Fundamental limitation of electrocatalytic methane conversion to methanol.

The electrochemical oxidation of methane to methanol at remote oil fields where methane is flared is the ultimate solution to harness this valuable energy resource. In this study we identify a fundamental surface catalytic limitation of this process in terms of a compromise between selectivity and activity, as oxygen evolution is a competing reaction. By investigating two classes of materials, rutile oxides and two-dimensional transition metal nitrides and carbides (MXenes), we find a linear relationship between the energy needed to activate methane, i.

Band structure engineered layered metals for low-loss plasmonics.

Plasmonics currently faces the problem of seemingly inevitable optical losses occurring in the metallic components that challenges the implementation of essentially any application. In this work, we show that Ohmic losses are reduced in certain layered metals, such as the transition metal dichalcogenide TaS, due to an extraordinarily small density of states for scattering in the near-IR originating from their special electronic band structure. On the basis of this observation, we propose a new class of band structure engineered van der Waals layered metals composed of hexagonal transition metal chalcogenide-halide layers with greatly suppressed intrinsic losses.

Band Gap Tuning and Defect Tolerance of Atomically Thin Two-Dimensional Organic-Inorganic Halide Perovskites.

Organic-inorganic halide perovskites have proven highly successful for photovoltaics but suffer from low stability, which deteriorates their performance over time. Recent experiments have demonstrated that low dimensional phases of the hybrid perovskites may exhibit improved stability. Here we report first-principles calculations for isolated monolayers of the organometallic halide perovskites (CHNH)MXY, where M = Pb, Ge, Sn and X,Y = Cl, Br, I.

Defect-Tolerant Monolayer Transition Metal Dichalcogenides.

Localized electronic states formed inside the band gap of a semiconductor due to crystal defects can be detrimental to the material's optoelectronic properties. Semiconductors with a lower tendency to form defect induced deep gap states are termed defect-tolerant. Here we provide a systematic first-principles investigation of defect tolerance in 29 monolayer transition metal dichalcogenides (TMDs) of interest for nanoscale optoelectronics.

Two-Dimensional Metal Dichalcogenides and Oxides for Hydrogen Evolution: A Computational Screening Approach.

We explore the possibilities of hydrogen evolution by basal planes of 2D metal dichalcogenides and oxides in the 2H and 1T class of structures using the hydrogen binding energy as a computational activity descriptor. For some groups of systems like the Ti, Zr, and Hf dichalcogenides the hydrogen bonding to the 2H structure is stronger than that to the 1T structure, while for the Cr, Mo, and W dichalcogenides the behavior is opposite. This is rationalized by investigating shifts in the chalcogenide p levels comparing the two structures.

Hydroxylation induced stabilization of near-surface rocksalt nanostructure on wurtzite ZnO structure.

We present a density functional study of the structural behavior of zinc oxide nanostructures in basic growth condition which consequently leads to the formation of few layers of hydroxylated rocksalt structure over the wurtzite ZnO structure. We demonstrate the greater stability of the few layers of hydroxylated zinc oxide polar surface in rocksalt structure as compared to wurtzite structure. This coerces the near-surface layers of the nanostructure to acquire rocksalt structure giving rise to a trilayer structure consisting of a layer of hydroxyls on ZnO surface, rocksalt near-surface layers, and wurtzite bulk(or wurtzite sub-surface).

Stabilization and growth of non-native nanocrystals at low and atmospheric pressures.

The stabilization and growth of nanocrystals in "non-native" structures is explored via density functional calculations. Non-native and "native" bulk structures differ in their discrete translational symmetry. Computations suggest that the lower surface energy of the non-native structures always facilitates their stabilization in the early stages of crystal growth.