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.

Activity And Stability of Single- And Di-Atom Catalysts for the O2 Reduction Reaction.

Efficient and inexpensive catalysts for the O2 reduction reaction (ORR) are needed for the advancement of renewable energy technologies. In this study, we designed a computational catalyst-screening method to identify single and di-atom metal dopants from first-row transition elements supported on defect-containing nitrogenated graphene surfaces for the ORR. Based on formation-energy calculations and micro-kinetic modelling of reaction pathways using intermediate binding free energies, we have identified four potentially interesting single-atom catalysts (SACs) and fifteen di-atom catalysts (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, 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.

Bio-inspired Cu(II) amido-quinoline complexes as catalysts for aromatic C-H bond hydroxylation.

Cu(II) complexes supported by tetradentate amido-quinoline acyclic ligands (L1 & L2) have been synthesized, characterized, and employed as catalysts for aromatic C-H hydroxylation using H2O2 as an oxidant in the absence of an external base with a high selectivity of around 90% for phenols via the non-radical pathway (TON ≥720). The KIE value, various spectroscopic studies and DFT calculation supported the involvement of Cu(II)-OOH species.

Oxygen Evolution and Reduction on Two-Dimensional Transition Metal Dichalcogenides.

Motivated by the need to find good electrocatalysts for water oxidation and O2 reduction, composed of nontoxic and earth-abundant elements, a systematic screening of two-dimensional (2D) transition metal dichalcogenides (TMDCs) is performed. To identify compounds that are intrinsically active and can fully take advantage of the high surface area of 2D catalysts, this study focuses on the properties of the ideal basal planes of 2D TMDCs, in the 2H, 1T, and 1T' phases. Over two hundred materials proposed in computational databases are studied by means of first-principles-based simulations coupled with continuum embedding models to account for the presence of electrochemical environments. The best candidates with overpotentials for the oxygen evolution and reduction reactions (OER and ORR) lower than 0.5 V under acidic conditions and higher stability against degradation in electrochemical environments are selected. For OER, the designed workflow identifies one active and thermodynamically stable material, and seven materials that are metastable at the oxidative potentials and acidic pH. On the other hand, for ORR, we identify 20 materials with overpotentials less than 0.5 V. Among these compounds, six bifunctional materials have been experimentally reported, with 1T-NbTe2 and 1T'-MoTe2 being the best performing catalysts for OER and ORR, respectively.

Computational Screening of Single and Di-Atom Catalysts for Electrochemical CO2 Reduction.

Supported single atom catalysts on defected graphene show great potential for electrochemical reduction of CO2 to CO. In this study, we perform a computational screening of single and di-atom catalysts (MNCs and FeMNC respectively) with M varying from Sc to Zn on nitrogen-doped graphene for CO2 reduction using hybrid-density functional theory and potential dependent micro-kinetic modeling. The formation energy calculations reveal several stable single and di-atom doping site motifs. We consider the kinetics of CO2 using the binding energies of CO2* and COOH* intermediates as the descriptors to analyze the activity of these catalysts. In comparison to (211) transition metal (TM) surfaces, both MNCs and FeMNCs show a variety of binding motifs of the reaction intermediates on different metal dopants. We find four MNCs as CrNC, MnNC, FeNC, and CoNC with high catalytic efficiency for CO2R. Among the different FeMNCs with varying doping geometry and surrounding N-coordination, we have identified 11 candidates having high TOF for CO production and lower selectivity for the hydrogen evolution reaction. FeMnNC shows the highest activity for CO2R. Large CO2* dipole-field interactions in both the MNCs and FeMNCs give rise to deviations in scaling from TM surfaces.

A theoretical analysis of the structure and properties of B26H30 isomers. Consequences to the laser and semiconductor doping capabilities of large borane clusters.

Decaborane(14), nido-B10H14, is the major commercially available molecular building block in boron cluster chemistry. The condensation of two such {nido-B10} blocks gives the known isomers of B18H22- a molecule used in the fabrication of p-type semiconductors and capable of blue laser emission. Here, we computationally determine the structures and thermodynamic stabilities of 20 possible B26H30 regioisomers constructed from the fusion of three {nido-B10} blocks with the three subclusters conjoined by two-boron atom shared edges. In addition, density functional theory, time-dependent (TD)-DFT and multiconfigurational CASPT2 methods have been used to model and investigate the physical and photophysical properties of the three most stable of these isomers. Our findings predict these isomers to be potentially useful materials for the semiconductor industry, as high boron-content doping agents, and in the fabrication of new optical materials.

Overlap of Radial Dangling Orbitals Controls the Relative Stabilities of Polyhedral B nH n- x Isomers ( n = 5-12, x = 0 to n - 1).

The removal of H atoms from polyhedral boranes results in the formation of dangling radial orbitals with one electron each. If there is a requirement of electrons for skeletal bonding to meet the Wade's rule, these are provided from the exohedral orbitals. Additional electrons occupy a linear combination of the dangling orbitals. Stabilization of these molecular orbitals depends on their overlap. The lateral (sideways) overlap of dangling orbitals decreases with the decreasing cluster size from 12 to 5 boron atoms as the orbitals become more and more splayed out. Thus, as the number of dangling orbitals increases, the destabilization of their combinations increases at a higher rate for smaller polyhedral boranes, leading to flat structures with the removal of a fewer number of hydrogens. Though exohedral orbitals form better overlap in larger polyhedral clusters, the increase of electrons with the removal of H atoms results in occupancy of antibonding skeletal orbitals (beyond Wade's rules) and leads to flat structures. The reverse happens when hydrogens are added to a flat cluster. Substitution of BH by Si does not change structural patterns.

Nanoisozymes: Crystal-Facet-Dependent Enzyme-Mimetic Activity of V2 O5 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 (H2 O2 ) level. Herein we report, for the first time, that the redox properties and GPx-like activity of V2 O5 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.

The Role of Holes in Borophenes: An Ab†Initio Study of Their Structure and Stability with and without Metal Templates.

An electron-counting strategy starting from magnesium boride was used to show the inevitability of hexagonal holes in 2D borophene. The number (hole density, HD) and distribution of the hexagonal holes determine the binding energy per boron atom in monolayer borophenes. The relationship between binding energy and HD changes dramatically when the borophene is placed on a Ag(111) surface. The distribution of holes in borophenes on Ag(111) surfaces depends on the temperature. DFT calculations show that aside from the previously reported S1 and S2 borophene phases, other polymorphs may also be competitive. Plots of the electron density distribution of the boron sheets suggest that the observed STM image of an S2 phase corresponds to a sheet with a HD of 2/15 instead of a sheet with a HD of 1/5. The hole density and the hole distribution echo the distribution of vacancies and extra occupancies in complex ß-rhombohedral boron.

Exohedral Complexation of B40 , C60 and Arenes with Transition Metals: A Comparative DFT Study.

Holes are inevitable in borospherenes. The surface topography of B40 and its π MOs isolobal to benzene allow for better η7 -, η6 - and η3 - exohedral complexation with transition metal fragments than it is possible with C60 and arenes. η7 -complexes of B40 is lower in energy than the η6 -complexes for metal fragments such as C5 H5 Mn, C4 H4 Fe, and C3 H3 Co that have relatively diffuse frontier orbitals. The fragment C6 H6 Cr prefers η6 -coordination. Near-isodesmic equations based on density functional theory computations of the transition metal complexes of B40 , C60 and C6 H6 support these anticipations. Transition metal complexation increases the stability of B40 .