First-principles investigation of the adsorption of the 2,5-pyridine di-carboxylic acid onto the Cu(011) surface

Unveiling the role of 2D monolayer Mn-doped MoS2 material: toward an efficient electrocatalyst for H2 evolution reaction

Two-dimensional (2D) monolayer pristine MoS₂ transition metal dichalcogenide (TMD) is the most studied material because of its potential applications as nonprecious electrocatalyst for the hydrogen evolution reaction (HER). Previous studies have shown that the basal planes of 2D MoS₂ are catalytically inert, and hence it cannot be used directly in desired applications such as electrochemical HER in industry. Here, we thoroughly studied a defect-engineered Mn-doped 2D monolayer MoS₂ (Mn-MoS₂) material, where Mn was doped in pristine MoS₂ to activate its inert basal planes. Using the density functional theory (DFT) method, we performed rigorous inspection of the electronic structures and properties of the 2D monolayer Mn-MoS₂ as a promising alternative to noble metal-free catalyst for effective HER. A periodic 2D slab of monolayer Mn-MoS₂ was created to study the electronic properties (such as band gap, band structures and total density of states (DOS)) and the reaction pathways occurring on the surface of this material. The detailed HER mechanism was explored by creating an Mn₁Mo₉S₂₁ non-periodic finite molecular cluster model system using the M06-L DFT method including solvation effects to determine the reaction barriers and kinetics. Our study revealed that the 2D Mn-MoS₂ follows the most favorable Volmer-Heyrovsky reaction mechanism with a very low energy barrier during H₂ evolution. It was found that the change in the free energy barrier (ΔG) during the H˙-migration (i.e., Volmer) and Heyrovsky reactions is about 10.34-10.79 kcal mol^-1 (computed in the solvent phase), indicating that this material is an exceptional electrocatalyst for the HER. The Tafel slope (y) was lower in the case of the 2D monolayer Mn-MoS₂ material due to the overlap of the s-orbital of hydrogen and d-orbitals of the Mn atoms in the HOMO and LUMO transition states (TS1 and TS2) of both the Volmer and Heyrovsky reaction steps, respectively. The better stabilization of the atomic orbitals in the HER rate-limiting step Heyrovsky TS2 is the key for reducing the reaction barrier, and thus the overall catalysis, indicating a better electrocatalytic performance for H₂ evolution. This study focused on designing low-cost and efficient electrocatalysts for the HER using earth abundant transition metal dichalcogenides (TMDs) and decreasing the activation energy barriers by scrutinizing the kinetics of the reaction to achieve high reactivity.

A topological model for predicting adsorption energies of polycyclic aromatic hydrocarbons on late-transition metal surfaces

A topological model for the adsorption of PAHs is derived based on an analogy with the formation enthalpies of metal complexes.

We introduce and validate by first-principles calculations an analogy between metal coordination chemistry and the adsorption of polycyclic aromatic hydrocarbons (PAHs) at metal surfaces for the derivation of a model for predicting the PAH adsorption energies. We correlate the binding of PAH on the metal surface with the coordination between metal atom and the ligands in the metal complex, where the formation enthalpy of metal complexes is mainly determined by the strength of a single metal–ligand (M–L) bond and by the number of the M–L bonds. This analogy allows estimation of the adsorption energies only on the basis of the structure of the PAHs and of their adsorption configurations. The adsorption energies of PAHs are found to depend on simple geometric parameters, such as the number of metal–carbon bonds. Moreover, when the lattice of the metal surface is commensurate with the size of benzene rings, the contribution to the adsorption energy from η²-coordination is about twice that from η¹-coordination. These results show that the principles of coordination chemistry can facilitate the modeling of processes at metal surfaces, and pave the way to systematically model reactions involving complex adsorbates at surfaces.