Nickel Sulfide Research Articles

Hexagonal Morphology Nickel Sulfide Anchored on Graphene Oxide–Modified Glassy Carbon Electrode for the Sensitive Detection of Paracetamol in Biological Samples

Hexagonal Morphology Nickel Sulfide Anchored on Graphene Oxide–Modified Glassy Carbon Electrode for the Sensitive Detection of Paracetamol in Biological Samples

Optimizing cobalt/nickle sulfide heterojunction interface with ordered porous framework for efficient rechargeable zinc-air batteries

Developing efficient oxygen evolution/reduction reaction (OER/ORR) bifunctional catalysts is essential to improve zinc-air batteries (ZABs) performance. In this study, an OER/ORR bifunctional catalyst consists of cobalt and nickel sulfide heterojunction with three-dimensional ordered mesoporous structure is fabricated (3DOM Co9S8/Ni3S4). In-situ attenuated total reflection Fourier transform infrared tests and theoretical calculations reveal that the heterojunction structure promotes electrons transfer from Co9S8 to Ni3S4 and modulates the d-band center, thus optimizing the adsorption/desorption of *OH, *O and *OOH oxygen-containing intermediates and contributing to the improvement of the reactivity of the catalyst. In-situ Raman analysis shows that 3DOM Co9S8/Ni3S4 undergoes surface reconstruction to form highly reactive NiOOH species during the OER process. Meanwhile, the 3DOM framework structure also increases the catalyst specific surface area and benefits the mass transfer process during the reactions. As a result, 3DOM Co9S8/Ni3S4 exhibits a low OER overpotential (334 mV) at 10 mA cm−2 and the ORR half-wave potential is 0.77 V vs. RHE. The rechargeable ZABs with 3DOM Co9S8/Ni3S4 cathode deliver an energy density of 760.73 mAh g−1 at 10 mA cm−2 and stable cycling performance for 100 hours. This study provides guidance for developing efficient heterojunction bifunctional catalysts for ZABs.

Electronic Structure of Diatomic Nickel Sulfide.

The nature of the Ni-S bond is investigated due to its role in the absorption of atmospheric Lewis acid gases such as SO2 and SO3 onto Ni surfaces. The vibrational frequency and electronic structure of NiS were predicted using CCSD(T), CASSCF, and internally contracted multireference configuration interaction (icMRCI) + Q. 43 density functional theory (DFT) functionals were benchmarked. CASSCF predicted the ground state of NiS to be the 5Δ state arising from the 3d8(3F)4s2 (3F) and 3d9(2D)4s (3D) electronic configurations of Ni. When dynamical correlation effects are included at the icMRCI + Q level, the ground state of Ni-S is predicted to be 3Σ- consistent with the experiment. The vibrational frequency of Ni-S is calculated to be 519.1 cm-1 at the icMRCI + Q level, in reasonable agreement with the experimental value of 512.68 cm-1. CCSD(T) predicts the frequency of Ni-S to be 543.2 cm-1 when extrapolated to the complete basis set (CBS) limit. The Feller-Peterson-Dixon value based on the CCSD(T)/CBS extrapolation for the bond dissociation energy of NiS is 350.6 kJ/mol, within <4 kJ/mol of experiment. Of the 43 DFT functionals, BP86 and O3LYP predicted the vibrational frequency in closest agreement with the experiment. The applicability of DFT to such acid gas systems was further demonstrated by calculating the energy for displacement of NiO by SO to yield NiS and O2. This displacement energy was calculated to be within experimental error for ∼50% of the DFT functionals, but large differences were also predicted for some functionals.

Design and Optimization of MoS2@rGO@NiFeS Nanocomposites for Hybrid Supercapattery Performance and Sensitive Electrochemical Detection.

Metal sulfide-based composites have become increasingly common as materials used for electrodes in supercapacitors because of their excellent conductivity, electrochemical activity, and redox capacity. This study synthesized a composite of NiFeS@MoS2@rGO nanostructure using a simple hydrothermal approach. The synthesized nanocomposite consisted of the composite of nickel sulfide and iron sulfide doped with MoS2@rGO. A three-electrode cell is employed to investigate the electrochemical properties of the NiFeS@MoS2@rGO electrode. The results demonstrated an optimal specific capacitance of 3188 F/g at 1.4 A/g in a 1 M KOH electrolyte. Furthermore, a supercapattery is designed utilizing NiFeS@MoS2@rGO//AC as the positive electrode and activated carbon (AC) as the negative electrode materials. The resulting supercapattery is designed at a cell voltage of 1.6 V, achieving a specific capacity value of 189 C/g at 1.4 A/g. It also demonstrated an excellent energy density of 55 Wh/kg with an enhanced power density of 3800 W/kg. Furthermore, the hybrid device demonstrated remarkable stability with a cycling stability of 95% over 30,000 charge-discharge cycles at a current density of 1.4 A/g. The supercapattery, which has excellent energy storage capabilities, is used as a power source for operating different portable electronic devices.

Homogeneous Crystallization of Nickel as Ni₃S₄ in a Fluidized Bed Reactor with Supersaturation Control

This study investigates the recovery of nickel sulfide (NiS) using fluidized bed homogeneous crystallization (FBHC), emphasizing the process from nucleation to crystallization. Sludge production in conventional chemical precipitation becomes a drawback in treating wastewater economically and efficiently. FBHC offers a promising alternative by minimizing sludge generation. The study examines various operational parameters, including hydraulic retention times (HRT), reflux ratio (R), initial nickel concentration, and static bed height (SBH), to optimize NiS recovery. Results show that FBHC achieves high total removal efficiency (TR) and crystallization ratio (CR), under the optimum condition of HRT = 15min, R = 8.3, initial nickel concentration = 147mg/L, and SBH = 35cm. The agglomeration of Ni(OH)2 was found to be crucial for the crystal growth during the surface oxidation of Ni3S4. This technological approach to wastewater treatment offers highly efficient heavy metal removal from wastewater.

Tantalum-induced reconstruction of nickel sulfide for enhanced bifunctional water splitting: Separate activation of the lattice oxygen oxidation and hydrogen spillover

Designing highly active and stable bifunctional catalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) under alkaline conditions is crucial for sustainable overall water splitting. Herein, we present a targeted reconstruction of Ni3S2 by introducing tantalum, achieving remarkable overall water splitting performance through the separate activation of the lattice oxygen mechanism and hydrogen spillover. Electrochemical Mass Spectrometry and in-situ Raman spectroscopy reveal that tantalum induces Ni3S2 to reconstruct into nickel hydroxide during OER, thereby enhancing catalytic activity via the activation of the lattice oxygen mechanism. In the corresponding HER, tantalum promotes the reconstruction of Ni3S2 into oxysulfide, facilitates hydrogen spillover, and acts as an anchor to shorten the spillover distance, improving the HER catalytic performance, as verified by the kinetic isotope effect and theoretical calculations. Therefore, the catalyst-based anion exchange membrane water electrolyzer system achieves a current density of 1 A cm−2 at just 1.97 V, maintaining continuous operation for 500 h. This study offers new insights into the design of bifunctional catalysts, advancing the development of efficient and robust overall water splitting catalysts.

Structural and electrical characterization of nickel sulfide nanoparticles

Nickel sulfide nanoparticles were successfully synthesized through a meticulous process involving a well-mixed powder of Ni(CH3COO)2∙2H2O and Thiourea. The X-ray diffraction analysis provided insights into the structural nature of NiS, revealing its polycrystalline characteristics with a hexagonal system. This information is fundamental, as it forms the basis for understanding the material’s behavior and functionality in various applications. Determining the average values of mean crystallite size, microstrain, and dislocation Nickel sulfide nanoparticles were successfully synthesized through a careful process involving a well-mixed powder of Ni(II)2∙2H2O and Thiourea. The X-ray diffraction analysis provided insights into the structural nature of NiS, revealing its polycrystalline characteristics with a hexagonal system. This information is crucial as it forms the basis for understanding the material’s behavior and functionality in various applications. Determining the average values of mean crystallite size, microstrain, and dislocation density for the (100) plane (32.62 nm, 0.000296, and 0.000939 nm-2, respectively) contributes to a comprehensive understanding of the material’s structural features. The photoluminescence spectrum of NiS in the visible region revealed split peaks at 405.8 and 428.25 nm, shedding light on the radiative recombination process between electrons and holes. The confirmation of thermal stability through a thermogravimetry diagram is essential for applications in elevated temperature environments, ensuring the material’s reliability under varying conditions. Analyzing the stoichiometry of NiS using energy dispersive spectroscopy attached to transmission electron microscopy provides insights into the material’s composition. Cyclic voltammetry results indicating a diffusion coefficient greater than that of NiS added to carbon hold significance for electrochemical applications. The unique characteristic peaks observed in cyclic voltammetry for fuel cell applications suggest the potential use of NiS in energy conversion technologies, broadening its scope of application. The confirmation of NiS’s ability to elucidate the physical and electronic properties of electrochemical systems through electrochemical impedance spectroscopy underlines its importance as a versatile material in various research and practical domains.

A Review of Stoichiometric Nickel Sulfide-Based Catalysts for Hydrogen Evolution Reaction in Alkaline Media

Efficient and cost-effective catalysts for hydrogen evolution reaction (HER) are essential for large-scale hydrogen production, which is a critical step toward reducing carbon emissions and advancing the global transition to sustainable energy. Nickel sulfide-based catalysts, which exist in various stoichiometries, show promise for HER in alkaline media. However, as single-phase materials, they do not demonstrate superior activity compared to Pt-based catalysts. This review highlights recent strategies to enhance the HER performance of nickel sulfides, including heteroatom doping, heterostructure construction, and vacancy engineering, tailored to their different stoichiometric ratios. The study also examines synthesis methods, characterizations, and their impact on HER performance. Furthermore, it discusses the challenges and limitations of current research and suggests future directions for improvement.

Sustainable hydrogen production with synergistic electron transfer enhancement in nickel-based alkaline HER electrocatalyst empowered by graphene oxide

The hydrogen evolution reaction (HER) plays a crucial role in driving forward the transition to a hydrogen-based economy by providing a means to generate pure hydrogen. However, the efficient and cost-effective production of hydrogen via HER faces significant challenges, particularly at the cathode. To address these challenges, we produced a hybrid material – 2D graphene oxide (GO) sheets coated onto nickel sulfide (NiS) microspheres anchored on Ni Foam (GO@NiS/Ni Foam) using a straightforward synthesis technique. Our research highlights the significant influence of the interaction between GO and NiS on the performance of HER, attributed to the enhancement of electron transport at the interface. Furthermore, the GO@NiS/Ni Foam composite exhibits remarkable durability over extended periods, maintaining its superior functionality for up to 40 h of continuous operation. This underscores its potential for practical implementation in efficient water-splitting processes, offering a promising solution to the challenges hindering widespread adoption of hydrogen technology.

Improved HER/OER Performance of NiS2/MoS2 Composite Modified by CeO2 and LDH.

In recent years, there has been significant interest in transition-metal sulfides (TMSs) due to their economic affordability and excellent catalytic activity. Nevertheless, it is difficult for TMSs to achieve satisfactory performance due to problems such as low conductivity, limited catalytic activity, and inadequate stability. Therefore, a catalyst with a heterostructure constituted of a nickel-iron-layered double hydroxide, nickel sulfide, molybdenum disulfide, and cerium dioxide was designed. At the current density of 10 mA cm-2 in an alkaline solution, the catalyst exhibits a HER overpotential of 116 mV. In addition, an overpotential of 235 mV@150 mA cm-2 was displayed for OER. The catalyst showed a good retention rate (94.7% for HER, 98.6% for OER) after 160 h stability tests. The excellent electrochemical performance is attributed to the following points: 1. The self-supporting three-dimensional hierarchical structure provides abundant sites, fast ion diffusion channels, and electron transfer paths, and ensures structural stability. 2. The strong interfacial electron interaction between Ni3S2/MoS2 heterojunction and NiFe-LDH improves the OER reaction kinetics. 3. The Ce3+ and oxygen vacancies in CeO2 promote the dissociation of H2O and promote the HER reaction kinetics. This approach paves the way for developing highly efficient electrocatalysts for various electrochemical applications.

Formation of Ni‐MOF Derived Nickel Sulfides as Efficient Electrocatalysts for Oxygen Evolution Reaction Through Optimizing the Sulfur Sources Selection

AbstractDeveloping low‐cost and exceedingly efficient electrocatalysts for oxygen evolution reaction (OER) is vital for application of hydrogen production from water splitting. Herein, three different nickel sulfides on nickel foam were fabricated via a simple sulfuring the as‐formed Ni‐MOF with different sulfide as the sulfur source. The effect of sulfur source on OER performance, morphology and structure of the as‐prepared product are well discussed. The optimized Ni‐MOF/NF‐SS deliver overpotentials of 253 and 330 mV to reach current densities of 10 and 100 mA cm−2 with a small Tafel slope of 70.9 mVdec−1, and stability of over 50 h. This work provides insights into the relationship between the OER activity and the structures of nickel sulfides, but also affords a new route to fabricate nickel sulfides‐based electrocatalysts for OER.

Doping-mediated interface engineered Ni3S2: Economically viable electrochemical methanol-mediated water splitting

Electrochemical water splitting is the front runner to meet the global green hydrogen demand. The development of a noble metal-free earth-abundant electrocatalyst is desired to rationalize an economically viable electrochemical water-splitting system. The sluggish anodic oxygen evolution reaction (OER) is the bottleneck of the electrochemical water-splitting system. Herein, to improve OER kinetics, group VIB elements such as chromium (Cr), molybdenum (Mo), and tungsten (W) doped nickel sulfides (Ni3S2) nanosheets (NSs) are synthesized by two-step hydrothermal method to modulate the intrinsic electrocatalytic activity of the pure Ni3S2. Among all the doped samples, the Cr-doped Ni3S2 catalyst exhibited excellent OER with an ultra-low overpotential of 248 mV and MOR with a potential of 1.36 V @ 10 mA cm−2 vs RHE achieving a lower Tafel slope of 95.5 mV/dec and 46.4 mV/dec and outstanding durability with negligible degradation respectively. Furthermore, the Pt/C||Cr-Ni3S2 (1.48 V) system outperforms commercial Pt/C||RuO2 (1.53 V @ 10 mA cm−2) in a two-electrode configuration. The methanol-mediated hybrid water splitting system only warranted a cell voltage of 1.38 V to attain 10 mA cm−2 for the Pt/C||Cr-Ni3S2 system in the presence of 0.1 M methanol (MeOH). The methanol oxidation reaction (MOR) mediated the hybrid water electrolyzer system demonstrates reduced operation cell voltage while additionally electro-synthesizing formate as a value-added chemical. The overall work is motivated to rationalize the importance of doping-mediated interface-engineered catalyst synthesis to improve the electrocatalytic efficiency of the hybrid water electrolyzer.

Boosted Electrochemical Hydrogen Evolution Activity via the Core-Shell Heterostructure of Nickel Sulfide Nanoframe-Supported Layered Rhenium Disulfide.

The strategic design of a heterostructure catalyst with a core-shell nanoarchitecture is imperative for enhancing the efficiency of the electrocatalytic hydrogen evolution reaction (HER). Herein, the core-shell catalyst comprising the rhenium disulfide nanosheets was vertically integrated onto a hollow nickel sulfide (NiS@ReS2) via coprecipitation and hydrothermal treatment. The morphology involves the sulfurization of a nickel-based Prussian blue analogue, effectively mitigating the aggregation of ReS2 nanosheets and maximizing the exposed active sites. By the synergistic effect of morphological design and heterostructure formation, the overpotential of NiS@ReS2 is 136 mV at 10 mA cm-2 in an alkaline electrolyte, and the rapid kinetics is confirmed by the small Tafel slope and low charge transfer resistance during the HER process. Moreover, the electrocatalytic durability of NiS@ReS2 is elucidated, and the boosted catalytic activity of NiS@ReS2 is confirmed by density functional theory. This study unveils a promising method for advancing ReS2-based electrocatalysts with potential implications for producing hydrogen.

A facile one-step route to synthesize of novel porous reduced graphene oxide@nickel sulfide (rGO@Ni3S2) core shell nanostructures for high-performance supercapacitor electrodes

In the last decade, there has been significant interest in the use of supercapacitors with high power density and cycle stability in a wide range of applications. Graphene-based hybrid electrodes are considered a very promising option for supercapacitors owing to the synergistic effects they exhibit. In this study, we provide a novel and efficient method for synthesising a core-shell nanocomposite consisting of reduced graphene oxide (rGO) wrapped around nickel sulphide (Ni3S2) using a one-step hydrothermal process. The resulting rGO@Ni3S2 composite exhibits excellent performance as a supercapacitor electrode while also being cost-effective. As a promising supercapacitor electrode, a relatively high specific capacitance of 1052.5 Fg−1 at current density of 1 Ag−1 in 1 mol.L−1 KOH aqueous solution, along with good cycling stability (with a 94.5 % retention rate after 10,000 cycles) were demonstrated for the rGO@Ni3S2 core shell composite electrode. In addition, excellent electrochemical performances were also demonstrated for the asymmetric supercapacitor (ASC) by using rGO@Ni3S2 as the cathode and activated carbon, respectively. The fabricated ASC showed with a high energy density of 61.9 Whkg−1 at the power density of 585.7 W kg−1. Such high performance of rGO@Ni3S2 core shell electrode can enrich the prospects for future practical applications in energy storage.

Improving photoelectrochemical performance of transferred TiO2 nanotubes onto FTO substrate with Mo2C and NiS as Co-catalyst

The photoelectrochemical (PEC) performance of titanium dioxide nanotube (TiO2 NT) photoelectrodes for sustainable hydrogen production has garnered significant research interest. Despite the advantages of TiO2 NT fabricated via anodization of titanium metal, such as their well-ordered vertical structure, challenges persist including the thick oxide barrier layer, limited optical transparancy, and the wide energy band gap (∼3.0 eV), which constrain their practical efficiency in PEC applications. This study addresses these limitations by introducing a novel approch to transfer TiO2 NT onto a fluorine-doped tin oxide (FTO) substrate. TiO2 NTs were synthesized with varying anodization times and steps to achieve optimal free-standing structures. To further enhance PEC performance, co-catalyst including molybdenum carbide (Mo2C) and nickel sulfide (NiS) were incorporated using immersion and successive ionic layer adsorption reaction (SILAR) methods, respectively. Comprehensive characterization using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), ultraviolet–visible–near infrared (UV–Vis–NIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) provided insights into the crystal phase, morphological structure, band gap, and elemental composition of the photoelectrodes. Photoelectrochemical and photostability evaluations were conducted through linear scan voltammetry (LSV) and chronoamperometry under dark and light conditions. Results indicate that transferring TiO2 NTs onto FTO significantly enhanced photocurrent density, achieving a 2.5-fold increase at 0.7 V versus a TiO2 NT/Ti substrate. The incorporating of co-catalysts Mo2C, NiS and the combined NiS/Mo2C further enhanced the photocurrent density to 2.20, 3.00 and 8.00 mA cm−2 respectively, with a remarkable 31-fold enhancement compared to the TiO2 NT/Ti substrate. This findings underscore the potential of the TiO₂ NT/FTO photoelectrode with optimized co-catalyst integration for advanced photoelectrochemical applications.

Nickel sulfide nanorods encapsulated in Nitrogen-Doped carbon on nickel foam in situ derived from Saccharomycetes cerevisiae for the selective oxidation of biomass

The design and development of an efficient catalyst for the electrocatalytic oxidation reaction of 5-hydroxymethylfurfural (HMF) require a novel, cost-effective, environmentally friendly, and safe preparation method. In this study, we synthesized nickel sulfide nanorods encapsulated by nitrogen-doped carbon on a nickel foam substrate (Ni3S2@NC/NF), derived in situ from Saccharomyces cerevisiae. The utilization of a gas-phase route facilitated the binding of C, N and S elements to the NF substrate. The resulting Ni3S2@NC/NF catalyst exhibited excellent electrocatalytic performance in the HMF oxidation reaction (HMFOR), achieving a complete conversion of HMF, a selectivity of 95.6 % for 2,5-furandicarboxylic acid, and a Faraday efficiency of 88.9 % at a potential of 1.45 V. Moreover, in situ electrochemical impedance spectroscopy revealed an enhanced charge transfer rate for the Ni3S2@NC/NF catalyst during the interfacial HMFOR. Additionally, the catalyst demonstrated outstanding stability after five cycles of electrolysis. Therefore, this work provides a valuable guide for using microorganisms as sources of C, N, and S in the targeted synthesis of metallic electrocatalysts.

Advanced corrosion resistance and mechanistic insights of electroless Ni-P-PTFE coatings on L245NS substrate in H2S-saturated environments

The extraction and transportation of oil and gas pose significant challenges due to corrosive environments, particularly hydrogen sulfide (H2S) exposure. This study investigates the use of polytetrafluoroethylene (PTFE) to enhance the corrosion resistance of nickel‑phosphorus (NiP) coatings in H2S-rich environments. Electroless deposition was employed to prepare Ni-P/PTFE coatings, which were then subjected to simulated H2S corrosion tests. Results indicate that the incorporation of PTFE led to a more uniform NiP coating with reduced porosity, significantly improving corrosion resistance. The coatings exhibited enhanced protective performance by stabilizing corrosion product layers and preventing the formation of corrosion channels. Ni-P-PTFE coatings overcame the existing research challenge of NiP coatings' corrosion in H2S environments, showing no penetration of the corrosive medium into the substrate after 720 h of immersion. The corrosion rate of the coating is only 0.0261 mm/year, only 4.27 % of the corrosion rate of the L245NS substrate in the early stage of corrosion. Moreover, after characterization by SEM, XRD and XPS, it was found that the presence of PTFE altered the corrosion mechanism, promoting the formation of stable nickel sulfide and oxide layers on the surface. This study sheds light on the mechanisms underlying PTFE-enhanced corrosion resistance in NiP coatings, offering promising implications for extending the lifespan of equipment in the oil and gas industry.

Eco-Friendly synergistic energy generation: Co-Ni2S4 nanoparticles with S-g-C3N4 as a dual-action electrocatalyst for sustainable water splitting

The most appealing technique for producing hydrogen fuel is electrochemical water splitting, which uses natural water cycle capabilities from renewable sources. The transition metal sulfide family includes nickel sulfide (NiS), which is promising for electrochemical water splitting as an exceptionally efficient, stable, and active electrocatalyst. Nickel sulfide (NiS), a series of cobalt-doped nickel sulfide (CoNi2S4) by varying weight percentages of Co (2, 4, 6, 8, wt %) and a series of sulfur-doped graphitic carbon nitride (SGCN) composite with 6 % CoNi2S4 by varying weight percentage of SGCN (10, 30, 50, 70, 90, wt %) were all synthesized using one-pot hydrothermal method. Structural morphologies and composition of the synthesized nanoparticles (NPs) and nanocomposites (NCs) were investigated using SEM, EDX, FTIR, and XRD characterization techniques. The electrochemical performance was examined via voltammetric, electrochemical impedance, and chronoamperometric studies. Outcomes suggest that composite 70 % SGCN@6 % CNS is the best electrocatalyst with the smaller Tafel slope (107 mVdec-1), lowest overpotentials (440 mV@10 mAcm−2), and minor charge transfer resistance (15 Ω) as electrode materials for electrochemical water splitting. The present research provides a workable approach for creating efficient bifunctional electrocatalysts for total water splitting, it can be inferred from the data.

Review on Recent Advances of Nickel Sulfide Nano Electrocatalysts for Hydrogen Evolution

AbstractHydrogen is an important energy carrier without carbon emissions. To achieve a carbon‐neutral world, the demand for hydrogen is very significant. In the process of producing green hydrogen, water splitting using electrocatalysts is a desirable process among many methods. The ideal electrocatalyst for hydrogen evolution is the platinum group of metals; however, the limitations of high cost and low abundance hinder large‐scale hydrogen production. Hence, researchers are trying to develop materials from more abundant and less expensive. Hence, in this review, we focus on the fundamental principles of hydrogen evolution reaction (HER) and various synthesis methods and strategies. From the material perspective, we focus on nickel sulfide‐based nanomaterials of different phases during the last four years of development. We compared the electrocatalyst parameters concerning the synthesis methods and strategies chosen. Finally, we have also discussed future challenges. Ultimately, by synthesizing the collective knowledge amassed in the field of HER research, this review endeavors to offer a comprehensive resource for researchers, engineers, and policymakers striving to advance hydrogen‐based energy technologies. In doing so, we aspire to foster continued innovation and collaboration toward realizing a sustainable energy future powered by hydrogen.

Achieving Complete Conversion from Nickel Foam to Nickel Sulfide Foam for a Freestanding Hybrid‐Supercapacitor Electrode

AbstractWe present a unique, one‐step, hydrothermal process to prepare nickel sulfide (Ni3S2) foam by a simple and direct conversion from nickel foam, which contributes both as a scaffold for the reaction and as reactant. The Ni3S2 foam exhibits remarkable mechanical stability, retaining the structural integrity of the foam and excellent crystallinity even after ultrasonication at 200 W for 30 mins. We document the transformation of the nickel foam template into a Ni3S2 foam, highlighting the role of synthesis duration on the phase evolution and unique morphology of Ni3S2. PXRD and SEM analyses reveal a complete transformation after 24 hours from the nickel foam to a pure Ni3S2 foam, which has a highly porous and interconnected ultra‐thin nanosheet architecture. This significantly enhances the surface area and provides many electrochemical reaction sites. In a three‐electrode cell, the capacity of the Ni3S2 foam electrode is 3.9 C cm−2 at 8 mA cm−2, which is higher than previous reports for Ni3S2. In a hybrid supercapacitor device, the Ni3S2 foam demonstrates significant increase in capacitance through 500 cycles and the capacitance plateaus after 2000 cycles. Even after 8500 continued charge‐discharge cycles, the device exhibits excellent cycle stability indicating improvement with age.