Activity and Stability of Single- and Di-atom catalysts for O₂ reduction reaction

Efficient and in-expensive catalysts for the O2 reduction reaction (ORR) is needed for advancement of renewable energy technologies. In this study, we design a computational catalyst screening method to identify single and di-atom metal dopants from first-row transition elements supported on defected nitrogenated graphene surfaces for ORR. Based upon the formation energy calculations and micro-kinetic modelling of reaction pathways using the intermediate binding free energies, we have identified four potentially interesting SACs and fifteen DACs with relatively high estimated catalytic activity at 0.8 V vs RHE. Among the best SACs, MnNC shows high stability in both acidic and alkaline media according to our model. For the DACs, we found four possible candidates as MnMn, FeFe, CoCo and MnNi doped on quad-atom vacancy sites having considerable stability over a wide pH range. The remaining SACs and DACs with high activity are either less stable or show a stability region at an alkaline pH

Fragment approach to the electronic structure of tau -boron allotrope

The presence of nonconventional bonding features is an intriguing part of elemental boron. The recent addition of tau boron to the family of three-dimensional boron allotropes is no exception. We provide an understanding of the electronic structure of t boron using a fragment molecular approach, where the effect of symmetry reduction on skeletal bands of B-12 and the B-57 fragments are examined qualitatively by analyzing the projected density of states of these fragments. In spite of the structural resemblance to beta boron, the reduction of symmetry from a rhombohedral space group to the orthorhombic one destabilizes the bands and reduces the electronic requirements. This suggests the presence of the partially occupied boron sites, as seen for a beta boron unit cell, and draws the possibility for the existence of different energetically similar polymorphs. tau boron has a lower binding energy than beta boron

The dynamic behavior of the exohedral transition metal complexes of B-40 : eta(6)- and eta(7)-B40Cr(CO)(3) and Cr(CO)(3)-eta(7)-B-40-eta(7)-Cr(CO)(3)

The dynamic nature of the exohedral - and the -complexes of with has been explored using density functional theory. The ab initio molecular dynamic simulations were performed at 1200 K to investigate the fluxionality of the heptagonal and hexagonal faces of exohedral complexes. Our computations show that the coordination of the faces with fragment reduces its fluxionality to a limited extent. The activation barrier for the inter-conversion of the heptagonal and hexagonal rings in - complex is around 15.2 kcal/mol whereas in the - complex, it is slightly higher at around 19.7 kcal/mol. The coordination with another fragment is found to be equally exergonic, with a barrier for interconversion of 21.5 kcal/mol. The HOMO-LUMO gap is almost similar as the mono-metallated complexes. The di-metallated complexes also show a dynamical behavior of the six and seven membered rings at 1200 K

Metal Templates and Boron Sources Controlling Borophene Structures: An Ab Initio Study

Interlayer binding of 2D borophene phases are determined as a function of hole density (HD) and metal surfaces Cu, Ag, and Au. The Cu surface prefers formation of monolayers whereas the Au surface shows multilayer stacking. Ag surface enables formation of monolayers with higher HD and bilayers for borophenes with lower HD. The growth pattern of bilayers on metal templates are investigated using <i>ab</i>-initio molecular dynamic simulations. Formation of icosahedral B₁₂ clusters and extension to sheets are also studied on Cu surface. Icosahedral sheet formation by boron atom deposition is found to be a thermodynamically unfavorable process on this surface. Thus, structure of borophene phases could also be tuned by modulating the parameters such as boron source or the metal templates, in addition to the substrate temperature and boron atom deposition rate

Thermodynamic and Kinetic Modeling of Electrocatalytic Reactions Using a First-Principles Approach

The computational modeling of electrochemical interfaces and their applications in electrocatalysis has attracted great attention in recent years. While tremendous progress has been made in this area, however, the accurate atomistic descriptions at the electrode/electrolyte interfaces remain a great challenge. The Computational Hydrogen Electrode (CHE) method and continuum modeling of the solvent and electrolyte interactions form the basis for most of these methodological developments. Several posterior corrections have been added to the CHE method to improve its accuracy and widen its applications. The most recently developed grand canonical potential approaches with the embedded diffuse layer models have shown considerable improvement in defining interfacial interactions at electrode/electrolyte interfaces over the state-of-the-art computational models for electrocatalysis. In this Review, we present an overview of these different computational models developed over the years to quantitatively probe the thermodynamics and kinetics of electrochemical reactions in the presence of an electrified catalyst surface under various electrochemical environments. We begin our discussion by giving a brief picture of the different continuum solvation approaches, implemented within the ab initio method to effectively model the solvent and electrolyte interactions. Next, we present the thermodynamic and kinetic modeling approaches to determine the activity and stability of the electrocatalysts. A few applications to these approaches are also discussed. We conclude by giving an outlook on the different machine learning models that have been integrated with the thermodynamic approaches to improve their efficiency and widen their applicability

Nanoisozymes: Crystal-Facet-Dependent Enzyme-Mimetic Activity of V2O5 Nanomaterials

Nanomaterials with enzyme-like activity (nanozymes) attract significant interest owing to their applications in biomedical research. Particularly, redox nanozymes that exhibit glutathione peroxidase (GPx)-like activity play important roles in cellular signaling by controlling the hydrogen peroxide (H2O2) level. Herein we report, for the first time, that the redox properties and GPx-like activity of V2O5 nanozyme depends not only on the size and morphology, but also on the crystal facets exposed on the surface within the same crystal system of the nanomaterials. These results suggest that the surface of the nanomaterials can be engineered to fine-tune their redox properties to act as nanoisozymes for specific biological applications