Chenteng Sun,Qian Xu,Yongxiang Yang,Xingli Zou,Hongwei Cheng,Xionggang Lu
The electrochemical behaviors of Li+ and Nd3+ were investigated on W, liquid Sn pool and Sn film electrodes in LiCl-KCl-NdCl3 melt at 673 K. Various electrochemical techniques, such as cyclic voltammogram, square wave voltammogram, and open circuit chronopotentiometry, were conducted to evaluate the electrochemical behaviors of Li+ and Nd3+. The reduction of Nd3+ was found to be a two-step process in the W electrode and a one-step process in the liquid Sn electrode. During the formation of the Nd-Sn intermetallic compounds, only the NdSn3 would be formed without the reduction of the Li+ in the liquid Sn electrode. When the reduction potential moves over −2.77 V vs Cl2/Cl−, the Li+ in the electrolyte would inevitable be reduced into the liquid Sn electrode. The Nd-Sn intermetallic compounds were deposited on the liquid Sn pool electrode at −2.74 V vs Cl2/Cl− in the LiCl-KCl-NdCl3 melts for 5 h. The products were characterized by SEM-EDS and XRD. The loose product on the surface of the deposition displayed the existence of NdSn3 in Nd-Sn intermetallic compounds. The high content of Nd inclusion formed by segregation was detected in the solidified Sn electrode.
Potassium (K) cannot be produced by molten-salt electrolysis due to its high vapor pressure and erosion of the graphite anode by K. To overcome this problem, a liquid tin (Sn) electrode was employed to enable the electrolysis by accommodating K in the form of K-Sn alloy that can be separated into K gas and Sn by a following distillation approach. The so-called electrolysis-distillation (ED) approach was conducted in molten K 2 CO 3 -KCl along with a nickel (Ni)-based inert oxygen-evolution anode at 150 to 700 mA/cm 2 at 700 °C. The K-Sn alloys were obtained with a current efficiency of >70 pct at 350 mA/cm 2 without harmful chlorine gas (Cl 2 ) generation, and the chemical diffusion coefficient of K in liquid Sn is ~ 5.21×10 −5 cm 2 /s. Moreover, the Ni-based alloy inert anode was stably served for over 100 hours. The vacuum distillation was conducted at 650 °C for 90 minutes to obtain K metal with a purity of 99.99 pct and a recovery rate of 93.5 pct. Therefore, the ED approach developed here is an efficient and clean route to produce K metal.
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