RESUMO
The Fe-based Prussian blue (Fe-PB) composite is considered as one of the most potential cathode materials for sodium-ion batteries because of its abundant iron resources and high theoretical capacity. However, the crystal water and vacancy in the Fe-PB structure will lead to poor capacity and cycle stability. In this work, a Cu-modified Fe-PB composite (FeCu-PB@CuO) is successfully prepared through regulating the Fe-PB structure by Cu doping and engineering the surface by CuO coating. The density functional theory calculation results confirm that Cu preferentially replaces FeHS in the Fe-PB lattice and Cu doping reduces the bandgap. Our experiment results reveal that CuO coating can provide more active sites, inhibit side reactions, and potentially enhance the activity of FeHS. Due to the synergistic effect of Cu doping and CuO coating, FeCu-PB@CuO has a considerable initial discharge capacity of 123.5 mAh g-1 at 0.1 A g-1. In particular, at 2 A g-1, it delivers an impressive initial capacity of 84.3 mAh g-1, and the capacity decreasing rate of each cycle is only 0.02% over 1500 cycles. Therefore, the synergistic modification strategy of metal ion doping and metal oxide coating has tremendous application potential and can be extended to other electrode materials.
RESUMO
Iron-based Prussian blue (FeHCF) has great application potential in the large-scale production of sodium-ion (Na+) batteries because of its high theoretical capacity and abundant Fe ore resources. However, the Fe(CN)6 vacancies and crystal water seriously affect the electrochemical performance. Herein, a Cu-doped FeHCF (Cu-FeHCF) cathode material is successfully prepared directly by a coprecipitation method. After Cu doping, the monoclinic structure and the quasi-cubic morphology are retained, but the electrochemical performance is significantly improved. In addition to few Fe(CN)6 vacancies and low crystal water, the improved performance is also related to the enhanced electrochemical activity of low-spin Fe and the stabilizing effect of Cu on the crystal structure. Moreover, Cu doping also controls the side reaction to a certain extent. As a result, after Cu doping, the initial discharge capacity is enhanced from 107.9 to 127.4 mA h g-1 at 100 mA g-1, especially the capacities contributed by low-spin Fe increase from 30.0, 21.7, and 16.7 mA h g-1 to 48.8, 45.4, and 43.7 mA h g-1 for the first three cycles, respectively. Even at 2 A g-1, Cu-FeHCF still has a promising initial capacity of 82.3 mA h g-1 and only a 0.047% capacity decay rate for each cycle over 500 cycles. Therefore, Cu-FeHCF shows excellent application potential in the field of Na+ energy storage batteries.
RESUMO
OBJECTIVE: To investigate the association of plasma homocysteine and OSA (obstructive sleep apnea) syndrome in ischemic stroke (IS). METHODS: A total of 92 male IS patients were classified by apnea hypopnea index (AHI) into 2 groups: non-OSA group (AHI < 5/h) and OSA group (AHI > or = 5). All patients were tested for plasma homocysteine when polysomnography was finished at (14 +/- 2) d after the onset of IS. RESULTS: The mean level of homocysteine was significantly higher in the OSA group than that in the non-OSA group (17 +/- 5 vs 11 +/- 3 micromol/L, P < 0.01). Pearson correlation analysis revealed a positive correlation between the homocysteine level and the severity of AHI (r = 0.482, P < 0.01). Further multiple linear regression analysis showed that AHI and folate were independent predictors of homocysteine level (R2 = 0.553, P < 0.01, beta for AHI = 0.671, beta for folate = -0.256). CONCLUSION: The severity of OSA is significantly associated with an elevated level of homocysteine in IS patients. And this association is independent of other causative factors of an elevated level of homocysteine.