Preferred surface orientation for CO oxidation on SnO2 surfaces.

In the present study, we perform a comparative study on the oxidation mechanism of CO gas molecules on SnO2 (110), (101), and (100) surfaces. The optimized adsorption configurations show that the adsorption of CO molecules could occur similarly on the three SnO2 surfaces via two adsorption modes, physisorption of CO on the Sn5c site that is considered as the first step for CO oxidation, followed by CO chemisorption on the O2c site resulting in the formation of CO2 species. Based on the calculated adsorption energies and CO molecule diffusion on SnO2 surfaces, CO molecule adsorption on the (101) surface exhibits the highest adsorption energy and the lowest reaction barrier for CO oxidation compared to the widely considered (110) surface or the (100) surface. These findings are expected to have a major impact on improving sensing properties toward toxic gas by means of surface-orientation engineering.

Photocatalytic Properties of ZnO:Al/MAPbI3/Fe2O3 Heterostructure: First-Principles Calculations.

We report on theoretical investigations of a methylammonium lead halide perovskite system loaded with iron oxide and aluminum zinc oxide (ZnO:Al/MAPbI3/Fe2O3) as a potential photocatalyst. When excited with visible light, this heterostructure is demonstrated to achieve a high hydrogen production yield via a z-scheme photocatalysis mechanism. The Fe2O3: MAPbI3 heterojunction plays the role of an electron donor, favoring the hydrogen evolution reaction (HER), and the ZnO:Al compound acts as a shield against ions, preventing the surface degradation of MAPbI3 during the reaction, hence improving the charge transfer in the electrolyte. Moreover, our findings indicate that the ZnO:Al/MAPbI3 heterostructure effectively enhances electrons/holes separation and reduces their recombination, which drastically improves the photocatalytic activity. Based on our calculations, our heterostructure yields a high hydrogen production rate, estimated to be 265.05 µmol/g and 362.99 µmol/g, respectively, for a neutral pH and an acidic pH of 5. These theoretical yield values are very promising and provide interesting inputs for the development of stable halide perovskites known for their superlative photocatalytic properties.

A BC2N/blue phosphorene heterostructure as an anode material for high-performance sodium-ion batteries: first principles insights.

Blue phosphorene (Blu-Pn) is a new phosphorene allotrope capable of hosting a substantial amount of sodium (Na) atoms. However, it has been reported to exhibit low electrical conductivity, chemical sensitivity, and structural stability, thus limiting its utility as an anode material for Na-ion batteries (NIBs). In this work, we introduce BC2N as a protective layer for Blu-Pn. Based on van der Waals (vdW) corrected density functional theory (DFT), we conduct a comprehensive first-principles study to explore the main electrochemical properties of the BC2N/Blu-Pn vdW heterostructure. The BC2N/Blu-Pn system exhibits a small band-gap of 0.03 eV that fades away and indicates metallic behavior upon Na adsorption. Furthermore, the binding energy of Na incorporated into the inter-layer of the BC2N/Blu-Pn system is lower (-2.03 eV) compared with those of free-standing BC2N (-1.25 eV) and Blu-Pn monolayer (-1.52 eV). Therefore, the growth of Na dendrites can be avoided. Furthermore, the migration energy barrier for the BC2N/Blu-Pn system is about 0.11 eV, indicating fast Na diffusion and excellent rate performance. Moreover, the theoretical storage capacity is 763 mA h g-1. Finally, we show that the intercalation of Na in the BC2N/Blu-Pn system has the advantage of a small average voltage of approximately 0.24 V. Besides these properties, the proposed heterostructure is based on chemical elements that are widely available and technologically established and have low atomic mass, which are all advantages for Na-ion battery applications.

Improved Power Conversion Efficiency with Tunable Electronic Structures of the Cation-Engineered [Ai]PbI3 Perovskites for Solar Cells: First-Principles Calculations.

Higher power conversion efficiencies for photovoltaic devices can be achieved through simple and low production cost processing of APbI3(A=CH3NH3,CHN2H4,…) perovskites. Due to their limited long-term stability, however, there is an urgent need to find alternative structural combinations for this family of materials. In this study, we propose to investigate the prospects of cation-substitution within the A-site of the APbI3 perovskite by selecting nine substituting organic and inorganic cations to enhance the stability of the material. The tolerance and the octahedral factors are calculated and reported as two of the most critical geometrical features, in order to assess which perovskite compounds can be experimentally designed. Our results showed an improvement in the thermal stability of the organic cation substitutions in contrast to the inorganic cations, with an increase in the power conversion efficiency of the Hydroxyl-ammonium (NH3OH) substitute to η = 25.84%.