Design of Dual-Modified MoS2 with Nanoporous Ni and Graphene as Efficient Catalysts for the Hydrogen Evolution Reaction

High-performance heterometallic photocatalysts afforded by polyoxometalate synthons for efficient H2 production

MoS2-based materials have emerged as photoelectric semiconductors characterized by a narrow band gap, high capacity for absorbing visible light, and reduced H2 adsorption energy comparable to Pt. These attributes render them appealing for application in photocatalytic hydrogen production. Despite these advantages, the widespread adoption of MoS2-based materials remains hindered by challenges associated with limited exposure to active sites and suboptimal catalytic hydrogen production efficiency. To address these issues, we have designed and synthesized a new class of highly dispersed bimetallic/trimetallic sulfide materials. This was achieved by developing polyoxometalate synthons containing Ni-Mo elements, which were subsequently reacted with thiourea and CdS. The resulting Ni3S2-MoS2 and Ni3S2-MoS2-CdS materials achieve photocatalytic hydrogen production rates of 2770 and 2873 μmol g-1h-1, respectively. Notably, the rate of 2873 μmol g-1h-1 for Ni3S2-MoS2-CdS surpassed triple (3.23 times) the performance of CdS and nearly sextuple (5.77 times) that of single MoS2. These materials outperformed the majority of MoS2-based photocatalysts. Overall, this study introduces a straightforward methodology for synthesizing bimetallic/trimetallic sulfides with enhanced photocatalytic H2 evolution performance. Our findings underscore the potential of transition metal sulfide semiconductors in the realm of photocatalysis and pave the way for the development of more sustainable energy production systems.

Synergistic Effects of Carbon Vacancies in Conjunction with Phosphorus Dopant across Bilayer Graphene for the Enhanced Hydrogen Evolution Reaction

Bilayer graphene (BLG) exhibits distinct physical properties under external influences, such as torsion and structural defects, setting it apart from monolayer graphene. In this study, we explore the synergistic effects of carbon vacancies, in conjunction with phosphorus dopants, across BLG, focusing on their impact on structural, magnetic, electrical, and hydrogen adsorption properties. Our findings reveal that the substitutional doping of a phosphorus atom into a single carbon vacancy in a graphene layer induces substantial structural distortion in BLG. In contrast, doping phosphorus into a double vacancy maintains the flat structure of graphene layers. These distinct layer structures affect the electron distribution and spin arrangement, leading to varied electronic configurations and intriguing magnetic behaviors. Furthermore, the presence of abundant unsaturated electrons around the vacancy promotes the capture and bonding of hydrogen atoms. Hydrogen adsorption on BLG results in substantial orbital hybridization, accompanied by significant charge transfer. The calculated Gibbs free energies for hydrogen adsorption on BLG range from -0.08 to 0.09 eV, indicating exceptional catalytic activity for the hydrogen evolution reaction. These findings carry implications for optimizing the properties of graphene layers, making them highly desirable for applications such as catalysis.

Synthesize magnetic ZnFe2O4@C/Cd0.9Zn0.1S catalysts with S-scheme heterojunction to achieve extraordinary hydrogen production efficiency

Suppressing the electron-hole recombination rate of catalyst legitimately is one of the effective strategies to improve photocatalytic hydrogen evolution. Herein, carbon-coated metal oxide, ZnFe2O4@C (ZFO@C), nanoparticles were synthesized and employed to couple with quadrupedal Cd0.9Zn0.1S (CZS) via an ordinary ultrasonic self-assembly method combined with calcination to form a novel ZFO@C/CZS catalyst with step-scheme (S-scheme) heterojunction. The photocatalytic hydrogen evolution reaction (HER) was conducted to verify the enhanced photoactivity of ZFO@C/CZS. The optimal ZFO@C/CZS exhibits an extraordinary photocatalytic HER rate of 111.3 ± 0.9 mmol g-1 h-1 under visible-light irradiation, corresponding to an apparent quantum efficiency as high as (76.2 ± 0.9)% at 450 nm. Additionally, the as-synthesized ZFO@C/CZS composite exhibits high stability and recyclability. The excellent photocatalytic hydrogen evolution performance should arise from the formed S-scheme heterojunction and the unique ZFO@C core-shell structure, which inhibit electron hole recombination as well as provide more reactive sites. The pathway of S-scheme charge transfer was validated through density functional theory calculations and electrochemical measurements. This work provides a rational strategy for the synthesis of unique magnetic S-scheme heterojunction photocatalysts for water splitting under visible light irradiation.

Hierarchical SiC-Graphene Composite Aerogel-Supported Ni-Mo-S Nanosheets for Efficient pH-Universal Electrocatalytic Hydrogen Evolution

MoS₂ exhibits good prospects in electrocatalytic hydrogen evolution. Whereas, the electrocatalytic property of MoS₂ is restrained by its insufficient active sites, low electrical conductivity, and slow water dissociation processes. Herein, an aerogel composed of silicon carbide (SiC) and graphene (SiCnw-RGO) was constructed by growing SiC nanowires (SiCnw) in the graphene aerogel (RGO) via the CVD method, and then Ni-Mo-S nanosheets were hydrothermally synthesized on the SiCnw-RGO composite aerogel to develop an efficient pH-universal electrocatalyst. Ni-Mo-S nanosheets supported on SiCnw-RGO (Ni-Mo-S@SiCnw-RGO) exhibit an interesting hierarchical three-dimensional interconnected structure of composite aerogel. The optimal Ni-Mo-S@SiCnw-RGO electrocatalyst exhibits excellent catalytic performance with low Tafel slopes of 60 mV/dec under acidic conditions and 90 mV/dec under alkaline conditions. Density functional theory calculations demonstrate a composite catalyst exhibits advantageous hydrogen adsorption free energy and water dissociation energy barrier. This study provides a reference to design an efficient hierarchical aerogel electrocatalyst.

Engineering active heterojunction architecture with oxygenated-Co, Mo bimetallic sulfide heteronanosheet and graphene oxide for peroxymonosulfate activation

Bimetallic sulfides have distinctive catalytic property in activating peroxymonosulfate (PMS) for water remediation. Polyoxometalates as potential precursors have rarely been reported for the catalytic degradation of refractory organic pollutants. Herein, a composite catalyst of Co-Mo bimetallic sulfides supported onto graphene oxide (O-CoMoS/GO) with a heterojunction architecture was synthesized through a hydrothermal strategy with polyoxometalates ((NH₄)₄[Co^IIMo₆O₂₄H₆]·6H₂O) as the precursor and applied in the PMS activation. This material showed a superior performance for the catalytic degradation of the model organic pollutant, 4-chlorophenol (rapidly removed within 10 min with an apparent reaction rate constant of 0.5458 min^-1). O-CoMoS/GO outperformed most of the reported catalysts in terms of activity and had a strong tolerance towards common organic and inorganic compounds in water, and could perform well in different real water systems. Experimental and theoretical results indicated that the introduction of GO could achieve the enrichment of electrons on the metals and reduce the d band center (ε_d) of Co close to the Fermi level (ε_F), thereby facilitating the interfacial electron transfer process. The activation mechanism was due to the as-prepared bimetallic sulfides and the formation of heterojunction structure with GO, where Co(II) as the active center could be regenerated by the adjacent Mo element (as co-catalyst) and by gathering electrons from GO through the Co/Mo-O-C coupling. This work provides insights into the design of bimetallic sulfide catalysts in activating PMS for water remediation.

Morphology-Controlled Synthesis of V1.11S2 for Electrocatalytic Hydrogen Evolution Reaction in Acid Media

High-performance low-cost catalysts are in high demand for the hydrogen evolution reaction (HER). In the present study, we reported that V_1.11S₂ materials with flower-like, flake-like, and porous morphologies were successfully synthesized by hydrothermal synthesis and subsequent calcination. The effects of morphology on hydrogen evolution performance were studied. Results show that flower-like V_1.11S₂ exhibits the best electrocatalytic activity for HER, achieving both high activity and preferable stability in 0.5 M H₂SO₄ solution. The main reason can be ascribed to the abundance of catalytically active sites and low charge transfer resistance.

Facile synthesis of novel molybdenum disulfide decorated banana peel porous carbon electrode for hydrogen evolution reaction

Hydrogen is one of the cleanest renewable and environmentally friendly energy resource that can be generated through water splitting. However, hydrogen evolution occurs at high overpotential, and efficient hydrogen evolution catalysts are desired to replace state-of-the-art catalysts such as platinum. In the present work, a novel molybdenum disulfide decorated banana peel porous carbon (MoS₂@BPPC) catalyst has been developed using banana peel carbon and molybdenum disulfide (MoS₂) for hydrogen evolution reaction (HER). Banana peel porous carbon (BPPC) was initially synthesized from the banana peel (biowaste) by a simple carbonization method. Subsequently, 20 wt% of bare MoS₂ was distributed on the pristine BPPC matrix using the dry-impregnation method. The resulting MoS₂@BPPC composites were systematically investigated to determine the morphology and structure. Finally, using a three-electrode cell system, pristine BPPC, bare MoS₂, and MoS₂@BPPC composite were used as HER electrocatalysts. The developed MoS₂@BPPC composite showed greater HER activity and possessed excellent stability in the acid solution, including an overpotential of 150 mV at a current density of -10 mA cm^-2, and a Tafel slope of 51 mV dec^-1. This Tafel study suggests that the HER takes place by Volmer-Heyrovsky mechanism with a rate-determining Heyrovsky step. The excellent electrochemical performance of MoS₂@BPPC composite for HER can be ascribed to its unique porous nanoarchitecture. Further, due to the synergetic effect between MoS₂ and porous carbon. The HER activity using the MoS₂@BPPC electrode advises that the prepared catalyst may hold great promise for practical applications.

Recent Progress in Phase Regulation, Functionalization, and Biosensing Applications of Polyphase MoS2

The disulfide compounds of molybdenum (MoS₂ ) are layered van der Waals materials that exhibit a rich array of polymorphic structures. MoS₂ can be roughly divided into semiconductive phase and metallic phase according to the difference in electron filling state of the 4d orbital of Mo atom. The two phases show completely different properties, leading to their diverse applications in biosensors. But to some extent, they compensate for each other. This review first introduces the relationship between phase state and the chemical/physical structures and properties of MoS₂ . Furthermore, the synthetic methods are summarized and the preparation strategies for metastable phases are highlighted. In addition, examples of electronic and chemical property designs of MoS₂ by means of doping and surface modification are outlined. Finally, studies on biosensors based on MoS₂ in recent years are presented and classified, and the roles of MoS₂ with different phases are highlighted. This review offers references for the selection of materials to construct different types of biosensors based on MoS₂ , and provides inspiration for sensing performance enhancement.

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.

Construction of reduced graphene oxide coupled with CoSe2-MoSe2 heterostructure for enhanced electrocatalytic hydrogen production

It is important to develop novel energy to solve energy shortage and environmental problems. Hydrogen evolution reaction (HER) is envisaged as a viable technology that can be used to develop sustainable clean energy. Herein, we report a catalyst with CoSe₂-MoSe₂ heterostructure grown on reduced graphene oxide with an optimum Co/Mo proportion of 1:1 (CoSe₂-MoSe₂(1-1)/rGO). It exhibits good HER activities in both acidic and alkaline conditions. The CoSe₂-MoSe₂(1-1)/rGO shows an overpotential of 107 mV at 10 mA cm^-2 with a Tafel slope of 56 mV dec^-1 under acidic condition. Meanwhile, CoSe₂-MoSe₂(1-1)/rGO also presents an overpotential of 182 mV at 10 mA cm^-2 and with a Tafel slope of 89 mV dec^-1 under alkaline condition. These impressive performances of the catalyst are mainly due to the excellent electronic transmission capability of rGO and the abundant active sites of CoSe₂-MoSe₂ heterostructure as well as the optimized hydrogen adsorption energy of CoSe₂-MoSe₂ interface. The design of CoSe₂-MoSe₂(1-1)/rGO provides a meaningful guide for manufacturing electrode in energy storage and conversion.

Metallic phase WSe2 nanoscrolls for the hydrogen evolution reaction

Nanostructured metastable metallic phase transition-metal dichalcogenides (TMDs) have attracted tremendous attention due to their promising practical applications in the hydrogen evolution reaction (HER).

Ultralow Ru-incorporated MoS2 nanosheet arrays for efficient electrocatalytic hydrogen evolution in dual-pH

Ru-MoS2/CC nanosheet arrays were prepared for efficient electrocatalytic hydrogen evolution reaction at dual-pH.

Enhanced hydrogen evolution reaction in alkaline solution by constructing strong metal-support interaction on Pd-CeO2-x-NC hybrids

Diminishing the size of metal nanostructures can significantly improve the performance of catalysts. However, the self-aggregation of small particles is still an insurmountable obstacle, resulting in the unfavorable stability and recyclability. Herein, we designed and fabricated the Pd-CeO_2-x-NC catalyst though an accurate deposition strategy to downsize the Pd particle to sub-nanometer level and enhance its running stability. The CeO_2-x nanoclusters were firstly dispersed on the nitrogen-doped carbon nanosheets. Further, the active Pd sub-nanoclusters were accurately scattered on the surface of CeO_2-x ascribing to the strong metal-support interaction (SMSI) between Pd and CeO_2-x, which was beneficial to promote the catalytic activity. Subsequently, the high oxidation state Pdⁿ⁺ species were formed due to the electron transfer from Pd to CeO_2-x caused by the SMSI effect. Strikingly, the HER performance of Pd-CeO_2-x-NC was surprisingly correlated with the ratio of Pdⁿ⁺, suggesting Pdⁿ⁺ acted as the dominant active species. Besides, the SMSI effect stabilized the valence state of active Pdⁿ⁺ species and prevented the sub-nanometer Pd clusters from aggregation, which played a vital role for the enhanced stability of the hybrid catalyst. This synthetic process described here is contributed to prepare various nanostructured catalysts with satisfactory stability through the direct targeting strategy.

Theoretical insights into TM@PHEs as single-atom catalysts for water splitting based on density functional theory

Single-atom catalysis is the new frontier of heterogeneous catalysis and has attracted considerable attention as it exhibits great potential in hydrogen evolution to mitigate energy crisis and environmental issues. The support materials for single-atom catalysts (SACs) play a significant role in stabilizing the metal atoms, preventing their aggregation, and enhancing the catalytic activity. Two-dimensional sp² hybridized PHE-graphene might be a real support for SACs due to the potential energy well induced by its enneagon, hexagon and pentagon carbon rings. In this study, eleven transition metal (TM) atoms adsorbed on PHE-graphene (TM@PHEs) are taken into account based on density functional theory (DFT) and PHE-graphene is proved to be an ideal single-atom carrier for water splitting. In particular, the TM@PHEs (TM = Fe, Ni, Ru, and Pd) exhibit high catalytic activity toward the hydrogen evolution reaction (HER). The reaction path of water splitting is also determined. Due to their much lower energy barrier, both Fe@PHE and Ru@PHE are more promising SACs. In addition, the charge density difference, Bader charge analysis and spin projected density of states (PDOS) are investigated.

Interface Engineering of CoP3/Ni2P for Boosting the Wide pH Range Water-Splitting Activity

Developing electrocatalysts with low price, high energy efficiency, and universal pH value for hydrogen/oxygen evolution reaction (HER and OER) is very important for the wide application of electrochemical water splitting in hydrogen production. The results of density functional theory show that the interface region of CoP3/Ni2P heterostructures can significantly boost all of the catalytic performances. High-resolution transmission electron microscopy and X-ray photoelectron spectroscopy were used to confirm the abundant structural defects and the corresponding adjustment of the electronic state, thus ameliorating the activation energy, conductivity, and active area of the catalyst. Benefiting from these, CoP3/Ni2P heterostructures exhibit superior performance of both HER and OER in a wide pH range. CoP3/Ni2P can also be used for water splitting (1.557 V at 10 mA cm-2) more than 40 h, superior to benchmark pairs of Pt/C and RuO2 on Ni foam.

Electrocatalytic hydrogen evolution on the noble metal-free MoS2/carbon nanotube heterostructure: a theoretical study

Molybdenum disulfide (MoS₂) is considered as a promising noble-metal-free electrocatalyst for the Hydrogen Evolution Reaction (HER). However, to effectively employ such material in the HER process, the corresponding electrocatalytic activity should be comparable or even higher than that of Pt-based materials. Thus, efforts in structural design of MoS₂ electrocatalyst should be taken to enhance the respective physico-chemical properties, particularly, the electronic properties. Indeed, no report has yet appeared about the possibility of an HER electrocatalytic association between the MoS₂ and carbon nanotubes (CNT). Hence, this paper investigates the synergistic electrocatalytic activity of MoS₂/ CNT heterostructure for HER by Density Functional Theory simulations. The characteristics of the heterostructure, including density of states, binding energies, charge transfer, bandgap structure and minimum-energy path for the HER process were discussed. It was found that regardless of its configuration, CNT is bound to MoS₂ with an atomic interlayer gap of 3.37 Å and binding energy of 0.467 eV per carbon atom, suggesting a weak interaction between CNT and MoS₂. In addition, the energy barrier of HER process was calculated lower in MoS₂/CNT, 0.024 eV, than in the MoS₂ monolayer, 0.067 eV. Thus, the study elaborately predicts that the proposed heterostructure improves the intrinsic electrocatalytic activity of MoS₂.

Anchoring Metallic MoS2 Quantum Dots over MWCNTs for Highly Sensitive Detection of Postharvest Fungicide in Traditional Chinese Medicines

Carbendazim, a very common contamination to the traditional Chinese medicines (TCMs), has posed serious threat to the environment and human health. However, sensitive and selective detection of carbendazim (MBC) in the TCMs is a big challenge for their complex chemical constituents. In this work, a 0D/1D nanohybrid was developed by anchoring 1T-phased MoS₂ quantum dots (QDs) over multiwall carbon nanotubes (MWCNTs) via a facile assembly method. High-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis (TGA) together with EIS reveal that the 1T-phased QDs can anchor over MWCNTs via van der Waals forces, and the anchoring improves the nanohybrid surface area and conductivity. Therefore, the electrochemical sensor fabricated based on the MoS₂ QDs@MWCNT nanohybrid shows excellent catalytic activity to MBC oxidation. Under optimized conditions, the sensor presents a linear voltammetry response to MBC concentration from 0.04 to 1.00 μmol·L^-1, a low detection limit of 2.6 × 10^-8 mol·L^-1, as well as high selectivity, good reproducibility, and long-term stability. Moreover, the sensor has been successfully employed to determine MBC in two typical TCMs and the obtained recoveries are in good accordance with the results achieved by HPLC, showing that the constructed sensor plate holds great practical application in MBC analysis with complex matrix.

Ultrathin 2D flower-like CoP@C with the active (211) facet for efficient electrocatalytic water splitting

Due to the more exposed (211) facet, the electrocatalytic water splitting activity of 2D CoP@C is superior to that of its counterpart 3D structure.

Hydrogen evolution of a MoS2/AOCF electrocatalyst doped with Ni element

The introduced polymers ability can replace the traditional Nafion adhesive, uniformly disperse particles and increase active sites.

1T/2H Mixed Phase MoS2 Nanosheets Integrated by a 3D Nitrogen-Doped Graphene Derivative for Enhanced Electrocatalytic Hydrogen Evolution

Molybdenum disulfide (MoS₂) has become one of the most promising non-platinum-based electrocatalysts for the hydrogen evolution reaction (HER) because of its unique layered structure. However, the catalytic performance of the thermodynamically stable MoS₂ is hindered by its poor conductivity and scarce active sites. We developed a 3D porous N-doped graphene derivative-integrated metal-semiconductor (1T-2H) mixed phase MoS₂ (MNG) using urea as a doping reagent. The highly exposed active sites were achieved by inducing the phase transition of MoS₂ from 2H phase to 1T phase and the inclusion of highly N-incorporated reduced graphene oxide, both of which were simultaneously realized by optimizing the concentration of the doping reagent. Moreover, the charge/proton transfer was enhanced by the well-designed porous architecture and hydrophilic 1T-MoS₂. With these advantages, the optimized MNG-40 catalyst has a small overpotential of 157 mV at a cathodic current density of 10 mA cm^-2, a relatively low Tafel slope of 45.8 mV dec^-1, and an excellent stability. This work represents a new strategy to design higher-performance HER catalysts and provides new insights into the structural regulation of metal composite transitions.

Modulation of electronic structures in two-dimensional electrocatalysts for the hydrogen evolution reaction

The electrocatalytic hydrogen evolution reaction (HER) has attracted substantial attention owing to its important role in realizing economic and sustainable hydrogen production via water electrolysis. Designing two-dimensional (2D) materials with large surface area, highly exposed surface sites and facile charge transport pathways is highly attractive for promoting the HER activity of the earth-abundant catalysts, and conducting rational modulations in the electronic structures is considered to be promising in further optimizing the intrinsic HER activity and thus realizing promoted HER performance. In this Feature Article, we systematically summarize recent progress in the modulation of the electronic structures of 2D HER electrocatalysts via multiple strategies including elemental doping, formation of alloyed structures, defect engineering, facet engineering, phase regulation, interface engineering and hybridization of the nanocatalysts with 2D substrates, and discuss the role of electronic structures in optimizing the intrinsic HER activity of 2D HER catalysts. We anticipate that this Feature Article will offer helpful guidance for oriented design and optimization of efficient electrocatalysts for scalable and economic hydrogen production.

Toward enhanced photocatalytic activity of graphite carbon nitride through rational design of noble metal-free dual cocatalysts

The g-C3N4-MoS2-M(OH)x ternary heterostructures were designed and fabricated for the first time. The embedding of noble-metal-free MoS2-M(OH)x dual cocatalysts over g-C3N4 nanosheets led to obvious synergistic effect for improving the transport as well as utilization efficiency of photo-generated charge carriers. Consequently, the optimal ternary heterostructure (g-C3N4-MoS2-Ni(OH)2) exhibited photocatalytic hydrogen production activity 4.5 times larger than the sum of the photocatalytic HER activity of g-C3N4-MoS2 and g-C3N4-Ni(OH)2. More significantly, even in the absence of the sacrificial agent, the g-C3N4-MoS2-Ni(OH)2 ternary heterostructure exhibited a photocatalytic HER activity of 0.3 mmol h-1 g-1 with considerable H2O2 production under UV-visible light.

Emerging One-/Two-Dimensional Heteronanostructure Integrating SiC Nanowires with MoS2 Nanosheets for Efficient Electrocatalytic Hydrogen Evolution

MoS₂ has emerged as a good application prospect in the electrocatalytic hydrogen evolution reaction (HER). Nevertheless, the catalytic activity of MoS₂ is greatly restricted by its inferior electrical conductivity, inadequate exposure of active edge sites, and sluggish water dissociation dynamics. Herein, a 1D/2D heteronanostructure composed of SiC nanowires wrapped with MoS₂ nanosheets was prepared via the hydrothermal synthesis of MoS₂ on highly connected SiC nanowires (SiCnw). The nanocomposites exhibit an emerging tectorum-like morphology with interface connections of C-Mo bonds, which benefit the efficient interfacial transmission of electrons. Due to the synergetic catalytic effects of MoS₂ nanosheets and SiC nanowires, the MoS₂/SiCnw nanocomposites possess efficient catalytic performance with a low Tafel slope (55 mV/dec). SiC nanocrystals could reduce the activated water dissociation energy barrier, and the morphologies of connected nanowires could improve the active site exposure and charge transport. The nanocomposites possess favorable hydrogen adsorption free energy from density functional theory (DFT) calculations. The electrocatalytic performance of MoS₂/SiCnw nanocomposites could be further improved by assembling the nanocomposites on a carbon fiber paper to enhance the electronic transmission efficiency.

Engineering interfacial structures to accelerate hydrogen evolution efficiency of MoS2 over a wide pH range

Developing low-cost electrocatalysts with outstanding electrochemical performance for water splitting over a wide pH range is urgently desired to meet the practical needs in different areas. Herein, a highly efficient hierarchical flower-like CoS₂@MoS₂ core-shell nanostructured electrocatalyst is fabricated by a two-step strategy, in which MoS₂ nanosheets with a layered structure are grown on the CoS₂ core supported on carbon paper (CP) and used as hydrogen evolution reaction (HER) electrocatalysts working in the whole pH range (0-14). Remarkably, benefiting from the interface-engineering in this 3D core-shell structure of the electrocatalyst, the optimum CoS₂@MoS₂/CP catalyst exhibits outstanding HER activity over a wide range of pH values and an overpotential of 69 mV in acidic solution, 145 mV in neutral solution and 82 mV in alkaline solution, respectively, to afford the standard current density of 10 mA cm^-2. Furthermore, it demonstrates superior stability under different pH conditions for at least 48 h. Density functional theory (DFT) calculations are performed to gain further insight into the effect of CoS₂@MoS₂ interfaces, revealing that the strong interfacial interaction between CoS₂ and MoS₂ dramatically reduces the Gibbs free energy of hydrogen adsorption and the energy barrier for water dissociation, thus enhancing the electrochemical HER activity in the whole pH range (0-14).

Theoretical investigation on the hydrogen evolution reaction mechanism at MoS2 heterostructures: the essential role of the 1T/2H phase interface

DFT calculations have been performed to study the HER mechanism at 1T/2H MoS₂ heterostructures. The HER activity along the 1T/2H phase interface is comparable with those at the Mo-edge of 2H MoS₂ and the basal plane of 1T MoS₂.

Cobalt-doped MoS2 enhances the evolution of hydrogen by piezo-electric catalysis under the 850 nm near-infrared light irradiation

Hydrogen is a clean shuttle of energy storage that can naturally reserve solar and wind energy, and it can be released.

Achieving high hydrogen evolution reaction activity of a Mo2C monolayer

Two-dimensional Mo2C materials (1T and 2H phases) have emerged as promising electrocatalysts for the hydrogen evolution reaction (HER) due to their low cost, inherent metallicity, and high stability. Unfortunately, the catalytic activity of Mo2C is lower than that of Pt, and it needs to be substantially improved for practical applications. It is necessary and urgent to consider the effect of synergetic interactions among defects, functions, and strain on the HER activity. In this study, the geometric structures, electronic properties, and the HER activity of the Mo2C monolayer, with vacancy defects (i.e. Mo and C), oxygen functionalization, and strain, are studied by using first-principles calculations. According to our results, the combination of Mo vacancies, which can be obtained under C-rich conditions, and oxygen functionalization is the most effective way to improve the HER activity of 1T- and 2H-Mo2C. Considering the abundant active sites and optimal Gibbs free energy of hydrogen adsorption, the 1T phase we obtained shows excellent HER activity even at high H coverage and improves the utilization of active sites, for which the HER activity is comparable to that of Pt. This can be attributed to the fact that oxygen atoms gain more electrons from Mo2C, which weakens the strength of the O-H bond. Our work provides not only an opportunity to better understand the catalytic mechanism, but also a guide to achieving high HER activity of a Mo2C monolayer.

Rational Design of Multisite Trielement Ru-Ni-Fe Alloy Nanocatalysts with Efficient and Durable Catalytic Hydrogenation Performances

The co-decomposition of non-noble metals into Ru nanoparticles (NPs) would provide multiple active centers as well as synergistically alter the reaction pathway, enhancing the catalytic hydrogenation performance. Herein, a facile route for synthesizing trielement Ru-Ni-Fe alloy NPs was proposed. The catalytic hydrogenation performance of NPs was measured using p-nitrophenol as a model. The synergistic effect of these three elements (Ru, Ni, and Fe) and synergistic catalysis of multiple crystal faces greatly improved the catalytic hydrogenation performance of Ru₄₄Ni₂₈Fe₂₈ alloy NPs. Ru with more vacant orbitals showed a strong coordination with BH₄^- for the generation of active H species. Ni played a major role in transporting electrons and active H species, increasing the accessibility of catalytically active sites. Fe could cooperate with BH₄^- to produce active H species and promote electrons transfer. Ru₄₄Ni₂₈Fe₂₈ alloy NPs could be reused and applied for the fabrication of films at the oil-water (ethyl acetate-water) interface. The densely packed Ru₄₄Ni₂₈Fe₂₈ NP films were good Raman substrates for monitoring the complete conversion of 4-nitrothiophenol into 4-aminothiophenol. The rational design of Ru₄₄Ni₂₈Fe₂₈ will broaden the application range of Ru-based catalysts and provide new insights into the rational design of other multisite alloy catalysts.

Graphene Nanoarchitectonics: Recent Advances in Graphene-Based Electrocatalysts for Hydrogen Evolution Reaction

Under the double pressures of both the energy crisis and environmental pollution, the exploitation and utilization of hydrogen, a clean and renewable power resource, has become an important trend in the development of sustainable energy-production and energy-consumption systems. In this regard, the electrocatalytic hydrogen evolution reaction (HER) provides an efficient and clean pathway for the mass production of hydrogen fuel and has motivated the design and construction of highly active HER electrocatalysts of an acceptable cost. In particular, graphene-based electrocatalysts commonly exhibit an enhanced HER performance owing to their distinctive structural merits, including a large surface area, high electrical conductivity, and good chemical stability. Considering the rapidly growing research enthusiasm for this topic over the last several years, herein, a panoramic review of recent advances in graphene-based electrocatalysts is presented, covering various advanced synthetic strategies, microstructural characterizations, and the applications of such materials in HER electrocatalysis. Lastly, future perspectives on the challenges and opportunities awaiting this emerging field are proposed and discussed.

Stimulated Electrocatalytic Hydrogen Evolution Activity of MOF-Derived MoS2 Basal Domains via Charge Injection through Surface Functionalization and Heteroatom Doping

The design of MoS2-based electrocatalysts with exceptional reactivity and robustness remains a challenge due to thermodynamic instability of active phases and catalytic passiveness of basal planes. This study details a viable in situ reconstruction of zinc-nitrogen coordinated cobalt-molybdenum disulfide from structure directing metal-organic framework (MOF) to constitute specific heteroatomic coordination and surface ligand functionalization. Comprehensive experimental spectroscopic studies and first-principle calculations reveal that the rationally designed electron-rich centers warrant efficient charge injection to the inert MoS2 basal planes and augment the electronic structure of the inactive sites. The zinc-nitrogen coordinated cobalt-molybdenum disulfide shows exceptional catalytic activity and stability toward the hydrogen evolution reaction with a low overpotential of 72.6 mV at -10 mA cm-2 and a small Tafel slope of 37.6 mV dec-1. The present study opens up a new opportunity to stimulate catalytic activity of the in-plane MoS2 basal domains for enhanced electrochemistry and redox reactivity through a "molecular reassembly-to-heteroatomic coordination and surface ligand functionalization" based on highly adaptable MOF template.

Monolayer triphosphates MP3 (M = Sn, Ge) with excellent basal catalytic activity for hydrogen evolution reaction

Atomically thin two-dimensional (2D) materials have received intense research interest due to their novel properties and promising applications in nanodevices. By using density functional theory (DFT) calculations, we investigate catalytic activities of several newly predicted two-dimensional (2D) triphosphides GeP₃, SnP₃ and InP₃ monolayers for hydrogen evolution reaction (HER). The calculation results show that GeP₃ and SnP₃ monolayers are active catalysts for HER with suitable free energy of hydrogen adsorption in the basal plane. In particular, the Gibbs free energy of hydrogen adsorption (ΔG_H*) of GeP₃ is 0.024 eV, a value even more favorable compared to the precious-group-metal (PGM) catalyst Pt. Moreover, the 2D GeP₃ and SnP₃ are intrinsically compatible with the graphene substrate so that the HER performance can be improved via building a hybrid multilayer with graphene sheet. The charge transfer from GeP₃ or SnP₃ to graphene, estimated to be 0.1278e or 0.2157e, can significantly enhance the electric conductivity and promote the electrocatalytic activity. Although the electronic band structure of GeP₃ and SnP₃ can be tuned by external strain, we find that the HER performance of GeP₃ and SnP₃ monolayer is actually insensitive to the external strain, a feature desirable for the catalytic application. The desirable properties for HER with nearly zero Gibbs free energy render 2D GeP₃ and SnP₃ promising candidates for future application in electrocatalysis.

Ru x Se@MoS2 hybrid as a highly efficient electrocatalyst toward hydrogen evolution reaction

Alkaline hydrogen evolution reaction (HER) requires highly efficient and stable catalytic materials, the engineering of which needs overall consideration of the water dissociation process as well as the intermediate hydrogen adsorption process. Herein, a Ru x Se@MoS2 hybrid catalyst was synthesized by the decoration of MoS2 with Ru x Se nanoparticles through a two-step hydrothermal reaction. Due to the bifunctionality mechanism in which Ru promotes the water dissociation and the nearby Se atoms, unsaturated Mo and/or S atoms act as active sites for the intermediate hydrogen adsorption, the hybrid catalyst exhibits an exceptional HER performance in basic media with a rather low overpotential of 45 mV at a current density of 10 mA cm-2 and a small Tafel slope of 42.9 mV dec-1. The synergetic effect between Ru x Se and MoS2 not only enables more catalytically active sites, but also increases the inherent conductivity of the hybrid catalyst, leading to more favorable HER kinetics under both alkaline and acidic conditions. As a result, Ru x Se@MoS2 also demonstrates an enhanced catalytic activity toward HER in 0.5 M H2SO4 in comparison with pure Ru x Se and MoS2, which requires an overpotential of 120 mV to deliver a 10 mA cm-2 current density and gives a Tafel slope of 72.2 mV dec-1. In addition, the hybrid electrocatalyst also exhibits superior electrochemical stability during the long-term HER process in both acidic media and alkaline media.

Nesting Co3Mo Binary Alloy Nanoparticles onto Molybdenum Oxide Nanosheet Arrays for Superior Hydrogen Evolution Reaction

Transition-metal alloys have attracted a great deal of attention as an alternative to Pt-based catalysts for hydrogen evolution reaction (HER) in alkaline. Herein, a facile and convenient strategy to fabricate Co₃Mo binary alloy nanoparticles nesting onto molybdenum oxide nanosheet arrays on nickel foam is developed. By modulating the annealing time and temperature, the Co₃Mo alloy catalyst displays a superior HER performance. Owing to substantial active sites of nanoparticles on nanosheets as well as the intrinsic HER activity of Co₃Mo alloy and no use of binders, the obtained catalyst requires an extremely low overpotential of only 68 mV at 10 mA cm^-2 in alkaline, with a corresponding Tafel slope of 61 mV dec^-1. At the same time, the catalyst demonstrates excellent stability during the long-term measurements. The density functional theory calculation provides a deeper insight into the HER mechanism, unveiling that the active sites on the Co₃Mo-based catalyst are Mo atoms. This strategy of combining catalytic active species with hierarchical nanoscale materials can be extended to other applications and provides a candidate of nonnoble metal catalysts for practical electrochemical water splitting.

One-dimensional CoS2-MoS2 nano-flakes decorated MoO2 sub-micro-wires for synergistically enhanced hydrogen evolution

CoS2-MoS2 nanoflakes decorated MoO2 (CoMoOS) hybrid submicro-wires with rich active interfaces were synthesized via the sulfuration of CoMoO4. They showed excellent activity while synergistically catalyzing the hydrogen evolultion reaction (HER) in basic media by promoting both the water dissociation and hydrogen absorption steps. Thus, the CoMoOS catalysts only needed 123 mV to achieve 10 mA cm-2 with a small Tafel slope in alkaline solutions, and required 1.68 V to obtain the same current density when assembled into an alkaline electrolyser.

Understanding electro-catalysis by using density functional theory

DFT calculations are indispensable for understanding the electro-catalysis through explanation of the experimental phenomena, prediction of experimental results, and guiding of the experimental investigation.