Co3Se4 nanosheets embedded on N-CNT as an efficient electroactive material for hydrogen evolution and supercapacitor applications

NiCo-compounds inside and outside N-doped carbon nanotubes to construct a double-enhanced hierarchical structure for high energy density supercapacitors

Attaining a high energy density that aligns with practical application requirements is a crucial indicator in the advancement of supercapacitors. In this paper, a hybrid hierarchical electrode structure of N-doped carbon nanotube (NCNT) spheres encapsulated with NiCo-Se nanoparticles (NPs) and coated with nickel-cobalt layered double hydroxide (NiCo-LDH) multilayer nanosheets was successfully synthesized on a nickel foam (NF) substrate. The self-supporting strategy enables nickel-cobalt Prussian blue analogues (Ni-Co PBAs) to be directly attached to the NF surface, which results in fluffy NCNTs with a high length-diameter ratio and considerable yield and greatly enhances the conductivity of the electrode material. The synergistic interaction between the dual transition metal compounds inside and outside the NCNTs enables the hybrid electrode material to achieve an impressive specific capacity of 1899 F g-1 (211.0 mA h g-1) at 1 A g-1. The asymmetric supercapacitor (ASC) exhibits an excellent energy density of 57.6 W h kg-1 at a power density of 798 W kg-1. This study not only provides an attractive strategy for obtaining CNTs with excellent properties from Ni-Co PBA and synthesizing hybrid electrodes with efficient synergistic effects, but also achieves a high energy density that aligns with the practical application demands of supercapacitors.

Multifunctional metal selenide-based materials synthesized via a one-pot solvothermal approach for electrochemical energy storage and conversion applications

Highly-efficient electroactive materials with distinctive electrochemical features, along with suitable strategies to prepare hetero-nanoarchitectures incorporating two or more transition metal selenides, are currently required to increase charge storage ability. Herein, a one-pot solvothermal approach is used to develop iron-nickel selenide spring-lawn-like architectures (FeNiSe SLAs) on nickel (Ni) foam. The porous Ni foam scaffold not only enables the uniform growth of FeNiSe SLAs but also serves as an Ni source. The effect of reaction time on their morphological and electrochemical properties is investigated. The FeNiSe-15 h electrode shows high areal capacity (493.2 μA h cm-2) and superior cycling constancy. The as-assembled aqueous hybrid cell (AHC) demonstrates high areal capacity and a decent rate capability of 59.4% (50 mA cm-2). The AHC exhibits good energy and power densities, along with excellent cycling stability. Furthermore, to confirm its practicability, the AHC is employed to drive portable electronic appliances by charging it with wind energy. The electrocatalytic activity of FeNiSe-based materials to complete the oxygen evolution reaction (OER) is explored. Among them, the FeNiSe-15 h catalyst shows good OER performance at a current density of 50 mA cm-2. This general synthesis approach may initiate a strategy of advanced metal selenide-based materials for multifunctional applications.

Hybrid Nanostructured Compounds of Mo2C on Vertical Graphene Nanoflakes for a Highly Efficient Hydrogen Evolution Reaction

Organizing a post-fossil fuel economy requires the development of sustainable energy carriers. Hydrogen is expected to play a significant role as an alternative fuel as it is among the most efficient energy carriers. Therefore, nowadays, the demand for hydrogen production is increasing. Green hydrogen produced by water splitting produces zero carbon emissions but requires the use of expensive catalysts. Therefore, the demand for efficient and economical catalysts is constantly growing. Transition-metal carbides, and especially Mo2C, have attracted great attention from the scientific community since they are abundantly available and hold great promises for efficient performance toward the hydrogen evolution reaction (HER). This study presents a bottom-up approach for depositing Mo carbide nanostructures on vertical graphene nanowall templates via chemical vapor deposition, magnetron sputtering, and thermal annealing processes. Electrochemical results highlight the importance of adequate loading of graphene templates with the optimum amount of Mo carbides, controlled by both deposition and annealing time, to enrich the available active sites. The resulting compounds exhibit exceptional activities toward the HER in acidic media, requiring overpotentials of 82 mV at -10 mA/cm2 and demonstrating a Tafel slope of 56 mV/dec. The high double-layer capacitance and low charge transfer resistance of these Mo2C on GNW hybrid compounds are the main causes of the enhanced HER activity. This study is expected to pave the way for the design of hybrid nanostructures based on nanocatalyst deposition on three-dimensional graphene templates.

Ni-soc-MOF derived carbon hollow sphere encapsulated Ni3Se4 nanocrystals for high-rate supercapacitors

Carbon hollow sphere encapsulated Ni₃Se₄ (Ni₃Se₄@CHS) nanocrystals are prepared using the Ni-soc-MOF by pyrolysis and further selenization. Ni₃Se₄@CHS exhibits a capacitance of 1720 F g^-1 at 1 A g^-1 and a capacitance retention of 97% after 6000 cycles at 5 A g^-1. Moreover, the asymmetric supercapacitor of Ni₃Se₄@CHS//AC displays a wide potential window of 1.6 V, an energy density of 45.2 W h kg^-1 at a power density of 800 W kg^-1, and excellent cycling stability (89% capacitance retention) after 5000 cycles. Overall, this work establishes a significant step to synthesize a new carbon-based material with appreciable capacitance and long cycling durability for potential applications in energy storage and beyond.

Facile Synthesis of 1T-Phase MoS2 Nanosheets on N-Doped Carbon Nanotubes towards Highly Efficient Hydrogen Evolution

1T-phase molybdenum disulfide is supposed to be one of the non-precious metal-based electrocatalysts for the hydrogen evolution reaction with the highest potential. Herein, 1T-MoS₂ nanosheets were anchored on N-doped carbon nanotubes by a simple hydrothermal process with the assistance of urea promotion transition of the 1T phase. Based on the 1T-MoS₂ nanosheets anchored on the N-doped carbon nanotubes structures, 1T-MoS₂ nanosheets can be said to have highly exposed active sites from edges and the basal plane, and the dopant N in carbon nanotubes can promote electron transfer between N-doped carbon nanotubes and 1T-MoS₂ nanosheets. With the synergistic effects of this structure, the excellent 1T-MoS₂/ N-doped carbon nanotubes catalyst has a small overpotential of 150 mV at 10 mA cm⁻², a relatively low Tafel slope of 63 mV dec⁻¹, and superior stability. This work proposes a new strategy to design high-performance hydrogen evolution reaction catalysts.

Mixed Cu2 Se Hexagonal Nanosheets@Co3 Se4 Nanospheres for High-Performance Asymmetric Supercapacitors

Rational designing and constructing multiphase hybrid electrode materials is an effective method to compensate for the performance defects of the single component. Based on this strategy, Cu₂ Se hexagonal nanosheets@Co₃ Se₄ nanospheres mixed structures have been fabricated by a facile two-step hydrothermal method. Under the synergistic effect of the high ionic conductivity of Cu₂ Se and the remarkable cycling stability of Co₃ Se₄ , Cu₂ Se@Co₃ Se₄ can exhibit outstanding electrochemical performance as a novel electrode material. The as-prepared Cu₂ Se@Co₃ Se₄ electrode displays high specific capacitance of 1005 F g^-1 at 1 A g^-1 with enhanced rate capability (56 % capacitance retention at 10 A g^-1 ), and ultralong lifespan (94.2 % after 10 000 cycles at 20 A g^-1 ). An asymmetric supercapacitor is assembled applying the Cu₂ Se@Co₃ Se₄ as anode and graphene as cathode, which delivers a wide work potential window of 1.6 V, high energy density (30.9 Wh kg^-1 at 0.74 kW kg^-1 ), high power density (21.0 Wh kg^-1 at 7.50 kW kg^-1 ), and excellent cycling stability (85.8 % after 10 000 cycles at 10 A g^-1 ).

Construction of hierarchical nickel/cobalt iron-hydroxide and nickel/cobalt selenide nanotubes for efficient electrocatalytic water splitting

Hierarchical Ni/CoFeOH and Ni/CoSe₂ nanotube arrays were fabricated via a three-step strategy, and exhibited enhanced electrochemical performance for OER and HER, respectively.

Liquid phase reduction synthesis of a cobalt boride–activated carbon composite with improved specific capacitance and retention rate as a new positive electrode material for supercapacitors

Amorphous cobalt boride–activated carbon was synthesized via a one-step liquid phase reduction method and its electrochemical performance was studied.