Reduced Graphene Oxide/O-MWCNT Hybrids Functionalized with p‑Phenylenediamine as High-Performance MoS₂ Electrocatalyst Support for Hydrogen Evolution Reaction

Efficient hydrogen evolution through water splitting at low overpotentials is crucial to develop renewable energy technology, which depends on the design of efficient and durable electrocatalysts composed of earth-abundant elements. Herein, a highly and stable electrocatalyst for hydrogen evolution reaction (HER) has been developed on the basis of MoS₂ on p-phenylenediamine (PPD)-functionalized reduced graphene oxide/O-containing carbon nanotubes (rGO/O-MWCNT) hybrids via facile and green hydrothermal process. Among the prepared catalysts, the optimized MoS₂/rGO/PPD/O-MWCNT with nanosized and highly dispersed MoS₂ sheets provides a large amount of available edge sites and the improved electron transfer in 3D conductive networks. It exhibits excellent HER activity with a low overpotential of 90 mV and large current density of 47.6 mA·cm^–2 at 200 mV, as well as excellent stability in an acidic medium. The Tafel slope of 48 mV·dec^–1 reveals the Volmer–Heyrovsky mechanism for HER. Thus, this work paves a potential pathway for designing efficient MoS₂-based electrocatalysts for HER by functionalized conductive substrates

Co-Doped MoS₂ Nanosheets with the Dominant CoMoS Phase Coated on Carbon as an Excellent Electrocatalyst for Hydrogen Evolution

Highly active and low-cost catalysts for hydrogen evolution reaction (HER) are crucial for the development of efficient water splitting. Molybdenum disulfide (MoS₂) nanosheets possess unique physical and chemical properties, which make them promising candidates for HER. Herein, we reported a facile, effective, and scalable strategy by a deposition–precipitation method to fabricate metal-doped (Fe, Co, Ni) molybdenum sulfide with a few layers on carbon black as noble metal–free electrocatalysts for HER. The CoMoS phase after thermal annealing in Co-doped MoS₂ plays a crucial role for the enhanced HER. The optimized Co-doped MoS₂ catalyst shows superior HER performance with a high exchange current density of 0.03 mA·cm^–2, low onset potential of 90 mV, and small Tafel slope of 50 mV·dec^–1, which also exhibits excellent stability of 10000 cycles with negligible loss of the cathodic current. The superior HER activity originates from the synergistically structural and electronic modulations between MoS₂ and Co ions, abundant defects in the active edge sites, as well as the good balance between active sites and electronic conductivity. Thanks to their ease of synthesis, low cost, and high activity, the Co-doped MoS₂ catalysts appear to be promising HER catalysts for electrochemical water splitting

Structure Effects of 2D Materials on α‑Nickel Hydroxide for Oxygen Evolution Reaction

To engineer low-cost, high-efficiency, and stable oxygen evolution reaction (OER) catalysts, structure effects should be primarily understood. Focusing on this, we systematically investigated the relationship between structures of materials and their OER performances by taking four 2D α-Ni­(OH)₂ as model materials, including layer-stacked bud-like Ni­(OH)₂-NB, flower-like Ni­(OH)₂-NF, and petal-like Ni­(OH)₂-NP as well as the ultralarge sheet-like Ni­(OH)₂-NS. For the first three (layer-stacking) catalysts, with the decrease of stacked layers, their accessible surface areas, abilities to adsorb OH^–, diffusion properties, and the intrinsic activities of active sites increase, which accounts for their steadily enhanced activity. As expected, Ni­(OH)₂-NP shows the lowest overpotential (260 mV at 10 mA cm^–2) and Tafel slope (78.6 mV dec^–1) with a robust stability over 10 h among the samples, which also outperforms the benchmark IrO₂ (360 mV and 115.8 mV dec^–1) catalyst. Interestingly, Ni­(OH)₂-NS relative to Ni­(OH)₂-NP exhibits even faster substance diffusion due to the sheet-like structure, but shows inferior OER activity, which is mainly because the Ni­(OH)₂-NP with a smaller size possesses more active boundary sites (higher reactivity of active sites) than Ni­(OH)₂-NS, considering the adsorption properties and accessible surface areas of the two samples are quite similar. By comparing the different structures and their OER behaviors of four α-Ni­(OH)₂ samples, our work may shed some light on the structure effect of 2D materials and accelerate the development of efficient OER catalysts

Tungsten-Doped Molybdenum Sulfide with Dominant Double-Layer Structure on Mixed MgAl Oxide for Higher Alcohol Synthesis in CO Hydrogenation

Improving the C₂+ alcohols selectivity is highly desirable for higher alcohols synthesis in CO hydrogenation. Herein, an effective method was developed for Mo-based supported catalysts by the combination of tungsten-doping and surfactant-assisted hydrothermal strategy. The tungsten-doping enhanced the interaction between Ni and W/Mo metal species to form more of the Ni-MoW-S phase with tunable slab size and stacking layers, and thus promoted the chain growth of alcohol to form a greater amount of higher alcohols in CO hydrogenation. The optimal K,Ni–Mo_0.75W_0.25/MMO-S exhibited a dominant double-layer structure (∼39.0%) and highly synergetic effects between Ni and W/Mo species, resulting in the highest total alcohol selectivity (76.1%) and in higher alcohols selectivity. This work provides a new route for tuning the morphology of MoS₂/WS₂ and synergetic effects between Ni and W/Mo species in supported catalysts to improve the selectivity of higher alcohols

Molybdenum Polysulfide Anchored on Porous Zr-Metal Organic Framework To Enhance the Performance of Hydrogen Evolution Reaction

Replacement of precious platinum with efficient and low-cost catalysts for electrocatalytic hydrogen evolution reaction (HER) at low overpotentials holds tremendous promise for clean energy devices. Herein, molybdenum polysulfide (MoS_<i>x</i>) anchored on a porous Zr-metal organic framework (Zr-MOF, UiO-66-NH₂) by chemical interactions is fabricated by a facile and one-pot solvothermal method for HER application. The distinctive design of the Zr-MOF stabilized MoS_<i>x</i> composite enables remarkable electrochemical HER activity with a Tafel slope of 59 mV·dec^–1, a lower onset potential of nearly 125 mV, and a cathode current of 10 mA·cm^–2 at an overpotential of 200 mV, which also exhibits excellent durability in an acid medium. The superior HER performance should ascribe to the fast electron transport from the less conducting MoS_<i>x</i> nanosheets to the electrode, high effective surface area, and number of active sites, as well as the favorable delivery for local protons in the porous Zr-MOF structure during the electrocatalytic reaction. Thus, this work paves a potential pathway for designing efficient Mo-based HER electrocatalysts by the combination of molybdenum polysulfide and versatile proton-conductive MOFs

Metallic Cobalt Encapsulated in Bamboo-Like and Nitrogen-Rich Carbonitride Nanotubes for Hydrogen Evolution Reaction

Despite being technically possible, the hydrogen production by means of electrocatalytic water splitting is still practically unreachable mainly because of the lack of inexpensive and high active catalysts. Herein, a novel and facile approach by melamine polymerization, exfoliation and Co²⁺-assisted thermal annealing is developed to fabricate Co nanoparticles embedded in bamboo-like and nitrogen-rich carbonitride nanotubes (Co@NCN). The electronic interaction between the embedded Co nanoparticles and N-rich carbonitride nanotubes could strongly promote the HER performance. The optimized Co@NCN-800 exhibits outstanding HER activity with an onset potential of −89 mV (vs RHE), a large exchange current density of 62.2 μA cm^–2, and small Tafel slope of 82 mV dec^–1, as well as excellent stability (5000 cycles) in acid media, demonstrating the potential for the replacement of Pt-based catalysts. Control experiments reveal that the superior performance should be ascribed to the synergistic effects between embedded Co nanoparticles and N-rich carbonitride nanotubes, which originate from the high pyridinic N content, fast charge transfer rate from Co particles to electrodes via electronic coupling, and porous and bamboo-like carbonitride nanotubes for more active sites in HER

Morphology Design of IRMOF‑3 Crystal by Coordination Modulation

A one-pot synthesis design on shape-controlled growth of Zn-based isoreticular metal–organic framework (i.e., IRMOF-3) was carried out in this work with the controllable crystal morphological evolution from simple cubes to several complex shapes. A new synthetic protocol was devised where poly­(vinylpyrrolidone) (PVP), noble metal source (AgNO₃), mixed solvents (<i>N</i>,<i>N</i>-dimethylformamide (DMF)–ethanol mixture) and tetramethylammonium bromide (TMAB) were mutually introduced to the reaction medium as surfactant, adjuvant, accelerator, and structure-directing agent (SDA), respectively. Meanwhile, the crystallization process was investigated by a series of time-dependent experiments. Indeed, the added modulators and crystallization time were able to regulate the growth and thus the morphology of the final products. The resulting homogeneous IRMOF-3-Ag-<i><b>n</b></i> materials with unique and novel crystal morphologies were characterized via scanning electron microscopy (SEM), X-ray powder diffraction (XRD), thermogravimetric and differential thermal analyses (TG-DTA), transmission electron microscopy (TEM), infrared spectrum (IR), and optical microscope characterizations. Various shapes of IRMOF-3-Ag-<i><b>n</b></i> crystals as sorbents for capturing dibenzothiophene (DBT) were evaluated. Among all the morphology-controlled samples, IRMOF-3-Ag-<b>5</b> with hollow sphere morphology was demonstrated to show the highest DBT capture capacity due to its unique morphology

Strongly Coupled FeNi Alloys/NiFe₂O₄@Carbonitride Layers-Assembled Microboxes for Enhanced Oxygen Evolution Reaction

Hydrogen produced from electrocatalytic water splitting is a promising route due to the sustainable powers derived from the solar and wind energy. However, the sluggish kinetics at the anode for water splitting makes the highly effective and inexpensive electrocatalysts desirable in oxygen evolution reaction (OER) by structure and composition modulations. Metal–organic frameworks (MOFs) have been intensively used as the templates/precursors to synthesize complex hollow structures for various energy-related applications. Herein, an effective and facile template-engaged strategy originated from bimetal MOFs is developed to construct hollow microcubes assembled by interconnected nanopolyhedron, consisting of intimately dominant FeNi alloys coupled with a small NiFe₂O₄ oxide, which was confined within carbonitride outer shell (denoted as FeNi/NiFe₂O₄@NC) via one-step annealing treatment. The optimized FeNi/NiFe₂O₄@NC exhibits excellent electrocatalytic performances toward OER in alkaline media, showing 10 mA·cm^–2 at η = 316 mV, lower Tafel slope (60 mV·dec^–1), and excellent durability without decay after 5000 CV cycles, which also surpasses the IrO₂ catalyst and most of non-noble catalysts in the OER, demonstrating a great perspective. The superior OER performance is ascribed to the hollow interior for fast mass transport, in situ formed strong coupling between FeNi alloys and NiFe₂O₄ for electron transfer, and the protection of carbonitride layers for long stability

One-Pot Synthesis of Ternary Pt–Ni–Cu Nanocrystals with High Catalytic Performance

Shape-controlled synthesis of multicomponent metal nanocrystals (NCs) bounded by high-index facets (HIFs) is of significant importance in the design and synthesis of highly active catalysts. It is a highly challenging task to design and synthesize ternary alloy NCs with HIFs due to the formidable difficulties in controlling the nucleation/growth kinetics of NCs in the presence of three metal precursors with different reduction potentials. We report herein, for the first time, the preparation of Pt–Ni–Cu alloy NCs by tuning their shape from crossed, dendritic, concave nanocubic (CNC) to rough octahedral (ROH) NCs through a facile one-pot solvothermal synthesis method. Specifically, the crossed and CNC Pt–Ni–Cu alloy NCs are bounded by high-index {<i>hk</i>0} facets and ROH with rich lattice defects. The electrocatalytic activities of these Pt–Ni–Cu alloy NCs toward methanol and formic acid oxidation were tested. It was shown that these Pt–Ni–Cu alloy NCs exhibited enhanced activity and stability compared to commercial Pt black and Pt/C catalysts as well as previous Pt–Ni and Pt CNCs under the same reaction conditions, demonstrating the superior electrocatalytic activity of Pt–Ni–Cu ternary alloys compared to monometal and binary Pt–Ni NCs. Surprisingly, we have found that the Pt–Ni–Cu ROH NCs have exhibited a higher specific catalytic activity than the crossed and CNC Pt–Ni–Cu alloy NCs with HIFs. The electronic and structure effects have been extensively discussed to shed light on the excellent electrocatalytic performance of Pt–Ni–Cu ROH NCs

In Situ Synthesis of Core–Shell Pt–Cu Frame@Metal–Organic Frameworks as Multifunctional Catalysts for Hydrogenation Reaction

Controllable integration of metal nanoparticles (NPs) and metal–organic frameworks (MOFs) is of significant importance in many applications owing to their unique properties. In situ efficient synthesis of metal NPs with different structures into MOFs is a great challenge. Herein, we report the nanostructures of octahedron and flower Pt–Cu frame@HKUST-1, which is successfully synthesized under a microwave irradiation method in only 30 min. In this study, Pt–Cu alloys, serving as the self-template, are synthesized first, followed by the HKUST-1 shell growing in situ via the consumption of Cu⁰. As multifunctional catalysts, the core–shell structures exhibit excellent performance for the hydrogenation of 1-hexene. Notably, octahedron Pt–Cu frame@HKUST-1 displays high turnover number (TON) and turnover frequency (TOF) of 1004 and 2008 h^–1, respectively. Thanks to the protective effect of HKUST-1, the octahedron Pt–Cu frame@HKUST-1 can be recycled for at least four runs without serious loss of activity and obvious aggregation of Pt–Cu alloys. Furthermore, the size-selective catalysis is also well-demonstrated by choosing 1-hexene, <i>cis</i>-cyclooctene, and styrene as substrates