Jakub Kopenec1,2,Pavel Galar1,2,Katerina Kusova1,Martin Muller1
Institute of Physics the Czech Academy of Sciences1,University of Chemistry and Technology Prague2
Jakub Kopenec1,2,Pavel Galar1,2,Katerina Kusova1,Martin Muller1
Institute of Physics the Czech Academy of Sciences1,University of Chemistry and Technology Prague2
Silicon (Si) proved to be one of the essential elements of current electronics, energetics and of many other technological fields. When in the form of a nanostructure, e. g. as silicon nanoparticles (SiNPs) Si properties are altered by a complex synergy between quantum effects and an influence of high surface to volume ratio. In comparison with bulk Si, SiNPs show high surface reactivity, mechanical resistance and, despite being an indirect semiconductor, also effective light emission. The combination of Si original and nano-gained properties is beneficial for many optoelectronic, electronic, or biological applications. In addition to these applications, in Li-Ion technology is of special interest here, because silicon possesses the highest theoretical gravimetric (specific) capacity of all elements and in the form of a nanostructure, it is able to withstand extreme volume changes during the lithiation and delithiation proces.<br/><br/>In this study, we demonstrate the potential of SiNCs being used as an energy-storage material. One of the most perspective ways of high-gain synthesis of SiNPs is the utilization of non-thermal plasma. However, at specific synthesis conditions, the plasma-prepared SiNPs (nanoparticles in general) can be highly flammable. They can be ignited even by a weak laser with light intensity of units of mW/mm<sup>2</sup> or by temperatures above approximately 90°C. The origin of this effect is based on the presence of hydrogen in the synthesis chamber and its following efficient integration onto the SiNPs surface. Thus, after synthesis, SiNPs store significant amounts of energy (up to 7000 cal/g), which they release after being ignited. We observed a significant dependence of the ignition conditions on the crystallinity and size of SiNPs and also on the amount of additional hydrogen in the synthesis chamber. Infrared spectroscopy proved that it is the type of the bond (Si-H, Si-H<sub>2</sub>, Si-H<sub>3</sub>) that plays an important role in the stability/flammability of SiNPs. In particular, SiNPs containing SiH<sub>3</sub> structures on its surface were easier ignited in contrast to the ones containing SiH which were highly stable. The microscopic interpretation of this effect is presented. These findings are potentially important not only for applications in explosives, but they also point towards the possibility of using SiNPs as a hydrogen/energy-storing material.