In situ grown Ni9S8 nanorod/O-MoS2 nanosheet nanocomposite on carbon cloth as a free binder supercapacitor electrode and hydrogen evolution catalyst

Anchoring Ni(OH)2-CeOx Heterostructure on FeOOH-Modified Nickel-Mesh for Efficient Alkaline Water-Splitting Performance with Improved Stability under Quasi-Industrial Conditions

Developing low-cost and industrially viable electrode materials for efficient water-splitting performance and constructing intrinsically active materials with abundant active sites is still challenging. In this study, a self-supported porous network Ni(OH)2-CeOx heterostructure layer on a FeOOH-modified Ni-mesh (NiCe/Fe@NM) electrode is successfully prepared by a facile, scalable two-electrode electrodeposition strategy for overall alkaline water splitting. The optimized NiCe0.05/Fe@NM catalyst reaches a current density of 100 mA cm-2 at an overpotential of 163 and 262 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, in 1.0 m KOH with excellent stability. Additionally, NiCe0.05/Fe@NM demonstrates exceptional HER performance in alkaline seawater, requiring only 148 mV overpotential at 100 mA cm-2. Under real water splitting conditions, NiCe0.05/Fe@NM requires only 1.701 V to achieve 100 mA cm-2 with robust stability over 1000 h in an alkaline medium. The remarkable water-splitting performance and stability of the NiCe0.05/Fe@NM catalyst result from a synergistic combination of factors, including well-optimized surface and electronic structures facilitated by an optimal Ce ratio, rapid reaction kinetics, a superhydrophilic/superaerophobic interface, and enhanced intrinsic catalytic activity. This study presents a simple two-electrode electrodeposition method for the scalable production of self-supported electrocatalysts, paving the way for their practical application in industrial water-splitting processes.

Construction of Nickel Molybdenum Sulfide/Black Phosphorous 3D Hierarchical Structure Toward High Performance Supercapacitor Electrodes

Supercapacitors (SCs) with outstanding versatility have a lot of potential applications in next-generation electronics. However, their practical uses are limited by their short working potential window and ultralow-specific capacity. Herein, the facile one-step in-situ hydrothermal synthesis is employed for the construction of a NiMo3S4/BP (black phosphorous) hybrid with a 3D hierarchical structure. After optimization, the NiMo3S4/BP hybrid displays a high specific capacitance of 830 F/g at 1 A/g compared to the pristine NiMo3S4 electrode. The fabricated NiMo3S4/BP//NiCo2S4/Ti3C2Tx asymmetric supercapacitor exhibits a better specific capacitance of 120 F/g at 0.5 A/g, which also demonstrates a high energy density of 54 Wh/kg at 1148.53 W/kg and good cycle stability with capacity retention of 86% and 97% of Coulombic efficiency after 6000 cycles. Further from the DFT simulations, the hybrid NiMo3S4/BP structure shows higher conductivity and quantum capacitance, which demonstrate greater charge storage capability, due to enhanced electronic states near the Fermi level. The lower diffusion energy barrier for the electrolyte K+ ions in the hybrid structure is facilitated by improved charge transfer performance for the hybrid NiMo3S4/BP. This work highlights the potential significance of hybrid nanoarchitectonics and compositional tunability as an emerging method for improving the charge storage capabilities of active electrodes.

Facile Fabrication of Ni9 S8 /Ag2 S Intertwined Structures for Oxygen and Hydrogen Evolution Reactions

Here, we report the fabrication of the unique intertwined Ni₉ S₈ /Ag₂ S composite structure with hexagonal shape from their molecular precursors by one-pot thermal decomposition. Various spectroscopic and microscopic techniques were utilized to confirm the Ni₉ S₈ /Ag₂ S intertwined structure. Powder X-ray Powder Diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis suggest that there is an enrichment of Ni₉ S₈ phase in Ni₉ S₈ /Ag₂ S. The presence of Ag₂ S in Ni₉ S₈ /Ag₂ S improves the conductivity by reducing the interfacial energy and charge transfer resistance. When Ni₉ S₈ /Ag₂ S is employed as an electrocatalyst for electrochemical oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activity, it requires a low overpotential of 152 mV for HER and 277 mV for OER to obtain the geometrical current density of 10 mA cm^-2 , which is definitely superior to that of its components Ni₉ S₈ and Ag₂ S. This work provides a simple design route to develop an efficient and durable electrocatalyst with outstanding OER and HER performance and the present catalyst (Ni₉ S₈ /Ag₂ S) deserves as a potential candidate in the field of energy conversion systems.

Hetero-architectured core-shell NiMoO4@Ni9S8/MoS2 nanorods enabling high-performance supercapacitors

ABSTRACT

An effective technique for improving electrochemical efficiency is to rationally design hierarchical nanostructures that completely optimize the advantages of single components and establish an interfacial effect between structures. In this study, core-shell NiMoO₄@Ni₉S₈/MoS₂ hetero-structured nanorods are prepared via a facile hydrothermal process followed by a direct sulfurization. The resulting hierarchical architecture with outer Ni₉S₈/MoS₂ nanoflakes shell on the inner NiMoO₄ core offers plentiful active sites and ample charge transfer pathways in continuous heterointerfaces. Ascribing to the porous core-shell configuration and synergistic effect of bimetal sulfides, the obtained NiMoO₄@Ni₉S₈/MoS₂ as electrode material presents an unsurpassed specific capacity of 373.4 F g^-1 at 10 A g^-1 and remarkable cycling performance in the 6 M KOH electrolyte. This work delivers a rational method for designing highly efficient electrodes for supercapacitors, enlightening the road of exploring low-cost materials in the energy storage domain.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1557/s43578-021-00318-y.

High-rate transition metal-based cathode materials for battery-supercapacitor hybrid devices

With the rapid development of portable electronic devices, electric vehicles and large-scale grid energy storage devices, there is a need to enhance the specific energy density and specific power density of related electrochemical devices to meet the fast-growing requirements of energy storage. Battery-supercapacitor hybrid devices (BSHDs), combining the high-energy-density feature of batteries and the high-power-density properties of supercapacitors, have attracted mass attention in terms of energy storage. However, the electrochemical performances of cathode materials for BSHDs are severely limited by poor electrical conductivity and ion transport kinetics. As the rich redox reactions induced by transition metal compounds are able to offer high specific capacity, they are an ideal choice of cathode materials. Therefore, this paper reviews the currently advanced progress of transition metal compound-based cathodes with high-rate performance in BSHDs. We discuss some efficient strategies of enhancing the rate performance of transition metal compounds, including developing intrinsic electrode materials with high conductivity and fast ion transport; modifying materials, such as inserting defects and doping; building composite structures and 3D nano-array structures; interfacial engineering and catalytic effects. Finally, some suggestions are proposed for the potential development of cathodes for BSHDs, which may provide a reference for significant progress in the future.

Advanced Carbon-Nickel Sulfide Hybrid Nanostructures: Extending the Limits of Battery-Type Electrodes for Redox-Based Supercapacitor Applications

Transition-metal sulfides combined with conductive carbon nanostructures are considered promising electrode materials for redox-based supercapacitors due to their high specific capacity. However, the low rate capability of these electrodes, still considered "battery-type" electrodes, presents an obstacle for general use. In this work, we demonstrate a successful and fast fabrication process of metal sulfide-carbon nanostructures ideal for charge-storage electrodes with ultra-high capacity and outstanding rate capability. The novel hybrid binder-free electrode material consists of a vertically aligned carbon nanotube (VCN), terminated by a nanosized single-crystal metallic Ni grain; Ni is covered by a nickel nitride (Ni₃N) interlayer and topped by trinickel disulfide (Ni₃S₂, heazlewoodite). Thus, the electrode is formed by a Ni₃S₂/Ni₃N/Ni@NVCN architecture with a unique broccoli-like morphology. Electrochemical measurements show that these hybrid binder-free electrodes exhibit one of the best electrochemical performances compared to the other reported Ni₃S₂-based electrodes, evidencing an ultra-high specific capacity (856.3 C g^-1 at 3 A g^-1), outstanding rate capability (77.2% retention at 13 A g^-1), and excellent cycling stability (83% retention after 4000 cycles at 13 A g^-1). The remarkable electrochemical performance of the binder-free Ni₃S₂/Ni₃N/Ni@NVCN electrodes is a significant step forward, improving rate capability and capacity for redox-based supercapacitor applications.

CuS nanoparticles decorated MoS2 sheets as an efficient nanozyme for selective detection and photocatalytic degradation of hydroquinone in water

Cost effective and efficient CuS–MoS₂ nanocomposite with enhanced peroxidase enzyme mimetics and photocatalytic activity was synthesized by simple hydrothermal method and successfully utilized for sensing and detection of toxic hydroquinone molecules in aqueous medium.

Facile synthesis of Mn-doped MoS2 nanosheets on carbon nanotubes as efficient electrocatalyst for hydrogen evolution reaction

As a substitute of Pt-based catalysts, MoS₂-based catalysts have been widely used in hydrogen evolution reaction, but the inherent low conductivity, limited active edges, self-stacking and agglomeration still hinder their activities. In this work, Mn-doped MoS₂ nanosheets were vertically anchored on carbon nanotubes (CNTs) by the one-step hydrothermal reaction, in which Mn-O-C/Mo-O-C was considered as a bridge between Mn-MoS₂ and CNTs. The doping of the Mn element enables the spreading of MoS₂ on CNTs and the rapid escape of hydrogen bubbles from the electrode, while conductive CNTs with hydrophilicity can accelerate the electron transport process between the electrolyte and the material. With an overpotential of 150 mV at a current density of -10 mA cm^-2 and a Tafel slope of 39 mV dec^-1, this material exhibited excellent catalytic hydrogen evolution activity, which could open the path for designing commercial electrocatalysts.

Decorated nickel phosphide nanoparticles with nitrogen and phosphorus co-doped porous carbon for enhanced electrochemical water splitting

A novel free-standing electrode consisting of nickel phosphide (Ni₂P) nanoparticles on nitrogen and phosphorus co-doped porous carbon (NPC) are synthesized on carbon cloth (CC). Polyaniline (PANI) and nickel (Ni) are sequentially electro-deposited on the surface of CC, which are then transformed into NPC and Ni₂P by an in-situ carbonization-phosphorization combined process. The electrode surface is distributed with large amounts of uniform macropores, which could expose more active sites and enhance the interfacial exchange with the electrolyte. The Ni₂P@NPC@CC electrode delivers early overpotentials of 92 and 280 mV vs. Reversible Hydrogen Electrode (RHE) at 10 mA cm^-2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline condition, respectively. The electrolytic cell with Ni₂P@NPC@CC electrode both as anode and cathode can achieve 10 mA cm^-2 at a small bias of 1.54 V for the overall water splitting. Density functional theory (DFT) calculation indicates that combination with Ni₂P and NPC can decrease Gibbs free energy for H* adsorption (ΔG_H*) and increase charge density on the interface, thus could lead to the enhanced activity for water splitting. The free-standing and noble-metal free Ni₂P@NPC@CC electrode is stable, highly active and cost effective, thus have great potential for the hydrogen production.

Unveiling the Effect of the Structure of Carbon Material on the Charge Storage Mechanism in MoS2-Based Supercapacitors

MoS₂ is a 2D material that has been widely used in supercapacitor applications because of its layered structure that provides a large surface area and allows for high electric double-layer charge storage. To enhance the cycling stability and capacitance of MoS₂, it is usually mixed with carbon materials. However, the dependence of the charge storage mechanism on the structure of the carbon material is still unclear in literature. Herein, the effect of the structure of the carbon material on the charge storage mechanism in 2H flower-shaped MoS₂ is investigated in detail. Specifically, 2H MoS₂ was mixed with either 8 nm-diameter carbon nanotubes (CNTs) or graphene nanoflakes (GNFs) in different weight ratios. Also, a composite of MoS₂, CNTs, and GNFs (1:1:1) was also studied. The charge storage mechanism was found to depend on the structure and content of the carbon material. Insights into the possible storage mechanism(s) were discussed. The MoS₂/CNT/GNF composite showed a predominant pseudocapacitive charge storage mechanism where the diffusion current was ∼89%, with 88.31% of the resulted capacitance being due to faradic processes.

Recent Advances in Metal Chalcogenides (MX; X = S, Se) Nanostructures for Electrochemical Supercapacitor Applications: A Brief Review

Supercapacitors (SCs) have received a great deal of attention and play an important role for future self-powered devices, mainly owing to their higher power density. Among all types of electrical energy storage devices, electrochemical supercapacitors are considered to be the most promising because of their superior performance characteristics, including short charging time, high power density, safety, easy fabrication procedures, and long operational life. An SC consists of two foremost components, namely electrode materials, and electrolyte. The selection of appropriate electrode materials with rational nanostructured designs has resulted in improved electrochemical properties for high performance and has reduced the cost of SCs. In this review, we mainly spotlight the non-metallic oxide, especially metal chalcogenides (MX; X = S, Se) based nanostructured electrode materials for electrochemical SCs. Different non-metallic oxide materials are highlighted in various categories, such as transition metal sulfides and selenides materials. Finally, the designing strategy and future improvements on metal chalcogenide materials for the application of electrochemical SCs are also discussed.