First-principles study of mercaptoundecanoic acid molecule adsorption and gas molecule penetration onto silver surface: an insight for corrosion protection.

Recently, 11-mercaptoundecanoic acid (MUA) molecule has attracted attention as a promising passivation agent of Ag nanowire (NW) network electrode for corrosion inhibition, but the underneath mechanism has not been elaborated. In this work, we investigate adsorption of MUA molecule on Ag(1 0 0) and Ag(1 1 1) surface, adsorption of air gas molecules of H2O, H2S and O2 on MUA molecular end surface, and their penetrations into the Ag surface using the first-principles calculations. Our calculations reveal that the MUA molecule is strongly bound to the Ag surface with the binding energies ranging from -0.47 to -2.06 eV and the Ag-S bond lengths of 2.68-2.97 Å by Lewis acid-base reaction. Furthermore, we find attractive interactions between the gas molecules and the MUA@Ag complexes upon their adsorptions and calculate activation barriers for their migrations from the outermost end of the complexes to the top of Ag surface. It is found that the penetrations of H2O and H2S are more difficult than the O2 penetration due to their higher activation barriers, while the O2 penetration is still difficult, confirming the corrosion protection of Ag NW network by adsorbing the uniform monolayer of MUA. With these findings, this work can contribute to finding a better passivation agent in the strategy of corrosion protection of Ag NW network electrode.

First-principles study of sodium adsorption on defective graphene under propylene carbonate electrolyte conditions.

Hard carbon (HC) has been predominantly used as a typical anode material of sodium-ion batteries (SIBs) but its sodiation mechanism has been debated. In this work, we investigate the adsorption of Na atoms on defective graphene under propylene carbonate (PC) and water solvent as well as vacuum conditions to clarify the sodiation mechanism of HC. Within the joint density functional theory framework, we use the nonlinear polarizable continuum model for PC and the charge-asymmetric nonlocally-determined local electric solvation model for water. Our calculations reveal that the centre of each point defect such as mono-vacancy (MV), di-vacancy (DV) and Stone-Wales is a preferable adsorption site and the electrolyte enhances the Na adsorption through implicit interaction. Furthermore, we calculate the formation energies of multiple Na atom arrangements on the defective graphene and estimate the electrode potential versus Na/Na+, verifying that the multiple Na adsorption on the MV and DV defective graphene under the PC electrolyte conditions is related to the slope region of the discharge curve in HC. This reveals new prospects for optimizing anodes and electrolytes for high performance SIBs.

Point defects and their impact on electrochemical performance in Na0.44MnO2 for sodium-ion battery cathode application.

Sodium manganese oxide Na0.44MnO2 (NMO) in an open structure with large tunnels is of great interest for sodium-ion battery cathode materials due to its high electrode voltage and capacity. However, its practical application is limited by poor rate performance, which can be tuned and improved by controlling point defects. We herein present a comprehensive study of intrinsic point defects in NMO using density functional theory (DFT) calculations in combination with thermodynamics. Using the DFT+U approach, we determine the formation energies of elementary defects and defect complexes depending on the sets of atomic chemical potentials, corresponding to a certain thermodynamic condition for the synthesis of stable NMO. Sodium interstitials are found to have the lowest formation energies in the relevant ranges of temperature and pressure. Other intrinsic point defects such as oxygen vacancies, sodium vacancies and manganese antisites can also be formed with proper formation energies and have an impact on the cathode performance. Compared to the perfect system, oxygen vacancies lower the electrode voltage, whereas manganese vacancies and antisites increase the voltage. We find that most point defects and defect complexes improve the sodium ion diffusivity, highlighting a proper control of defect formation for enhancing the performance of sodium-ion batteries.

Effect of roscovitine pretreatment for increased utilization of small follicle-derived oocytes on developmental competence of somatic cell nuclear transfer embryos in pigs.

The objective of this study was to evaluate the effect of roscovitine pretreatment on the number of matured oocytes per ovary available for somatic cell nuclear transfer (SCNT) and their developmental competence. Irrespective of reproduction status (prepuberty/puberty), the average number of small follicles per ovary (19.3/17.2) was higher than that of medium follicles (1.5/2.7). In the small follicle group, the in vitro maturation rate of COCs pretreated with 50 µM roscovitine (56.1%) was significantly (P < 0.05) higher than that of the control, 25 or 75 µM treatment (15.5%, 23.7% and 35.2%, respectively), while, in the medium follicle group, there was no significant difference between the control, 25, 50 and 75 µM treatment (76.4%, 78.3%, 80.9% and 60.6%, respectively). As a result, a total number of matured oocytes per ovary was greater for 50 µM treatment (11.8) than for the control, 25 or 75 µM treatment (4.4, 5.0 and 6.3, respectively). In the small follicle group, COCs pretreated with 50 µM roscovitine showed dramatically increased blastocyst rate (16.0%) compared to the control (2.9%) (P < 0.05), whereas, in the medium follicle group, there was no significant difference between groups independent of roscovitine treatment (20.8 vs 23.0%). The cloning efficiency in the roscovitine-treated group was not significantly different from that in the control (2.6 vs 1.4%). In conclusion, the present study indicates that roscovitine treatment increased the number of matured oocytes per ovary available for SCNT and did not have any adverse effect on cloning efficiency in pigs.