Transition-metal monochalcogenide nanowires: highly efficient bi-functional catalysts for the oxygen evolution/reduction reactions

Enhanced oxygen evolution reaction activity on two-dimensional vdW ferromagnetic Cr2Ge2Te6 through synergism between two active sites

To design an efficient, low-cost, and easily recoverable oxygen evolution reaction (OER) electrocatalyst, this work focuses on two-dimensional vdW ferromagnetic Cr2Ge2Te6. Based on the density functional theory (DFT) calculations, the adsorption of oxygen-containing intermediates during the OER process will gradually decrease the bandgap of Cr2Ge2Te6, thus increasing its electrical conductivity. More importantly, we propose a two active sites synergistic mechanism through a hydroxyl-boosted pathway. With the combined action of the two active sites, the binding between the oxygen-containing intermediates and the surfaces is enhanced. The enhancement comes from dramatic charge-transfer-induced Te-3p and O-2p orbital enhancement. As a result, the overpotential of the OER reduces from 1.25 to 0.59 V. We hope these findings will pave the way for more experimental and theoretical research to explore the potential applications of two-dimensional vdW ferromagnetic materials in energy storage and conversion.

Transition metal dichalcogenide magnetic atomic chains

Reducing the dimensions of a material to the atomic scale endows them with novel properties that are significantly different from their bulk counterparts. A family of stoichiometric transition metal dichalcogenide (TMD) MX₂ (M = Ti to Mn, and X = S to Te) atomic chains is proposed. The results reveal that the MX₂ atomic chains, the smallest possible nanostructure of a TMD, are lattice-dynamically stable, as confirmed from their phonon spectra and ab initio molecular dynamics simulations. In contrast to their bulk and two-dimensional (2D) counterparts, the TiX₂ atomic chains are nonmagnetic semiconductors, while the VX₂, CrX₂, and MnX₂ chains are unipolar magnetic, bipolar magnetic, and antiferromagnetic semiconductors, respectively. In addition, the VX₂, CrX₂, and MnX₂ chains can be converted via carrier doping from magnetic semiconductors to half metals with reversible spin-polarization orientation at the Fermi level. Of these chains, the MnX₂ chains exhibit either ferromagnetic or antiferromagnetic half metallicity depending on the injected carrier type and concentration. The diverse and tunable electronic and magnetic properties in the MX₂ chains originate, based on crystal field theory, from the occupation of the metal d orbitals and the exchange interaction between the tetrahedrally coordinated metal atoms in the atomic chain. The calculated interaction between the carbon nanotubes and the MX₂ chains implies that armchair (7,7) or armchair (8,8) carbon nanotubes are appropriate sheaths for growing MX₂ atomic single-chains in a confined channel. This study reveals the diverse magnetic properties of MX₂ atomic single-chains and provides a promising building block for nanoscale electronic and spintronic devices.