Wrinkled Ni-doped Mo2C coating on carbon fiber paper: An advanced electrocatalyst prepared by molten-salt method for hydrogen evolution reaction

Strongly Coupled Nitrogen-Doped Mo2C@CoNi Alloy Hybrid Architecture toward Efficient Hydrogen Evolution Reaction

Development of high-efficiency electrocatalysts for water splitting is a promising channel to produce clean hydrogen energy. Herein, we demonstrate that the combination of nitrogen-doped Mo₂C and CoNi alloy to form a hybrid architecture is an effective way to produce hydrogen from electrochemical water splitting. Benefiting from a combination of mechanisms, the optimized N-Mo₂C@CoNi-650 shows remarkable hydrogen evolution reaction (HER) activity with small overpotentials of 35, 123, and 220 mV to reach the current density of 10, 50, and 100 mA cm^-2 in alkaline media, respectively, outperforming most previously reported HER electrocatalysts. The efficient electrocatalytic performance is ascribed to the highly exposed active sites, fast reaction kinetics, and improved charge-transfer steaming from the synergistic effect between each component. This work presents a new insight into designing and preparing highly efficient electrocatalysts toward the HER.

Smart Designs of Mo Based Electrocatalysts for Hydrogen Evolution Reaction

As a sustainable and clean energy source, hydrogen can be generated by electrolytic water splitting (i.e., a hydrogen evolution reaction, HER). Compared with conventional noble metal catalysts (e.g., Pt), Mo based materials have been deemed as a promising alternative, with a relatively low cost and comparable catalytic performances. In this review, we demonstrate a comprehensive summary of various Mo based materials, such as MoO2, MoS2 and Mo2C. Moreover, state of the art designs of the catalyst structures are presented, to improve the activity and stability for hydrogen evolution, including Mo based carbon composites, heteroatom doping and heterostructure construction. The structure–performance relationships relating to the number of active sites, electron/ion conductivity, H/H2O binding and activation energy, as well as hydrophilicity, are discussed in depth. Finally, conclusive remarks and future works are proposed.

Metal (Mo, W, Ti) Carbide Catalysts: Synthesis and Application as Alternative Catalysts for Dry Reforming of Hydrocarbons-A Review

Dry reforming of hydrocarbons (DRH) is a pro-environmental method for syngas production. It owes its pro-environmental character to the use of carbon dioxide, which is one of the main greenhouse gases. Currently used nickel catalysts on oxide supports suffer from rapid deactivation due to sintering of active metal particles or the deposition of carbon deposits blocking the flow of gases through the reaction tube. In this view, new alternative catalysts are highly sought after. Transition metal carbides (TMCs) can potentially replace traditional nickel catalysts due to their stability and activity in DR processes. The catalytic activity of carbides results from the synthesis-dependent structural properties of carbides. In this respect, this review presents the most important methods of titanium, molybdenum, and tungsten carbide synthesis and the influence of their properties on activity in catalyzing the reaction of methane with carbon dioxide.

Nanostructured Molybdenum Oxides from Aluminium-Based Intermetallic Compound: Synthesis and Application in Hydrogen Evolution Reaction

Characterized by a large surface area to volume ratio, nanostructured metal oxides possess unique chemical and physical properties with applications in electronics, catalysis, sensors, etc. In this study, Mo₃Al₈, an intermetallic compound, has been used as a precursor to obtain nanostructured molybdenum oxides. It was prepared into ribbons by arc-melting and melt-spinning techniques. Single and double-step free corrosion of the as-quenched material have been studied in 1 M KOH, 1 M HF and 1.25 M FeCl₃ at room temperature. In both cases, nanostructured molybdenum oxides were obtained on a surface layer a few microns thick. Two of the as-prepared samples were tested for their electrocatalytic capability for hydrogen evolution reaction (HER) in 0.5 M H₂SO₄ giving low onset potential (−50 mV, −45 mV), small Tafel slopes (92 mV dec⁻¹, 9 mV dec⁻¹) and high exchange current densities (0.08 mA cm⁻², 0.35 mA cm⁻² respectively). The proposed nanostructured molybdenum oxides are cost-effective and sustainable due to the cheap and abundant starting material used and the simple synthetic route, paving the way for their possible application as HER electrocatalysts.

Self-supported nickel-doped molybdenum carbide nanoflower clusters on carbon fiber paper for an efficient hydrogen evolution reaction

Developing an efficient, stable and low-cost noble-metal-free electrocatalyst for the hydrogen evolution reaction (HER) is an effective way to alleviate the energy crisis. Herein, we report a simple and facile approach to synthesize self-supported Ni-doped Mo₂C via a molten salt method. By optimizing the content of Ni, the concentration of Ni(NO₃)₂, and the annealing time, self-supported nanoflower-like electrocatalysts composed of ultrathin nanosheets on carbon fiber paper (CFP) can be achieved. Such a fluffy and porous nanoflower-like structure has a large specific surface area, which can expose many active sites, and promote charge transfer; moreover, all of the above is beneficial for improving the HER performance. Density functional theory (DFT) calculations reveal that the doping of Ni leads to a down shift of the value of the d band center (ε_d), so that the adsorbed hydrogen (H_ads) is easier to desorb from the catalyst surface, thus leading to an enhanced intrinsic catalytic activity of Ni doped Mo₂C based catalysts. As a result, Mo₂C-3 M Ni(NO₃)₂/CFP with a nanoflower-like structure prepared at 1000 °C for 6 h exhibits the best electrocatalytic performance for the HER in 0.5 M H₂SO₄, with a low overpotential of 56 mV (at j = 10 mA cm^-2) and a Tafel slope (27.4 mV dec^-1) comparable to that of commercial Pt/C (25.8 mV dec^-1). The excellent performance surpasses most of the noble-metal-free electrocatalysts. In addition, the outstanding long-term durability of Mo₂C-3 M Ni(NO₃)₂/CFP is demonstrated by showing no obvious fluctuations during 35 h of the HER testing. This work provides a simple and facile strategy for the preparation of nanoelectrocatalysts with high specific surface areas and high catalytic activities, both of which promote an efficient HER.

Molten salt synthesis of carbon-doped boron nitride nanosheets with enhanced adsorption performance

Owing to their large specific areas, high thermal stability and chemical inertness, two-dimensional boron carbon nitride nanosheets (BCNNs) have captured much attention in recent years in the field of adsorption of pollutants. The formation of BCNNs via incorporating carbon into boron nitride (BN) can effectively improve the photoelectric and adsorption properties of the latter. In this work, carbon-doped BN (BCN) nanosheets were prepared at 1100 °C via a molten salt route using boric acid, melamine and glucose as the main starting materials. The effects of molten salt type and carbon doping level on the formation of BCN were investigated, and their isothermal adsorption properties in a methylene blue (MB) aqueous solution were evaluated based on the Langmuir and Freundlich models. The results indicated that using molten LiCl-KCl as a liquid medium was more favorable than NaCl-KCl to the formation of BCNNs. As-prepared BC_0.4N sample possessed a sheet-like structure of about 10 nm thick and a specific surface area as high as 484 m² g^-1. Moreover, the adsorption test of MB demonstrated a high adsorption capacity of 249.04 mg g^-1, which was about 14 times higher than that in the case of the pristine BN, and the kinetic rate constant value in the case of using BC_0.4N is about ten times as high as that of BN following a pseudo-second-order model, suggesting that the as-formed BC_0.4N nanosheets could be potentially used as a value-added effective adsorbent for future wastewater remediation.

Defect Engineering of Molybdenum-Based Materials for Electrocatalysis

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

Synergistic Tuning of the Electronic Structure of Mo2C by P and Ni Codoping for Optimizing Electrocatalytic Hydrogen Evolution

Developing earth-abundant and highly efficient nonprecious metal catalysts for hydrogen evolution reaction (HER) is critical for the storage and conversion of renewable energy sources. Molybdenum carbide (Mo₂C) has been extensively investigated as one of the most promising nonprecious electrocatalysts for boosting HER because of its low cost, high electrical conductivity, good chemical structure, and similar electronic structure to that of Pt. However, Mo₂C always exhibits the negative hydrogen-binding energy, which can largely prevent adsorbed H desorption during the HER process. Herein, we report P- and Ni-dual-doped Mo₂C in porous nitrogen-doped carbon (P/Ni-Mo₂C) as an electrocatalyst for the HER, exhibiting excellent activity and durability with a low overpotential of 165 mV at 10 mA cm^-2 in alkaline electrolyte. Density functional theory (DFT) calculations proved that P and Ni acted as the anion and cation, respectively, to synergistically tune the electronic properties of Mo₂C to decrease the negative hydrogen-binding energy, endowing the catalyst with excellent catalytic performance for the HER.

Improving Artificial Photosynthesis over Carbon Nitride by Gas-Liquid-Solid Interface Management for Full Light-Induced CO2 Reduction to C1 and C2 Fuels and O2

The activity and selectivity of simple photocatalysts for CO2 reduction remain limited by the insufficient photophysics of the catalysts, as well as the low solubility and slow mass transport of gas molecules in/through aqueous solution. In this study, these limitations are overcome by constructing a triphasic photocatalytic system, in which polymeric carbon nitride (CN) is immobilized onto a hydrophobic substrate, and the photocatalytic reduction reaction occurs at a gas-liquid-solid (CO2 -water-catalyst) triple interface. CN anchored onto the surface of a hydrophobic substrate exhibits an approximately 7.2-fold enhancement in total CO2 conversion, with a rate of 415.50 μmol m-2  h-1 under simulated solar light irradiation. This value corresponds to an overall photosynthetic efficiency for full water-CO2 conversion of 0.33 %, which is very close to biological systems. A remarkable enhancement of direct C2 hydrocarbon production and a high CO2 conversion selectivity of 97.7 % are observed. Going from water oxidation to phosphate oxidation, the quantum yield is increased to 1.28 %.

Micro-Nano Carbon Structures with Platelet, Glassy and Tube-Like Morphologies

Carbon source precursors for high-grade, clean, and low-carbon refractories were obtained by in situ exfoliation of flake graphite (FG) and phenol–formaldehyde resin (PF) composites with three-roll milling (TRM) for the fabrication of graphite nanoplatelets. In addition, by using Ni(NO₃)₂·6H₂O as a catalyst in the pyrolysis process, multidimensional carbon nanostructures were obtained with coexisting graphite nanoplatelets (GNPs), glassy carbon (GC), and carbon nanotubes (CNTs). The resulting GNPs (exfoliated 16 times) had sizes of 10–30 μm, thicknesses of 30–50 nm, and could be uniformly dispersed in GC from the PF pyrolysis. Moreover, Ni(NO₃)₂·6H₂O played a key role in the formation and growth of CNTs from a catalytic pyrolysis of partial PF with the V–S/tip growth mechanisms. The resulting multidimensional carbon nanostructures with GNPs/GC/CNTs are attributed to the shear force of the TRM process, pyrolysis, and catalytic action of nitrates. This method reduced the production costs of carbon source precursors for low-carbon refractories, and the precursors exhibited excellent performances when fabricated on large scales.