Mingyong Wang

Preparation of electrolytic copper powders with high current efficiency enhanced by super gravity field and its mechanism

Abstract Super gravity field was employed to enhance electrolytic reaction for the preparation of copper powders. The morphology, microstructure and size of copper powders were characterized by scanning electron microscopy, X-ray diffractometry and laser particle analysis. The results indicated that current efficiencies of electrolytic copper powders under super gravity field increased by more than 20% compared with that under normal gravity condition. Cell voltage under super gravity field was also much lower. The size of copper powders decreased with the increase of gravity coefficient (G). The increase of current efficiency can be contributed to the disturbance of electrode/electrolyte interface and enhanced mass transfer of Cu2+ in super gravity field. Meanwhile, the huge gravity acceleration would promote the detachment of copper powders from electrode surface during electrolytic process, which can prevent the growth of copper powders.

Sulfur removal from bauxite water slurry (BWS) electrolysis intensified by ultrasonic

Effects of ultrasonic on desulfurization ratio from bauxite water slurry (BWS) electrolysis in NaOH solution were examined under constant current. The results indicated that ultrasonic improved the desulfurization ratio at high temperatures because of the diffusion and transfer of oxygen gas in electrolyte. However, due to the increase in oxygen gas emission, ultrasonic could not improve the desulfurization ratio obviously at low temperatures. Additionally, the particle size of bauxite became fine in the presence of ultrasonic, indicating that the mass transfer of FeS2 phase was improved. According to the polarization curves, the current density increased in the presence of ultrasonic, indicating that the mass transfer of liquid phase was improved. The apparent activation energy (AAE) of electrode reaction revealed that ultrasonic did not change the pathway of water electrolysis. However, ultrasonic changed the pathway of BWS electrolysis, converting indirect oxidation into direct oxidation. The AAE of BWS electrolysis in the presence of ultrasonic was higher than that in the absence of ultrasonic. And the low AAEs (less than 20 kJ/mol) clearly indicated the diffusion control during BWS electrolysis reaction.

Hierarchically 3D porous films electrochemically constructed on gas–liquid–solid three-phase interface for energy application

Hierarchically porous films as catalysts or supports are fascinating electrode materials for the electrochemical conversion and storage of energy due to the short transportation paths of electrons and ions. A novel and feasible method to construct 3D porous films is developed by direct electrodeposition on a gas–liquid–solid (GLS) three-phase interface. The formation mechanism of the porous structure is discussed based on bubble behavior and electrocrystallization. The progress toward the preparation of porous metals/alloys on cathodes and metal oxides/polymers on anodes is reviewed. The surface decoration of porous metal films by noble metals or non-metal compounds is summarized. The promising energy applications of porous films are highlighted.

Roles of Electrolyte Characterization on Bauxite Electrolysis Desulfurization with Regeneration and Recycling

The recycling of NaCl used as supporting electrolyte for bauxite electrolysis was carried out in this study. The electrolyte was regenerated by adding anhydrous CaCl2 into the solution after filtration, and effects of electrolyte characterization on bauxite electrolysis were examined by observing the change in desulfurization ratio and cell voltage. The results indicated that the desulfurization ratio increased with increasing recycling times of electrolyte. In the meantime, the increase in recycling times has led to the decrease in pH value as well as the increase in Fe ion concentration in the electrolyte, which were the main reasons for the increase in the desulfurization ratio with increasing recycling of electrolyte. The pH value of electrolyte after second electrolysis was lower than 1.5, and the desulfurization ratio increased obviously due to the increase in Fe3+ concentration and suppression of jarosite formation. The increase in Ca2+ concentration did not apparently change desulfurization ratio and anode surface activity. However, with Ca2+ addition, the cathode surface was covered by CaSO4·nH2O, thus resulting in the increase of cell voltage.

Effects of electrolyte recycling on desulfurization from bauxite water slurry electrolysis

Abstract To lower the cost of bauxite electrolysis desulfurization using NaOH solution as the supporting electrolyte, effects of electrolyte recycling on bauxite electrolysis desulfurization were investigated. The results indicate that electrode corrosion, cell voltage, the desulfurization rate and the pH value of the electrolyte have no obvious changes with the increase of cycle times. Additionally, there were some transitive valence S-containing ions in electrolyte after the electrolysis, such as SO32−, S2O32−. However, most of the sulfur in bauxite was eventually oxidized into SO42− into the electrolyte, and these S-containing ions did not affect the recycling utilization for electrolyte.

Desulfurization from Bauxite Water Slurry (BWS) Electrolysis

Feasibility of high-sulfur bauxite electrolysis desulfurization was examined using the electrochemical characterization, XRD, DTA, and FTIR. The cyclic voltammetry curves indicated that bauxite water slurry (BWS) electrolysis in NaOH system was controlled by diffusion. Additionally, the desulfurization effect of NaCl as the electrolyte was significantly better than that of NaOH as an electrolyte. As the stirring rate increased, the desulfurization ratio in NaCl system was not increased obviously, while the desulfurization ratio in NaOH system increased significantly, indicating further that electrolysis desulfurization in NaOH solution was controlled by diffusion. According to XRD, DTA, and FTIR analysis, the characteristic peaks of sulfur-containing phase in bauxite after electrolysis weakened or disappeared, indicating that the pyrite in bauxite was removed from electrolysis. Finally, the electrolytic desulfurization technology of bauxite was proposed based on the characteristics of BWS electrolysis.

Modulation of active Cr(III) complexes by bath preparation to adjust Cr(III) electrodeposition

The preparation process of the Cr(III) bath was studied based on a perspective of accelerating the formation of active Cr(III) complexes. The results of ultraviolet-visible absorption spectroscopy (UV-Vis) and electrodeposition showed that active Cr(III) complexes in the bath prepared at room temperature in several days were rare for depositing chromium. The increase of heating temperature, time, and pH value during the bath preparation promoted the formation of active Cr(III) complexes. The chromium deposition rate increased with the concentration of active Cr(III) complexes increasing. Increasing the heating temperature from 60 to 96°C, the chromium deposition rate increased from 0.40 to 0.71 μm/min. When the concentration of active Cr(III) complexes increased, the grain size of Cr coatings increased, and the carbon content of the coating decreased. It is deduced that Cr(H2O)4(OH)L2+ (L is an organic ligand, and its valence is omitted) is a primary active Cr(III) complex.

Electrochemical preparation of V2O3 from NaVO3 and its reduction mechanism

Vanadium trioxide (V2O3) was directly prepared by NaVO3 electrolysis in NaCl molten salts. Electrolysis products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The existing state and electrochemical behavior of NaVO3 were also studied. The results indicated that V2O3 can be obtained from NaVO3. VC and C were also formed at high cell voltage, high temperature, and long electrolysis time. During electrolysis, NaVO3 was dissociated to Na+ and VO3− in NaCl molten salt. NaVO3 was initially electro- reduced to V2O3 on cathode and Na2O was released simultaneously. Na2CO3 was formed due to the reaction between Na2O and CO2. The production of C was ascribed to the electro-reduction of CO32−. VC was produced due to the reaction between C and V2O3.