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In situ O2-emission assisted synthesis of molybdenum carbide nanomaterials as an efficient electrocatalyst for hydrogen production in both acidic and alkaline media

We report here a unique in situ O2-emission assisted synthesis method to prepare molybdenum carbide (MoxC) nanomaterials with dense active sites and high effective surface area. The key to this protocol is the delicate design and synthesis of polymeric hybrid precursors by taking advantage of the synergy among the reactants. Oxidative polymerization of aniline (ANI) to form polyaniline (PANI), which acted as the nitrogen-rich carbon source, was initiated by adding aqueous H2O2 instead of the conventionally used ammonium persulfate (APS), and phosphomolybdate anions (PMo12) were doped into the positively charged PANI matrix via coulombic interactions. During the polymerization, vigorous O2 bubbles were in situ produced by H2O2 decomposition catalyzed by PMo12, which mechanically broke down the precursor into nanosized polymeric hybrids with a porous and loose morphology. The MoxC electrocatalyst was optimized by varying the feeding content of PMo12 and carbonization temperature, exhibiting remarkable catalytic activity and stability toward the hydrogen evolution reaction (HER) in both acidic and alkaline solutions. It requires an overpotential of only 144 mV and 141 mV to reach a current density of 10 mA cm−2 in 0.5 M H2SO4 and in 1 M NaOH, respectively, making it among the best of the reported MoxC-based electrocatalysts.

N,P-Doped Molybdenum Carbide Nanofibers for Efficient Hydrogen Production

Molybdenum (Mo) carbide-based electrocatalysts are considered promising candidates to replace Pt-based materials toward the hydrogen evolution reaction (HER). Among different crystal phases of Mo carbides, although Mo2C exhibits the highest catalytic performance, the activity is still restricted by the strong Mo-H bonding. To weaken the strong Mo-H bonding, creating abundant Mo2C/MoC interfaces and/or doping a proper amount of electron-rich (such as N and P) dopants into the Mo2C crystal lattice are effective because of the electron transfer from Mo to surrounding C in carbides and/or N/P dopants. In addition, Mo carbides with well-defined nanostructures, such as one-dimensional nanostructure, are desirable to achieve abundant catalytic active sites. Herein, well-defined N,P-codoped Mo2C/MoC nanofibers (N,P-Mo xC NF) were prepared by pyrolysis of phosphomolybdic ([PMo12O40]3-, PMo12) acid-doped polyaniline nanofibers at 900 °C under an Ar atmosphere, in which the hybrid polymeric precursor was synthesized via a facile interfacial polymerization method. The experimental results indicate that the judicious choice of pyrolysis temperature is essential for creating abundant Mo2C/MoC interfaces and regulating the N,P-doping level in both Mo carbides and carbon matrixes, which leads to optimized electronic properties for accelerating HER kinetics. As a result, N,P-Mo xC NF exhibits excellent HER catalytic activity in both acidic and alkaline media. It requires an overpotential of only 107 and 135 mV to reach a current density of 10 mA cm-2 in 0.5 M H2SO4 and 1 M KOH, respectively, which is comparable and even superior to the best of Mo carbide-based electrocatalysts and other noble metal-free electrocatalysts.

Nickel‐Based (Photo)Electrocatalysts for Hydrogen Production

Hydrogen is considered a promising energy carrier for replacing traditional fossil fuels. Electrochemical or solar-driven water splitting is a green and sustainable method of producing hydrogen. To lower the overpotential and minimize energy costs, numerous reports have focused on developing noble-metal-free catalysts for hydrogen production, with special attention paid to nickel-based materials. Herein, the current state of research on the use of Ni-based materials as electrocatalysts, cocatalysts, and photoactive materials in hydrogen production is reviewed. Recent research efforts toward the development of various Ni-based (photo)electrocatalysts, their applications in hydrogen production, and the corresponding mechanisms are covered. The approaches used to improve or optimize these materials are summarized, and the key remaining challenges are discussed.

Differentiation of biothiols from other sulfur-containing biomolecules using iodide-capped gold nanoparticles

We describe here a simple method based on the aggregation of gold nanoparticles (GNPs) to differentiate biothiols, such as cysteine, homocysteine, cysteinylglycine and glutathione from other sulfur-containing biomolecules, such as disulfide, thioether and thiocarbonyl molecules. The GNPs are capped with iodide ions (I−), which react with the GNPs to form a chemisorbed compact layer. The aggregation of the GNPs could be induced by biothiols, but not by other sulfur-containing biomolecules and uric acid, ascorbic acid, glucose, and bovine serum albumin. The added iodide exhibits both a stabilizing effect and salt effect on the aggregation of GNPs. The significance of these two opposite effects is dependent on the concentration of iodide and the binding ability of biothiols on the GNPs. The combination of the two effects leads to quite different aggregation kinetics of GNPs from that with other halide (chloride or bromide) ions which exhibit only the salt effect. Compared to other surfactants-capped GNPs, the iodide-capped GNPs are unique with a strong and compact adsorbed layer with small steric hindrance, which accounts for the selective response towards biothiols.

Walnut-like Transition Metal Carbides with Three-Dimensional Networks by a Versatile Electropolymerization-Assisted Method for Efficient Hydrogen Evolution

Mo2C@NPC (N,P-doped carbon) electrocatalysts are developed on carbon cloth (CC) as binder-free cathodes for efficient hydrogen evolution through a facile route of electropolymerization followed by pyrolysis. Electropolymerization of pyrrole to form polypyrrole occurs with the homogeneous incorporation of PMo12, driven by Coulombic force between the positively charged polymer backbone and PMo12 anions. This electrochemical synthesis is easily scaled up, requiring neither complex instrumentation nor an intentionally added electrolyte (PMo12 also acts as an electrolyte). After pyrolysis, the resultant Mo2C@NPC/CC electrode exhibits a unique interconnected walnut-like porous structure, which ensures strong adhesion between the active material and the substrate and favors electrolyte penetration into the electrocatalyst. This method is effective with other monomers such as aniline and is readily extended to fabricate other metal carbide electrodes such as WC@NPC/CC. These carbide electrodes exhibit high catalytic performance for hydrogen production, for example, WC@NPC/CC can deliver an unprecedented current density of 600 mA cm-2 at an overpotential of only 200 mV either in an acidic or an alkaline solution. Considering the simplicity, scalability, and versatility of the synthetic method, the unique electrode structure, and the excellent catalysis performance, this study opens up new avenues for the design of various novel binder-free metal carbide cathodes based on electropolymerization.

Crystal structure of di­bromido­tetra­kis(propan-2-ol-κO)nickel(II)

The asymmetric unit of the mononuclear title complex, [NiBr2(C3H8O)4], comprises a NiII cation located on a centre of inversion, one Br− anion and two propan-2-ol ligands. The NiII cation exhibits a distorted trans-Br2O4 environment. There are O—H⋯Br hydrogen bonds connecting neighbouring molecules into rows along [100]. These rows are arranged in a distorted hexagonal packing and are held together by van der Waals forces only.