Active Edge Research Articles

The Synergetic Effect of MoSO2/Graphite Nanosheets as Highly Efficient for Electrochemical Water Splitting in Acidic Media

Metal oxide nanoarchitectures have a wide range of qualities that can be used to produce novel technologies in the field of renewable energy, such as energy conversion solar fuels and storage via the photovoltaic effect, and electrochemical water splitting. The approach for the synthesis of earth abundant metal oxide nanostructures is facile and cost effective and involves scalable methodologies for the development of functional devices. The composite material exhibits enhanced active edge sites for the potential HER. The electrochemical experiments revealed satisfactory results of electrocatalytic gas production HER. The composite sample produces a current density at 10 mAcm−2 an over potential of 345 mV and Tafel value of 60 mVdec−1 it exhibits at which predominantly ensures the swift charge transfer kinetics during HER. The sample 3 remains durable and stable for 30 hours. EIS shown value of 21.88 Ohms as charge transfer resistance which further strengthened HER and Tafel results. The sample 3 exhibits a 4.69 µFcm−2 capacitance double layer and surface area of 177.25 cm2 it further supports the unique productivity for HER activity. The small Tafel slope which relatively close to Pt shows a clear and high potential of as prepared MoS2/Graphite nanosheets composite material for the replacement of noble metals in the field of renewable energy. The tiny Tafel slope value suggests that the efficient hydrogen evolution reaction has a lot of promise. This developed method provides the alternative method for the development of other materials for the energy harvesting applications.

Manganese oxide nanoflakes grown around cobalt oxide nanobundles with improved charge-storage performance for supercapacitors

Cobalt oxide nanobundle arrays (denoted as CoO) consisting of nanorods were homogeneously grown around the stainless steel wire mesh (SSWM) through a simple hydrothermal synthesis and subsequent heat treatment. The highly dispersed CoO can act as a supporting platform for the deposition of manganese oxide (MnO2) nanoflakes to engineer a CoO@MnO2 core-shell array structure. Without the CoO supports, the MnO2 was found to be prone to form aggregated nanoflakes on the SSWM substrate. CoO arrays with a one-dimensional nanorod skeleton can mitigate the aggregation of two-dimensional MnO2 nanoflakes. The CoO@MnO2 core-shell arrays integrate the advantages of abundant active edge sites, conductive networks for charge transfer, and pore channels for easy transport of electrolyte. The CoO@MnO2 electrode realizes a larger charge-storage capacity than the pristine MnO2 electrode in an aqueous sodium sulfate solution (1 M). The specific capacitances of CoO@MnO2 under 0.15 mA cm-2 and 7.50 mA cm-2 reach 79 mF cm-2 and 53 mF cm-2, respectively, much more than that of MnO2 (31 mF cm-2 and 20 mF cm-2). The CoO@MnO2 core-shell electrode shows a definite improvement in supercapacitive behavior compared to the pristine MnO2 electrode, resulting from reduced charge- and mass-transfer resistance during charge-storage process.

Study on the Water Invasion and Its Effect on the Production from Multilayer Unconsolidated Sandstone Gas Reservoirs

Water invasion is a common occurrence in multilayer unconsolidated gas reservoirs, which results in excessive water production and reduces the economic life of gas wells. However, due to multiple layers, active edge water, and strong heterogeneity, the mechanism of water invasion and its effect in the unconsolidated sandstone gas reservoir require understanding in order to improve efficiency and minimize economic cost. In this study, an experimental study on edge water invasion of the multilayer commingled production in unconsolidated sandstone gas reservoirs was conducted to understand the water invasion process along with different permeability layers. The results show that the edge water invasion in the commingling production is mainly affected by two major factors including reservoir permeability and gas production rate, which jointly control the encroaching water advance path and speed. The nonuniform invade of edge water may occur easily and water prefers to invade toward the gas well along with high permeability layers when the commingling production is in the condition of large permeability gradient and high production rate. The bypass flow will occur when there are high permeability channels between the layers, which causes water blocking to low-permeability layers and periphery reservoirs far away from gas wells. The findings of this study can help for a better understanding of water invasion and the effects of reservoir properties so as to optimize extraction conditions and predict gas productivity in unconsolidated sandstone gas reservoirs.

Facile Production of Phosphorene Nanoribbons towards Application in Lithium Metal Battery.

Like phosphorene, phosphorene nanoribbon (PNR) promises exotic properties but unzipping phosphorene into edge-defined PNR is non-trivial because of uncontrolled cutting of phosphorene along random directions. Here a facile electrochemical strategy to fabricate zigzag-edged PNRs in high yield (>80%) is reported. The presence of chemically active zigzag edges in PNR allows it to spontaneously react with Li to form a Li+ ion conducting Li3 P phase, which can be used as a protective layer on Li metal anode in lithium metal batteries (LMBs). PNR protective layer prevents the parasitic reaction between lithium metal and electrolyte and promotes Li+ ion diffusion kinetics, enabling homogenous Li+ ion flux and long-time cycling stability up to 1100h at a current density of 1mAcm-2 . LiFePO4 |PNR-Li full-cell batteries with an areal capacity of 2mAhcm-2 , a lean electrolyte (20µlmAh-1 ) and a negative/positive (N/P) electrodes ratio of 3.5 can be stably cycled over 100 cycles.

One-step ionothermal accompanied thermolysis strategy for N-doped carbon quantum dots hybridized NiFe LDH ultrathin nanosheets for electrocatalytic water oxidation

Herein, we have developed a one-step ionothermal accompanied thermolysis strategy based on metal chloride deep eutectic solvent (DES) precursors to synthesize NiFe layered double-hydroxide ultrathin nanosheets hybridized with N-doped carbon quantum dots (NCD@NiFe-LDH). The NCD@NiFe-LDH hybrid shows hierarchical three-dimensional flower-like morphology assembled with ~1.4 nm ultrathin nanosheets possessing higher surface area values and well conductivity. The as-synthesized NCD@NiFe-LDH hybrid exhibits excellent performance for oxygen evolution reaction (OER) and just require 363 mV to achieve a higher current density of 500 mA cm−2 compared to the state-of-the-art IrO2 in 0.1M KOH. Besides, NCD@NiFe-LDH hybrid shows long-term stability and satisfactory durability even at 1000 mA cm−2. Such an excellent OER performance at high current density can be ascribed to the unique porous ultrathin structure with abundant active edges and sites and the synergistic effect of the NCD and NiFe-LDH. The work offers a new way for the design and synthesis of other carbon-hybridized LDH ultrathin nanosheets with unique electrochemical properties.

Hierarchical NiCo / NiO / NiCo 2 O 4 composite formation by solvothermal reaction as a potential electrode material for hydrogen evolutions and asymmetric supercapacitors

Electrochemical energy storage and conversion mechanisms are highly viable routes in the current scenario, and hence supercapacitor and electrolysis of water splitting have gained significant attention in recent times. Thus, transition metal nickel cobalt oxides are widely inspected as promising electrode materials for electrocatalysis and supercapacitors. However, the pure NiCo2O4 was highly hindered by its widespread uses due to low electronic conductivity and deficient active edges. This study is aimed to fabricate the NiCo/NiO/NiCo2O4 composite using a solvothermal process with different ratios of solvents. The inherent NiCo/NiO/NiCo2O4 composite holds plentiful active edges and improved electrical conductivity than the pure. Interestingly, the electrocatalytic results revealed that the NiCo/NiO/NiCo2O4 (NC) composite prepared by a solvent ratio of (double distilled water (DDW) to N, N-Dimethylformamide (DMF)) 2:1 (NC1) displayed the small overpotentials of 144 and 142 mV to realize 10 mA cm−2 with the robust durability during a 24 hours hydrogen evolution reaction (HER) test in the acid and alkaline electrolyte, respectively. Moreover, the designed NC1 composite as a supercapacitor electrode exhibited considerable capacitance of 638 F g−1 at a current density of 1 A g−1. In comparison, the analog DDW to DMF ratio 1:1 (NC2) and 1:2 (NC3) structures showed 514 F g−1 and 415 F g−1, respectively. Further, a dual-electrode device was fabricated using the NC1 composite and activated carbon, exhibited an energy density of 28.14 W h kg−1 at 414.45 W kg−1 power density with excellent device stability (89.4%) for 10 000 charge/discharge cycles.

Activating Both Basal Plane and Edge Sites of Layered Cobalt Oxides for Boosted Water Oxidation

AbstractLayered AxCoO2 materials built by stacking layers of CoO2 slabs and inserting alkali ions in between them have shown a promising activity of oxygen evolution reaction (OER) due to their active edge sites. However, the large basal plane areas of the CoO2 slabs show too strong adsorption energy to the reaction intermediates, which is unfavorable for the release of O2. Here, a simple cation‐exchange strategy based on Fe3+ and alkali ions is proposed to simultaneously activate both the basal plane and edge sites of AxCoO2 for the OER. X‐ray absorption spectroscopy has revealed that the Fe3+ ions deposit both on the surface and edge sites of the CoO2 slabs and enter the interlayer. The cation‐exchanged AxCoO2 electrodes show a boosted activity compared to their pristine and conventional Fe‐doped AxCoO2 counterparts. This phenomenon is mainly ascribed to the abundant edge‐sharing Co–Fe motifs at the edge sites and the charge redistribution in the basal plane sites induced by the insertion of Fe3+ ions. This work provides a novel method to fully exploit layer‐structured materials for efficient energy conversion.

Edge sites-driven accelerated kinetics in ultrafine Fe2O3 nanocrystals anchored graphene for enhanced alkali metal ion storage

Iron oxides have been recognized as a potential electrode material for lithium-ion and sodium-ion batteries owing to their relatively ultrahigh theoretical capacity, low-cost and earth-rich resources. Nevertheless, the rapid capacity degradation and sluggish kinetics seriously limit their practical applications. Herein, the kinetics enhanced ultrafine Fe2O3 nanocrystals (~5 nm) well anchored on graphene are prepared for high-rate lithium and sodium storage. The unique structure could provide abundant electrochemical active edge sites, short ion/electron diffusion pathways, and excellent electrical conductivity, allowing for enhanced electron/ion transport/diffusion kinetics. The fabricated Fe2O3/reduced graphene oxide nanocomposite shows impressive discharge capacity (1175 mAh g−1 at 0.2 A g−1), significant rate performance (822 mAhg−1 at 5 A g−1) and stable long-term cycle durability (993 mAh g−1 after 500 cycles at 1 Ag−1) as a lithium-ion battery anode. As for sodium-ion storage, it also shows high discharge capacity of 701 mAh g−1 at 0.1 A g−1 and remarkable rate performance (253 mAh g−1 at 2 A g−1). These above intriguing electrochemical performances outperform most of the so-far recorded Fe2O3 based electrodes. Such material design strategy may pave a new way for the development of outstanding performance anode materials based on earth-rich materials for energy storage application.

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.

Physical Simulation Experimental Technology and Mechanism of Water Invasion in Fractured-Porous Gas Reservoir: A Review

In the development process for a fractured-porous gas reservoir with developed fracture and active water, edge water or bottom water easily bursts rapidly along the fracture to the production well, and the reservoir matrix will absorb water, reducing the gas percolation channel and increasing the gas phase percolation resistance of the reservoir matrix, therefor reducing the stable production capacity and recovery efficiency of the gas reservoir. For this reason, this paper investigates physical simulation experimental technology and mechanisms as reported by both domestic and foreign scholars regarding water invasion in fractured-porous gas reservoirs. In this paper, it is considered that the future trend and focus of water invasion experiments will be to establish a more realistic three-dimensional physical model on the basis of fine geological description, combined with gas reservoir well pattern deployment and production characteristics, and to fully consider the difference between horizontal and vertical water invasion along the reservoir side; at the same time, dynamic parameters such as model pressure field and water saturation field can be obtained in real time. Based on this understanding of the water invasion mechanism of fractured-porous gas reservoirs, we propose the next research direction and the development countermeasures such as water controls, drainage, and dissolved water seals and water locks to combat water invasion in reservoirs, along with the injection of gas to replenish formation energy, etc., so as to slow down and control the influence of water invasion.

Low-temperature synthesis of vertically aligned graphene through microwave-assisted chemical vapour deposition

The intrinsic properties of vertically aligned graphene (VG), such as a high ratio of exposed active edge sites compared to inert basal sites, non-stacking morphology and large surface-to-volume ratio make it applicable to numerous advanced technologies such as sensors, flexible electronics and fuel cells. Plasma-enhanced chemical vapour deposition has emerged as a promising technique to synthesise graphene at lower temperatures than a conventional chemical vapour deposition (CVD) process, providing a better control over the deposition parameters to tailor graphene properties.This study presents a cost effective, scalable, single step synthesis of a high quality VG at low temperatures. The samples were synthesised in a microwave (MW) assisted CVD reactor, which allowed for the decomposition of CH4 and H2 gas mixtures in Ar as a carrier gas, and VG growth directly onto Si wafer substrates without any additional heat applied to the substrate. Deposition conditions, such as MW power, gas ratio, and substrate-to-plasma separation were optimized to tailor the morphology, growth rate and electrochemical performance of the VG. The physiochemical analysis revealed that the fabricated VG consisted of high quality vertically aligned sp2 graphene, whilst a cyclic voltammetry analysis confirmed that the structures are electrochemically active and demonstrate a typical characteristics of quasi-reversible processes.

Bi4O5Br2 anchored on Ti3C2 MXene with ohmic heterojunction in photocatalytic NH3 production: Insights from combined experimental and theoretical calculations

Nitrogen-to-ammonia conversion under mild conditions offers a tremendous prospect as a sustainable technology for synthesizing ammonia (NH3) in the future. In this study, we elaborately designed Bi4O5Br2/Ti3C2 heterojunction combined with electrostatic adsorption with in-situ growth to form a photocatalyst with a 2D/2D structure. This unique structure substantially improved the exposure of active edge sites for photocatalytic dinitrogen reduction reaction. Notably, Ti3C2 MXene acted as an efficient cocatalyst for the conversion of N2 to NH3 of Bi4O5Br2/Ti3C2 with a yield of 277.74 μmol g−1h−1 without the use of a sacrificial agent; this yield was five times higher than that of Bi4O5Br2. Density functional theory calculations demonstrated that the ohmic contact was at the Bi4O5Br2/Ti3C2 interface. The ohmic heterojunction could expedite the separation of spatial carriers and extraction of photoexcited charge carriers, which had outstanding reducibility to cleavage the N≡N bond. This work provides a novel strategy for designing highly efficient Bi4O5Br2-based photocatalysts through the integration of multifunctional materials. This work also offers guidance for implementing high-performance nitrogen-to-ammonia conversion by introducing interfacial modifiers.

Graphene Nanoribbon Grids of Sub-10 nm Widths with High Electrical Connectivity.

Quasi-one-dimensional (1D) graphene nanoribbons (GNRs) have finite band gaps and active edge states and therefore can be useful for advanced chemical and electronic devices. Here, we present the formation of GNR grids via seed-assisted chemical vapor deposition on Ge(100) substrates. Nucleation seeds, provided by unzipped C60, initiated growth of the GNRs. The GNRs grew toward two orthogonal directions in an anisotropic manner, templated by the single crystalline substrate, thereby forming grids that had lateral stitching over centimeter scales. The spatially uniform grid can be transferred and patterned for batch fabrication of devices. The GNR grids showed percolative conduction with a high electrical sheet conductance of ∼2 μS·sq and field-effect mobility of ∼5 cm2/(V·s) in the macroscopic channels, which confirm excellent lateral stitching between domains. From transconductance measurements, the intrinsic band gap of GNRs with sub-10 nm widths was estimated as ∼80 meV, similar to theoretical expectation. Our method presents a scalable way to fabricate atomically thin elements with 1D characteristics for integration with various nanodevices.

Active flap control with the trailing edge flap hinge moment as a sensor: using it to estimate local blade inflow conditions and to reduce extreme blade loads and deflections

Abstract. Active trailing edge flaps are a promising technology that can potentially enable further increases in wind turbine sizes without the disproportionate increase in loads, thus reducing the cost of wind energy even further. Extreme loads and critical deflections of the blade are design-driving issues that can effectively be reduced by flaps. In this paper, we consider the flap hinge moment as a local input sensor for a simple flap controller that reduces extreme loads and critical deflections of the DTU 10 MW Reference Wind Turbine blade. We present a model to calculate the unsteady flap hinge moment that can be used in aeroelastic simulations in the time domain. This model is used to develop an observer that estimates the local angle of attack and relative wind velocity of a blade section based on local sensor information including the flap hinge moment of the blade section. For steady wind conditions that include yawed inflow and wind shear, the observer is able to estimate the local inflow conditions with errors in the mean angle of attack below 0.2∘ and mean relative wind speed errors below 0.4 %. For fully turbulent wind conditions, the observer is able to estimate the low-frequency content of the local angle of attack and relative velocity even when it is lacking information on the incoming turbulent wind. We include this observer as part of a simple flap controller to reduce extreme loads and critical deflections of the blade. The flap controller's performance is tested in load simulations of the reference turbine with active flaps according to the IEC 61400-1 power production with extreme turbulence group. We used the lifting line free vortex wake method to calculate the aerodynamic loads. Results show a reduction of the maximum out-of-plane and resulting blade root bending moments of 8 % and 7.6 %, respectively, when compared to a baseline case without flaps. The critical blade tip deflection is reduced by 7.1 %. Furthermore, a sector load analysis considering extreme loading in all load directions shows a reduction of the extreme resulting bending moment in an angular region covering 30∘ around the positive out-of-plane blade root bending moment. Further analysis reveals that a fast reaction time of the flap system proves to be critical for its performance. This is achieved with the use of local sensors as input for the flap controller. A larger reduction potential of the system is identified but not reached mainly because of a combination of challenging controller objectives and the simple controller architecture.

Razor flip-flop based Detector/Corrector System for Correcting Timing violations in Digital Circuits

In a flip flop, the difference in time between transitions of data input and the active edge of the clock is called its setup time. If the data input changes during this time window, the storage will not be correct. This is called setup time violation. Hold time is the minimum time during which data must be stable after the active edge of the clock. Hold time violation will cause incorrect data storage. The objective of the paper is to design an efficient Detector/Corrector system that monitors and corrects any setup/hold time violations. A Razor flipflop based Detector circuit is proposed in this paper. The Detector block compares data and clock to produce an error signal which in turn makes the Corrector block to correct the clock that assures the desired setup/hold time. The system avoids the setup/hold time violations by simply inverting the clock signal timing. The system is tested using the following digital circuits: ISCAS89 S27 benchmark circuit and a 2×1 multiplexer. Simulation is done using Cadence Virtuoso with 180nm technology. The results are analyzed with existing and proposed detector/corrector systems. The results show that the proposed detector/corrector system is capable of correcting both the setup/hold time violations and also has lesser power consumption when compared with the existing system.

Photo-assisted electrocatalysis of black phosphorus quantum dots/molybdenum disulfide heterostructure for oxygen evolution reaction

Molybdenum Disulfide (MoS2), as a typical two-dimensional (2D) material, has abundant reserves and unique electronic structures. However, the limited number of active sites severely hinders its application in electrocatalytic oxygen evolution reaction (OER). Black phosphorus quantum dots (BP QDs), with large exposed surface areas and a mass of active edge sites, are suitable for loading on MoS2 nanosheets to form type-II heterojunctions, resulting in additional active sites and higher mobility, thereby improving the OER performance of MoS2. In addition, photo-assistance was applied to reduce high energy barriers and the energy loss, thus improving the overall efficiency of energy conversion. Here, BP QDs and MoS2 nanosheets were prepared by liquid phase exfoliation and mixed-dimensional BP QDs/MoS2 heterojunctions were constructed. The experimental results show that the BP QDs/MoS2 heterojunctions have been successfully synthesized and the OER performance of the heterojunctions outperform pure MoS2 and BP QDs, with lower onset potentials and Tafel slope. Meanwhile, both photo-assistance and changing KOH concentration can adjust the OER performance of BP QDs/MoS2 heterojunction. Furthermore, the as-prepared heterojunctions demonstrated strong stability in KOH aqueous solution. This work identifies that constructing BP QDs/MoS2 heterojunctions and photo-assistance are effective strategies to facilitate the electrocatalytic OER performance.

Introducing a self-improving catalyst for hydrogen evolution and efficient catalyst for oxygen evolution reaction

Herein, MoS2/Ni3S2 nano-cubic rods (NCR) is fabricated on Ni foam via a two-step process including modified solution method and thiourea phosphate-assisted strategy. The resultant material serves as a self-improving high intrinsic catalyst for hydrogen evolution reaction (HER), and exhibits desirable activity for oxygen evolution reaction (OER) in alkaline media. Results demonstrated that two different phases of MoS2 and Ni3S2 along with the presence of abundant active sulfur edge sites and particular structure lead to the enhanced electrocatalytic activity. The most interesting point is the self-improving behavior of MoS2/Ni3S2 NCR by proceeding the HER. It means by time and catalyzing the hydrogen evolution reaction the performance of catalyst improved, so that after long time HER the catalyst reaches 10 and 20 mA cm−2 at overpotential of 40 and 85 mV, respectively. It is found that the improvement in catalytic performance can be assigned to the charge transfer enhancement and increasing in active surface area as HER proceeds. Further, characterization investigations show that thiourea phosphate-assisted strategy plays a key role to attain the nano-cubic rods structure. Indeed, the generated MoS2 nanolayers act as a substrate for anchoring and growing of Ni3S2 nano-cubic particles and consequently lead to preparation of cubic nano rods structures. Besides, low onset potential with the overpotential of 200 mV was obtained for OER using MoS2/Ni3S2 NCR.

Insights into the Mechanism of Elemental Mercury Adsorption on Graphitic Carbon Nitride: A Density Functional Theory Study

Recently, graphitic carbon nitride (g-C3N4) has been proven to be a novel and effective carbon-based adsorbent for elemental mercury (Hg0) removal in flue gas due to its peculiar π-conjugated electronic structure and chemical and thermal stability. However, the active sites and detailed reaction pathways occurring on the g-C3N4 surface are still unknown. Here, g-C3N4 nanoplates with abundant active edge sites (surface defects) are successfully prepared via a thermal polymerization method, which display good Hg0 adsorption ability. The adsorption behavior of Hg0 over g-C3N4 is further studied using quantum chemistry calculations based on density functional theory (DFT), aiming at gaining a better understanding of the Hg0 adsorption structures and bonding mechanisms on the g-C3N4 surface at the atomic level. The calculation results show that the adsorption of Hg0 on intact g-C3N4 surfaces is poor due to the stable chemical structure of intact g-C3N4 and lack of active electron orbitals. In contrast, g-C3N4 with surface defects, i.e., exposed C or N sites, possesses enhanced Hg0 adsorption ability probably owing to the unsaturated coordination bond environment and the formation of chemical bonds with mercury atoms at the defective sites. The location of defects also has a big influence on the mercury capture ability of g-C3N4. The exposed surface nitrogen is more favorable for mercury capture than the exposed surface carbon.

Supercapacitor with Carbon/MoS2 Composites

Transition metal dichalcogenides (TMDs) with a two-dimensional character are promising electrode materials for an electrochemical capacitor (EC) owing to their unique crystallographic structure, available specific surface area, and large variety of compounds. TMDs combine the capacitive and faradaic contribution in the electrochemical response. However, due to the fact that the TMDs have a strong catalytic effect of promoting hydrogen and oxygen evolution reaction (HER and OER), their usage in aqueous ECs is questioned. Our study shows a hydrothermal l-cysteine–assisted synthesis of two composites based on different carbon materials—multiwalled carbon nanotubes (NTs) and carbon black (Black Pearl-BP2000)—on which MoS2 nanolayers were deposited. The samples were subjected to physicochemical characterization such as X-ray diffraction and Raman spectroscopy which proved that the expected materials were obtained. Scanning electron microscopy coupled with electron dispersive spectroscopy (SEM/EDS) as well as transmission electron microscopy images confirmed vertical position of few-layered MoS2 structures deposited on the carbon supports. The synthetized samples were employed as electrode materials in symmetric ECs, and their electrochemical performance was evaluated and compared to their pure carbon supports. Among the composites, NTs/MoS2 demonstrated the best electrochemical metrics considering the conductivity and capacitance (150 Fg−1), whereas BP2000/MoS2 reached 110 Fg−1 at a current load of 0.2 Ag−1. The composites were also employed in a two-electrode cell equipped with an additional reference electrode to monitor the potential range of both electrodes during voltage extension. It has been shown that the active edge sites of MoS2 catalyze the hydrogen evolution, and this limits the EC operational voltage below 1 V. Additional tests with linear sweep voltammetry allowed to determine the operational working voltage for the cells with all materials. It has been proven that the MoS2/carbon composites possess limited operating voltage, that is, comparable to a pure MoS2 material.

Metal‐Assisted Efficient Nanotubular Electrocatalyst of MoS2 for Hydrogen Production

AbstractInspired by the catalytic activity along the edge sites of layered‐structured MoS2 for the hydrogen evolution reaction (HER), maximizing the specific active edge sites per unit geometric area via material architectural design is the most common strategy for enhancing HER performance. Here, we report a convenient growth approach using atomic layer deposition (ALD) to obtain novel nanostructures of MoS2 nanotube arrays with a high number of exposed active edge sites. MoS2 NTs were spontaneously immobilized in an ordered arrangement of anodic aluminum oxide (AAO) template with a well‐defined size and shape. Ordered MoS2 NTs array were fabricated with highly conductive, large electrochemical active area as an efficient HER catalyst. Strikingly, by engineering the contact metal serving as the current collector, the contact properties were revealed to be important factors for the electrocatalytic performance of the metal‐assisted MoS2 electrodes. Our material system shows a significantly low overpotential of 260 mV at 10 mA/cm2 and a Tafel slope of 55 mV/dec, while it remains stable during long‐term operation in strong acidic media.