Effective methane conversion to methanol on bi-functional graphene-oxide-supported platinum nanoclusters (Pt5) - a DFT study.

Nowadays identifying a high-performance catalyst for converting methane to methanol is crucial because methanol serves as an excellent energy source and has wide chemical applications. In the present study, we used DFT, a computational chemistry method, to investigate the reaction mechanism of methanol production by conversion of methane on Pt5 nanoparticles supported on graphene oxide (GO) substrates. Computational results predicted that the Pt5/GO system exhibits excellent catalysis efficiency, compared with those of the previously examined Pt2/GO and Pt2O2/GO systems. Energetics of examined molecular species and the reaction mechanism showed that the Pt5/GO system exhibits high stability in this catalysis reaction and catalyzes the reaction efficiently. Moreover, between the two investigated surfaces GO and UGO, GO performed better and should be a promising catalyst support to convert methane into methanol.

Termination Effects of Pt/v-Ti n+1C nT2 MXene Surfaces for Oxygen Reduction Reaction Catalysis.

Ideal catalysts for the oxygen reduction reaction (ORR) have been searched and researched for decades with the goal to overcome the overpotential problem in proton exchange membrane fuel cells. A recent experimental study reports the application of Pt nanoparticles on the newly discovered 2D material, MXene, with high stability and good performance in ORR. In this work, we simulate the Ti n+1C nT x and the Pt-decorated Pt/v-Ti n+1C nT x ( n = 1-3, T = O and/or F) surfaces by first-principles calculations. We focus on the termination effects of MXene, which may be an important factor to enhance the performance of ORR. The properties of different surfaces are clarified by exhaustive computational analyses on the geometries, charges, and their electronic structures. The free-energy diagrams as well as the volcano plots for ORR are also calculated. On the basis of our results, the F-terminated surfaces are predicted to show a better performance for ORR but with a lower stability than the O-terminated counterparts, and the underlying mechanisms are investigated in detail. This study provides a better understanding of the electronic effect induced by the terminators and may inspire realizations of practical MXene systems for ORR catalysis.

Cation-Directed Selective Polysulfide Stabilization in Alkali Metal-Sulfur Batteries.

Alkali metal sulfur redox chemistry offers promising potential for high-energy-density energy storage. Fundamental understanding of alkali metal sulfur redox reactions is the prerequisite for rational designs of electrode and electrolyte. Here, we revealed a strong impact of alkali metal cation (Li+, Na+, K+, and Rb+) on polysulfide (PS) stability, redox reversibility, and solid product passivation. We employed operando UV-vis spectroscopy to show that strongly negatively charged short-chain PS (e.g., S42-/S32-) is more stabilized in the electrolyte with larger cation (e.g., Rb+) than that with the smaller cation (e.g., Li+), which is attributed to a stronger cation-anion electrostatic interaction between Rb+ and S42-/S32- owing to its weaker solvation energy. In contrast, Li+ is much more strongly solvated by solvent and thus exhibits a weaker electrostatic interaction with S42-/S32-. The stabilization of short-chain PS in K+-, Rb+-sulfur cells promotes the reduction of long-chain PS to short-chain PS, leading to high discharge potential. However, it discourages the oxidation of short-chain PS to long-chain PS, leading to poor charge reversibility. Our work directly probes alkali metal-sulfur redox chemistry in operando and provides critical insights into alkali metal sulfur reaction mechanism.

Adsorption and dehydrogenation of ethane, propane and butane on Rh13 clusters supported on unzipped graphene oxide and TiO2(110) - a DFT study.

The catalytic activity for the adsorption and dehydrogenation of alkanes (CnH2n+2, n = 2, 3, 4) on a low-symmetry Rh13 cluster (Rh13-Ls) is compared with a system consisting of the same cluster (Rh13-Ls) supported on either an unzipped graphene-oxide (UGO) sheet (Rh13-Ls/UGO) or a TiO2(110) surface (Rh13-Ls/TiO2). The adsorption energies of these alkanes, calculated using density-functional theory, follow the order Rh13-Ls/TiO2 ≈ Rh13-Ls/UGO > Rh13-Ls. Our proposed reaction path for the dehydrogenation of ethane, propane and butane on Rh13-Ls/UGO has first barrier heights of 0.21, 0.22 and 0.16 eV for the dissociation of a terminal C-H bond to form -C2H5, -C3H7 and -C4H9, respectively. Compared with the barriers on Rh13-Ls and Rh13-Ls/TiO2, the barrier on Rh13-Ls/UGO is the lowest for all alkanes. The calculated data, including the electronic distribution and the density of states of alkanes adsorbed on Rh13-Ls/UGO, Rh13-Ls and Rh13-Ls/TiO2, to support our results are presented.