Effect of the oxygen vacancy electronic state on Ni migration in Li0.5(Ni0.8Mn0.1Co0.1)O2 cathode material.

Cation migration coupled with oxygen vacancy formation is known to drive the layered to disordered spinel/rock-salt phase transformation in the high-Ni layered oxide cathodes of Li-ion batteries. However, the effect of different electronic states of oxygen vacancies on the cation migration still remains elusive. Here, we investigate Ni migration in delithiated Ni-rich Li0.5Ni0.8Mn0.1Co0.1O2 (hence Li0.5NMC811) in the presence of neutral and charged oxygen vacancies by means of first-principles density functional theory (DFT) calculations coupled with the nudged elastic band (NEB) method. We find that oxygen vacancies with neutral or +2 charge favor the Ni migration to Li tetrahedral and/or octahedral sites, both thermodynamically and kinetically. As for the case of +1 charged oxygen vacancies, while they thermodynamicaly favor the Ni migration to the Li site, the relatively high migration barrier suggests that they kinetically prohibit the Ni migration. Our results suggest that controlling the formation of oxygen vacancies is the key to enhancing the Ni-rich NMC structural stability in particular in their charged states.

Molecular insight into the role of zeolite lattice constraints on methane activation over the Cu-O-Cu active site.

Understanding the factors that influence the activity of a catalyst toward CH4 activation is of high importance for tuning the catalyst performance or designing new, better catalysts. Here, we performed a set of density functional theory (DFT) calculations on the H-CH3 bond cleavage over the Cu-O-Cu active site in the MOR zeolite with various Al-pair arrangements to obtain molecular insight into the structure-activity relation and clarify key parameters that define the Cu-O-Cu reactivity toward CH4. We found that weakening of the Cu-O-Cu bond during CH4 activation is crucial for determining the O-H bond strength and thus the Cu-O-Cu reactivity. In this regard, the zeolite lattice constraints are found to play a significant role as, on the one hand, it strengthens the Cu⋯Cu interaction and consequently weakens the Cu-O-Cu bonds and, on the other hand, it forces the Cu-O-Cu bond elongation process to destabilize the active site structure. The non-planar Cu-O-Cu geometry, due to lattice constraints, is also found to make the CH4 adsorption site, whether positioned closer to the µ-O or the Cu atom, crucial in determining the C-H activation product, i.e., a ˙CH3 radical or a Cu2-CH3- ligand.

Tunable Concave Surface Features of Mesoporous Palladium Nanocrystals Prepared from Supramolecular Micellar Templates.

Concave metallic nanocrystals with a high density of low-coordinated atoms on the surface are essential for the realization of unique catalytic properties. Herein, mesoporous palladium nanocrystals (MPNs) that possess various degrees of curvature are successfully synthesized following an approach that relies on a facile polymeric micelle assembly approach. The as-prepared MPNs exhibit larger surface areas compared to conventional Pd nanocrystals and their nonporous counterparts. The MPNs display enhanced electrocatalytic activity for ethanol oxidation when compared to state-of-the-art commercial palladium black and conventional palladium nanocubes used as catalysts. Interestingly, as the degree of curvature increases, the surface-area-normalized activity also increases, demonstrating that the curvature of MPNs and the presence of high-index facets are crucial considerations for the design of electrocatalysts.

DFT and microkinetic investigation of methanol synthesis via CO2 hydrogenation on Ni(111)-based surfaces.

A DFT study of methanol production via CO2 hydrogenation reactions on clean Ni(111) and Ni(111)-M (M = Cu, Pd, Pt, or Rh) surfaces has been performed. The reaction network of this synthesis reaction has been determined using energy profiles. The competing reaction network between the formate-mediated route and the carboxyl-mediated route is also presented. Both routes are equally possible in mediating the overall synthesis reactions. A simple selectivity analysis based on the energy barrier shows that methanol synthesis is more preferred rather than formic acid (HCOOH) or carbon monoxide (CO) production. A mean-field kinetic analysis is also employed to determine the kinetic performance of all catalytic surfaces. The formate-mediated route is found to be energetically and kinetically more dominant than the carboxyl-mediated route. Cu, Pd, and Pt dopants are successful in increasing the kinetic performance of the clean Ni(111) surface in the formate route and Cu, Pt, and Rh dopants in the carboxyl route.

Density functional study of methyl butanoate adsorption and its C-O bonds cleavage on MoS2-based catalyst with various loads of Ni promoters.

Due to the increasing demands of new and renewable energy sources by utilising plant oils, uncovering the underlying physico-chemical phenomena at the atomic level responsible for the effective deoxygenation plays a vital role in improving the performance of well-known as well as in looking for the possible new catalysts. This study aims at investigating the adsorption and C-O bonds cleavage of methyl butanoate (MB) over MoS2-based catalyst with various loads of Ni promoters by using first-principles density functional theory (DFT). This study employs surface model that never been used by previous researchers for their investigations of adsorption and bonds cleavage on Ni promoted MoS2-based catalysts. The introduction of nickel into MoS2-based catalyst allows the surface charges when interacts with MB to redistribute in such a way that induces stronger Coulombic attractive forces. This in turn could result in a more stable adsorption configuration. However only in certain Ni-loads will results in the most stable adsorption. Nevertheless the most stable adsorption of MB occurs on M-edge configuration which consists of two Ni atoms, i.e. M-2-Ni-A with adsorption energy at about -2.96 eV. As a comparison, the adsorption energy of MoS2 with the absent of Ni, i.e. M-0-Ni is just -2.79 eV. Since there are three C-O bonds in MB, this study proposes three possible reactions for these bonds to cleave. By using CI-NEB method, the activation energies of those three reaction are calculated. It shows that the presence of Ni with appropriate load could promote C-O bond cleavage, especially in one reaction C-O bond is weaken considerably. Further evaluation on bond dissociation energies of the closest C-C bond to the catalyst surface, M-2-Ni-A shows better reactivity on C-C bond cleavage than M-0-Ni, disregarding of those three reaction routes.

First principles calculation on the adsorption of water on lithium-montmorillonite (Li-MMT).

The interaction of water molecules and lithium-montmorillonite (Li-MMT) is theoretically investigated using density functional theory (DFT) based first principles calculation. The mechanism of water adsorption at two different water concentrations on Li-MMT as well as their structural and electronic properties are investigated. It is found that the adsorption stability in Li-MMT is higher in higher water concentration. It is also found that an adsorbed water molecule on Li-MMT causes the Li to protrude from the MMT surface, so it is expected that Li may be mobile on H(2)O/Li-MMT.