Series of Halogen Engineered Ni(OH)2 Nanosheet for Pseudocapacitive Energy Storage with High Energy Density.

Ni(OH)2 nanosheet, acting as a potential active material for supercapacitors, commonly suffers from sluggish reaction kinetics and low intrinsic conductivity, which results in suboptimal energy density and long cycle life. Herein, a convenient electrochemical halogen functionalization strategy is applied for the preparation of mono/bihalogen engineered Ni(OH)2 electrode materials. The theoretical calculations and experimental results found that thanks to the extraordinarily high electronegativity, optimal reversibility, electronic conductivity, and reaction kinetics could be achieved through F functionalization . However, benefiting from the largest ionic radius, INi(OH)2 contributes the best specific capacity and morphology transformation, which is a new finding that distinguishes it from previous reports in the literature. The exploration of the interaction effect of halogens (F, INi(OH)2 , F, BrNi(OH)2 , and Cl, INi(OH)2 ) manifests that F, INi(OH)2 delivers a higher specific capacity of 200.6 mAh g-1 and an excellent rate capability of 58.2% due to the weaker electrostatic repulsion, abundant defect structure, and large layer spacing. Moreover, the F, INi(OH)2 //FeOOH@NrGO device achieves a high energy density of 97.4 Wh kg-1 and an extremely high power density of 32426.7 W kg-1 , as well as good cycling stability. This work develops a pioneering tactic for designing energy storage materials to meet various demands.

Controlling the electrochemical activity of dahlia-like ß-NiS@rGO by interface polarization.

Transition metal sulfides have become more and more important in the field of energy storage due to their superior chemical and physical properties. Herein, dahlia ß-NiS with a rough surface and ß-NiS@reduced graphene oxide (rGO) have been green synthesized by a one-step hydrothermal method. The interface characteristics of ß-NiS@ rGO composites have been systematically studied by XPS, Raman, and first-principles calculations. It is found that the residual O atoms in the interface and the polarization charge generated by them play an important role in performance enhancement. The NiS@rGO composite material has the best electrochemical performance when the C/O ratio is 6.48. Furthermore, we designed a NiS@rGO//rGO asymmetric supercapacitor with a potential window of 1.7 V. Its excellent energy density and power density demonstrate the advantages of the optimized NiS@rGO electrode. When the power density is 850 W kg-1, the energy density can reach 40.4 W h kg-1. Even at a power density of up to 6800 W kg-1, the energy density can be maintained at 17.6 W h kg-1. These encouraging results provide a possible pathway for designing asymmetric supercapacitors with ultra-high performance and a feasible strategy for the precise control of electrochemical performance.

Doping-driven electronic structure and conductivity modification of nickel sulfide.

The lack of electrical conductivity limits the electrochemical kinetic rate of the electrode material, resulting in the inability to reach its theoretical capacity. A facile method is adopted to improve the intrinsic conductivity of binary NiS2/Ni3S4 hybrid nickel sulfide, with the doping of transition metal atoms Co, Mn and Ag. Through the introduction of heteroatoms, the electronic structure of the electrode material is modified and the electrical conductivity is significantly improved, thus enhancing its electrochemical performance. The improvement of conductivity is attributed to the formation of intermediate bands of transition metals and the redistribution of electrons, and the result is demonstrated by experimental and density functional theory (DFT) calculations. As a result, the NiS2/Ni3S4 hybrid nickel sulfide after 0.5% amount of Co-doping reaches the highest specific capacitance of 2874 F g-1 at 1 A g-1, increasing specific capacitance of 653 F g-1 as 29.4% of the specific capacitance of non-doped nickel sulfide. The Co doped nickel sulfide also exhibits remarkable cycling stability compared with non-doped nickel sulfide. The assembled 2% Co-doped nickel sulfide//rGO, 0.5% Mn-doped nickel sulfide//rGO and 0.5% Ag-doped nickel sulfide//rGO asymmetric supercapacitors show a specific energy density of 36.6, 36.1 and 36.0 W h kg-1 at a power density of 800 W kg-1. This study provides a useful insight into the fabrication of high performance pseudocapacitive materials.

Coordination agent-dominated phase control of nickel sulfide for high-performance hybrid supercapacitor.

The property of an active material is not only influenced by its morphology and size, but also by its crystal phase. The present phase regulation of nickel sulfide is mainly achieved by controlling the participation of sulfur source in reaction. Thus, new perspectives direct at phase control need to be explored and supplemented. Herein, we proposed a novel coordination agent-dominated phase modulation strategy assisted by a hydrothermal process. It is found that increasing the amount of coordination agent can drove the phase transformation from the initial composite of ß-NiS/α-NiS/Ni3S4 to ß-NiS/α-NiS, and then to pure ß-NiS. The mechanism of phase regulation has been proposed, and the general application of this method has been demonstrated. By employing coordination agent, the size of resulted products is reduced, and the morphology is optimized. As a result, all of the pure ß-NiS electrodes indicate significantly enhanced specific capacity than the pristine ß-NiS/α-NiS/Ni3S4 composite. Notably, the sample synthesized with 3 mmol of urea (S11) shows uniform morphology and smallest size, and it gives a highest specific capacity of 223.8 mAh g-1 at 1 A g-1, almost 1.5 times of the original sample. The fabricated S11//rGO device delivers a high energy density of 56.6 Wh·kg-1 at a power density of 407.5 W·kg-1, and keeps an impressive capacity retention of 84% after 20,000 cycles. This work put forwards a new prospect for controlling the phase and composition of nickel sulfide based on coordination chemistry.

Template-free synthesis of ß-NiS ball-in-ball microspheres for a high-performance asymmetrical supercapacitor.

While significant advances have been made in the synthesis of core-/multi-shell materials, the synthetic process usually involves a soft/hard template and complicated procedures. In particular, it is extremely difficult to fabricate single-component core-shell structures for nickel sulfides (NSs) with a controlled phase. In this work, we demonstrate a novel facile method to synthesize a single-component ß-NiS ball-in-ball microsphere. The ball-in-ball structure is easily obtained by uniquely employing 2-mercaptopropionic acid (2-MPA) as the sulfur source and ethanol as the solvent based on the Ostwald ripening process. In particular, our work demonstrates that the chemical structure of sulfur sources and solvents plays a key role in the formation of the pure ß-NiS ball-in-ball structure. When used as an electrode active material, the ß-NiS ball-in-ball microspheres exhibit two times stronger specific capacity and three times higher rate performance than NSs produced by a hydrothermal method. The fabricated NS-2//rGO asymmetrical supercapacitor (ASC) displays an energy density of 46.4 W h kg-1 at a power density of 799.0 W kg-1 and good cycling performance. Thus, this study provides a new method for controlling the phase and morphology of NSs.

Selenium Defect Boosted Electrochemical Performance of Binder-Free VSe2 Nanosheets for Aqueous Zinc-Ion Batteries.

As a typical transition-metal dichalcogenides, vanadium diselenide (VSe2) is a promising electrode material for aqueous zinc-ion batteries due to its metallic characteristics and excellent electronic conductivity. In this work, we propose a strategy of hydrothermal reduction synthesis of stainless-steel (SS)-supported VSe2 nanosheets with defect (VSe2-x-SS), thereby further improving the conductivity and activity of VSe2-x-SS. Density functional theory calculations confirmed that Se defect can adjust the adsorption energy of Zn2+ ions. This means that the adsorption/desorption process of Zn2+ ions on VSe2-x-SS is more reversible than that on pure SS-supported VSe2 (VSe2-SS). As a result, the Zn//VSe2-x-SS battery showed more excellent electrochemical performance than Zn//VSe2-SS. The VSe2-x-SS electrode shows a good specific capacity of 265.2 mA h g-1 (0.2 A g-1 after 150 cycles), satisfactory rate performance, and impressive cyclic stability. In addition, we also have explored the energy-storage mechanism of Zn2+ ions in this VSe2-x-SS electrode material. This study provides an effective strategy for the rational design of electrode materials for electrochemical energy-storage devices.

Facile fabrication of core-shell structured Ni(OH)2/Ni(PO3)2 composite via one-step electrodeposition for high performance asymmetric supercapacitor.

Metal metaphosphates, particularly those with core-shell structure, have showed extraordinary potential in energy storage field due to their superior chemical and physical properties. However, the core-shell metal metaphosphates with high energy density in supercapacitor application is rarely reported. Here, the core-shell structured Ni(OH)2/Ni(PO3)2 (NNP) hybrid electrode were prepared by one-step electrodeposition, which exhibits a superior specific capacitance of 1477 F g-1 at a current density of 1 A g-1. Furthermore, an aqueous asymmetric supercapacitor (ASC) based on NNP hybrid composite as cathode and reduced graphene oxide (rGO) as anode is assembled successfully to deliver a prominent energy density of 67 Wh kg-1 at 775 W kg-1 and splendid stability with capacitance retention of 81% after 8000 cycles. The outstanding electrochemical capabilities are attributed to the porous nanoflake and hierarchical core-shell structure of NNP hybrid composite, which can accelerate ion diffusion and charge transfer in redox reaction. These results indicate that nanohybrid NNP material has promise to be an advanced energy storage material.

Hyperbranched molecules having multiple functional groups as effective corrosion inhibitors for Al alloys in aqueous NaCl.

Hyperbranched molecules are a kind of promising materials due to their unique structures. In this work, two hyperbranched molecules (GON and GOH) are used as effective inhibitors for Al alloys in NaCl solution. Their inhibitive performances are evaluated by electrochemical measurements and surface characterization. The results indicate that inhibition performances of GON and GOH are closely related to the concentrations, influenced by the combination of steric hindrance and bonding effects. At relatively low concentrations (0.03-0.10 mM), GON displays a more pronounced ability to inhibit corrosion than GOH, owing to more anchoring functional groups. Oppositely, GOH has good inhibition performance at higher concentrations (0.50-1.00 mM). The interaction between the Al electrode and GOH results in the formation of a more condenser protective film than GON at high concentrations. In addition, the adsorption mechanism of two hyperbranched molecules is revealed by theoretical calculations.

Ultrathin nickel manganese nanosheets with rich oxygen-vacancy as a durability electrode for aqueous Ni//Zn batteries.

Advanced aqueous batteries with abundant global reserves, large discharge capacity and long life span are crucial research objectives. Herein, a kind of aqueous Zn-ion battery was fabricated with ultra-thin Ni-Mn nanosheet electrode and zinc foil. A simple H2-annealing process was employed to handle the NiMnxOy nanosheets to form oxygen vacancy. Based on the formation of fast ion diffusion channels and the increase of active sites, the fabricated H-NiMnxOy nanosheet electrode displays an areal capacity of 0.68 mA h cm-2 at a current density of 2 mA cm-2 and an excellent cycling performance (almost no reduction after 6000 cycles). The fabricated H-NiMnxOy//Zn battery obtains a high areal capacity, up to 0.66 mA h cm-2 at a current density of 4 mA cm-2, and shows a long cycling stability (88.5% capacity retention after 5500 cycles). In particular, it has a high energy density, up to 1.13 mW cm-2 at a power density of 3.34 mW cm-2, more than many other similar devices. Thus, this research provides a new idea for the wide application of aqueous Zn-ion battery in intelligent equipment and electric vehicles.

An intermittent microwave-exfoliated non-expansive graphite oxide process for highly-efficient production of high-quality graphene.

Redox methods represented by Hummers' method are the most frequently-used pathways to prepare graphene, but to date still very low-efficient, because of its time-consuming washing and hard reduction process. Here we report an intermittent microwave-exfoliated non-expansive graphite oxide (GtO) process to prepare a wrinkled graphene with a high reduction degree (C/O: 19.0), a high defect degree, and a high specific surface area (1333.7 m2 g-1). Findings show that the non-expansive GtO without water washing indicates an almost 100% exfoliated success rate during this intermittent microwave process. The obtained graphene shows easy dispersity in organic solvents, and excellent supercapacitor performance in specific capacitance, rate capacity, and especially in cycling lifetime with no decay after 80,000 cycles at 30 A g-1. Consequently, this special microwave process successfully solves the problems of tedious washing and hard reduction in redox methods, thus exponentially boosting the efficiency of preparing graphene.