Dual-Metal Active Sites Mediated by p-Block Elements: Knowledge-Driven Design of Oxygen Reduction Reaction Catalysts.

In this study, the oxygen reduction reaction (ORR) process of dual-metal active site catalysts (FeMN6-Gra, M = Mn, Ni, Co, or Cu) mediated by p-block elements was investigated using density functional theory calculations. The obtained results demonstrate that, in most cases, the B-doped FeMN6-Gra (M = Mn, Ni, Co, or Cu) catalysts exhibit higher catalytic performance than their undoped counterparts. Among the investigated catalysts, FeNiN6-Gra doping by B modulates the adsorption strength of the metal center on the oxygen-containing intermediates, showing the largest increase in the onset potential (from 0.66 to 0.94 V). Importantly, we found a new law that B-doping affects the total charge of the metal adsorption site and the four surrounding N atoms and that there is a linear relationship between the total charge and the Gibbs free energy. Transition state analysis shows that the energy barrier of the thermodynamic rate-determining step (*OH hydrogenation to H2O) in the FeNiN6B1-Gra-catalyzed ORR process is 0.17 eV, which is smaller than that of the FeNiN6-Gra-catalyzed process (0.28 eV). Overall, the results demonstrate that B-doping can improve the activity of FeMN6-Gra catalysts and provide a new method for the future development of efficient electrocatalysts.

Rational design of M-N4-Gr/V2C heterostructures as highly active ORR catalysts: a density functional theory study.

Inspired by the composites of N-doped graphene and transition metal-based materials as well as MXene-based materials, heterostructures (M-N4-Gr/V2C) of eight different transition metals (M = Ti, Cr, Mn, Fe, Co, Ni, Cu, and Zn) doped with nitrogen-coordinated graphene and V2C as potential catalysts for the oxygen reduction reaction (ORR) using density functional theory (DFT) were designed and are described herein. The calculations showed that the heterostructure catalysts (except for Zn-N4-Gr/V2C) were thermodynamically stable. Ni-N4-Gr/V2C and Co-N4-Gr/V2C showed higher activities towards the ORR, with overpotentials as low as 0.32 and 0.45 V, respectively. Excellent catalytic performance results were observed from the change in electronic structure caused by the strong interaction between V2C and the graphene layers as well as the synergistic effect between the MN4 groups and the graphene layers. This study further provides insights into the practical application of ORR catalysts for MXene systems through the modulation of the electronic structure of two-dimensional materials.

Study of photogenerated exciton dissociation in transition metal dichalcogenide van der Waals heterojunction A2-MWS4: a first-principles study.

In order to explore the photocatalytic hydrogen production efficiency of the MoS2/WSe2 heterostructure (A2-MWS4) as a photocatalyst, it is highly desirable to study the photogenerated exciton dissociation related to photocatalysis. The electronic properties, optical absorption, and lattice dynamic properties of A2-MWS4 were investigated using a first-principles approach. The results show that the type II energy band alignment of A2-MWS4 facilitates the dissociation of photogenerated excitons (electrons and holes). The highly localized d-state electrons of A2-MWS4 induce the formation of internal potentials that promote the dissociation of photogenerated excitons. The hot carrier diffuses its extra energy into the lattice by scattering with phonons and forms a hot spot in the lattice while releasing phonons, which are dragged away from the hot spot by Ridley decay to promote exciton dissociation. These findings could provide insights for research studies on photochemical reactions and photovoltaic devices.

A study on hydrogen storage performance of Ti decorated vacancies graphene structure on the first principle.

The structural properties, formation energy, adsorption energy, and electronic properties of vacancy graphene are studied by first-principles analysis. We found that the formation energy and adsorption energy of double vacancy graphene (DVG-4) are the largest. A single defect in DVG-4 can adsorb at least nine hydrogen molecules, and compared with Ti modified single vacancy graphene (SVG-Ti), the adsorption capacity is increased by 80%. When DVG-4 adsorbs the second, third, and fourth hydrogen molecules, the adsorption energy is greater than 0.7 eV, which is not conducive to the release. Density of state (DOS) and electron density difference (EDIFF) results reveal that charge transfer occurs among hydrogen molecules, Ti atoms, and DVG-4, decreasing the hydrogen adsorption capacity of DVG-4 by 33%. DVG - 4 has the potential to become an excellent hydrogen storage material.

Mechanism for hydrogen evolution from water splitting based on a MoS2/WSe2 heterojunction photocatalyst: a first-principle study.

In this study, density functional theory and hybrid functional theory are used to calculate the work function and energy band structure of MoS2 and WSe2, as well as the binding energy, work function, energy band structure, density of states, charge density difference, energy band alignment, Bader charge, and H adsorption free energy of MoS2/WSe2. The difference in work function led to the formation of a built-in electric field from WSe2 to MoS2, and the energy band alignment indicated that the redox reactions were located on the MoS2 and WSe2 semiconductors, respectively. The binding energy of MoS2 and WSe2 indicated that the thermodynamic properties of the heterogeneous structure were stable. MoS2 and WSe2 gathered electrons and holes, respectively, and redistributed them under the action of the built-in electric field. The photogenerated electrons and holes were enriched on the surface of WSe2 and MoS2, which greatly improved the efficiency of hydrogen production by photocatalytic water splitting.