Hierarchically Structured Cu-Based Electrocatalysts with Nanowires Array for Water Splitting

We report here the fabrication of CuO nanowires and their use as efficient electrocatalyst for the oxygen evolution reaction (OER) or as precursor for preparation of Cu₃P nanowires for the hydrogen evolution reaction (HER). The surface-bound Cu­(OH)₂ nanowires are <i>in situ</i> grown on a three-dimensional copper foam (CF) by anodic treatment, which are then converted to CuO nanowires by calcination in air. The direct growth of nanowires from the underlying conductive substrate can eliminate the use of any conductive agents and binders, which ensures good electrical contact between the electrocatalyst and the conductive substrate. The hierarchically nanostructured Cu-based electrode exhibits excellent catalytic performance toward OER in 1 M KOH solution. Phosphorization of the CuO/CF electrode generates the Cu₃P/CF electrode, which can act as an excellent electrocatalyst for HER in 1 M KOH. An alkaline electrolyzer is constructed using CuO and Cu₃P nanowires coated copper foams as anode and cathode, which can realize overall water splitting with a current density of 102 mA/cm² at an applied cell voltage of 2.2 V

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_<i>x</i>C 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_<i>x</i>C 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

Obtaining Chiral Metal–Organic Frameworks via a Prochirality Synthetic Strategy with Achiral Ligands Step-by-Step

Although some achievements of constructing chiral metal–organic frameworks (MOFs) with diverse achiral ligands have been made, there is still a lack of full understanding of the origin and formation mechanism of chirality, as well as the reasonable principles for the design and construction of chiral frameworks. The concept of prochirality in organic molecules and complex systems inspires us to explore the synthetic strategy of chiral MOFs based on achiral sources. Here, an achiral compound [Cu­(en)]­[(VO₃)₂] (<b>1</b>) was isolated in the CuCl₂/NH₄VO₃/en system, while further chiral frameworks [Cu­(en)­(Im)₂]­[(VO₃)₂] (<b>2a</b> and <b>2b</b>) were obtained by the reaction between compound <b>1</b> and another achiral ligand Im (ethanediamine = en and imidazole = Im). In the present system, compound <b>1</b> has the characteristic of a quasi-plane structure unit. Further reaction of compound <b>1</b> and the achiral ligand (Im) induced the formation of chiral Λ/Δ Cu centers, and then a pair of chiral frameworks containing one-dimensional (1D) helical chains was formed. The chiral symmetry breaking phenomenon of compounds <b>2a</b> and <b>2b</b> can also be expected and explained based on this kind of prochirality synthetic strategy