Amorphous MoS2 Decorated Ni3 S2 with a Core-shell Structure of Urchin-Like on Nickel-Foam Efficient Hydrogen Evolution in Acidic and Alkaline Media.

The large-scale commercialization of the hydrogen evolution reaction (HER) necessitates the development of cost-effective and highly efficient electrocatalysts. Although transition metal sulfides, such as MoS2 and Ni3 S2 , hold great potential in the field of HER, their catalytic performance has been unsatisfactory due to incomplete exposure of active sites and poor electrical conductivity. In this work, via a simple hydrothermal strategy, amorphous MoS2 nanoshells in the form of urchin-like MoS2 -Ni3 S2 core-shell heterogeneous structure is realized and in situ loaded on nickel foam (A-MoS2 -Ni3 S2 -NF). In particular, XPS analysis results show that the coupling of amorphous MoS2 and Ni3 S2 makes the electrode surface exhibit electron-abundant property, which will have a positive impact on HER catalytic activity. In addition, the fully exposed active site of amorphous MoS2 is another crucial factor contributing to its high catalytic performance of A-MoS2 -Ni3 S2 -NF electrode. In particular, at a current density of 10 mA cm⁻2 , the overpotential of electrode is 95 mV (1.0 m KOH) and 145 mV (0.5 m H2 SO4 ). This work highlights the importance of amorphous MoS2 and MoS2 -Ni3 S2 of sea-urchin core-shell structure in optimizing HER performance, which provides an important reference for HER research.

Bifunctional Ni Foam Supported TiO2 @Ni3 S2 core@shell Nanorod Arrays for Boosting Electrocatalytic Biomass Upgrading and H2 Production Reactions.

Replacing traditional oxygen evoltion reaction (OER) with biomass oxidation reaction (BOR) is an advantageous alternative choice to obtain green hydrogen energy from electrocatalytic water splitting. Herein, a novel of extremely homogeneous Ni3 S2 nanosheets covered TiO2 nanorod arrays are in situ growth on conductive Ni foam (Ni/TiO2 @Ni3 S2 ). The Ni/TiO2 @Ni3 S2 electrode exhibits excellent electrocatalytic activity and long-term stability for both BOR and hydrogen evolution reaction (HER). Especially, taking glucose as a typical biomass, the average hydrogen production rate of the HER-glucose oxidation reaction (GOR) two-electrode system reached 984.74 µmol h-1 , about 2.7 times higher than that of in a common HER//OER two-electrode water splitting system (365.50 µmol h-1 ). The calculated power energy saving efficiency of the GOR//HER system is about 13% less than that of the OER//HER system. Meanwhile, the corresponding selectivity of the value-added formic acid produced by GOR reaches about 80%. Moreover, the Ni/TiO2 @Ni3 S2 electrode also exhibits excellent electrocatalytic activity on a diverse range of typical biomass intermediates, such as urea, sucrose, fructose, furfuryl alcohol (FFA), 5-hydroxymethylfurfural (HMF), and alcohol (EtOH). These results show that Ni/TiO2 @Ni3 S2 has great potential in electrocatalysis, especially in replacing OER reaction with BOR reaction and promoting the sustainable development of hydrogen production.

Iron, Tungsten Dual-Doped Nickel Sulfide as Efficient Bifunctional Catalyst for Overall Water Splitting.

Developing low-cost and highly efficient bifunctional catalysts for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) is a challenging problem in electrochemical overall water splitting. Here, iron, tungsten dual-doped nickel sulfide catalyst (Fe/W-Ni3S2) is synthesized on the nickel foam, and it exhibits excellent OER and HER performance. As a result, the water electrolyze based on Fe/W-Ni3S2 bifunctional catalyst illustrates 10 mA cm-2 at 1.69 V (without iR-compensation) and highly durable overall water splitting over 100 h tested under 500 mA cm-2. Experimental results and DFT calculations indicate that the synergistic interaction between Fe doping and Ni vacancy induced by W leaching during the in situ oxidation process can maximize exposed OER active sites on the reconstructed NiOOH species for accelerating OER kinetics, while the Fe/W dual-doping optimizes the electronic structure of Fe/W-Ni3S2 and the binding strength of intermediates for boosting HER. This study unlocks the different promoting mechanisms of incorporating Fe and W for boosting the OER and HER activity of Ni3S2 for water splitting, which provides significant guidance for designing high-performance bifunctional catalysts for overall water splitting.

Strong Interface Coupling Enables Stability of Amorphous Meta-Stable State in CoS/Ni3S2 for Efficient Oxygen Evolution.

Rational design of heterostructure catalysts through phase engineering strategy plays a critical role in heightening the electrocatalytic performance of catalysts. Herein, a novel amorphous/crystalline (a/c) heterostructure (a-CoS/Ni3S2) is manufactured by a facile hydrothermal sulfurization method. Strikingly, the interface coupling between amorphous phase (a-CoS) and crystalline phase (Ni3S2) in a-CoS/Ni3S2 is much stronger than that between crystalline phase (c-CoS) and crystalline phase (Ni3S2) in crystalline/crystalline (c/c) heterostructure (c-CoS/Ni3S2) as control sample, which makes the meta-stable amorphous structure more stable. Meanwhile, a-CoS/Ni3S2 has more S vacancies (Sv) than c-CoS/Ni3S2 because of the presence of an amorphous phase. Eventually, for the oxygen evolution reaction (OER), the a-CoS/Ni3S2 exhibits a significantly lower overpotential of 192 mV at 10 mA cm-2 compared to the c-CoS/Ni3S2 (242 mV). An exceptionally low cell voltage of 1.51 V is required to achieve a current density of 50 mA cm-2 for overall water splitting in the assembled cell (a-CoS/Ni3S2 || Pt/C). Theoretical calculations reveal that more charges transfer from a-CoS to Ni3S2 in a-CoS/Ni3S2 than in c-CoS/Ni3S2, which promotes the enhancement of OER activity. This work will bring into play a fabrication strategy of a/c catalysts and the understanding of the catalytic mechanism of a/c heterostructures.

In Situ Raman Study of Surface Reconstruction of FeOOH/Ni3S2 Oxygen Evolution Reaction Electrocatalysts.

Construction of heterojunctions is an effective strategy to enhanced electrocatalytic oxygen evolution reaction (OER), but the structural evolution of the active phases and synergistic mechanism still lack in-depth understanding. Here, an FeOOH/Ni3S2 heterostructure supported on nickel foam (NF) through a two-step hydrothermal-chemical etching method is reported. In situ Raman spectroscopy study of the surface reconstruction behaviors of FeOOH/Ni3S2/NF indicates that Ni3S2 can be rapidly converted to NiOOH, accompanied by the phase transition from α-FeOOH to ß-FeOOH during the OER process. Importantly, a deep analysis of Ni─O bond reveals that the phase transition of FeOOH can regulate the lattice disorder of NiOOH for improved catalytic activity. Density functional theory (DFT) calculations further confirm that NiOOH/FeOOH heterostructure possess strengthened adsorption for O-containing intermediates, as well as lower energy barrier toward the OER. As a result, FeOOH/Ni3S2/NF exhibits promising OER activity and stability in alkaline conditions, requiring an overpotential of 268 mV @ 100 mA cm-2 and long-term stability over 200 h at a current density of 200 mA cm-2. This work provides a new perspective for understanding the synergistic mechanism of heterogeneous electrocatalysts during the OER process.

Nitrogen and Sulfur Co-Doped Carbon-Coated Ni3S2/MoO2 Nanowires as Bifunctional Catalysts for Alkaline Seawater Electrolysis.

Bifunctional catalysts have inherent advantages in simplifying electrolysis devices and reducing electrolysis costs. Developing efficient and stable bifunctional catalysts is of great significance for industrial hydrogen production. Herein, a bifunctional catalyst, composed of nitrogen and sulfur co-doped carbon-coated trinickel disulfide (Ni3S2)/molybdenum dioxide (MoO2) nanowires (NiMoS@NSC NWs), is developed for seawater electrolysis. The designed NiMoS@NSC exhibited high activity in alkaline electrolyte with only 52 and 191 mV overpotential to attain 10 mA cm-2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Significantly, the electrolyzer (NiMoS@NSC||NiMoS@NSC) based on this bifunctional catalyst drove 100 mA cm-2 at only 1.71 V along with a robust stability over 100 h in alkaline seawater, which is superior to a platinum/nickel-iron layered double hydroxide couple (Pt||NiFe LDH). Theoretical calculations indicated that interfacial interactions between Ni3S2 and MoO2 rearranged the charge at interfaces and endowed Mo sites at the interfaces with Pt-like HER activity, while Ni sites on Ni3S2 surfaces at non-interfaces are the active centers for OER. Meanwhile, theoretical calculations and experimental results also demonstrated that interfacial interactions improved the electrical conductivity, boosting reaction kinetics for both HER and OER. This study presented a novel insight into the design of high-performance bifunctional electrocatalysts for seawater splitting.

Hierarchical Sea Urchin-like Fe-doped Heazlewoodite for High-Efficient Oxygen Evolution.

Electrochemical water-splitting to produce hydrogen is potential to substitute the traditional industrial coal gasification, but the oxygen evolution kinetics at the anode remains sluggish. In this paper, sea urchin-like Fe doped Ni3S2 catalyst growing on nickel foam (NF) substrate is constructed via a simple two-step strategy, including surface iron activation and post sulfuration process. The NF-Fe-Ni3S2 obtains at temperature of 130 °C (NF-Fe-Ni3S2-130) features nanoneedle-like arrays which are vertically grown on the particles to form sea urchin-like morphology, features high electrochemical surface area. As oxygen evolution catalyst, NF-Fe-Ni3S2-130 exhibits excellent oxygen evolution activities, fast reaction kinetics, and superior reaction stability. The excellent OER performance of sea urchin-like NF-Fe-Ni3S2-130 is mainly ascribed to the high-vertically dispersive of nanoneedles and the existing Fe dopants, which obviously improved the reaction kinetics and the intrinsic catalytic properties. The simple preparation strategy is conducive to establish high-electrochemical-interface catalysts, which shows great potential in renewable energy conversion.

Super-Hydrophilic Microporous Ni(OH)x/Ni3 S2 Heterostructure Electrocatalyst for Large-Current-Density Hydrogen Evolution.

Exploiting active and stable non-precious metal electrocatalysts for alkaline hydrogen evolution reaction (HER) at large current density plays a key role in realizing large-scale industrial hydrogen generation. Herein, a self-supported microporous Ni(OH)x/Ni3 S2 heterostructure electrocatalyst on nickel foam (Ni(OH)x/Ni3 S2 /NF) that possesses super-hydrophilic property through an electrochemical process is rationally designed and fabricated. Benefiting from the super-hydrophilic property, microporous feature, and self-supported structure, the electrocatalyst exhibits an exceptional HER performance at large current density in 1.0 M KOH, only requiring low overpotential of 126, 193, and 238 mV to reach a current density of 100, 500, and 1000 mA cm-2 , respectively, and displaying a long-term durability up to 1000 h, which is among the state-of-the-art non-precious metal electrocatalysts. Combining hard X-rays absorption spectroscopy and first-principles calculation, it also reveals that the strong electronic coupling at the interface of the heterostructure facilitates the dissociation of H2 O molecular, accelerating the HER kinetics in alkaline electrolyte. This work sheds a light on developing advanced non-precious metal electrocatalysts for industrial hydrogen production by means of constructing a super-hydrophilic microporous heterostructure.

CDs Regulated Sulfur-Based Flexible Electrode with Range pH Values for Efficient and Durable Hydrogen Evolution Reaction.

How to mildly structure a high intrinsic activity and stable catalytic electrode to realize long-term catalytic water splitting to produce hydrogen at a wide range of pH values at industrial high current is a challenge. Herein, this work creatively proposes to prepare industrial-grade catalytic electrodes with high efficiency and stability at high current density through carbon quantum dots (CDs) modification nickel sulfide on hydrophilic flexible filter paper via one-step mild chemical plating (denoted as CDs-Ni3 S2 @HFP). The intrinsic activity and surface area, electron transfer ability, and corrosion resistance of Ni3 S2 material are increased due to the regulation, homogenous, and high concentration doping of CDs. The overpotential of the flexible catalytic electrode is only 30, 35, and 87 mV in 1 m KOH, simulated seawater (1 m KOH + 0.5 m NaCl), and neutral electrolyte (0.5 m PBS) at a current density of 10 mA cm-2 . More attractively, the CDs-Ni3 S2 @HFP electrode achieves over 500 h of efficient and stable catalysis at industrial high current density (500 mA cm-2 ). Due to the advantages of mild, universal, and large-area preparation of catalytic materials, this work provides technical support for flexible catalytic electrodes in efficient catalysis toward water splitting, energy storage, and device preparation.

Bimetallic Multi-Level Layered Co-NiOOH/Ni3 S2 @NF Nanosheet for Hydrogen Evolution Reaction in Alkaline Medium.

Development of efficient non-noble metal catalysts for water splitting is of great significance but challenging due to the sluggish kinetics of the hydrogen evolution reaction (HER) in alkaline medium. Herein, a bimetallic multi-level layered catalytic electrode composed of Ni3 S2 nanosheets with secondary Co-NiOOH layer of 3D porous and free-standing cathode in alkaline medium is reported. This integrated synergistic catalytic electrode exhibits excellent HER electrocatalytic performance. The resultant Ni0.67 Co0.33 /Ni3 S2 @NF electrode displays the highest HER activity with only overpotentials of 87 and 203 mV to afford current densities of 10 and 100 mA·cm-2 , respectively, and its Tafel slope is 80 mV·dec-1 . The chronopotentiometry operated at high current density of 50 mA·cm-2 shows negligible deterioration, indicating better stability of Ni0.67 Co0.33 /Ni3 S2 @NF electrode than Pt/C (20 wt.%). Such a desirable catalytic performance is attributed to the modification of physical and electronic structure that exposes abundant active sites and improves the intrinsic catalytic activity toward HER, which is also confirmed by electrochemically active surface area and X-ray photoelectron spectroscopy analysis. This work provides a strong support for the rational design of high-performance bimetallic electrodes for industrial water splitting.

Controllable 3D Porous Ni Current Collector Coupled with Surface Phosphorization Enhances Na Storage of Ni3 S2 Nanosheet Arrays.

3D porous Ni is fabricated via an easily scalable electroless plating method using a dynamic template formed through in-situ hydrogen bubbles. The pore size in the range of several micrometers is controllable through adjusting the Ni2+ depositing rate and hydrogen bubbles releasing rate. The Ni3 S2 nanosheet arrays anode is then grown on the unique 3D porous Ni current collector followed by subsequent surface phosphorization. The tremendous interconnected pores and rich voids between the Ni3 S2 nanosheet arrays cannot only provide rapid transferring channels for Na+ , but also accommodate volumetric changes of the Ni3 S2 electrode during cycling, guaranteeing the integrity of the active material. In addition, the surface phosphorized layer enhances the electronic conductivity through providing an electron transport highway along the 3D Ni3 S2 , NiP2 layer, and 3D porous Ni current collector, and simultaneously stabilizes the electrode/electrolyte interphase as a protecting layer. Because of these merits, the phosphorized 3D porous Ni3 S2 (3D P-Ni3 S2 ) electrode is capable of delivering an ultra-stable capacity of 387.5 mAh g-1 at 0.1 A g-1 , and a high capacity retention of 85.3% even at a high current density of 1.6 A g-1 .

A sulfur defective Mn-doped Ni3S2-xnanosheet for enhanced overall water splitting.

Non-precious and stable electrocatalysts towards both oxygen and hydrogen evolution reaction (OER/HER) are essential for effective overall water splitting in alkaline solution. In this study, a sulfur defective and manganese-doped nickel sulfide nanosheet that uniformly grown on nickel foam substrate (Mn-Ni3S2-x@NF) is synthesized. In alkaline solution, the Mn-Ni3S2-x@NF showed a low overpotential of 76 and 110 mV for OER and HER at 10 mA cm-2, respectively, together exhibiting excellent stability for both OER and HER reaction. It was confirmed by the experimental results that sulfur defects and Mn-doping synergistically optimized the electronic structure of Mn-Ni3S2-xwith increased electrical conductivity and enhanced OER/HER activity. Moreover, amorphous nickel oxyhydroxide (NiOOH) was observed byin situRaman during the OER condition, suggesting NiOOH is the active phase for OER reaction. Furthermore, the electrolyzer assembled by Mn-Ni3S2-x@NF merely needs 1.46 V to reach 10 mA cm-2and shows good stability as well. This study provides a feasible way to prepare high-efficiency bifunctional catalysts for overall water splitting.

Ni(OH)2 Templated Synthesis of Ultrathin Ni3 S2 Nanosheets as Bifunctional Electrocatalyst for Overall Water Splitting.

Ultrathin nickel (Ni)-based sulfide nanosheets have been reported as excellent electrocatalysts for overall water splitting; however, the uncontrollability over thickness due to the nonlayered structure still hampers its practical application. Herein, a simple topochemical conversion strategy is employed to synthesize cobalt-doped Ni3 S2 (Co-Ni3 S2 ) ultrathin nanosheets on Ni foam. The Co-Ni3 S2 nanosheets are controlled synthesized by using Co-Ni(OH)2 ultrathin nanosheets as templates with anneal and sulfurization treatment, showing exceptional electrocatalytic activity. This template-assisted method can also be applied to obtain Ni, NiO, and NiPx nanosheets, providing a universal strategy to synthesize ultrathin nanosheets of nonlayered materials. The overall water splitting of this Co-Ni3 S2 ultrathin nanosheets achieves a low voltage of 1.54 V at a current density of 10 mA cm-2 and high durability in 1 m KOH, comparable to the best performance of electrochemical water splitting ever reported. The detailed structural transformation of Ni-based sulfides in the catalytic process and its mechanism are further explored both experimentally and theoretically.

3D-Stretched Film Ni3 S2 Nanosheet/Macromolecule Anthraquinone Derivative Polymers for Electrocatalytic Overall Water Splitting.

For the first time, a new polymer electrode AQS/S is prepared by compositing Ni3 S2 nanosheets and macromolecular anthraquinone derivative (AQD) supported on nickel foam with flying colors. The AQS/S exhibits high crystalline structure and abundant S defects. Density of state calculation shows that AQD has stable internal bonding and easy external bonding with metals, conducive to the dispersion of metal reaction sites, ensuring excellent activity and high stability. Under 1.0 m KOH solution, ultralow overpotentials of 62 and 133 mV at 10 mA cm-2 on AQS/S for hydrogen evolution reaction and on activated AQS/S (A-AQS/S) for oxygen evolution reaction, respectively, are achieved. 100 h chronopotentiometry and the cyclic voltammetry tests show that catalysts have high durability. The AQS/S‖A-AQS/S two-electrode system is also found to have good electrocatalytic activity for 1.43 V to get 10 mA cm-2  in overall water splitting, better than the state-of-the-art 20% Pt/C‖RuO2 combination.

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.

Stable and enhanced electrochemical performance based on hierarchical core-shell structure of CoMn2O4@Ni3S2electrode for hybrid supercapacitor.

Herein, accessible and low-cost CoMn2O4@Ni3S2core-shell nanoneedle arrays have been prepared via a two-step approach comprised with hydrothermal-calcination and electrochemical deposition procedures, successfully. In the beginning, CoMn2O4nanoneedle arrays took root on Ni foam to form the core skeleton and subsequently, hierarchical Ni3S2nanosheets uniformly overlaid on the surface of CoMn2O4nanoneedles shaping the shell structure. This CoMn2O4@Ni3S2material was measured directly as supercapacitor electrode and presented high specific capacity of 192.2 mAh g-1with current density of 1 A g-1. Besides, the electrode delivered outstanding cyclical stability as the capacity retention attained 90.2% after charge-discharge measurement at a large current density of 10 A g-1for 10 000 cycles. Furthermore, a hybrid supercapacitor assembled by CoMn2O4@Ni3S2cathode and activated carbon anode represented a high energy density of 51.2 Wh kg-1with the power density of 1030.0 W kg-1. This work shows a facile and inexpensive procedure to design high-performance and strong-stability supercapacitor electrodes.

Multifunctional Nickel Sulfide Nanosheet Arrays for Solar-Intensified Oxygen Evolution Reaction.

Electrochemical water splitting for hydrogen production is currently hindered by the sluggish kinetic of anodic oxygen evolution reaction (OER). By integrating photothermal materials into electrocatalytic network and thus allowing solar energy to work as additional driving force, the OER is expected to be boosted. However, the rational design of such electrochemical system still remains a challenge due to the spatial inconsistency between photothermal component and electrocatalytic component. Herein, it is reported that multifunctional nickel sulfide (Ni3 S2 ) nanosheet arrays show both photothermal and electrocatalytic properties for solar-intensified electrocatalytic system, which well eliminates the spatial inconsistency between the aforementioned two types of functional components by using one bifunctional material. The deliberate design of nanoarray architecture formed by the interconnected Ni3 S2 nanosheets endows larger surface area and higher surface roughness, thus enhancing light absorption by suppressing diffuse reflection and facilitating electron transfer in electrocatalytic reactions. Therefore, the OER activity is significantly improved. Under light illumination, the current density of Ni3 S2 nanosheets could reach 492.2 mA cm-2 at 1.55 V, about 2.5-fold that in dark conditions, with a Tafel slope of as low as 60 dec-1 . The solar-intensified electrochemical system based on multifunctional material presents prospective potential in electrochemical water splitting for efficient hydrogen production.

2D Free-Standing Nitrogen-Doped Ni-Ni3 S2 @Carbon Nanoplates Derived from Metal-Organic Frameworks for Enhanced Oxygen Evolution Reaction.

2D metal-organic frameworks (2D MOFs) are promising templates for the fabrication of carbon supported 2D metal/metal sulfide nanocomposites. Herein, controllable synthesis of a newly developed 2D Ni-based MOF nanoplates in well-defined rectangle morphology is first realized via a pyridine-assisted bottom-up solvothermal treatment of NiSO4 and 4,4'-bipyridine. The thickness of the MOF nanoplates can be controlled to below 20 nm, while the lateral size can be tuned in a wide range with different amounts of pyridine. Subsequent pyrolysis treatment converts the MOF nanoplates into 2D free-standing nitrogen-doped Ni-Ni3 S2 @carbon nanoplates. The obtained Ni-Ni3 S2 nanoparticles encapsulated in the N-doped carbon matrix exhibits high electrocatalytic activity in oxygen evolution reaction. A low overpotential of 284.7 mV at a current density of 10 mA cm-2 is achieved in alkaline solution, which is among the best reported performance of substrate-free nickel sulfides based nanomaterials.

Incorporating Nitrogen-Doped Graphene Quantum Dots and Ni3 S2 Nanosheets: A Synergistic Electrocatalyst with Highly Enhanced Activity for Overall Water Splitting.

A noble-metal-free electrocatalyst is fabricated via in situ formation of nanocomposite of nitrogen-doped graphene quantum dots (NGQDs) and Ni3 S2 nanosheets on the Ni foam (Ni3 S2 -NGQDs/NF). The resultant Ni3 S2 -NGQDs/NF can serve as an active, binder-free, and self-supported catalytic electrode for direct water splitting, which delivers a current density of 10 mA cm-2 at an overpotential of 216 mV for oxygen evolution reaction and 218 mV for hydrogen evolution reaction in alkaline media. This bifunctional electrocatalyst enables the construction of an alkali electrolyzer with a low cell voltage of 1.58 V versus reversible hydrogen electrode (RHE) at 10 mA cm-2 . The experimental results and theoretical calculations demonstrate that the synergistic effects of the constructed active interfaces are the key factor for excellent performance. The nanocomposite of NGQDs and Ni3 S2 nanosheets can be promising water splitting electrocatalyst for large-scale hydrogen generation or other energy storage and conversion applications.

Revealing the role of 1T- & 2H- molybdenum Disulfide/Nickel sulfide heterojunction for efficient overall water splitting.

In the ongoing quest for cost-effective and durable electrocatalysts for hydrogen production-a critical element of sustainable energy transformation-the 1T phase of Molybdenum Disulfide (MoS2) faces challenges due to its thermodynamic instability and the trade-off between efficiency and durability. Conversely, the 2H phase of MoS2, often disregarded in favor of the metallic 1T phase, suffers from its inert nature and limited active sites. To overcome these limitations, this study employs a straightforward hydrothermal synthesis strategy that couples both 1T and 2H phases of MoS2 with Ni3S2, forming 1T- and 2H- MoS2/Ni3S2 heterojunctions. Enhanced by Ni3S2's abundant active sites, improved electron transport capabilities, synergistic interface effects, and better structural stability, these heterojunctions achieve a high current density exceeding 500 mA cm-2 at low overpotentials, along with prolonged durability for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline electrolytes. Remarkably, an electrolyzer assembly utilizing 1T-MoS2/Ni3S2 as the cathode and 2H-MoS2/Ni3S2 as the anode demonstrates a competitive voltage of 1.58 V at 20 mA cm-2, showcasing superior performance in overall water splitting compared to other non-noble metal-based electrocatalysts. This study not only offers a viable method for synthesizing efficient and stable electrocatalysts for water splitting using transition metal-based heterogeneous structures but also addresses the fundamental challenges associated with 1T and 2H phases of MoS2.