Conversion of Intercalated MoO3 to Multi-Heteroatoms-Doped MoS2 with High Hydrogen Evolution Activity

Interlayer Engineering of Layered Materials for Efficient Ion Separation and Storage

Layered materials are characterized by strong in-plane covalent chemical bonds within each atomic layer and weak out-of-plane van der Waals (vdW) interactions between adjacent layers. The non-bonding nature between neighboring layers naturally results in a vdW gap, which enables the insertion of guest species into the interlayer gap. Rational design and regulation of interlayer nanochannels are crucial for converting these layered materials and their 2D derivatives into ion separation membranes or battery electrodes. Herein, based on the latest progress in layered materials and their derivative nanosheets, various interlayer engineering methods are briefly introduced, along with the effects of intercalated species on the crystal structure and interlayer coupling of the host layered materials. Their applications in the ion separation and energy storage fields are then summarized, with a focus on interlayer engineering to improve selective ion transport and ion storage performance. Finally, future research opportunities and challenges in this emerging field are comprehensively discussed.

Sublayer-Sulfur-Vacancy-Induced Charge Redistribution of FeCuS Nanoflower Awakening Alkaline Hydrogen Evolution

Advancing the progress of sustainable and green energy technologies requires the improvement of valid electrocatalysts for the hydrogen evolution reaction (HER). Reconfiguring charge distribution through heteroatom doping-induced vacancy serves as an effective approach to implement high performance for HER catalysts. Here, we successfully fabricated Fe-doped CuS (FeCuS) with the sublayer sulfur vacancy to judge its HER performance and dissect the activity origins. Density functional theory calculation further elucidates that the primary factor contributing to the heightened HER activity is that the sublayer sulfur vacancies awaken the charge redistribution. In addition to effectively decreasing the energy barrier associated with the Volmer step, it modulates the adsorption/desorption capacity of H*. As a result, its intrinsic activity for the HER has significantly increased. Concretely, the obtained FeCuS displays an excellent catalytic performance, whose Tafel slope is only 59 mV dec-1 and the overpotential (at 10 mA cm-2) is as low as 71 mV in an alkaline environment, surpassing the majority of previously documented catalysts in scientific literature. This work shows that the construction of sublayer sulfur vacancies by Fe doping can achieve the charge redistribution and precise tuning of electronic structure; thereby, the inert CuS can be transformed into highly efficient electrocatalysts.

Loading of Single Atoms of Iron, Cobalt, or Nickel to Enhance the Electrocatalytic Hydrogen Evolution Reaction of Two-Dimensional Titanium Carbide

The rational design of advanced electrocatalysts at the molecular or atomic level is important for improving the performance of hydrogen evolution reactions (HERs) and replacing precious metal catalysts. In this study, we describe the fabrication of electrocatalysts based on Fe, Co, or Ni single atoms supported on titanium carbide (TiC) using the molten salt method, i.e., TiC-FeSA, TiC-CoSA, or TiC-NiSA, to enhance HER performance. The introduction of uniformly distributed transition-metal single atoms successfully reduces the overpotential of HERs. Overpotentials of TiC-FeSA at 10 mA cm-2 are 123.4 mV with 61.1 mV dec-1 Tafel slope under acidic conditions and 184.2 mV with 85.1 mV dec-1 Tafel slope under alkaline conditions, which are superior to TiC-NiSA and TiC-CoSA. TiC samples loaded with transition-metal single atoms exhibit high catalytic activity and long stability under acidic and basic conditions. Density functional theory calculations indicate that the introduction of transition-metal single atoms effectively reduces the HER barrier of TiC-based electrocatalysts.

Accelerated Confined Mass Transfer of MoS2 1D Nanotube in Photo-Assisted Metal-Air Batteries

Applying solar energy into energy storage battery systems is challenging in achieving green and sustainable development, however, the efficient progress of photo-assisted metal-air batteries is restricted by the rapid recombination of photogenerated electrons and holes upon the photocathode. Herein, a 1D-ordered MoS2 nanotube (MoS2-ONT) with confined mass transfer can be used to extend the lifetime of photogenerated carriers, which is capable of overcoming the challenge of rapid recombination of electron and holes. The tubular confined space cannot only promote the orderly separation and migration of charge carriers but also realize the accumulation of charge and the rapid activation of oxygen molecules. The concave surface of MoS2-ONT can improve the carrier separation ability and prolong the carrier lifetime. Meanwhile, the ordered tubular confined space can effectively realize the rapid transfer of charge, ion, and oxygen. Under light irradiation, a fast oxygen reduction reaction kinetics of 70 mW cm-2 for photo-assisted Zn-air battery is achieved, which is the highest value reported for photo-assisted Zn-air batteries. Significantly, the photo-assisted Li-O2 battery based on MoS2-ONT also shows superior rate capability and other exciting battery performance. This work shows the universality of the confined carrier separation strategy in photo-assisted metal-air batteries.

Highly Sensitive Gas Sensor for Detection of Air Decomposition Pollutant (CO, NOx): Popular Metal Oxide (ZnO, TiO2)-Doped MoS2 Surface

When partial discharges occur in air-insulated equipment, the air decomposes to produce a variety of contamination products, resulting in a reduction in the insulation performance of the insulated equipment. By monitoring the concentration of typical decomposition products (CO, NO, and NO2) within the insulated equipment, potential insulation faults can be diagnosed. MoS2 has shown promising applications as a gas-sensitive semiconductor material, and doping metal oxides can improve the gas-sensitive properties of the material. Therefore, in this work, MoS2 has been doped using the popular metal oxides (ZnO, TiO2) of the day, and its gas-sensitive properties to the typical decomposition products of air have been analyzed and compared using density functional theory (DFT) calculations. The stability of the doped system was investigated using molecular dynamics methods. The related adsorption mechanism was analyzed by adsorption configuration, energy band structure, density of states (DOS) analysis, total electron density (TED) analysis, and differential charge density (DCD) analysis. Finally, the practical application of related sensing performance is evaluated. The results show that the doping of metal oxide nanoparticles greatly improves the conductivity, gas sensitivity, and adsorption selectivity of MoS2 monolayer to air decomposition products. The sensing response of ZnO-MoS2 for CO at room temperature (25 °C) reaches 161.86 with a good recovery time (0.046 s). TiO2-MoS2 sensing response to NO2 reaches 3.5 × 106 at 25 °C with a good recovery time (0.108 s). This study theoretically solves the industrial challenge of recycling sensing materials and provides theoretical value for the application of resistive chemical sensors in air-insulated equipment.

Hetero-Anionic Structure Activated CoS Bonds Promote Oxygen Electrocatalytic Activity for High-Efficiency Zinc-Air Batteries

The electronic structure of transition metal complexes can be modulated by replacing partial ion of complexes to obtain tuned intrinsic oxygen reduction reaction (ORR) or oxygen evolution reaction (OER) electrocatalytic activity. However, the anion-modulated transition metal complexes ORR activity of is still unsatisfactory, and the construction of hetero-anionic structure remains challenging. Herein, an atomic doping strategy is presented to prepare the CuCo2 O4-x Sx /NC-2 (CCSO/NC-2) as electrocatalysts, the structrual characterization results favorably demonstrate the partial substitution of S atoms for O in CCSO/NC-2, which shows excellent catalytic performance and durability for OER and ORR in 0.1 m KOH. In addition, the catalyst assembled Zinc-air battery with an open circuit potential of 1.43 V maintains performance after 300 h of cyclic stability. Theoretical calculations and differential charges illustrate that S doping optimizes the reaction kinetics and promotes electron redistribution. The superior performance of CCSO/NC-2 catalysis is mainly due to its unique S modulation of the electronic structure of the main body. The introduction of S promotes CoO covalency and constructs a fast electron transport channel, thus optimizing the adsorption degree of active site Co to the reaction intermediates.

Role of introduced Se element and induced anion vacancies in Mo(SSe)2-x/G van der Waals heterostructure for enhanced hydrogen evolution reaction

The Gibbs free energy of hydrogen adsorption at the edge of molybdenum disulfide (MoS₂) is close to that of Pt, meaning that MoS₂ is the best candidate to replace Pt-based materials. However, easy agglomeration between layers to mask active sites, lack of catalytic activity in the basal planes, and poor electronic conductivity make MoS₂ exhibit dissatisfactory hydrogen evolution reaction (HER) catalytic performance. Here, we successfully construct a van der Waals heterostructure stacked alternately with Mo(SSe)_2-x and graphene (Mo(SSe)_2-x/G) to enhance its catalytic ability. The introduction of Se into MoS₂ and the thermal treatment induce the sample to generate more anion vacancies. Theoretical and experimental results demonstrate the constructed van der Waals heterostructure, the introduced Se element, and the increased anion vacancies are in favor of promoting the number of active sites and improving the electronic conductivity of the catalyst. Therefore, Mo(SSe)_2-x/G exhibits superior HER catalytic performance (the overpotentials of 137 mV and 136 mV at a current of 10 mA cm^-2) and long-term stabilities (>90 h and 140 h at a current density of 20 mA cm^-2) in both acidic and alkaline media.

Three-Dimensional Fe Single-Atom Catalyst for High-Performance Cathode of Zn-Air Batteries

Designing cost-effective and highly active oxygen reduction reaction (ORR) catalysts is critical for the development of Zn-air batteries (ZABs). Iron-nitrogen-carbon (Fe-N-C) catalysts with single-atom Fe-N_x active sites are considered as one of the most promising alternatives to noble Pt but are hindered by unsatisfactory activity and durability. Herein, a NaCl template-assisted in situ pyrolysis technique is utilized to massively fabricate Fe-N-C single-atom catalysts (SACs) anchored on the three-dimensional open-pore carbon networks (denoted as 3D SAFe). The 3D SAFe catalyst exhibits ultrahigh activity with a half-wave potential of 0.90 V (vs RHE), benefiting from the enhanced mass diffusion and the increased amount of effective Fe-N₄ sites. Consequently, the ZABs assembled with 3D SAFe deliver high peak power density up to 156 mW cm^-2 and outstanding durability of 80 h, suggesting the application potential of the 3D SAFe catalyst. This work inspires the rational design and synthesis of highly efficient SACs for ZABs.

Scalable-doped Nanoporous 1T″ ReSe2 via a General Surface Co-Alloy Strategy

Reliable and controllable doping of 2D transition metal dichalcogenides is an efficient approach to tailor their physicochemical properties and expand their functional applications. However, precise control over dopant distribution and scalability of the process remains a challenge. Here, we report a general method to achieve scalable in situ doping of centimeter-sized bicontinuous nanoporous ReSe₂ films with transition metal atoms via surface coalloy growth. The distinct strains induced by the bending curvature of nanoporous structures and uniform dopants result in a local 1T' to 1T″ structure phase transition over nanoporous ReSe₂ films. The as-prepared nanoporous Ru-ReSe₂ with high 1T″ phase exhibits preferable electrochemical activity in hydrogen evolution reaction. The work demonstrates a unique and general approach to synthesize uniformly-doped transition metal dichalcogenides with 3D bicontinuous nanoporous structure, which can be scaled up to batch production for various applications.

Biaxially Strained MoS2 Nanoshells with Controllable Layers Boost Alkaline Hydrogen Evolution

Strain in layered transition-metal dichalcogenides (TMDs) is a type of effective approach to enhance the catalytic performance by activating their inert basal plane. However, compared with traditional uniaxial strain, the influence of biaxial strain and the TMD layer number on the local electronic configuration remains unexplored. Herein, via a new in situ self-vulcanization strategy, biaxially strained MoS₂ nanoshells in the form of a single-crystalline Ni₃ S₂ @MoS₂ core-shell heterostructure are realized, where the MoS₂ layer is precisely controlled between the 1 and 5 layers. In particular, an electrode with the bilayer MoS₂ nanoshells shows a remarkable hydrogen evolution reaction activity with a small overpotential of 78.1 mV at 10 mA cm^-2 , and negligible activity degradation after durability testing. Density functional theory calculations reveal the contribution of the optimized biaxial strain together with the induced sulfur vacancies and identify the origin of superior catalytic sites in these biaxially strained MoS₂ nanoshells. This work highlights the importance of the atomic-scale layer number and multiaxial strain in unlocking the potential of 2D TMD electrocatalysts.

Ultrafast self-heating synthesis of robust heterogeneous nanocarbides for high current density hydrogen evolution reaction

Designing cost-effective and high-efficiency catalysts to electrolyze water is an effective way of producing hydrogen. Practical applications require highly active and stable hydrogen evolution reaction catalysts working at high current densities (≥1000 mA cm⁻²). However, it is challenging to simultaneously enhance the catalytic activity and interface stability of these catalysts. Herein, we report a rapid, energy-saving, and self-heating method to synthesize high-efficiency Mo₂C/MoC/carbon nanotube hydrogen evolution reaction catalysts by ultrafast heating and cooling. The experiments and density functional theory calculations reveal that numerous Mo₂C/MoC hetero-interfaces offer abundant active sites with a moderate hydrogen adsorption free energy ΔG_H* (0.02 eV), and strong chemical bonding between the Mo₂C/MoC catalysts and carbon nanotube heater/electrode significantly enhances the mechanical stability owing to instantaneous high temperature. As a result, the Mo₂C/MoC/carbon nanotube catalyst achieves low overpotentials of 233 and 255 mV at 1000 and 1500 mA cm⁻² in 1 M KOH, respectively, and the overpotential shows only a slight change after working at 1000 mA cm⁻² for 14 days, suggesting the excellent activity and stability of the high-current-density hydrogen evolution reaction catalyst. The promising activity, excellent stability, and high productivity of our catalyst can fulfil the demands of hydrogen production in various applications.

Industry-level water splitting requires highly active and stable hydrogen evolution reaction (HER) catalysts. Herein, an ultrafast self-heating synthesis delivers robust Mo₂C/MoC/CNT HER catalysts that can work at 1000 mA cm⁻² for 14 days.

Phase-Selective Synthesis of Ruthenium Phosphide in Hybrid Structure Enables Efficient Hybrid Water Electrolysis Under pH-Universal Conditions

Hydrazine-assisted hybrid water electrolysis is an energy-saving approach to produce high-purity hydrogen, whereas the development of pH-universal bifunctional catalysts encounters a grand challenge. Herein, a phase-selective synthesis of ruthenium phosphide compounds hybrid with carbon forming pancake-like particles (denoted as Ru_x P/C-PAN, x = 1 or 2) is presented. The obtained RuP/C-PAN exhibits the highest catalytic activity among the control samples, delivering ultralow cell voltages of 0.03, 0.27, and 0.65 V to drive 10 mA cm^-2 using hybrid water electrolysis corresponding to pH values of 14, 7, and 0, respectively. Theoretical calculation deciphers that the RuP phase displays optimized free energy for hydrogen adsorption and reduced energy barrier for hydrazine dehydrogenation. This work may not only open up a new avenue in exploring universally compatible catalyst to transcend the limitation on the pH value of electrolytes, but also push forward the development of an energy-saving hydrogen generation technique based on emerging hybrid water electrolysis.

RuCo Alloy Nanoparticles Embedded into N-Doped Carbon for High Efficiency Hydrogen Evolution Electrocatalyst

For large-scale and sustainable water electrolysis, it is of great significance to develop cheap and efficient electrocatalysts that can replace platinum. Currently, it is difficult for most catalysts to combine high activity and stability. To solve this problem, we use cobalt to regulate the electronic structure of ruthenium to achieve high activity, and use carbon matrix to protect alloy nanoparticles to achieve high stability. Herein, based on the zeolitic imidazolate frameworks (ZIFs), a novel hybrid composed of RuCo alloy nano-particles and N-doped carbon was prepared via a facile pyrolysis-displacement-sintering strategy. Due to the unique porous structure and multi-component synergy, the optimal RuCo500@NC750 material in both acidic and alkaline media exhibited eminent HER catalytic activity. Notably, the 3-RuCo500@NC750 obtained a current density of 10 mA cm−2 at 22 mV and 31 mV in 0.5 M H2SO4 and 1.0 M KOH, respectively, comparable to that of the reference Pt/C catalyst. Furthermore, the Tafel slopes of the catalyst are 52 mV Dec−1 and 47 mV Dec−1, respectively, under acid and alkali conditions, and the catalyst has good stability, indicating that it has broad application prospects in practical electrolytic systems. This work contributes to understanding the role of carbon-supported polymetallic alloy in the electrocatalytic hydrogen evolution process, and provides some inspiration for the development of a high efficiency hydrogen evolution catalyst.

2D Molybdenum Sulfide-Based Materials for Photo-Excited Antibacterial Application

Bacterial infections have seriously threatened human health and the abuse of natural or artificial antibiotics leads to bacterial resistance, so development of a new generation of antibacterial agents and treatment methods is urgent. 2D molybdenum sulfide (MoS₂ ) has good biocompatibility, high specific surface area to facilitate surface modification and drug loading, adjustable energy bandgap, and high near-infrared photothermal conversion efficiency (PCE), so it is often used for antibacterial application through its photothermal or photodynamic effects. This review comprehensively summarizes and discusses the fabrication processes, structural characteristics, antibacterial performance, and the corresponding mechanisms of MoS₂ -based materials as well as their representative antibacterial applications. In addition, the outlooks on the remaining challenges that should be addressed in the field of MoS₂ are also proposed.

Pt Atom on the Wall of Atomic Layer Deposition (ALD)-Made MoS2 Nanotubes for Efficient Hydrogen Evolution

Single-atom catalysts (SACs) can achieve excellent catalytic efficiency at ultralow catalyst consumptions. Herein, platinum (Pt) atoms are fixed on the wall of atomic layer deposition (ALD)-made molybdenum disulfide nanotube arrays (MoS₂ -NTA) for efficient hydrogen evolution reaction (HER). More concretely, MoS₂ -NTA with different nanotube diameters and wall thicknesses are fabricated by a sacrificial strategy of anodic aluminum oxide (AAO) template via ALD; then Pt atoms are fixed on the wall of Ti₃ C₂ -supported MoS₂ -NTA as a catalytic system. The MoS₂ -NTA/Ti₃ C₂ decorated with 0.13 wt.% of Pt results in a low overpotential of 32 mV to deliver a current density of 10 mA cm^-2 , which is superior to 20 wt.% commercial Pt/C (41 mV). Ordered MoS₂ -NTA instead of 2D MoS₂ prevents Pt atoms from aggregating and then exerts catalytic activities. The density functional theory calculations suggest that the Pt atoms are more likely to occupy the sites on the tubular MoS₂ than the planar MoS₂ , and the Pt atoms accumulated at the Mo site of MoS₂ -NT have a moderate Gibbs free energy (close to zero).

Synergy between Palladium Single Atoms and Nanoparticles via Hydrogen Spillover for Enhancing CO2 Photoreduction to CH4

Selective photoreduction of carbon dioxide (CO₂ ) into carbon-neutral fuels such as methane (CH₄ ) is extremely desirable but remains a challenge since sluggish multiple proton-electron coupling transfer and various C₁ intermediates are involved. Herein, a synergistic function between single Pd atoms (Pd₁ ) and Pd nanoparticles (Pd_NPs ) on graphitic carbon nitride (C₃ N₄ ) for photocatalytic CO₂ methanation is presented. The catalyst achieves a high selectivity of 97.8% for CH₄ production with a yield of 20.3 µmol g_cat. ^-1 h^-1 in pure water. Mechanistic studies revealed that Pd₁ sites activated CO₂ , while Pd_NPs sites boosted water (H₂ O) dissociation for increased H* coverage. The H* produced by Pd_NPs migrate to the Pd₁ sites to promote multiple proton-electron coupling transfer via hydrogen spillover. Moreover, the adjacent Pd₁ and Pd_NPs effectively stabilized intermediates such as *CHO, thereby favoring the pathway for CH₄ production. This work provides a new perspective into the development of selective photocatalytic CO₂ conversion through the artful design of synergistic catalytic sites.

The synergistic effect of Hf-O-Ru bonds and oxygen vacancies in Ru/HfO2 for enhanced hydrogen evolution

Ru nanoparticles have been demonstrated to be highly active electrocatalysts for the hydrogen evolution reaction (HER). At present, most of Ru nanoparticles-based HER electrocatalysts with high activity are supported by heteroatom-doped carbon substrates. Few metal oxides with large band gap (more than 5 eV) as the substrates of Ru nanoparticles are employed for the HER. By using large band gap metal oxides substrates, we can distinguish the contribution of Ru nanoparticles from the substrates. Here, a highly efficient Ru/HfO₂ composite is developed by tuning numbers of Ru-O-Hf bonds and oxygen vacancies, resulting in a 20-fold enhancement in mass activity over commercial Pt/C in an alkaline medium. Density functional theory (DFT) calculations reveal that strong metal-support interaction via Ru-O-Hf bonds and the oxygen vacancies in the supported Ru samples synergistically lower the energy barrier for water dissociation to improve catalytic activities.

Although ruthenium nanomaterials have proven to be effective catalysts for H₂ evolution, there is still room for activity improvements. Here, authors develop an efficient Ru/HfO₂ electrocatalyst with tuned Ru-O-Hf bonds and oxygen vacancies that shows high activities for alkaline H₂ evolution.

Electronegativity-Induced Charge Balancing to Boost Stability and Activity of Amorphous Electrocatalysts

Amorphization is an efficient strategy to activate intrinsically inert catalysts. However, the low crystallinity of amorphous catalysts often causes high solubility and poor electrochemical stability in aqueous solution. Here, a different mechanism is developed to simultaneously stabilize and activate the water-soluble amorphous MoS_x O_y via a charge-balancing strategy, which is induced by different electronegativity between the co-dopants Rh (2.28) and Sn (1.96). The electron-rich Sn prefers to stabilize the unstable apical O sites in MoS_x O_y through charge transfer, which can prevent the H from attacking. Meanwhile, the Rh, as the charge regulator, shifts the main active sites on the basal plane from inert Sn to active apical Rh sites. As a result, the amorphous RhSn-MoS_x O_y exhibits drastic enhancement in electrochemical stability (η₁₀ increases only by 12 mV) after 1000 cycles and a distinct activity (η₁₀ : 26 mV and Tafel: 30.8 mV dec^-1 ) for the hydrogen evolution reaction in acidic solution. This work paves a route for turning impracticably water-soluble catalysts into treasure and inspires new ideas to design high-performance amorphous electrocatalysts.

Single-Atom Pt Anchored on Oxygen Vacancy of Monolayer Ti3C2Tx for Superior Hydrogen Evolution

Two-dimensional (2D) MXene-loaded single-atom (SA) catalysts have drawn increasing attention. SAs immobilized on oxygen vacancies (O_V) of MXene are predicted to have excellent catalytic performance; however, they have not yet been realized experimentally. Here Pt SAs immobilized on the O_V of monolayer Ti₃C₂T_x flakes are constructed by a rapid thermal shock technique under a H₂ atmosphere. The resultant Ti₃C₂T_x-Pt_SA catalyst exhibits excellent hydrogen evolution reaction (HER) performance, including a small overpotential of 38 mV at 10 mA cm^-2, a high mass activity of 23.21 A mg_Pt^-1, and a large turnover frequency of 23.45 s^-1 at an overpotential of 100 mV. Furthermore, density functional theory calculations demonstrate that anchoring the Pt SA on the O_V of Ti₃C₂T_x helps to decrease the binding energy and the hybridization strength between H atoms and the supports, contributing to rapid hydrogen adsorption-desorption kinetics and high activity for the HER.

Super-stable SnO2/MoS2 enhanced the electrocatalytic hydrogen evolution in acidic environments

We designed a superstable SnO2/MoS2 coupled nanosheet array on carbon cloth, which exhibited interface engineering of SnO2/MoS2 with fast electron transfer and proton adsorption boosting electrocatalytic hydrogen evolution in acidic environments.

Interfacial Microenvironment Modulation Enhancing Catalytic Kinetics of Binary Metal Sulfides Heterostructures for Advanced Water Splitting Electrocatalysts

Interfacial microenvironment modulation has been proven to be a promising route to fabricate highly efficient catalysts. In this work, the lattice defect-rich NiS₂ /MoS₂ nanoflakes (NMS NFs) electrocatalysts are successfully synthesized by a simple strategy. Benefiting from the abundant lattice defects and modulated interfacial microenvironment between NiS₂ and MoS₂ , the prepared NMS NFs show superior catalytic activity for water splitting. Particularly, the optimized NMS NFs (the molar ratio of Ni:Mo = 5:5) exhibit remarkable catalytic activity toward overall water splitting with a voltage of 1.60 V at 10 mA cm^-2 in alkaline media, which is lower than that of the noble-metal-based electrocatalysts (1.68 V at 10 mA cm^-2 ). The NMS NFs electrocatalysts also show exceptional long-term stability (>50 h) for overall water splitting. The density functional theory results demonstrate that the injection of NiS₂ into MoS₂ can greatly optimize the catalytic kinetics and reduce the energy barrier for hydrogen/oxygen evolution reactions. The work does not only offer a promising candidate for a highly efficient water splitting electrocatalyst but also highlights that interfacial microenvironment modulation is a potential strategy to optimize the catalytic kinetics.

The Underlying Molecular Mechanism of Fence Engineering to Break the Activity-stability Trade-off of Catalysts

Non-precious-metal (NPM) catalysts often face the formidable challenge of a trade-off between long-term stability and high activity, which has not yet been widely addressed. Here we propose distinct molecule-selective fence as a promising novel concept to solve this activity-stability trade-off. This unique fence has the characteristics of preventing poisonous species from invading catalysts, but allowing catalytic reaction-related species to diffuse freely. We applied this concept to construct CoS2 layer with the function of molecular selectivity on the external surface of highly active Co doped MoS2, achieving a remarkable catalytic stability towards alkaline hydrogen evolution reaction, along with a further optimized activity. In situ spectroscopy technologies uncovered the underlying molecule mechanism of the CoS2 fence for breaking the activity-stability trade-off of the MoS2 catalyst. This work offers valuable guidance for rationally designing efficient and stable NPM catalysts.

Three-dimensional cross-linked Co-MoS2 catalyst on carbon cloth for efficient hydrogen evolution reaction

MoS₂-Based materials are promising hydrogen evolution reaction (HER) electrocatalysts. However, their HER activities are restrained by the poor population of HER activated edge centers, the large area exposed HER inert basal planes, and low conductivity. Fixing these problems on one system is an effective strategy, but it remains a challenge due to the harsh synthetic conditions. Herein, cobalt carbonate hydroxide (CoCH) nanosheets were used as the substrate for preparing a three-dimensional self-supported cross-linked (3DSC) Co-MoS₂ nanostructured HER catalyst, which possesses abundant active centers and fast electronic transfer ability. In addition, Co activates the basal-plane sulfur atom in MoS₂ to be the HER reactive center effectively. Benefiting from these advantages, 3DSC Co-MoS₂ electrode integrated on carbon cloth (CC) shows that it can drive the current density of 10 and 100 mA cm^-2 with only 40 and 119 mV overpotentials, respectively, which is superior to other MoS₂-based HER catalysts reported recently. This research provides a facile strategy for the improvement of efficient HER electrocatalysts.

Single-Atom Engineering to Ignite 2D Transition Metal Dichalcogenide Based Catalysis: Fundamentals, Progress, and Beyond

Single-atom catalysis has been recognized as a pivotal milestone in the development history of heterogeneous catalysis by virtue of its superior catalytic performance, ultrahigh atomic utilization, and well-defined structure. Beyond single-atom protrusions, two more motifs of single-atom substitutions and single-atom vacancies along with synergistic single-atom motif assemblies have been progressively developed to enrich the single-atom family. On the other hand, besides traditional carbon material based substrates, a wide variety of 2D transitional metal dichalcogenides (TMDs) have been emerging as a promising platform for single-atom catalysis owing to their diverse elemental compositions, variable crystal structures, flexible electronic structures, and intrinsic activities toward many catalytic reactions. Such substantial expansion of both single-atom motifs and substrates provides an enriched toolbox to further optimize the geometric and electronic structures for pushing the performance limit. Concomitantly, higher requirements have been put forward for synthetic and characterization techniques with related technical bottlenecks being continuously conquered. Furthermore, this burgeoning single-atom catalyst (SAC) system has triggered serial scientific issues about their changeable single atom-2D substrate interaction, ambiguous synergistic effects of various atomic assemblies, as well as dynamic structure-performance correlations, all of which necessitate further clarification and comprehensive summary. In this context, this Review aims to summarize and critically discuss the single-atom engineering development in the whole field of 2D TMD based catalysis covering their evolution history, synthetic methodologies, characterization techniques, catalytic applications, and dynamic structure-performance correlations. In situ characterization techniques are highlighted regarding their critical roles in real-time detection of SAC reconstruction and reaction pathway evolution, thus shedding light on lifetime dynamic structure-performance correlations which lay a solid theoretical foundation for the whole catalytic field, especially for SACs.

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 NiP_x 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.

Wrapping Plasmonic Silver Nanoparticles inside One-Dimensional Nanoscrolls of Transition-Metal Dichalcogenides for Enhanced Photoresponse

The low light absorption of transition-metal dichalcogenide (TMDC) nanosheets hinders their application as high-performance optoelectronic devices. Rolling them up into one-dimensional (1D) nanoscrolls and decorating them with plasmonic nanoparticles (NPs) are both effective strategies for enhancing their performance. When these two approaches are combined, in this work, the light-matter interaction in TMDC nanosheets is greatly improved by encapsulating silver nanoparticles (Ag NPs) in TMDC nanoscrolls. After the silver nitrate (AgNO₃) solution was spin-coated on monolayer (1L) MoS₂ and WS₂ nanosheets grown by chemical vapor deposition, Ag NPs were homogeneously formed to obtain MoS₂-Ag and WS₂-Ag nanosheets due to the TMDC-assisted spontaneous reduction, and their size and density can be well controlled by tuning the concentration of the AgNO₃ solution. By the simple placement of alkaline droplets on MoS₂-Ag or WS₂-Ag hybrid nanosheets, MoS₂-Ag or WS₂-Ag nanoscrolls with large sizes were obtained in large area. The obtained hybrid nanoscrolls exhibited up to 500 times increased photosensitivities compared with 1L MoS₂ nanosheets, arising from the localized surface plasmon resonance effect of Ag NPs and the scrolled-nanosheet structure. Our work provides a reliable method for the facile and large-area preparation of NP/nanosheet hybrid nanoscrolls and demonstrates their great potential for high-performance optoelectronic devices.

Transferable Active Centers of Strongly Coupled MoS2@Sulfur and Molybdenum Co-doped g-C3N4 Heterostructure Electrocatalysts for Boosting Hydrogen Evolution Reaction in Both Acidic and Alkaline Media

Designing an excellent acidic and alkaline general-purpose hydrogen evolution electrocatalyst plays an important role in promoting the development of the energy field. Here, a feasible strategy is reported to use the strongly coupled MoS₂@sulfur and molybdenum co-doped g-C₃N₄ (MoS₂@Mo-S-C₃N₄) heterostructure with transferable active centers for catalytic reactions in acidic and alkaline media. Research studies have shown that the unsaturated S site at the edge of MoS₂ and the active N atom on the Mo-S-C₃N₄ substrate are, respectively, the active centers of acidic and alkaline hydrogen evolution reaction. Specifically, Mo-S-C₃N₄ is regarded as a synergistic catalyst for the active species MoS₂ in acidic hydrogen evolution, while MoS₂ acts as a co-catalyst when the alkaline active species are transferred to Mo-S-C₃N₄. The coordination of the electrons between the interfaces achieves a synergistic balance, which provides the optimal sites for the adsorption of the reactants. Such an electrocatalyst exhibits overpotentials of 193 and 290 mV at 10 mA cm^-2 in 0.5 M H₂SO₄ and 1 M KOH, respectively, which was better than numerous previous reports. This research provides an outstanding avenue to realize multifunctional electrocatalysts.

Promoting effect of MXenes on 1T/2H–MoSe2 for hydrogen evolution

The 1T/2H–MoSe₂/Ti₃C₂ composites integrated via a facile hydrothermal method exhibit an optimal overpotential of 150 mV at 10 mA cm⁻² in 1 M KOH, indicating that Ti₃C₂ is an ideal conductive support for building highly efficient electrocatalysts.

Defect Engineering of Molybdenum-Based Materials for Electrocatalysis

Molybdenum-based electrocatalysts have been widely applied in electrochemical energy conversion reactions. The essential roles of defects, including doping, vacancies, grain boundaries, and dislocations in improving various electrocatalytic performances have been reported. This review describes the latest development of defect engineering in molybdenum-based materials for hydrogen evolution, oxygen reduction, oxygen evolution, and nitrogen reduction reactions. The types of defects, preparation methods, characterization techniques, and applications of molybdenum-based defect materials are elucidated. Finally, challenges and future research directions for these types of materials are also discussed.