Honeycomb-like Ni3S2 nanosheet arrays for high-performance hybrid supercapacitors

XPS Depth Profiling of Surface Restructuring Responsible for Hydrogen Evolution Reaction Activity of Nickel Sulfides in Alkaline Electrolyte

Electrochemical water splitting provides a sustainable method for hydrogen production. However, the primary challenge for electrochemical hydrogen generation is the high cost and limited availability of platinum-based noble-metal catalysts. Transition-metal chalcogenides have been identified as low-cost and efficient electrocatalysts to promote the hydrogen evolution reaction (HER) in alkaline electrolytes. Nonetheless, the identification of active sites and the underlying catalytic mechanism remain elusive. In this study, phosphorus-doped nickel sulfide has been successfully synthesized, demonstrating enhanced activity for alkaline HER. Investigating surface chemistry through X-ray photoelectron spectroscopy (XPS), depth profiling revealed that surface restructuring occurs during the HER process. The presence of phosphorus significantly influences this transformation, promoting the formation of a novel active Ni-O layer. This Ni-O layer is responsible for enhanced catalytic activity by upshifting the d-band center and increasing the density of states near the Fermi level, along with expanding the electrochemical surface area. This study reveals that the surface restructuring of transition-metal sulfides is highly tied to the electronic structure of the parent catalysts. Gaining a comprehensive understanding of this surface restructuring is essential for predicting and exploring more efficient non-precious transition-metal sulfide electrocatalysts.

Electrochemical oxidation-driven formation of nickel/nickel-based compounds on hollow carbon shells: Mechanistic insights and energy storage applications

Hydrangea-like nickel/nickel-based compounds decorated hollow carbon shells were synthesized through low-temperature calcination and a facile electrochemical oxidation process. This three-dimensional hollow hierarchical structure ensures intimate contact between the electrically conductive nickel (Ni) substrate and uniformly distributed electrochemically active nickel-based compounds. This hierarchical structure offers abundant active sites and accessible pathways, maximizing energy storage, particularly during rapid charge-discharge cycles. With 30 min of electrochemical oxidation, the optimized Ni-compound-based electrode exhibits a specific capacity of 643 C g-1 at 1 A/g. When assembled into a nickel-zinc battery cell with a zinc foil anode, the cell demonstrates swift current responses, with full capacity recovery even after a twentyfold increase in current density, followed by a return to 1 A/g. Density functional theory computations reveal that the electrochemical oxidation, conducted for an optimized duration, results in partial oxidation of Ni(OH)2, reducing the surface adsorption energy of OH- from the electrolyte and improving charge storage capacity.

Promoting OH- Adsorption and Diffusion Enables Ultrahigh Capacity and Rate Capability of Nickel Sulfide Cathode for Aqueous Alkaline Zn-Based Batteries

Aqueous alkaline Zn-based batteries (AAZBs) possess great promise for large-scale applications thanks to their higher discharging plateau and unique reaction mechanism. However, the capacity and rate capability of Ni-based cathodes are still unsatisfactory due to their insufficient OH- adsorption and diffusion ability. Herein, heterostructured Ni3 S2 /Ni(OH)2 nanosheets with outstanding electrochemical performance are synthesized via a facile chemical etching strategy. The heterostructured Ni3 S2 /Ni(OH)2 nanosheet cathode shows significantly increased capacity and rate capability due to its boosted OH- adsorption and diffusion ability compared to Ni3 S2 . Consequently, the assembled Zn//Ni3 S2 /Ni(OH)2 cell can deliver an ultrahigh capacity of 2.26 mAh cm-2 , an excellent rate performance (0.91 mAh cm-2 at 100 mA cm-2 ) and a satisfying cycling stability (1.01 mAh cm-2 at 20 mA cm-2 after 500 cycles). Moreover, a prominent energy density of 3.86 mWh cm-2 is obtained, which exceeds the majority of recently reported AAZBs. This work is expected to provide a new modification direction for developing high-performance nickel sulfide cathode for AAZBs.

Facile Synthesis of Battery-Type CuMn2O4 Nanosheet Arrays on Ni Foam as an Efficient Binder-Free Electrode Material for High-Rate Supercapacitors

The development of battery-type electrode materials with hierarchical nanostructures has recently gained considerable attention in high-rate hybrid supercapacitors. For the first time, in the present study novel hierarchical CuMn₂O₄ nanosheet arrays (NSAs) nanostructures are developed using a one-step hydrothermal route on a nickel foam substrate and utilized as an enhanced battery-type electrode material for supercapacitors without the need of binders or conducting polymer additives. X-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques are used to study the phase, structural, and morphological characteristics of the CuMn₂O₄ electrode. SEM and TEM studies show that CuMn₂O₄ exhibits a nanosheet array morphology. According to the electrochemical data, CuMn₂O₄ NSAs give a Faradic battery-type redox activity that differs from the behavior of carbon-related materials (such as activated carbon, reduced graphene oxide, graphene, etc.). The battery-type CuMn₂O₄ NSAs electrode showed an excellent specific capacity of 125.56 mA h g^-1 at 1 A g^-1 with a remarkable rate capability of 84.1%, superb cycling stability of 92.15% over 5000 cycles, good mechanical stability and flexibility, and low internal resistance at the interface of electrode and electrolyte. Due to their excellent electrochemical properties, high-performance CuMn₂O₄ NSAs-like structures are prospective battery-type electrodes for high-rate supercapacitors.

Efficient Electrooxidation of 5-Hydroxymethylfurfural Using Co-Doped Ni3 S2 Catalyst: Promising for H2 Production under Industrial-Level Current Density

Replacing oxygen evolution reaction (OER) by electrooxidations of organic compounds has been considered as a promising approach to enhance the energy conversion efficiency of the electrolytic water splitting proces. Developing efficient electrocatalysts with low potentials and high current densities is crucial for the large-scale productions of H2 and other value-added chemicals. Herein, non-noble metal electrocatalysts Co-doped Ni3 S2 self-supported on a Ni foam (NF) substrate are prepared and used as catalysts for 5-hydroxymethylfurfural (HMF) oxidation reaction (HMFOR) under alkaline aqueous conditions. For HMFOR, the Co0.4 NiS@NF electode achieves an extremely low onset potential of 0.9 V versus reversible hydrogen electrode (RHE) and records a large current density of 497 mA cm-2 at 1.45 V versus RHE for HMFOR. During the HMFOR-assisted H2 production, the yield rates of 2,5-furandicarboxylic acid (FDCA) and H2 in a 10 mL electrolyte containing 10 × 10-3 M HMF are 330.4 µmol cm-2 h-1 and 1000 µmol cm-2 h-1 , respectively. The Co0.4 NiS@NF electrocatalyst displays a good cycling durability toward HMFOR and can be used for the electrooxidation of other biomass-derived chemicals. The findings present a facile route based on heteroatom doping to fabricate high-performance catalyses that can facilitate the industrial-level H2 production by coupling the conventional HER cathodic processes with HMFOR.

Three-Dimensional Porous Network Electrodes with Cu(OH)2 Nanosheet/Ni3S2 Nanowire 2D/1D Heterostructures for Remarkably Cycle-Stable Supercapacitors

Developing advanced electrode materials with highly improved charge and mass transfer is critical to obtain high specific capacities and long-term cycle life for energy storage. Herein, three-dimensionally (3D) porous network electrodes with Cu(OH)₂ nanosheets/Ni₃S₂ nanowire 2D/1D heterostructures are rationally fabricated. Different from traditional surface deposition, the 1D/2D heterostructure network is obtained by in situ hydrothermal chemical etching of the surface layer of nickel foam (NF) ligaments. The Cu(OH)₂/Ni₃S₂@NF electrode delivers a high specific capacity (1855 F g^-1 at 2 mA cm^-2) together with a remarkable stability. The capacity retention of the electrode is over 110% after 35,000 charge/discharge cycles at 20 mA cm^-2. The improved performance is attributed to the enhanced electron transfer between 1D Ni₃S₂ and 2D Cu(OH)₂, highly accessible sites of 3D network for electrolyte ions, and strong mechanical bonding and good electrical connection between Cu(OH)₂/Ni₃S₂ active materials and the conductive NF. Especially, the unique 1D/2D heterostructure alleviates structural pulverization during the ion insertion/desertion process. A symmetric device applying the Cu(OH)₂/Ni₃S₂@NF electrode exhibits a remarkable cycling stability with the capacitance retention maintaining over 98% after 30,000 cycles at 50 mA cm^-2. Therefore, the outstanding performance promises the architectural 1D/2D heterostructure to offer potential applications in future electrochemical energy storage.

Hierarchical Ni3S2nanorod@nanosheet arrays on Ni foam for high-performance supercapacitor

We successfully designed and prepared hierarchical Ni₃S₂nanorod@nanosheet arrays on three-dimensional Ni foam via facile hydrothermal sulfuration. We conducted a series of time- and temperature-dependent experiments to determine the Ostwald ripening process of hierarchical Ni₃S₂nanorod@nanosheet arrays. The rationally hierarchical architecture creates an excellent supercapacitor electrode for Ni₃S₂nanorod@nanosheet arrays. The areal capacitance of this array reaches 5.5 F cm^-2at 2 mA cm^-2, which is much higher than that of Ni₃S₂nanosheet arrays (1.5 F cm^-2). The corresponding asymmetric supercapacitor exhibits a wide potential window of 1.6 V and energy density up to 1.0 Wh cm^-2when the proposed array is utilized as the positive electrode with activated carbon as the negative electrode. This electrochemical performance enhancement is attributable to the hierarchical structure and synergistic cooperation of macroporous Ni foam and well-aligned Ni₃S₂nanorod@nanosheet arrays. Our results represent a promising approach to the preparation of hierarchical nanorod@nanosheet arrays as high-performing electrochemical capacitors.

In Situ Construction of ZnO/Ni2S3 Composite on Ni Foam by Combing Potentiostatic Deposition with Cyclic Voltammetric Electrodeposition

The ZnO/Ni2S3 composite has been designed and in situ synthesized on Ni foam substrate by two steps of electrodeposition. ZnO was achieved on Ni foam by a traditional potentiostatic deposition, followed by cyclic voltammetric (CV) electrodeposition, to generate Ni2S3, where the introduction of ZnO provides abundant active sites for the subsequent Ni2S3 electrodeposition. The amount of deposit during CV electrodeposition can be adjusted by setting the number of sweep segment and scan rate, and the electrochemical characteristics of the products can be readily optimized. The synergistic effect between the ZnO as backbones and the deposited Ni2S3 as the shell enhances the electrochemical properties of the sample significantly, including a highly specific capacitance of 2.19 F cm-2 at 2 mA cm-2, good coulombic efficiency of 98%, and long-term cyclic stability at 82.35% (4000 cycles).

MOF-derived ZnCo2O4@NiCo2S4@PPy core-shell nanosheets on Ni foam for high-performance supercapacitors

The ZnCo₂O₄@NiCo₂S₄@PPy core-shell nanosheets material is prepared by directly growing leaf-like ZnCo₂O₄ nanosheets derived from the metal-organic framework (MOF) on Ni foam (NiF) via chemical bath deposition and annealing methods and then combining with NiCo₂S₄ and PPy via electrodeposition methods. The special core-shell structure formed by MOF-derived ZnCo₂O₄, NiCo₂S₄ and PPy creates a bi-interface, which could significantly promote the contact between electrode and electrolyte, provide more active sites and accelerate electron/ion transfer. And the combination of these three materials also produces a strong synergistic effect, which could further improve the capacitive performance of the electrode. Therefore, the ZnCo₂O₄@NiCo₂S₄@PPy/NiF electrode exhibits the maximum areal capacitance (3.75 F cm^-2) and specific capacitance (2507.0 F g^-1) at 1 mA cm^-2 and 0.5 A g^-1, respectively. Moreover, its capacitance retention rate is still 83.2% after 5000 cycles. In addition, a coin-type hybrid supercapacitor is assembled and displays a high energy density of 44.15 Wh kg^-1 and good cycling performance.

Configuring hierarchical Ni/NiO 3D-network assisted with bamboo cellulose nanofibers for high-performance Ni-Zn aqueous batteries

The further application of Ni-Zn aqueous batteries is majorly restricted by nickel-based cathodes due to their low capacity and poor cycling stability, which requires the development of hierarchically nanostructured nickel and nickel oxides. Herein, we prepare a novel nickel-based electrode with hierarchical 3D networks by configuring nanostructured Ni and Ni/NiO nanoparticles onto bamboo-derived cellulose nanofibers (denoted as Ni/NiO-BCF). Owing to the high conductivity of carbonized nanofibers and enhanced Ni/NiO active sites exposed, the Ni/NiO-BCF electrode delivers a capacity of 248 mA h g^-1 at 0.625 A g^-1 and exhibits a good cycling stability (94.5% after 2000 cycles). The as-fabricated Ni/NiO-BCF//Zn battery shows a high capacity of 296 mA h g^-1 at 0.625 A g^-1 and excellent cycling stability (almost no decay after 1000 cycles). Notably, a peak energy density of 313.4 W h kg^-1 is also achieved from the Ni/NiO-BCF//Zn battery. This work provides novel insights into developing elaborately-nanostructured electrodes from natural and sustainable resources for high-capacity and long-cycle energy storage systems.

Dual-functional NiCo2S4 polyhedral architecture with superior electrochemical performance for supercapacitors and lithium-ion batteries

Dual-functional NiCo₂S₄ polyhedral architectures with outstanding electrochemical performance for supercapacitors and lithium-ion batteries (LIBs) have been rationally designed and successfully synthesized by a hydrothermal method. The as-synthesized NiCo₂S₄ electrode for supercapacitor exhibits an outstanding specific capacitance of 1298Fg^-1 at 1Ag^-1 and an excellent rate capability of ~80.4% at 20Ag^-1. Besides, capacitance retention of 90.44% is realized after 8000 cycles. In addition, the NiCo₂S₄ as anode in LIBs delivers high initial charge/discharge capacities of 807.6 and 972.8mAhg^-1 at 0.5C as well as good rate capability. In view of these points, this work provides a feasible pathway for assembling electrodes and devices with excellent electrochemical properties in the next generation energy storage applications.

Biomolecule-assisted synthesis of porous network-like Ni3S2 nanoarchitectures assembled with ultrathin nanosheets as integrated negative electrodes for high-performance lithium storage

Porous network-like Ni₃S₂ nanoarchitectures have been successfully synthesized on nickel foam via a facile eco-friendly biomolecule-assisted hydrothermal process, in which l-cysteine is served as both the sulfur source and the directing molecule.

Ultra-thin NiS nanosheets as advanced electrode for high energy density supercapacitors

The NiS electrodes show an ultra-high capacitance of 2587.4 F g⁻¹ and a high energy density of 38.2 W h kg⁻¹.

Dual carbon-modified nickel sulfide composites toward high-performance electrodes for supercapacitors

Dual carbon-modified nickel sulfide composites have been facilely prepared and they deliver excellent energy storage performance for supercapacitors.