The influence of the water content in the phosphonium ionic liquids, triethyl-pentyl-phosphonium bis(trifluoromethylsulfonyl) amide (P_(2225)TFSA) was investigated for the electrodeposited neodymium metal. For this purpose, the viscosity and the electrical conductivity were firstly researched in Nd(III)/P_(2225)TFSA with and without the water content and these correlations with temperature dependence showed a good linear relation based on Walden rule. These properties also revealed that the electrical conduction of the ionic liquid was mainly attributed to the mass transfer of Nd(III) complexes and ionic species even in the presence of water. In addition, from the electrochemical analysis, no cathodic peak related with the decomposition of water was observed in sufficiently dried Nd(III)/P_(2225)TFSA. Furthermore, the cathodic current in the dried Nd(III)/P_(2225)TFSA electrolyte was larger than that in undried electrolyte during the neodymium electrodeposition. Finally, the electrodeposits obtained by potentiostatic electrolysis on -3.1 V at 150°C were mainly consisted of the neodymium metallic state identified by XPS.
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