ABSTRACT
Cobalt-promoted molybdenum sulfide (CoMoS) is known as a promising catalyst for H2 evolution reaction and hydrogen desulfurization reaction. This material exhibits superior catalytic activity as compared to its pristine molybdenum sulfide counterpart. However, revealing the actual structure of cobalt-promoted molybdenum sulfide as well as the plausible contribution of a cobalt promoter is still challenging, especially when the material has an amorphous nature. Herein, we report, for the first time, on the use of positron annihilation spectroscopy (PAS), being a nondestructive nuclear radiation-based method, to visualize the position of a Co promoter within the structure of MoS at the atomic scale, which is inaccessible by conventional characterization tools. It is found that at low concentrations, a Co atom occupies preferably the Mo-vacancies, thus generating the ternary phase CoMoS whose structure is composed of a Co-S-Mo building block. Increasing the Co concentration, e.g., a Co/Mo molar ratio of higher than 1.12/1, leads to the occupation of both Mo-vacancies and S-vacancies by Co. In this case, secondary phases such as MoS and CoS are also produced together with the CoMoS one. Combining the PAS and electrochemical analyses, we highlight the important contribution of a Co promoter to enhancing the catalytic H2 evolution activity. Having more Co promoter in the Mo-vacancies promotes the H2 evolution rate, whereas having Co in the S-vacancies causes a drop in H2 evolution ability. Furthermore, the occupation of Co to the S-vacancies leads also to the destabilization of the CoMoS catalyst, resulting in a rapid degradation of catalytic activity.
ABSTRACT
OBJECTIVE: This study evaluated the effectiveness of Paraffin oil versus Mineral oil for day-5 embryo culture in couples undergoing assisted reproductive technology (ART). METHODS: We performed a multi-centre, retrospective cohort study at IVFMD (My Duc Hospital) and IVFMD Phu Nhuan (My Duc Phu Nhuan Hospital) from January 2019 to September 2019. We studied couples treated by intracytoplasmic sperm injection (ICSI), using fresh, ejaculated semen and undergoing day-5 embryo transfer. Couples who underwent in vitro maturation (IVM) or oocyte donation cycles or couples where the woman had uterine abnormalities were excluded. From January 2019 to May 2019, we used Mineral oil (LiteOil, LifeGlobal) while Paraffin oil (Liquid Paraffin, Origio) was used from June 2019 to September 2019. The primary outcome was live birth rate after the first transfer, either from a fresh transfer or frozen embryo transfer. RESULTS: Between 1st January 2019 to 30th September 2019, there were 2,312 couples undergoing ART in both centres, of which 762 (377 in the Paraffin group and 385 in the Mineral group) eligible couples were included in the study. Baseline characteristics of couples were comparable between the two groups, with mean female age 31.5 ± 4.3 versus 31.9 ± 4.7 in the Paraffin and Mineral group. Live birth after the first transfer occurred in 153 (40.6%) couples in the Paraffin group, compared to 152 (39.5%) couples in the Mineral group (risk ratio 1.02, 95% confidence interval 0.91 - 1.14). Other secondary outcomes were comparable between the two groups. CONCLUSION: In day-5 embryo culture, Paraffin and Mineral oil resulted in a comparable live birth rate.
