Engineering 2D Metal-Organic Framework/MoS2 Interface for Enhanced Alkaline Hydrogen Evolution

Electrocatalytic biomass upgrading coupled with hydrogen evolution and CO2 reduction

Clean energy production and CO2 utilization have attracted increasing interest. Electrocatalysis represents an effective way to produce green hydrogen from water and reduce CO2 to valuable compounds. However, for either the hydrogen evolution reaction (HER) or the CO2 reduction reaction (CO2RR), the reaction efficiency is significantly limited by the slow kinetics of the oxygen evolution reaction (OER) at the anode, which consumes most of the input energy. Therefore, great efforts have been made to replace the OER with organic oxidation reactions at the anode to decrease the reaction energy barrier. Biomass has an advantage of broad source, and when it is employed as an OER alternative in the anode oxidation reactions, not only can the reduction reaction efficiency at the cathode including the HER and CO2RR be enhanced but high-value chemicals can also be obtained, representing an attractive OER alternative. This review comprehensively summarizes the recent achievements in electrocatalytic biomass upgrading coupled with the HER and CO2RR, cataloged based on the type of biomass. The design of electrocatalysts for such coupled reaction systems is discussed. Finally, the challenges and perspectives in the field of this energy-saving and value-added coupling system are provided to inspire more efforts in pushing forward the development of this field.

Enhancing electrocatalytic hydrogen evolution via engineering unsaturated electronic structures in MoS2

The search for efficient, earth-abundant electrocatalysts for the hydrogen evolution reaction (HER) has identified unsaturated molybdenum disulfide (MoS2) as a leading candidate. This review synthesises recent advancements in the engineering of MoS2 to enhance its electrocatalytic properties. It focuses on strategies for designing an unsaturated electronic structure on metal catalytic centers and their role in boosting the efficiency of the hydrogen evolution reaction (HER). It also considers how to optimize the electronic structures of unsaturated MoS2 for enhanced catalytic performance. This review commences with an examination of the fundamental crystal structure of MoS2; it elucidates the classical unsaturated electron configurations and the intrinsic factors that contribute to such electronic structures. Furthermore, it introduces popular strategies for constructing unsaturated electronic structures at the atomic level, such as nanostructure engineering, surface chemical modification and interlayer coupling engineering. It also discusses the challenges and future research directions in the study of MoS2 electronic structures, with the aim of broadening their application in sustainable hydrogen production.

Engineering heterostructured Mo2C/MoS2 catalyst with hydrophilicity/aerophobicity via carbothermal shock for efficient alkaline hydrogen evolution

The exploration of high-performance hydrogen evolution reaction (HER) catalysts is conducive to the development of clean hydrogen energy, yet still remains a challenge. Herein, we rapidly synthesize the Mo2C/MoS2 heterostructure on carbon paper (Mo2C/MoS2-CP) via carbothermal shock in only two seconds. The construction of the Mo2C/MoS2 heterostructure regulates the electronic structure of the Mo site and facilitates charge transfer during the HER process. Moreover, the catalyst exhibits enhanced hydrophilicity and aerophobicity, facilitating optimal electrolyte-catalyst interaction and efficient hydrogen bubble detachment for accelerated mass transfer. Consequently, Mo2C/MoS2-CP exhibits superior intrinsic alkaline HER activity, and excellent stability for 100 h. This finding provides a novel insight into the development of outstanding HER catalysts.

Trimetallic FeCoNi Metal-Organic Framework with Enhanced Peroxidase-like Activity for the Construction of a Colorimetric Sensor for Rapid Detection of Thiophenol in Water Samples

In recent years, nanozymes have attracted particular interest and attention as catalysts because of their high catalytic efficiency and stability compared with natural enzymes, whereas how to use simple methods to further improve the catalytic activity of nanozymes is still challenging. In this work, we report a trimetallic metal-organic framework (MOF) based on Fe, Co and Ni, which was prepared by replacing partial original Fe nodes of the Fe-MOF with Co and Ni nodes. The obtained FeCoNi-MOF shows both oxidase-like activity and peroxidase-like activity. FeCoNi-MOF can not only oxidize the chromogenic substrate 3,3,5,5-tetramethylbenzidine (TMB) to its blue oxidation product oxTMB directly, but also catalyze the activation of H2O2 to oxidize the TMB. Compared with corresponding monometallic/bimetallic MOFs, the FeCoNi-MOF with equimolar metals hereby prepared exhibited higher peroxidase-like activity, faster colorimetric reaction speed (1.26-2.57 folds), shorter reaction time (20 min) and stronger affinity with TMB (2.50-5.89 folds) and H2O2 (1.73-3.94 folds), owing to the splendid synergistic electron transfer effect between Fe, Co and Ni. Considering its outstanding advantages, a promising FeCoNi-MOF-based sensing platform has been designated for the colorimetric detection of the biomarker H2O2 and environmental pollutant TP, and lower limits of detection (LODs) (1.75 μM for H2O2 and 0.045 μM for TP) and wider linear ranges (6-800 μM for H2O2 and 0.5-80 μM for TP) were obtained. In addition, the newly constructed colorimetric platform for TP has been applied successfully for the determination of TP in real water samples with average recoveries ranging from 94.6% to 112.1%. Finally, the colorimetric sensing platform based on FeCoNi-MOF is converted to a cost-effective paper strip sensor, which renders the detection of TP more rapid and convenient.

Molybdenum sulfide modified with nickel or platinum nanoparticles as an effective catalyst for hydrogen evolution reaction

In this study, we investigate the catalytic performance of molybdenum sulfide (MoS2) modified with either nickel (Ni) or platinum (Pt) nanoparticles as catalysts for the hydrogen evolution reaction (HER). The MoS2 was prepared on the TiO2 nanotube substrates via a facile hydrothermal method, followed by the deposition by magnetron sputtering of Ni or Pt nanoparticles on the MoS2 surface. Structural and morphological characterization confirmed the successful incorporation of Ni or Pt nanoparticles onto the MoS2 support. Electrochemical measurements revealed that Ni- and Pt-modified MoS2 catalysts exhibited enhanced HER activity compared to pristine MoS2. Obtained catalysts demonstrated a low onset potential, reduced overpotential, and increased current density, indicating efficient electrocatalytic performance. Furthermore, the Ni or Pt-modified MoS2 catalyst exhibited remarkable stability during prolonged HER operation. The improved catalytic activity can be attributed to the synergistic effect between metal nanoparticles and MoS2, facilitating charge transfer kinetics and promoting hydrogen adsorption and desorption. Incorporating Ni and Pt nanoparticles also provided additional active sites on the MoS2 surface, enhancing the catalytic activity.

Cr-doping promoted surface reconstruction of Ni3N electrocatalysts toward efficient overall water splitting

Understanding and utilizing the dynamic changes of electrocatalysts under working conditions are important for advancing the sustainable hydrogen production. Here, we for the first time report that Cr-doping can promote the in situ reconstruction of a self-supported Ni3N electrocatalyst (Cr-Ni3N/NF) during oxygen and hydrogen evolution reactions (OER and HER), and therefore improve the electrocatalytic water splitting performance. As identified by in situ measurements and theoretical calculations, Cr-doping enhances OH- adsorption during OER at anode and thereby boosts the transformation of Ni3N pre-catalysts to defect-rich nickel oxyhydroxide (NiOOH) active species. Meanwhile, it facilitates the generation of Ni3N/Ni(OH)2 at cathodes due to effective H2O activation, leading to the fast HER kinetics on the Ni3N/Ni(OH)2 interfaces. Notably, the optimal Cr-Ni3N/NF displays good OER and HER performance in 1.0 M KOH electrolytes, with low overpotentials of 316 and 188 mV to achieve the current density of ± 100 mA cm-2, respectively. Benefiting from its bi-functionality and self-supporting property, an alkaline electrolyzer equipped with Cr-Ni3N/NF as both anode and cathode affords a small voltage of 1.72 V at 100 mA cm-2, along with 100 h operation stability. Elucidating that Cr-doping can boost in situ reconfiguration and consequently the electrocatalytic activity, this work would shed new light on the rational design and synthesis of electrocatalysts via directional reconstructions.

Revealing Hydrogen Spillover on 1T/2H MoS2 Heterostructures for an Enhanced Hydrogen Evolution Reaction by Scanning Electrochemical Microscopy

The in situ characterization of the heterostructure active sites during the hydrogen evolution reaction (HER) process and the direct elucidation of the corresponding catalytic structure-activity relationships are essential for understanding the catalytic mechanism and designing catalysts with optimized activity. Hence, exploring the underlying reasons behind the exceptional catalytic performance necessitates a detailed analysis. Herein, we employed scanning electrochemical microscopy (SECM) to in situ image the topography and local electrocatalytic activity of 1T/2H MoS2 heterostructures on mixed-phase molybdenum disulfide (MoS2) with 20 nm spatial resolution. Our measurements provide direct data about HER activity, enabling us to differentiate the superior catalytic performance of 1T/2H MoS2 heterostructures compared to other active sites on the MoS2 surface. Combining this spatially resolved electrochemical information with density functional theory calculations and numerical simulations enables us to reveal the existence of hydrogen spillover from the 1T MoS2 surface to 1T/2H MoS2 heterostructures. Furthermore, it has been verified that hydrogen spillover can significantly enhance the electrocatalytic activity of the heterostructures, in addition to its strong electronic interaction. This study not only contributes to the future investigation of electrochemical processes at nanoscale active sites on structurally complex electrocatalysts but also provides new design strategies for improving the catalytic activity of 2D electrocatalysts.

Design and Development of Sustainable Cu2 (II)- and Mn2 (III)-Embedded Bifunctional Electrocatalysts: Enhanced Hydrogen and Oxygen Generation

Nowadays, environmentally friendly, low-cost-effective, and sustainable electrocatalysts used widely for hydrogen and oxygen evolution reactions have come into the limelight as a new research topic for scientists. This study highlights the preparation of two unique and symmetrical dinuclear Cu (II) and Mn (III) bifunctional catalysts by a facile simple slow evaporation and diffusion route. [C32H24Cu2F4N4O4] (1) and [C32H24Mn2F4N4O4] (2) both have monoclinic (C2/c (15)) crystal systems, with oxidation states +2 and +3, respectively. Prominent SPR peaks at 372 and 412 nm indicate an M-L charge transfer transition in both complexes. The synthesized electrocatalysts display exceptional catalytic activity for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Complex 1 exhibits enhanced hydrogen generation in 0.5 M H2SO4 with a small overpotential of 216 mV at -10 mA cm-2 along with a significantly lower Tafel value of 97 mV/dec compared to Complex 2. Moreover, Complex 1 is highly active for the OER in 1 M KOH with a small Tafel slope of 103 mV/dec and a low overpotential of 340 mV to acquire 10 mA cm-2 current density, compared to Complex 2. Complex 1 and Complex 2 remain stable up to 20 h in acidic electrolyte and up to 36 h and 20 h in the basic electrolyte, respectively.

Shape-Preserved CoFeNi-MOF/NF Exhibiting Superior Performance for Overall Water Splitting across Alkaline and Neutral Conditions

This study reported a multi-functional Co0.45Fe0.45Ni0.9-MOF/NF catalyst for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and overall water splitting, which was synthesized via a novel shape-preserving two-step hydrothermal method. The resulting bowknot flake structure on NF enhanced the exposure of active sites, fostering a superior electrocatalytic surface, and the synergistic effect between Co, Fe, and Ni enhanced the catalytic activity of the active site. In an alkaline environment, the catalyst exhibited impressive overpotentials of 244 mV and 287 mV at current densities of 50 mA cm-2 and 100 mA cm-2, respectively. Transitioning to a neutral environment, an overpotential of 505 mV at a current density of 10 mA cm-2 was achieved with the same catalyst, showing a superior property compared to similar catalysts. Furthermore, it was demonstrated that Co0.45Fe0.45Ni0.9-MOF/NF shows versatility as a bifunctional catalyst, excelling in both OER and HER, as well as overall water splitting. The innovative shape-preserving synthesis method presented in this study offers a facile method to develop an efficient electrocatalyst for OER under both alkaline and neutral conditions, which makes it a promising catalyst for hydrogen production by water splitting.

Strain-Induced Self-Assembly at Interface of Two-Dimensional Heterostructures Boosts CO2 Reduction to Methanol by H2O

CO2 conversion with pure H2O into CH3OH and O2 driven by solar energy can supply fuels and life-essential substances for extraterrestrial exploration. However, the effective production of CH3OH is significantly challenging. Here we report an organozinc complex/MoS2 heterostructure linked by well-defined zinc-sulfur covalent bonds derived by the structural deformation and intensive coupling of dx2 - y2(Zn)-p(S) orbitals at the interface, resulting in distinctive charge transfer behaviors and excellent redox capabilities as revealed by experimental characterizations and first-principle calculations. The synthesis strategy is further generalized to more organometallic compounds, achieving various heterostructures for CO2 photoreduction. The optimal catalyst delivers a promising CH3OH yield of 2.57 mmol gcat-1 h-1 and selectivity of more than 99.5%. The reverse water gas shift mechanism is identified for methanol formation. Meanwhile, energy-unfavorable adsorption of methanol on MoS2, where the photogenerated holes accumulate, ensures the selective oxidation of water over methanol.

Design Strategies towards Advanced Hydrogen Evolution Reaction Electrocatalysts at Large Current Densities

Hydrogen (H2), produced by water electrolysis with the electricity from renewable sources, is an ideal energy carrier for achieving a carbon-neutral and sustainable society. Hydrogen evolution reaction (HER) is the cathodic half-reaction of water electrolysis, which requires active and robust electrocatalysts to reduce the energy consumption for H2 generation. Despite numerous electrocatalysts have been reported by the academia for HER, most of them were only tested under relatively small current densities for a short period, which cannot meet the requirements for industrial water electrolysis. To bridge the gap between academia and industry, it is crucial to develop highly active HER electrocatalysts which can operate at large current densities for a long time. In this review, the mechanisms of HER in acidic and alkaline electrolytes are firstly introduced. Then, design strategies towards high-performance large-current-density HER electrocatalysts from five aspects including number of active sites, intrinsic activity of each site, charge transfer, mass transfer, and stability are discussed via featured examples. Finally, our own insights about the challenges and future opportunities in this emerging field are presented.

Construction of magnetic MoS2/NiFe2O4/MIL-101(Fe) hybrid nanostructures for separation of dyes and antibiotics from aqueous media

In this study, MoS2/NiFe2O4/MIL-101(Fe) nanocomposite was synthesized by hydrothermal method and used as an adsorbent for the elimination of organic dyes and some antibiotic drugs in aqueous solutions. The synthesized nanocomposite underwent characterization through different techniques, including scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), Brunauer-Emmett-Teller (BET) surface area analysis, Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), zeta potential analysis, vibrating sample magnetometry (VSM), and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). These results demonstrated the successful insertion of MoS2within the cavities of MIL-101(Fe). The as-prepared magnetic nanocomposite was used as a new magnetic adsorbent for removing methylene blue (MB) and rhodamine B (RhB) organic dyes and tetracycline (TC) and ciprofloxacin (CIP) antibiotic drugs. For achieving the optimized conditions, the effects of initial pH, initial dye and drug concentration, temperature, and adsorbent dose on MB, TC, and CIP elimination were investigated. The results revealed that at a temperature of 25 °C, the highest adsorption capacities of MoS2/NiFe2O4/MIL-101(Fe) for MB, TC, and CIP were determined to be 999.1, 2991.3, and 1994.2 mg g-1, respectively. The pseudo-second-order model and Freundlich model are considered suitable for explaining the adsorption behavior of the MoS2/NiFe2O4/MIL-101(Fe) nanocomposite. The magnetic nanocomposite was very stable and had good recycling capability without any change in its structure.

Recent Progress in 2D Metal-Organic Framework-Related Materials

2D metal-organic frameworks-based (2D MOF-related) materials benefit from variable topological structures, plentiful open active sites, and high specific surface areas, demonstrating promising applications in gas storage, adsorption and separation, energy conversion, and other domains. In recent years, researchers have innovatively designed multiple strategies to avoid the adverse effects of conventional methods on the synthesis of high-quality 2D MOFs. This review focuses on the latest advances in creative synthesis techniques for 2D MOF-related materials from both the top-down and bottom-up perspectives. Subsequently, the strategies are categorized and summarized for synthesizing 2D MOF-related composites and their derivatives. Finally, the current challenges are highlighted faced by 2D MOF-related materials and some targeted recommendations are put forward to inspire researchers to investigate more effective synthesis methods.

Fundamentals and Challenges of Engineering Charge Polarized Active Sites for CO2 Photoreduction toward C2 Products

ConspectusGlobal warming and climatic deterioration are partly caused by carbon dioxide (CO2) emission. Given this, CO2 reduction into valuable carbonaceous fuels is a win-win route to simultaneously alleviate the greenhouse effect and the energy crisis, where CO2 reduction into hydrocarbon fuels by solar energy may be a potential strategy. Up to now, most of the current photocatalysts photoconvert CO2 to C1 products. It is extremely difficult to achieve production of C2 products, which have higher economic value and energy density, due to the kinetic challenge of C-C coupling of the C1 intermediates. Therefore, to realize CO2 photoreduction to C2 fuels, design of high-activity photocatalysts to expedite the C-C coupling is significant. Besides, the current mechanism for CO2 photoreduction toward C2 fuels is usually uncertain, which is possibly attributed to the following two reasons: (1) It is arduous to determine the actual catalytic sites for the C-C coupling step. (2) It is hard to monitor the low-concentration active intermediates during the multielectron transfer step.Most traditional metal-based photocatalysts usually possess charge balanced active sites that have the same charge density. In this aspect, the neighboring C1 intermediates may also show the same charge distribution, which would lead to dipole-dipole repulsion, thus preventing C-C coupling for producing C2 fuels. By contrast, photocatalysts with charge polarized active sites possess obviously different charge distributions in the adjacent C1 intermediates, which can effectively suppress the electrostatic repulsion to steer the C-C coupling. Based on this analysis, higher asymmetric charge density on the active sites would be more beneficial to anchoring between the adjacent intermediates and active atoms in catalysts, which can boost C-C coupling.In this Account, we summarize various strategies, including vacancy engineering, doping engineering, loading engineering, and heterojunction engineering, for tailoring charge polarized active sites to boost the C-C coupling for the first time. Also, we overview diverse in situ characterization technologies, such as in situ X-ray photoelectron spectroscopy, in situ Raman spectroscopy, and in situ Fourier transform infrared spectroscopy, for determining charge polarized active sites and monitoring reaction intermediates, helping to reveal the internal catalytic mechanism of CO2 photoreduction toward C2 products. We hope this Account may help readers to understand the crucial function of charge polarized active sites during CO2 photoreduction toward C2 products and provide guidance for designing and preparing highly active catalysts for photocatalytic CO2 reduction.

Molybdenum Disulfide/Nickel-Metal Organic Framework Hybrid Nanosheets Based Disposable Electrochemical Sensor for Determination of 4-Aminophenol in Presence of Acetaminophen

The toxicity of commonly used drugs, such as acetaminophen (ACAP) and its degradation-derived metabolite of 4-aminophenol (4-AP), underscores the need to achieve an effective approach in their simultaneous electrochemical determination. Hence, the present study attempts to introduce an ultra-sensitive disposable electrochemical 4-AP and ACAP sensor based on surface modification of a screen-printed graphite electrode (SPGE) with a combination of MoS₂ nanosheets and a nickel-based metal organic framework (MoS₂/Ni-MOF/SPGE sensor). A simple hydrothermal protocol was implemented to fabricate MoS₂/Ni-MOF hybrid nanosheets, which was subsequently tested for properties using valid techniques including X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX), Fourier transformed infrared spectroscopy (FTIR), and N₂ adsorption-desorption isotherm. The 4-AP detection behavior on MoS₂/Ni-MOF/SPGE sensor was followed by cyclic voltammetry (CV), chronoamperometry and differential pulse voltammetry (DPV). Our experimental findings on the generated sensor confirmed a broad linear dynamic range (LDR) for 4-AP from 0.1 to 600 μM with a high sensitivity of 0.0666 μA/μM and a low limit of detection (LOD) of 0.04 μM. In addition, an analysis of real specimens such as tap water sample as well as a commercial sample (acetaminophen tablets) illuminated the successful applicability of as-developed sensor in determining ACAP and 4-AP, with an impressive recovery rate.

2D Metal-Organic Frameworks as Competent Electrocatalysts for Water Splitting

Hydrogen, a clean and flexible energy carrier, can be efficiently produced by electrocatalytic water splitting. To accelerate the sluggish hydrogen evolution reaction and oxygen evolution reaction kinetics in the splitting process, highly active electrocatalysts are essential for lowering the energy barriers, thereby improving the efficiency of overall water splitting. Combining the distinctive advantages of metal-organic frameworks (MOFs) with the physicochemical properties of 2D materials such as large surface area, tunable structure, accessible active sites, and enhanced conductivity, 2D MOFs have attracted intensive attention in the field of electrocatalysis. Different strategies, such as improving the conductivities of MOFs, reducing the thicknesses of MOF nanosheets, and integrating MOFs with conductive particles or substrates, are developed to promote the catalytic performances of pristine MOFs. This review summarizes the recent advances of pristine 2D MOF-based electrocatalysts for water electrolysis. In particular, their intrinsic electrocatalytic properties are detailly analyzed to reveal important roles of inherent MOF active centers, or other in situ generated active phases from MOFs responsible for the catalytic reactions. Finally, the challenges and development prospects of pristine 2D MOFs for the future applications in overall water splitting are discussed.

Interface Density Engineering on Heterogeneous Molybdenum Dichalcogenides Enabling Highly Efficient Hydrogen Evolution Catalysis and Sodium Ion Storage

Constructing active heterointerfaces is powerful to enhance the electrochemical performances of transition metal dichalcogenides, but the interface density regulation remains a huge challenge. Herein, MoO₂ /MoS₂ heterogeneous nanorods are encapsulated in nitrogen and sulfur co-doped carbon matrix (MoO₂ /MoS₂ @NSC) by controllable sulfidation. MoO₂ and MoS₂ are coupled intimately at atomic level, forming the MoO₂ /MoS₂ heterointerfaces with different distribution density. Strong electronic interactions are triggered at these MoO₂ /MoS₂ heterointerfaces for enhancing electron transfer. In alkaline media, the optimal material exhibits outstanding hydrogen evolution reaction (HER) performances that significantly surpass carbon-covered MoS₂ nanorods counterpart (η₁₀ : 156 mV vs 232 mV) and most of the MoS₂ -based heterostructures reported recently. First-principles calculation deciphers that MoO₂ /MoS₂ heterointerfaces greatly promote water dissociation and hydrogen atom adsorption via the O-Mo-S electronic bridges during HER process. Moreover, benefited from the high pseudocapacitance contribution, abundant "ion reservoir"-like channels, and low Na⁺ diffusion barrier appended by high-density MoO₂ /MoS₂ heterointerfaces, the material delivers high specific capacity of 888 mAh g^-1 , remarkable rate capability and cycling stability of 390 cycles at 0.1 A g^-1 as the anode of sodium ion battery. This work will undoubtedly light the way of interface density engineering for high-performance electrochemical energy conversion and storage systems.

Constructing abundant phase interfaces of the sulfides/metal-organic frameworks p-p heterojunction array for efficient overall water splitting and urea electrolysis

Designing efficient electrocatalysts to improve the overall water splitting and urea electrolysis efficiency for hydrogen generation can greatly solve the dilemma of energy shortage and environmental pollution. In this work, Co₈FeS₈@CoFe-MOF/NF heterojunction arrays were fabricated by embedding sulfides into the surface of metal-organic frameworks (MOFs) nanosheets as multifunctional electrocatalyst. The introduction of sulfide on CoFe-MOF/NF can not only adjust the electronic structure (electron-rich state) and change the surface properties (more hydrophilic), but also increase the active area to enhance the catalytic activity. The in situ Raman shows Co₈FeS₈@CoFe-MOF/NF is more easily to generate active species at low potentials and generates a higher content of active β-MOOH phase than CoFe-MOF/NF. Therefore, the Co₈FeS₈@CoFe-MOF/NF exhibits excellent oxygen evolution reaction (OER) performance with an overpotential of 213 mV at 10 mA cm^-2. Furthermore, when used as a urea oxidation reaction (UOR), only an ultralow potential of 1.311 V at 10 mA cm^-2. More importantly, the assembled two-electrode drives overall water splitting and urea electrolysis with cell voltages of 1.62 V and 1.55 V at 10 mA cm^-2, respectively. This work provides insights into the preparation of electrocatalysts with multifunctional heterostructure arrays for hydrogen production.

Plasma-assisted synthesis of hierarchical defect N-doped iron–cobalt sulfide@Co foam as an efficient bifunctional electrocatalyst for overall water splitting

N-doped CoFeS was synthesized via an ion exchange method to prepare a precursor, followed by sulphidation and plasma-assisted engraving in nitrogen gas.

Computational analysis of the enhancement of photoelectrolysis using transition metal dichalcogenide heterostructures

Finding a material with all the desired properties for a photocatalytic water splitter is a challenge yet to be overcome, requiring both a surface with ideal energetics for all steps in the hydrogen and oxygen evolution reactions (HER and OER) and a bulk band gap large enough to mediate said steps. We have instead examined separating these challenges by investigating the energetic properties of two-dimensional transition metal dichalcogenides (TMDCs) that could be used as a surface coating to a material with a large enough bulk band gap. First we investigated the energetics of monolayer MoS₂and PdSe₂using density functional theory and then investigated how these energetics changed when they were combined into a heterostructure. Our results show that the surface properties were practically (<0.2 eV) unchanged when combined and the MoS₂layer aligns well with the OER and HER. This work highlights the potential of TMDC monolayers as surface coatings for bulk materials that have sufficient band gaps for photocatalytic applications.

An integrated nanoflower-like MoS2@CuCo2O4 heterostructure for boosting electrochemical glucose sensing in beverage

Excessive glucose in food poses a non-negligible threat to its inherent quality and human health, which makes it imperative to develop a highly sensitive sensor for real-time glucose detection. In this work, an integrated electrochemical glucose sensor based on a nanoflower-like MoS₂@CuCo₂O₄ heterostructure was carefully constructed. Under optimal conditions, the as-fabricated sensor exhibited a high sensitivity of 1,303 μA mM^-1 cm^-2 over a wide range of 0.5-393.0 μmol/L, accompanied by a low determination limit (0.5 μmol/L) and short response time (2.1 s). The favorable sensing performance of the MoS₂@CuCo₂O₄ nanocomposite-modified electrode in electrochemical analyses was attributed to the introduction of unique nanoflower-like heterostructure and the synergistic effects between MoS₂ and CuCo₂O₄. Furthermore, the satisfactory applicability of this sensor in beverages was confirmed. These results demonstrate that the MoS₂@CuCo₂O₄/GCE may be a promising platform for sensitive monitoring of glucose content in food samples.

Two-Dimensional Metal-Organic Framework Nanosheets: Synthesis and Applications in Electrocatalysis and Photocatalysis

Two-dimensional metal-organic nanosheets (2D MONs) are an emerging class of ultrathin, porous, and crystalline materials. The organic/inorganic hybrid nature offers MONs distinct advantages over other inorganic nanosheets in terms of diversity of organic ligands and metal notes. Compared to bulk three-dimensional metal-organic frameworks, 2D MONs possess merits of high density and readily accessible catalytic sites, reduced diffusion pathways for reactants/products, and fast electron transport. These features endow MONs with enhanced physical/chemical properties and are ideal for heterogeneous catalysis. In this Review, state-of-the-art synthetic methods for the fabrication of 2D MONs were summarized. The advances of 2D MONs-based materials for electrocatalysis and photocatalysis, including hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), carbon dioxide reduction reaction (CO₂ RR), and electro-/photocatalytic organic transformations were systematically discussed. Finally, the challenges and perspectives regarding future design and synthesis of 2D MONs for high-performance electrocatalysis and photocatalysis were provided.

Ultra-stable two-dimensional metal-organic frameworks for photocatalytic H2 production

Two-dimensional (2D) metal-organic frameworks (MOFs) are some of the most promising photocatalysts owing to their high numbers of exposed active sites and excellent charge mobility. However, the synthesis of highly stable 2D MOF photocatalysts involves challenges, and examples have been rarely reported. Herein, a new kind of material, 2D indium-based porphyrin MOF cubic nanosheets (2D In-TCPP NS) with an average thickness of ∼3.97 nm, is synthesized via a surfactant-assisted approach, and it shows good chemical stability in the pH range of 2-11 in aqueous solution. In photocatalytic H₂-generation experiments, 2D In-TCPP NS exhibits activity that is enhanced by over one order of magnitude compared with the 3D bulk In-TCPP MOF, arising from its highly enhanced electron-hole separation abilities. Moreover, after 40 h of continuous photocatalysis testing, 2D In-TCPP NS shows nearly no activity decrease, which suggests its great potential for practical commercial use.

Surface engineering strategies for MoS2 towards electrochemical hydrogen evolution

Water splitting driven by renewable energy sources is an environmentally friendly and sustainable way to produce hydrogen as an ideal energy source in the future. Electrocatalysts can promote the water splitting performance at the both ends. Therefore, the development of cost-effective, high-performance electrocatalysis is a key factor in promoting water decomposition and renewable energy conversion. Among candidates, layered molybdenum disulfide (MoS 2 ) is considered as a most promising electrocatalyst to replace Pt for hydrogen evolution reaction (HER). Surface atomic engineering and interface engineering can induce new physicochemical properties for MoS 2 to greatly enhance HER activity. In this report, we summarize the latest improvement strategies and research progress to improve the catalytic activity of MoS 2 -based material catalysts through the surface and interface atomic and molecular engineering, thus effectively improving HER process. In addition, some unsolved problems in the large-scale application of modified MoS 2 catalyst are also discussed.

Multi-interface MoS2/Ni3S4/Mo2S3 composite as an efficient electrocatalyst for hydrogen evolution reaction over a wide pH range

The exploitation of cost-efficiently electrocatalysts for hydrogen evolution reaction (HER) over a wide pH range remains a challenge. Herein, we prepared a novel multi-interface MoS₂/Ni₃S₄/Mo₂S₃ composite on carbon cloth (CC) that acts as an efficient electrocatalyst over a wide pH range through a facile one-pot strategy, where (NH₄)₄[NiH₆Mo₆O₂₄]·5H₂O (abbreviated to NiMo₆) as a bimetallic precursor and Ni(NO₃)₂·6H₂O as one of the raw materials and salt are used together with thiourea (TU) for converting them into the MoS₂/Ni₃S₄/Mo₂S₃ load on CC (abbreviated as MoS₂/Ni₃S₄/Mo₂S₃/CC). MoS₂/Ni₃S₄/Mo₂S₃/CC-24 h shows a distinguished electrocatalytic performance towards HER with long-term stability in acid and alkaline media. It presents low overpotentials of 38 mV and 51 mV in 0.5 M H₂SO₄ and 1.0 M KOH at 10 mA cm^-2, respectively. This work can deliver a new idea to fabricate cost-efficient and long-term durability HER electrocatalysts over a broad pH range.

Recent advances in MoS2-based materials for electrocatalysis

The increasing energy demand and related environmental issues have drawn great attention of the world, thus necessitating the development of sustainable technologies to preserve the ecosystems for future generations. Electrocatalysts...

CO2-assisted synthesis of crystalline/amorphous NiFe-MOF heterostructure for high-efficiency electrocatalytic water oxidation

Modulating the crystalline phase and structure of metal organic frameworks (MOFs) for superior electrocatalytic oxygen evolution reaction (OER) performance is a significant but challenging topic. Herein, a facile CO2-assisted strategy...

Hierarchically Porous Metal-Organic Framework/MoS2 Interface for Selective Photocatalytic Conversion of CO2 with H2 O into CH3 COOH

Metal-organic frameworks (MOFs) provide a platform to design new heterogeneous catalysts for catalytic CO₂ reduction, but selective formation of C2 valuable liquid fuel products remains a challenge. Herein, we propose a strategy to synthesize composites by integrating MoS₂ nanosheets into hierarchically porous defective UiO-66 (d-UiO-66) to form Mo-O-Zr bimetallic sites on the interfaces between UiO-66 and MoS₂ . The active interfaces are favorable for the efficient transfer of photo-generated charge carriers and for promoting the activity, whereas, the synergy of the components at the interfaces achieves selectivity for C2 production. The d-UiO-66/MoS₂ composite facilitates the photo-catalytic conversion of gas phase CO₂ and H₂ O to CH₃ COOH under visible light irradiation without any other adducts. The evolution rate and selectivity of CH₃ COOH reached 39.0 μmol g^-1  h^-1 and 94 %, respectively, without any C1 products, suggesting a new approach for the design of highly efficient photocatalysts of CO₂ for C2 production. Theoretical calculations demonstrate the charge-polarized Zr-O-Mo aided the C-C coupling process with the largely reduced energy barrier.

Partial sulfur vacancies created by carbon-nitrogen deposition of MoS2 for high-performance overall electrocatalytic water splitting

Electrocatalytic water splitting is a promising energy-efficient solution to obtain clean hydrogen energy. Bifunctional electrocatalysts made up of cheap and abundant elements and suitable for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) are critically needed, yet their performance deserves substantial improvement. The catalytic activity could be improved by creating unsaturated defects, which so far has rarely been demonstrated. Here, we combine the effects of unsaturated sulfur vacancies and bi-elemental C and N doping in MoS₂ nanosheets to achieve high-performance bifunctional electrocatalysts. The new method to obtain C and N doped MoS₂ at high temperature is presented. The obtained C-N-MoS₂/CC-T catalysts with S unsaturated defect sites and Mo-N links exhibit high activity and improved electrical conductivity for both the HER and OER in alkaline media. Systematic experiments and density functional theory (DFT) analysis confirm that CN-doping exposes catalytically active sites and enhances water adsorption. The optimized C-N-MoS₂/CC-700 catalyst exhibits low overpotentials of 90 and 230 mV at 10 mA cm^-2 for the HER and OER, respectively. Importantly, the porous C-N-MoS₂/CC-700 nanosheets deliver low voltages of 1.58 V for the overall water splitting at 10 mA cm^-2 and robust operation for 30 h without any reduced activity. Such impressive performances are attributed to their unique structure with large specific surface area, abundant S unsaturated sites, Mo-N links, and shortened electron transfer paths. This partial defect filling by the bi-dopant incorporation approach is generic and is promising for a broad range of advanced energy materials.

Recent Advances on Transition Metal Dichalcogenides for Electrochemical Energy Conversion

Transition metal dichalcogenides (TMDCs) hold great promise for electrochemical energy conversion technologies in view of their unique structural features associated with the layered structure and ultrathin thickness. Because the inert basal plane accounts for the majority of a TMDC's bulk, activation of the basal plane sites is necessary to fully exploit the intrinsic potential of TMDCs. Here, recent advances on TMDCs-based hybrids/composites with greatly enhanced electrochemical activity are reviewed. After a summary of the synthesis of TMDCs with different sizes and morphologies, comprehensive in-plane activation strategies are described in detail, mainly including in-plane-modification-induced phase transformation, surface-layer modulation, and interlayer modification/coupling. Simultaneously, the underlying mechanisms for improved electrochemical activities are highlighted. Finally, the strategic evaluation on further research directions of TMDCs in-plane activation is featured. This work would shed some light on future design trends of TMDCs-based functional materials for electrochemical energy-related applications.

Electron Density Modulation of MoO2/Ni to Produce Superior Hydrogen Evolution and Oxidation Activities

Hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) have aroused great interest, but the high price of platinum group metals (PGMs) limits their development. The electronic reconstruction at the interface of a heterostructure is a promising strategy to enhance their catalytic performance. Here, MoO₂/Ni heterostructure was synthesized to provide effective HER in an alkaline electrolyte and exhibit excellent HOR performance. Theoretical and experimental analyses prove that the electron density around the Ni atom is reduced. The electron density modulation optimizes the hydrogen adsorption and hydroxide adsorption free energy, which can effectively improve the activity of both HER and HOR. Accordingly, the prepared MoO₂/Ni@NF catalyst reveals robust HER activity (η₁₀ = 50.48 mV) and HOR activity (j₀ = ∼1.21 mA cm^-2). This work demonstrates an effective method to design heterostructure interfaces and tailor the surface electronic structure to improve HER/HOR performance.

Surface-Adsorbed Carboxylate Ligands on Layered Double Hydroxides/Metal-Organic Frameworks Promote the Electrocatalytic Oxygen Evolution Reaction

Metal-organic frameworks (MOFs) with carboxylate ligands as co-catalysts are very efficient for the oxygen evolution reaction (OER). However, the role of local adsorbed carboxylate ligands around the in-situ-transformed metal (oxy)hydroxides during OER is often overlooked. We reveal the extraordinary role and mechanism of surface-adsorbed carboxylate ligands on bi/trimetallic layered double hydroxides (LDHs)/MOFs for OER electrocatalytic activity enhancement. The results of X-ray photoelectron spectroscopy (XPS), synchrotron X-ray absorption spectroscopy, and density functional theory (DFT) calculations show that the carboxylic groups around metal (oxy)hydroxides can efficiently induce interfacial electron redistribution, facilitate an abundant high-valence state of nickel species with a partially distorted octahedral structure, and optimize the d-band center together with the beneficial Gibbs free energy of the intermediate. Furthermore, the results of in situ Raman and FTIR spectra reveal that the surface-adsorbed carboxylate ligands as Lewis base can promote sluggish OER kinetics by accelerating proton transfer and facilitating adsorption, activation, and dissociation of hydroxyl ions (OH^- ).

Roadmap and Direction toward High-Performance MoS2 Hydrogen Evolution Catalysts

MoS₂ intrinsically show Pt-like hydrogen evolution reaction (HER) performance. Pristine MoS₂ displayed low HER activity, which was caused by low quantities of catalytic sites and unsatisfactory conductivity. Then, phase engineering and S vacancy were developed as effective strategies to elevate the intrinsic HER performance. Heterojunctions and dopants were successful strategies to improve HER performance significantly. A couple of state-of-the-art MoS₂ catalysts showed HER performance comparable to Pt. Applying multiple strategies in the same electrocatalyst was the key to furnish Pt-like HER performance. In this review, we summarize the available strategies to fabricate superior MoS₂ HER catalysts and tag the important works. We analyze the well-defined strategies for fabricating a superior MoS₂ electrocatalyst, propose complementary strategies which could help meet practical requirements, and help people design highly efficient MoS₂ electrocatalysts. We also provide a brief perspective on assembling practical electrochemical systems by high-performance MoS₂ electrocatalysts, apply MoS₂ in other important electrocatalysis reactions, and develop high-performance two-dimensional (2D) dichalcogenide HER catalysts not limited to MoS₂. This review will help researchers to obtain a better understanding of development of superior MoS₂ HER electrocatalysts, providing directions for next-generation catalyst development.

Facile fabrication of (2D/2D) MoS2@MIL-88(Fe) interface-driven catalyst for efficient degradation of organic pollutants under visible light irradiation

The present investigation describes the photocatalytic degradation of methylene blue (MB) and rhodamine-B (RhB) using molybdenum disulfide (MoS₂) anchored metal-organic frameworks (MOFs) under visible light irradiation. Herein, MIL-88(Fe) was successfully modified with MoS₂ to yield a novel heterogeneous MoS₂@MIL-88(Fe) hybrid composite. The prepared catalyst enhances the superior photocatalytic activity than the pristine form of MoS₂ and MIL-88(Fe) framework. The physico-chemical properties of the prepared catalyst were analytically investigated and the results exhibit greater photocatalytic efficiency towards the chosen dyes, with an optical band gap of 2.75 eV. The MoS₂ and MIL-88(Fe) framework could act as efficient oxidation and reduction sites in the as-synthesized MoS₂@MIL-88(Fe) composite, and generated the non-toxic by-products such as hydroxyl ^(•OH), and superoxide species ^(•O₂^-) for the mineralization of MB and RhB dyes. The degradation kinetics showed that the dye system followed a pseudo-first-order model which is well supported by the Langmuir-Hinshelwood mechanism. Moreover, the reusability studies showed excellent photocatalytic activity after five cycles. Finally, the photocatalytic degradation mechanism of MB and RhB dyes was suggested.