Influence of exchange-correlation functional on the structural and electronic properties of periodic structures with transition metal atoms

The influence of the exchange-correlation functional on the crystal fundamental property calculation is shown. CrGeTe3, compound with transition metals, was used for the simulation of structural and electronic properties. The calculations were carried out using such functional classes as LDA and GGA. It has been shown that LDA exhibits 0.4 % and 5.2 % overestimations of the lattice constants for a and c, respectively. GGA (OR) overestimates a by 0.58 % and underestimates c by 4 %. The influence of the Hubbard correction on the band gap was also investigated. If Ueff is applied to the d-electrons, then the band gap will decrease. This is due to the hybridization of the p-electrons of the chalcogen and the d-electrons of the transition metal. Thus, GGA demonstrates better agreement with the experiment. The convergence of the calculation of the total energy with a change in the k-points and the cutoff energy were also investigated.

High Absorption Electromagnetic Wave Properties of Composite CoFeO3 Synthesized by Simple Mechanical Alloying

Electronic equipment demand is strongly correlated to the electromagnetic wave interference (EMI), which causes severe effects on human health. Microwave absorbing materials (MAMs) are one method to protect human health from EMI. Cobalt nanoparticles show high performance as MAMs. Here, we have synthesized CoFeO3 by simple mechanical alloying for increased multiple reflections, interfacial polarization, magnetic domain loss, electron spin loss, internal resonance, hoping electron, conductive loss, and multiple scattering for improved absorption of EMI waves. We determined the electronic properties from the Quantum Espresso (QE) and corresponding results are discussed. The metallic character comes from the d-state of transition metal atoms Fe (II) and Co which are sufficiently large in magnitude in the Fermi level of band structure and density of state (DOS) distribution. Crystallite size in the range of 13.6 to 18.7 nm with surface morphology shows irregular shapes of the particles. For CoFeO3 as MAMs, we found that the reflection loss (RL) is -55 dB (lower than the previous reported -43.2 dB) at 10-11 GHz for a thickness of 8 mm, indicating that this study shows high potential of CoFeO3 as an alternative composite for MAMs applications.

Computational Study of the Curvature-Promoted Anchoring of Transition Metals for Water Splitting

Generating clean and sustainable hydrogen from water splitting processes represent a practical alternative to solve the energy crisis. Ultrathin two-dimensional materials exhibit attractive properties as catalysts for hydrogen production owing to their large surface-to-volume ratios and effective chemisorption sites. However, the catalytically inactive surfaces of the transition metal dichalcogenides (TMD) possess merely small areas of active chemical sites on the edge, thus decreasing their possibilities for practical applications. Here, we propose a new class of out-of-plane deformed TMD (cTMD) monolayer to anchor transition metal atoms for the activation of the inert surface. The calculated adsorption energy of metals (e.g., Pt) on curved MoS2 (cMoS2) can be greatly decreased by 72% via adding external compressions, compared to the basal plane. The enlarged diffusion barrier energy indicates that cMoS2 with an enhanced fixation of metals could be a potential candidate as a single atom catalyst (SAC). We made a well-rounded assessment of the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), which are two key processes in water splitting. The optimized Gibbs free energy of 0.02 for HER and low overpotential of 0.40 V for OER can be achieved when the proper compression and supported metals are selected. Our computational results provide inspiration and guidance towards the experimental design of TMD-based SACs.

Screening Highly Efficient Hetero-Diatomic Doped PC6 Electrocatalysts For Selective Nitrogen Reduction to Ammonia

Searching for highly efficient electrocatalysts toward nitrogen reduction reaction (NRR) is an important but challenging task for nitrogen utilization in industry. Here we have systematically designed a series of hetero-diatomic catalysts (DACs), in which transition metal atoms (Ti, V, Cr, Mn, Fe, Co, and Ni) are dispersed on PC6 monolayer to form AB@PC6 (A, B= Ti, V, Cr, Mn, Fe, Co, and Ni). Employing density functional theory (DFT) calculation, the V and Cr co-doped PC6 monolayer (VCr@PC6) among the 21 AB@PC6 catalysts is the most promising catalyst due to its low limiting potential of -0.41V, relatively low energy barrier, and high ammonia selectivity toward hydrogen evolution reaction (HER). Insights on the high NRR activity of VCr@PC6 are also explored. The synergistic effect in DACs facilitates the electron transfer from metal pairs to PC6 monolayer, as well as suppresses the HER, leading to high selectivity and Faradaic efficiency. This work not only aims to seek the efficient DACs towards N2 reduction but also provides insights towards synergistic effects between hetero-atoms for the rational design of DACs.