The disordered configuration, band structures, density of states, Mulliken population, elastic constants, zone center optic phonon modes and their Grüneisen parameters of M(CN)(2) (M =  Cd, Zn) have been studied for possible cyanide-ordering patterns by the first-principles plane-wave pseudopotential method based on density functional theory. Total energy calculations predict that MC(2)N(2)-MC(2)N(2) is the most favorable configuration for Cd(CN)(2) whereas all three possible configurations are near equally favorable for Zn(CN)(2). Effective charges and bond order analyses reveal that the M(CN)(2) (M =  Cd, Zn) frameworks include much stiffer [Formula: see text] and weaker M-C/N bonds, which account for the flexing of the M-CN-M linkage during the transverse motion of the cyanide-bridge. The transverse translational and the librational modes give rise to negative Grüneisen parameters and therefore contribute to the negative thermal expansion. Transverse vibrations of the C and N atoms in the same (transverse translational modes) or opposite (librational modes) directions have the same effect of drawing the anchoring metal atoms closer. Among all the optical phonon modes, the lowest-energy transverse translational optical modes which are neither Raman nor infrared active in Cd(CN)(2) and Zn(CN)(2) give rise to the largest contribution to the negative thermal expansion.

For the first time, we demonstrated that transition metal and nitrogen codoped carbon nanocomposites synthesized by pyrolysis and heat treatment showed excellent catalytic activity toward hydrogen evolution reaction (HER) in both acidic and alkaline media. The overpotential at 10 mA cm–2 was 235 mV in a 0.5 M H2SO4 solution at a catalyst loading of 0.765 mg cm–2 for Co–N–C. In a 1 M KOH solution, the overpotential was only slightly increased by 35 mV. The high activity and excellent durability (negligible loss after 1000 cycles in both acidic and alkaline media) make this carbon-based catalyst a promising alternative to noble metals for HER. Electrochemical and density functional theory (DFT) calculation results suggested that transition metals and nitrogen played a critical role in activity enhancement. The active sites for HER might be associated with metal/N/C moieties, which have been also proposed as reaction centers for oxygen reduction reaction.

No abstract

LDH is a controllable 2D material for fabricating heterostructures with another semiconductor.

No abstract

Cu 9 S 5 (digenite) is a p-type semiconductor with excellent electrical conductivity, high mobility of copper ions, and high work function. When used as the back electrode of CdTe solar cells, a high power conversion efficiency (PCE) is obtained. Density functional theory (DFT) method was used to study the structural and electronic properties of Cu 9 S 5 in this work. From the calculated band structures, we find that the Fermi level of the Cu 9 S 5 slightly crosses the valence band by about 0.08 eV below the valence band maximum (VBM), indicating a high hole concentration and potential high electrical conductivity as a p-type semiconductor. It is also found that the crystal structure of Cu 9 S 5 remained stable with a few Cu atoms diffused away, which introduces a p-type doping effect. Finally, we give a quantitative discussion on why CdTe solar cells with Cu 9 S 5 as the back electrode shows the high PCE.

No abstract

No abstract