The electrochemical behavior of titanium ions at a liquid tin cathode has been investigated by cyclic voltammetry and square wave voltammetry in a NaCl–KCl melt at 1023 K. The results show that the deposition potentials of alkali metals and titanium at liquid tin are more positive than those at a solid tungsten cathode. Meanwhile, the results prove that titanium(III) ions can be reduced at liquid tin with a one-step reduction, Ti3+ + 3e = Ti, which is a quasi-reversible process with diffusion-controlled mass transfer. The diffusion coefficient of titanium(III) ions is 1.05 × 10−5 cm2 s−1. Additionally, galvanostatic electrolysis has been carried out to clarify the effect of the current density on the cathodic products. The result demonstrates that a greater depth of titanium will be diffused into the liquid tin cathode during electrolysis with a lower current density.
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.
Abstract Lithium is a critical metal with a wide range of applications in energy, electronics, and chemical industry. Currently, the industrial method for Li metal extraction relies on electrolysis of molten LiCl and suffers from various safety, cost, and environmental issues. In this work, we report electrochemical extraction of Li from molten LiOH by using a liquid tin (Sn) cathode. The use of liquid Sn cathode offers various advantages, such as lowering the dissociation potential of LiOH and easy collection of the metallic Li. Electrochemical and materials characterization results reveal that a plunge of electrolysis current occurs in the electrolyser without using a porous alumina membrane, due to the formation of a Li 2 O passivation layer at the cathode/electrolyte interface. In the electrolyser with a porous alumina membrane, continuous electrolysis has been achieved, and the side surface of the liquid Sn is identified to be the effective interface for Li electrodeposition. In addition, we demonstrate the use of the Li–Sn product for the synthesis of acetylene (C 2 H 2 ), a widely used fuel and chemical feedstock. Graphical Abstract
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