. This high-performance composite electrode proposes a new and feasible general pathway as 3D electrode configuration for energy storage devices.