ELECTROCHEMICAL REACTIONS OF Si AND EVOLUTION OF SiH_4 IN MOLTEN ALKALI HALIDE SYSTEMS

摘要

In order to examine the practical possibility of using metal grade Si in the novel SiH_4 production method, electrode behavior of metal grade Si has been investigated in molten LiCl-KCl-LiH systems at 673 K. The obtained cyclic voltammograms showed the almost similar behavior with the single crystal Si electrode. From the IR absorption spectroscopy of the evolved gas, SiH_4 production was confirmed. Furthermore, in order to improve current efficiency and reduce electrolysis voltage, the effect of F~- ion addition has been studied systematically by using single crystal Si electrode. Cyclic voltammetry in molten LiCl-KCl-LiF systems with various LiF concentrations revealed that the highest LiF concentration (5 mol%) system was most advantageous for promoting the anodic dissolution of Si. By IR absorption spectroscopy, the evolved gas during anodic electrolysis was confirmed to be SiF_4. By using the new LiCl-KCl-LiF(5 mol%)-LiH(0.8 mol%) system, formation potential of SiH_4 was reduced to be 2.3 V and the current efficiency was improved to be approximately 35 %.