Porous silicon has found wide applications in many different fields including catalysis and lithium-ion batteries. Three-dimensional hierarchical macro-/mesoporous silicon is synthesized from zero-dimensional Stöber silica particles through a facile and scalable magnesiothermic reduction process. By systematic structure characterization of the macro-/mesoporous silicon, a self-templating mechanism governing the formation of the porous silicon is proposed. Applications as lithium-ion battery anode and photocatalytic hydrogen evolution catalyst are demonstrated. It is found that the macro-/mesoporous silicon shows significantly improved cyclic and rate performance over the commercial nanosized and micrometer-sized silicon particles. After 300 cycles at 0.2 A g, the reversible specific capacity is still retained as much as 959 mAh g with a high mass loading density of 1.4 mg cm. With the large current density of 2 A g, a reversible capacity of 632 mAh g is exhibited. The coexistence of both macro- and mesoporous structures is responsible for the enhanced performance. The macro-/mesoporous silicon also shows superior catalytic performance for photocatalytic hydrogen evolution compared to the silicon nanoparticles.

Extensive studies have focused on improving the operational stability of perovskite solar cells but few surveyed the fundamental degradation mechanisms. One aspect overlooked in earlier works is the effect of the atmosphere on the device performance during operation.Here, we investigate the degradation mechanisms of perovskite solar cells operated under vacuum and a nitrogen atmosphere using synchrotron radiation-based operando grazingincidence X-ray scattering methods. Unlike what was seen in previous reports, we find that light-induced phase segregation, lattice shrinkage, and morphology deformation occur under vacuum. Under nitrogen, only lattice shrinkage appears during the operation of solar cells resulting in a better device stability. The different behavior in nitrogen is attributed a larger energy barrier for lattice distortion and phase segregation. Finally, we find that the migration of excessive PbI2 to the interface between the perovskite and the hole transport layer degrade the performance of devices either under vacuum or nitrogen.3 Solution-processed hybrid halide perovskite materials have attracted strong interest for next-generation thin-film photovoltaic applications due to their high power conversion efficiency (PCE) and low fabrication costs compared to silicon photovoltaics 1 . With solvent engineering, compositional tuning, and surface passivation 2-4 , the highest PCE of perovskite solar cells (PSCs) has reached 25.5 % 5 . Moreover, possibility of fabricating PSCs on flexible substrates opens up promising manufacturing routes, and novel application fields are explored, such as lightweight photovoltaic devices for space applications. Previous studies showed that PSCs were successfully operated in space with low vacuum conditions such as on a highaltitude balloon and a suborbital rocket [6][7][8] . Although these pioneers confirmed the possibility of operating PSCs in space, the operational stability of PSCs is unknown under such conditions.In terrestrial studies, vacuum conditions play a major role in the performance loss of PSCs during operation. Thus, although there is such a rapid increase in the PCE, very significant challenges remain. More research is required to increase the stability of the materials and the longevity of the devices, as long-term operational stability remains the main challenge for realworld applications of hybrid halide perovskite materials. Therefore, investigating the performance degradation mechanism of PSCs under different atmospheric conditions is one key approach to further improving the long-term operational stability of PSCs 9 .Exposure to above-bandgap illumination can cause a loss of phase and structure stability for perovskite materials. For instance, phase segregation introduced by lattice distortion, halide migration, and crystalline reorganization can cause an open-circuit voltage penalty arising from halide segregation 10 . In addition, several studies have indicated that a lattice distortion under illumination originates from light excitation or therm...

Silicon (Si) has been regarded as one of the most promising anodes for next-generation lithium-ion batteries (LIBs) due to its exceptional capacity, appropriate voltage profile, and reliable operation safety. However, poor cyclic stability and moderate rate performance have been critical drawbacks to hamper the practical application of Si-based anodes. It has been one of the central issues to develop new strategies to improve the cyclic and rate performance of the Si-based lithium-ion battery anodes. In this work, super-small metal nanoparticles (2.9 nm in diameter) are in situ synthesized and homogeneously embedded in the in situ formed nitrogen-doped carbon matrix, as demonstrated by the Si/Ag/C nanohybrid, where epoxy resin monomers are used as solvent and carbon source. With tiny amount of silver (2.59% by mass), the Si/Ag/C nanohybrid exhibits superior rate performance compared to the bare Si/C sample. Systematic structure characterization and electrochemical performance tests of the Si/Ag/C nanohybrids have been performed. The mechanism for the enhanced rate performance is investigated and elaborated. The temperature-dependent I-V behavior of the Si/Ag/C nanohybrids with tuned silver contents is measured. Based on the model, it is found that the super-small silver nanoparticles mainly increase charge carrier mobility instead of the charge carrier density in the Si/Ag/C nanohybrids. The evaluation of the total electron transportation length provided by the silver nanoparticles within the electrode also suggests significantly enhanced charge carrier mobility. The existence of tremendous amounts of super-small silver nanoparticles with excellent mechanical properties also contributes to the slightly improved cyclic stability compared to that of simple Si/C anodes.