Synergy between in-situ immobilized MoS2 nanosheets and TiO2 nanotubes for efficient electrocatalytic hydrogen evolution

MoS₂ electrocatalyst exhibits a significant potential to substitute platinum in hydrogen evolution reaction (HER), but its immobilization on practical supports is still challenging. Herein, a facile hydrothermal method is developed for in-situ immobilizing MoS₂ nanosheets on titanium nanotubes (TNTs) support. Easy to mount electrodes with a uniform and dense layer of MoS₂ on TNTs are achieved. An overpotential of ?200 mV_RHE is ample to deliver ?10 mA/cm² from an acidic medium. This overpotential is much lower than those of the electrodes developed by drop-casting MoS₂ on TNTs, glassy carbon (274 mV), and in-situ immobilized on Ti foil (264 mV). The results revealed that the synergy between the in-situ immobilized MoS₂ and TNTs enhances the electrochemical surface area and the adsorption capacity of hydronium ions. The electronic interaction between MoS₂ and TNTs facilitates the mobility of electrons and reduces the charge transfer resistance at the electrode/electrolyte interface.     

Self-standing and efficient bifunctional electrocatalyst for overall water splitting under alkaline media enabled by Mo1-xCoxS2 nanosheets anchored on carbon fiber paper

The layered MoS₂ nanostructures have been widely used in the electrochemical hydrogen evolution reaction (HER), but rarely applied in overall water splitting application for their ignorable oxygen evolution reaction (OER) activity. To address this issue, a novel self-standing and bifunctional electrocatalyst, consisting of Co-doped MoS₂ nanosheets anchored on carbon fiber paper, has been prepared via hydrothermal method. Taking advantage of conductive substrate of carbon fiber paper, sufficient-exposed active edges of MoS₂ sheets, and metallic character caused by Co-doping, our electrode exhibits high-efficient bifunctional activities for the overall water splitting in alkaline electrolyte (1 M KOH), which can produce a current density of 20 mA cm⁻² at an overpotential of 197 mV for HER and 235 mV for OER.     

Interfacing perovskite strontium molybdate to molybdenum disulfide nanoplatelts for boosting HER from water

Due to low hydrogen adsorption free energy at the edges of 2D-MoS₂ layered sheets, nanostructured MoS₂ materials recently are assigned to prospective electrocatalysts for hydrogen evolution reaction (HER) from water. However, the efficiency and stability of HER onto the MoS₂ designed on the conductive substrates are poor. To significantly increase the number of active sites and achieve a long-time working stability, the design of hybrid-type electrodes is crucial. Here, we report the synthesis of a new hybrid material composed of molybdenum disulfide and molybdenum oxides heterostructured with strontium molybdate. For this, a facile one-pot hydrothermal process was developed directly onto the TiO₂ nanotube carpet substrate. The interfacing of strontium molybdate at the electrode substrate verified by X-ray photoelectron spectroscopy and Time of flight secondary ions mass spectrometry (ToF SIMS) techniques. Considerable higher catalytic activity at the surface of this hybrid film, with the onset potential of 190 mV vs RHE and a Tafel slope of 66 mV dec^?1 attaining ~80 mA cm^?2 at 0.35 V overvoltage was ascertained. Exciting HER stability in comparison with the pure synthetic MoS₂ was verified by a prolonged potential cycling from 0.05 to ?0.35 V versus RHE potential and 45 h continuous HER processing at a constant current density.     

MoS2-graphene-CuNi2S4 nanocomposite an efficient electrocatalyst for the hydrogen evolution reaction

We present a facile methodology for the synthesis of a novel 2D-MoS₂, graphene and CuNi₂S₄ (MoS₂-g-CuNi₂S₄) nanocomposite that displays highly efficient electrocatalytic activity towards the production of hydrogen. The intrinsic hydrogen evolution reaction (HER) activity of MoS₂ nanosheets was significantly enhanced by increasing the affinity of the active edge sites towards H⁺ adsorption using transition metal (Cu and Ni₂) dopants, whilst also increasing the edge sites exposure by anchoring them to a graphene framework. Detailed XPS analysis reveals a higher percentage of surface exposed S at 17.04%, of which 48.83% is metal bonded S (sulfide). The resultant MoS₂-g-CuNi₂S₄ nanocomposites are immobilized upon screen-printed electrodes (SPEs) and exhibit a HER onset potential and Tafel slope value of – 0.05 V (vs. RHE) and 29.3 mV dec⁻¹, respectively. These values are close to that of the polycrystalline Pt electrode (near zero potential (vs. RHE) and 21.0 mV dec⁻¹, respectively) and enhanced over a bare/unmodified SPE (– 0.43 V (vs. RHE) and 149.1 mV dec⁻¹, respectively). Given the efficient, HER activity displayed by the novel MoS₂-g-CuNi₂S₄/SPE electrochemical platform and the comparatively low associated cost of production for this nanocomposite, it has potential to be a cost-effective alternative to Pt within electrolyser technologies.     

Three-dimensional interconnected MoS2 nanosheets on industrial 316L stainless steel mesh as an efficient hydrogen evolution electrode

The development of inexpensive and competent electrocatalysts for high-efficiency hydrogen evolution reaction (HER) has been greatly significant to realize hydrogen production in large scale. In this paper, we selected the inexpensive and commercially accessible stainless steel as the conductive substrate for loading MoS₂ as a cathode for efficient HER under alkaline condition. Interconnected MoS₂ nanosheets were grown uniformly on 316-type stainless steel meshes with different mesh numbers via a facile hydrothermal way. And the optimized MoS₂/stainless steel electrocatalysts exhibited superior electrocatalytic performance for HER with a low overpotential of 160 mV at 10 mA cm⁻² and a small Tafel slope of 61 mV dec⁻¹ in 1 M KOH. Systematic study of the electrochemical properties was performed on the MoS₂/stainless steel electrocatalysts in comparison with the commonly used carbon cloth to better comprehend the origin of the superior HER performance as well as stability. By collaborative optimization of MoS₂ nanosheets and the cheap stainless steel substrate, the interconnected MoS₂ nanosheets on stainless steel provide an alternative strategy for the development of efficient and robust HER catalysts in strong alkaline environment.     

Study of the electrochemical properties of Fe3O4/C–Bi composites prepared by spray drying and their use in cylindrical sealed nickel iron batteries

In this paper, Fe₃O₄/C–Bi composites with carbon coating and bismuth added were prepared by step-by-step precipitation, spray carbon coating drying and high temperature treatment. The composite materials are spherical particles, which are composed of primary nanoparticles coated with carbon, and the thickness of the carbon coating layer is 2 nm. Electrochemical test results show that the synergistic effect of Bi and C can effectively inhibit hydrogen evolution and passivation of iron electrodes. The Fe₃O₄/C–Bi composite materials have excellent electrochemical properties, among which the Fe₃O₄/C–Bi(5%) electrode has the best performance. At a current density of 300 mA g^?1, the discharge capacitance is close to 700.0 mAh g^?1, the coulombic efficiency is as high as 95.2%, and the rate performance is also excellent. At a current density of 2400 mA g^?1, the discharge capacity reaches 500.0 mAh g^?1. AA600 cylindrical iron nickel batteries prepared with an Fe₃O₄/C–Bi(5%) composite as the active material for iron negative electrodes realized sealing for the first time.     

Thermally reduced graphite oxide/carbon nanotubes supported molybdenum disulfide as catalysts for hydrogen evolution reaction

We report an efficient molybdenum disulfide (MoS₂) supported by thermally reduced graphite oxide and carbon nanotubes (TRGO-CNT) for hydrogen evolution reaction. The TRGO-CNT-MoS₂ composite is successfully prepared by a simple sonication process, exhibiting excellent catalytic activity of the hydrogen evolution reaction (HER) with a low overpotential of −0.14 V, which is much lower compared to that of MoS₂, CNT-MoS₂ and TRGO-MoS₂, respectively. TRGO-CNT-MoS₂ also exhibits high stability even after 1000 cycles and strong durability after 48 h. The high HER performance of TRGO-CNT-MoS₂ attributes to a synergic effect of thermal reduced GO and CNT that support MoS₂ due to significant decrease of electrochemical impedance and reliable supporting material for the efficient HER.     

MoS2-supported on free-standing TiO2-nanotubes for efficient hydrogen evolution reaction

The electrochemical production of hydrogen is a promising and flexible approach towards the conversion of intermittent renewable energy sources into clean chemical fuel. However, low-cost, efficient, and durable electrocatalysts are yet to be developed to attain economies of scale in hydrogen generation. In this study, we fabricated highly ordered free-standing TiO₂ nanotube arrays (TiO₂-NTs), by simply anodizing Ti foils. The tube length, diameter, wall thickness, and surface structure of the TiO₂-NTs can be controlled by adjusting the anodization conditions. Subsequently, we synthesized and supported MoS₂ layers on free-standing TiO₂-NTs as an active material for the hydrogen evolution reaction (HER), using a slow evaporation method. The layers of MoS₂ uniformly disperse on the entire surface of the TiO₂-NTs composite. The electrochemical test shows that the MoS₂-supported free-standing (MoS₂/TiO₂-NTs) system exhibits excellent HER performance in acidic media with a low overpotential at 10 mA cm⁻² (170 mV), as well as small Tafel slope (70 mV decade⁻¹). Also, the MoS₂/TiO₂-NTs displays superior durability for HER after 5000 continuous potential cycles between −0.4 and + 0.2 (V vs. RHE). Our results demonstrate the potential application of MoS₂/TiO₂-NTs composite for cost-effective electrochemical production of hydrogen.     

Modification of the ultrasonication derived-g-C3N4 nanosheets/quantum dots by MoS2 nanostructures to improve electrocatalytic hydrogen evolution reaction

In this work, graphitic carbon nitride (g-C₃N₄) nanosheets/quantum dots (NS/QD) was prepared using a simple and low-cost procedure. By two steps exfoliation in a bath and tip sonicator, the g-C₃N₄ (NS/QD) was produced from bulk g-C₃N₄. To improve electrocatalytic hydrogen evolution reaction (HER), the g-C₃N₄ (NS/QD) were modified by the MoS₂ nanostructures. Nanocomposite of the g-C₃N₄ (NS/QD) with MoS₂ nanostructures was deposited on a flexible, conductive and three dimensional carbon cloth by a facile and binder-free electrophoretic technique. This electrode exhibited a Tafel slope of 88 mV/dec and an overpotential of 0.28 V vs RHE at −2 mA/cm², lower than that of the g-C₃N₄, and good stability after 1000 cycles and 100 days for HER. The enhanced electrocatalytic performance was attributed to the MoS₂ and g-C₃N₄ nanostructures on three dimensional carbon cloth, leading to high surface area and more number of the exposed active sites for HER. This heterostructure improved charge transport, proton adsorption and hydrogen evolution on the electrode. This work proposes cost-effective, stable and three dimensional g-C₃N₄ based electrode for hydrogen evolution reaction.     

Electrocatalytic properties of porous Ni-Co-WC composite electrode toward hydrogen evolution reaction in acid medium

Porous Ni-Co-(WC)_x ternary composite electrodes were fabricated by means of electrodeposition on a foam Ni substrate. The surface morphology and microstructure of the electrodes were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The electrocatalytic properties of porous Ni-Co-(WC)_x electrodes for hydrogen evolution reaction (HER) in 0.5 M H₂SO₄ solution at temperatures from 25 to 50 °C were conducted by means of cathodic polarization, electrochemical impedance spectroscopy (EIS), cyclic voltammetry and chronoamperometry (CA). These Ni-Co-WC electrodes are efficient electrocatalysts for HER. Compared with the porous Ni-Co electrode, the porous Ni-Co-(WC)_x electrode exhibited a lower HER overpotential, a lower electrochemical impedance, a lower apparent activation energy and a higher exchange current density. The apparent exchange current density of porous Ni-Co-(WC)_x (x = 10, 20, 30 and 40 g/l) is 2.01, 3.01, 7.8 and 19.91 times of porous Ni-Co electrode, respectively. With the increase of WC concentration and temperature, the apparent exchange current density of HER was enhanced. With the increase of WC concentration and potential, the HER resistance and the activation energy decreased. The Ni-Co-(WC_)x electrode exhibited superior corrosion resistance and stability for HER.     

Ultrathin-layered MoS2 hollow nanospheres decorating Ni3S2 nanowires as high effective self-supporting electrode for hydrogen evolution reaction

High-activity and cost-effective transition metal sulfides (TMSs) have attracted tremendous attention as promising catalysts for hydrogen evolution reaction (HER). However, a significant challenge is the simultaneous construction of abundant electrochemical active sites and the fast electronic transmission path to boost a high-efficient HER. Herein, we demonstrate a facile one-step hydrothermal preparation of MoS₂ hollow nanospheres decorating Ni₃S₂ nanowires supported on Ni foam (NF), without any other additional template, surfactant or annealing. In this three-dimensional (3D) heterostructure, the ultrathin-layered MoS₂ hollow nanospheres contribute to the promotion of the total surface area and the electrochemical active sites. Meanwhile, the Ni₃S₂ nanowires are beneficial to the high electrical conductivity. Consequently, the optimized MoS₂/Ni₃S₂/NF-200-24 electrocatalyst presents an extremely superior HER activity to that of individual MoS₂/NF and Ni₃S₂/NF. The HER overpotentials are 85 mV at 10 mA cm⁻² and 189 mV at 100 mA cm⁻², which are also comparable with the state-of-the-art 20% Pt/C/NF electrode at both low and high current.     

Electrodeposited laser – nanostructured electrodes for increased hydrogen production

In the present work, a novel approach has been employed to effectively enlarge the electrocatalytic area of the electrodes in an alkaline electrolysis setup. This approach consists of a two-step electrode fabrication process: In the first step, ultrashort laser pulses have been used to nanostructure the electrode surface. In the second step, electrodeposition of nickel particles was performed in a modified Watt's bath. The resulting electrodes have been found to exhibit a significantly increased hydrogen evolution reaction (HER) activity. Compared to the laser-nanostructured electrode (LN) and an untreated (i.e., flat) electrode, the electrodeposited-laser-nanostructured (ELN) electrode provides (i) enhanced electrochemical values (ii) a significant increase of double-layer capacitance (C_DL) (values up to 1945 μF cm^?2) compared to that of an LN electrode (288 μF cm^?2) (iii) higher J_peaks at CVs sweeps and (iv) lower Tafel slopes (?121 mV dec^?1 compared to ?157 mv dec^?1). The ELN electrode provides an overpotential value of |η|₁₀₀ = 264 mV, which shows a noteworthy 34% decrease compared to a flat Ni electrode and a 15% decrease to an (LN) electrode. Scanning electron microscopy (SEM) revealed that the electrodeposition of nickel on the LN nickel electrodes results in a dendrite-like morphology of the surface. Thus, the enhancement of the HER has been attributed to the dendrite-like geometry and the concomitant enlargement of the electrocatalytic area of the electrode, which presents an electrochemical active surface area (ECSA) = 97 cm^?2 compared to 2.8 cm^?2 of the flat electrode. The electrodes have also been tested in actual hydrogen production condition, and it was found that the ELN electrode produces 4.5 times more hydrogen gas than a flat Ni electrode and 20% more hydrogen gas than an LN electrode (i.e. without the extra nickel electrodeposition).     

Three-dimensional ZnCo/MoS2–Co3S4/NF heterostructure supported on nickel foam as highly efficient catalyst for hydrogen evolution reaction

Exploring inexpensive and earth-abundant electrocatalysts for hydrogen evolution reactions is crucial in electrochemical sustainable chemistry field. In this work, a high-efficiency and inexpensive non-noble metal catalysts as alternatives to hydrogen evolution reaction (HER) was designed by one-step hydrothermal and two-step electrodeposition method. The as-prepared catalyst is composed of the synergistic MoS₂–Co₃S₄ layer decorated by ZnCo layered double hydroxides (ZnCo-LDH), which forms a multi-layer heterostructure (ZnCo/MoS₂–Co₃S₄/NF). The synthesized ZnCo/MoS₂–Co₃S₄/NF exhibits a small overpotential of 31 mV and a low Tafel plot of 53.13 mV dec^?1 at a current density of 10 mA cm^?2, which is close to the HER performance of the overpotential (26 mV) of Pt/C/NF. The synthesized ZnCo/MoS₂–Co₃S₄/NF also has good stability in alkaline solution. The excellent electrochemical performance of ZnCo/MoS₂–Co₃S₄/NF electrode originates from its abundant active sites and good electronic conductivity brought by the multilayer heterostructure. This work provides a simple and feasible way to design alkaline HER electrocatalysts by growing heterostructures on macroscopic substrates.     

Transition metal doped MoS2 nanosheets for electrocatalytic hydrogen evolution reaction

In the present work, the effect of transition metals (Ni, Fe, Co) doping on 2-dimensional (2D) molybdenum disulfide (MoS₂) nanosheets for electrocatalytic hydrogen evolution reaction (HER) was explored. A simple and cost-effective hydrothermal method was adopted to synthesis transition metals doped MoS₂ nanosheets. The morphological and spectroscopic studies evidence the formation of high-quality MoS₂ nanosheets with the randomly doped metal ions. Notably, the Ni–MoS₂ displayed superior HER performance with an overpotential of ?0.302 V vs. reversible hydrogen electrode (RHE) (to attain the current density of 10 mA cm^?2) as compared to the other transition metals doped MoS₂ (Co–MoS₂, Fe–MoS₂). From the Nyquist plot, superior charge transport from the electrocatalyst to the electrolyte in Ni–MoS₂ was realized and confirmed that Ni doping provides the necessary catalytic active sites for rapid hydrogen production. The stable performance was confirmed with the cyclic test and chronoamperometry measurement and envisaged that hydrothermally synthesized Ni–MoS₂ is a highly desirable cost-effective approach for electrocatalytic hydrogen generation.     

Novel peapod-like Ni2P@N-doped carbon nanorods array on carbon fiber for efficient electrocatalytic urea oxidation and hydrogen evolution reaction

Designing and optimizing structure is an effective method to enhance electrocatalytic performance of transition metal-based catalysts. In this work, an innovative nanostructured electrode, consisted of peapod-like Ni₂P@N-doped carbon nanorods array coating on carbon fiber (CF@p-Ni₂P@NC), is devised and synthesized. The N-doped carbon layer is crucial for maintaining the peapod-like nanostructure, which allows for multi-channel electrolyte transport and gas product release. And the carbon layer coating Ni₂P nanoparticles also enhance electrical conductivity and stability, thus ensuring fast electron transport from/to active sites and the long-term stability of catalyst during urea oxidation reaction (UOR)/hydrogen evolution reaction (HER). Benefit from the reasonable structure, CF@p-Ni₂P@NC present perfect performance with getting 100 mA cm^?2 at potential/overpotential of 1.417/0.194 V for UOR/HER in 1.0 M KOH containing 0.5 M urea. In addition, the overall urea-electrolysis system using CF@p-Ni₂P@NC bifunctional electrode only requires 1.590 V to obtain 100 mA cm^?2.     

Defect-rich MoSx/carbon nanofiber arrays on carbon cloth for highly efficient electrocatalytic hydrogen evolution

Engineering MoS₂ catalysts with more active sites and higher conductivity is an effective way to improve its electrochemical activity. Herein, defect-rich amorphous MoS_x/carbon nanofiber (CF) arrays on carbon cloth (CC) support (denoted as MoS_x/CF/CC) was designed and fabricated, which served as an efficient free-standing electrocatalyst for hydrogen evolution reaction (HER) in acid media. This architecture was beneficial to expose more active catalytic sites and improve the electron/ion transport. In addition, abundant defects altered preferred growth direction of MoS_x, resulting in the formation of irregular MoS_x particles at the surface of CF arrays. The as-synthesized MoS_x/CF/CC-2 exhibited excellent stability and superior HER activity, with a small onset overpotential (107 mV) and low Tafel slope (51 mV dec^?1). Such excellent electrochemical performance was attributed to the enriched active sites and shortened charge diffusion distance. This work would pave a new way for rational design and fabrication of defect-rich MoS_x-based composite electrode for renewable energy applications.     

Stable and highly efficient MoS2/Si NWs hybrid heterostructure for photoelectrocatalytic hydrogen evolution reaction

We report, the fabrication of molybdenum disulphide (MoS₂) wrapped silicon nanowires (Si NWs) for visible light driven water splitting applications. The morphological and elemental studies ensure the vertical alignment of Si NWs wrapped with 2D layered MoS₂. The photoelectrocatalytic (PEC) results evidence the significant enhancement in performance of MoS₂/Si NWs based hybrid photocathode with ~300 mV (under reversible hydrogen electrode (RHE)) anodic shift in onset potential as that of pristine Si NWs (+0.194 V vs. RHE), and the current density of −26.5 mA/cm² was achieved at the applied bias of 0 V vs. RHE. Further, the electrochemical impedance studies ensure the interface resistance-free charge transfer between Si NWs and electrolyte via 2D MoS₂ layer which provokes rapid hydrogen production. The wrapping of Si NWs with MoS₂ protects the superlative photocathode from harsh acid electrolyte environment. The overgrown MoS₂ triangular particles with active sulphur edge sites are found to eventually augment the solar hydrogen evolution rate. Further, the PEC performance of our MoS₂/Si NWs is also comparable with stable Pt/Si NWs photoelectrode. It is note-worthy that, MoS₂/Si NWs hybrid heterostructure would be a potential candidate in future large scale, low cost and day-to-day solar water splitting applications.     

Synthesis and electrocatalytic activity of Ni0.85Se/MoS2 for hydrogen evolution reaction

Recently, the replacement of expensive platinum-based catalytic materials with non-precious metal materials to electrolyze water for hydrogen separation has attracted much attention. In this work, Ni_0.85Se, MoS₂ and their composite Ni_0.85Se/MoS₂ with different mole ratios are prepared successfully, as electrocatalysts to catalyze the hydrogen evolution reaction (HER) in water splitting. The result shows that MoS₂/Ni_0.85Se with a molar ratio of Mo/Ni = 30 (denoted as M30) has the best catalytic performance towards HER, with the lowest overpotential of 118 mV at 10 mA cm⁻², smallest Tafel slope of 49 mV·dec⁻¹ among all the synthesized materials. Long-term electrochemical testing shows that M30 has good stability for HER over at least 30 h. These results maybe due to the large electrochemical active surface area and high conductivity. This work shows that transition metal selenides and sulfides can form effective electrocatalyst for HER.     

Flower-like HEA/MoS2/MoP heterostructure based on interface engineering for efficient overall water splitting

The development of cheap, efficient, and active non-noble metal electrocatalysts for total hydrolysis of water (oxygen evolution reaction (OER) and hydrogen evolution reaction (HER)) is of great significance to promote the application of water splitting. Herein, a heterogeneous structured electrode based on FeAlCrMoV high-entropy alloy (HEA) was synthesized as a cost-effective electrocatalyst for hydrogen and oxygen evolution reactions in alkaline media. In combination of the interfacial synergistic effect and the high-entropy coordination environment, flower-like HEA/MoS₂/MoP exhibited the excellent HER and OER electrocatalytic performance. It showed a low overpotential of 230 mV at the current density of 10 mA cm⁻² for OER and 148 mV for HER in alkaline electrolyte, respectively. Furthermore, HEA/MoS₂/MoP as both anode and cathode also exhibited an overpotential of 1.60 V for overall water splitting. This work provides a new strategy for heterogeneous structure construction and overall water splitting based on high-entropy alloys.     

Nano-pom-pom multiphasic MoS2 grown on carbonized wood as electrode for efficient hydrogen evolution in acidic and alkaline media

Molybdenum disulfide (MoS₂), attracts great attention in hydrogen evolution reaction (HER) field, however, low catalytic activity sites and poor conductivity still limit its further application. In this study, an efficient hydrogen evolution electrode with nano-pom-pom multiphasic MoS₂ uniformly grew on porous carbonized wood (NP MoS₂/CW) was developed. Interestingly, the nano-pom-pom are stacked from sheets of MoS₂. Fully exposed active edges of nano-pom-pom MoS₂ and high excellent electrical conductivity of carbonized wood enhance collectively electrocatalytic performance for HER. Specifically, the NP MoS₂/CW electrode requires an overpotential of 109.5 mV and 305 mV to achieve the current density of 10 mA cm⁻² and 400 mA cm⁻², respectively (0.5 M H₂SO₄). NP MoS₂/CW has excellent electrocatalytic performance and stability in acidic and alkaline media due to the perfect combination of NP MoS₂ unique nanostructure and the unique properties of CW. Therefore, the present work provides a promising strategy into the rational development and utilization of MoS₂ for the development of hydrogen evolution.