Bu-ming Chen

Morphology of alpha-lead dioxide electrodeposited on aluminum substrate electrode

Abstract Alpha-lead dioxide was deposited by anodization of alkaline solution containing HPbO 2 − anions. Scanning electron microscopy (SEM) results show that the morphology is remarkably affected by the current density, concentration of HPbO 2 − anions, bath temperature and electroplating time. Compact and well adherent layers are possibly obtained under conditions of current densities ≤3 mA/cm 2 electrolyte containing 4 mol/L NaOH and 0.12–0.14 mol/L lead (II), bath temperature of 40 °C, and electroplating time of 2 h. EDS analyses show that the PbO 2 deposited in alkaline condition is highly non-stoichiometric at high current density.

Effect of the current density on electrodepositing alpha-lead dioxide coating on aluminum substrate

The α-PbO2 electrodes are prepared by anodic electrodeposition on A1/conductive coating electrode from alkaline plumbite solutions in order to investigate the effect of the different current densities on the properties of α-PbO2 electrodes. The physicochemical properties of the α-PbO2 electrodes are analyzed by using SEM, EDS, XRD, Tafel plot, linear sweep voltammetry (LSV) and A.C. impedance. A compact and uniform layer of lead dioxide was obtained at the current density of 3 mA·cm−2. A further increase in current density results in smaller particles with high porosity. EDS and XRD analyses have shown that the PbO2 deposited in alkaline conditions is highly non stoichiometric, and the PbO impurities are formed on the surface layer besides the α-PbO2. The corrosion resistance of α-PbO2 at the low current density is superior to that of the high current density. It can be attributed to a porous layer of deposited films at high current densities. When used as anodes for oxygen evolution in aqueous Zn2+ 50 g·L−1, H2SO4 150 g·L−1, the Al/conductive coating/α-PbO2 exhibits lower potential compared to Pb electrode. Al/conductive coating/α-PbO2 electrode with the best electrocatalytic activity was obtained at current density of 1 mA cm−2. The lowest roughness factor was obtained at 1 mA cm−2.

Polyaniline anode for zinc electrowinning from sulfate electrolytes

Abstract Polyaniline (Pani) anode is tested to highlight the feasibility of reduction of both energy consumption and capital costs in zinc electrowinning from sulfate solution without any modification to the existing plant. Current density, electrolyte temperature, added gelatin, added Mn 2+ , oxygen-evolution potential, cell potential and long duration tests were investigated. The zinc deposits were also studied by means of scanning electron microscope (SEM) and X-ray diffraction (XRD). The results show that current density and added gelatin change the preferred crystal orientations of the zinc deposits. Compared with Pb-Ag(1%) anode used in industry, the cell voltage decreases by 0.15–0.30 V, energy consumption of Zn is 2.46–2.70 kW·h/kg which results in 20% energy savings. Long duration tests show that Pani anode can represent a good alterative ability for zinc electrowinning. Zinc deposits obtained have no Pb pollution. The additions of Mn 2+ ions and gelatin also change the surface morphology and deposit quality of the electrodeposited zinc, affecting the crystal orientation. These researches demonstrate that Pani anode has distinct advantages over acidic electrowinning process.

Effects of polyaniline on electrochemical properties of composite inert anodes used in zinc electrowinning

Abstract In order to search for a suitable anode material used in zinc electrowinning in place of Pb–Ag alloy, Al/Pb–PANI (polyaniline)–WC (tungsten carbide) composite inert anodes were prepared on aluminum alloy substrate by double pulse electrodeposition (DPE) of PANI and WC particles with Pb2+ from an original plating bath. Thereafter, anodic polarization curves, cyclic voltammetry curves and Tafel polarization curves for the composite inert anodes obtained under different PANI concentrations in the original plating bath were measured, and the microstructural features were also investigated by scanning electron microscopy (SEM). The results show that Al/Pb–PANI–WC composite inert anode obtained under PANI concentration of 20 g/L in the original plating bath possesses uniform microstructures and composition distributions, higher electrocatalytic activity, better reversibility of electrode reaction and corrosion resistance in a synthetic zinc electrowinning electrolyte of 50 g/L Zn2+, 150 g/L H2SO4 at 35 °C. Compared with Pb–1%Ag alloy, the overpotential of oxygen evolutions for the composite inert anode are decreased by 185 mV and 166 mV, respectively, under 500 A/m2 and 1000 A/m2.

Effects of current density on preparation and performance of Al/conductive coating/a-PbO2-CeO2-TiO2/ß-PbO2-MnO2-WC-ZrO2 composite electrode materials

Abstract Al/conductive coating/ a -PbO 2 -CeO 2 -TiO 2 / β -PbO 2 -MnO 2 -WC-ZrO 2 composite electrode material was prepared on Al/conductive coating/ a -PbO 2 -CeO 2 -TiO 2 substrate by electrochemical oxidation co-deposition technique. The effects of current density on the chemical composition, electrocatalytic activity, and stability of the composite anode material were investigated by energy dispersive X-ray spectroscopy (EDXS), anode polarization curves, quasi-stationary polarization (Tafel) curves, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Results reveal that the composite electrode obtained at 1 A/dm 2 possesses the lowest overpotential (0.610 V at 500 A/m 2 ) for oxygen evolution, the best electrocatalytic activity, the longest service life (360 h at 40 °C in 150 g/L H 2 SO 4 solution under 2 A/cm 2 ), and the lowest cell voltage (2.75 V at 500 A/m 2 ). Furthermore, with increasing current density, the coating exhibits grain growth and the decrease of content of MnO 2 . Only a slight effect on crystalline structure is observed.

Electrosynthesis and physicochemical properties of α–PbO2–CeO2–TiO2 composite electrodes

Abstract In order to investigate the effect of solid particles dopants on physicochemical properties of α-PbO2 electrodes, α-PbO2 composite electrodes doped with nano-TiO2 and nano-CeO2 particles were respectively prepared on Al/conductive coating electrodes in 4 mol/L NaOH solution with addition of PbO until saturation by anodic codeposition. The electrodeposition mechanism, morphology, composition and structure of the composite electrodes were characterized by cyclic voltammogram (CV), SEM, EDAX and XRD. Results show that the doping solid particles can not change reaction mechanism of α-PbO2 electrode in alkaline or acid plating bath, but can improve deposition rate and reduce oxygen evolution potential. The doping solid particles can inhibit the growth of α-PbO2 unit cell and improve specific surface area. The diffraction peak intensity of α-PbO2-CeO2-TiO2 composite electrode is lower than that of pure α-PbO2 electrode. The electrocatalytic activity of α-PbO2-2.12%CeO2-3.71%TiO2 composite electrode is the best. The Guglielmi model for CeO2 and TiO2 codeposition with α-PbO2 is also proposed.

Electrosynthesis of Al/Pb/α-PbO2 composite inert anode materials

The alpha-PbO2 deposition layers were prepared on the surface of Al/Pb substrates by constant current electrosynthesis from an alkaline bath, and Al/Pb/alpha-PbO2 composite inert anode materials were obtained. The effects of the bath composition and bath temperature on the electrosynthesis of alpha-PbO2 were investigated by means of anodic polarization method, the phase structures and surface microstructures of Al/Pb and alpha-PbO2 deposition layers were tested by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The experimental data have shown that the process of alpha-PbO2 formation have several stages. The appropriate conditions can effectively improve the formation rate of alpha-PbO2 and avoid the occurrence of oxygen evolution reaction. The alpha-PbO2 deposition layer obtained in alkaline bath possesses rhombic structure, and it is composed of well developed spherical unit cells.

Anodic behavior and microstructure of Al/Pb–Ag anode during zinc electrowinning

Abstract Anodic behaviors and oxygen evolution kinetics of Pb–0.8%Ag and Al/Pb–0.8%Ag anodes during the initial 24 h zinc electrowinning were investigated with cyclic voltammetry (CV) curves and electrochemical impedance spectroscopy (EIS). The results reveal that the anodic behaviors and reaction kinetics of the two anodes vary a lot during the anodic polarization which indicate the formation and stabilization of anodic layer. Compared with conventional Pb–0.8%Ag anode, Al/Pb–0.8%Ag anode has longer time of anodic polarization. At the very beginning of anodic polarization, the two anodes all exhibit higher potential of oxygen evolution reaction (OER) since the reaction is controlled by the transformation step of intermediates. Then, its OER potential is largely diminished and OER rate is deduced from the formation and adsorption of the first intermediate (S–OHads). In the prolonged anodic polarization, the anodic potential of Al/Pb–0.8%Ag gradually decreases and the final value is more stable than that of conventional Pb–0.8%Ag anode. On the anodic layer after 24 h of anodic polarization, the OER potential is controlled by the formation and adsorption of intermediate. The microstructures of Al/Pb–0.8%Ag and Pb–0.8%Ag anodes after 24 h of anodic polarization were analyzed by scanning electron microscope (SEM).

Effect of cooling ways on properties of Al/Pb-0.2%Ag rolled alloy for zinc electrowinning

Abstract In order to study the new anode materials for zinc electrowinning, Al/Pb-0.2%Ag rolled alloy was produced by composite casting and hot rolling. Then the effect of cooling ways on properties of Al/Pb-0.2%Ag rolled alloy was investigated. As the results of metallographic test indicated, with the increasing of cooling intensity, both Vickers hardness and yield strength of Al/Pb-0.2%Ag rolled alloy increase. Furthermore, the Al/Pb-0.2%Ag rolled alloy, cooled by ice salt, presents the finest grain size and shows the lowest oxygen evolution potential (1.5902 V), while that of alloy cooled by water and air are 1.6143 V and 1.6288 V, respectively. However, the corrosion current density and corrosion rate of the Al/Pb-0.2%Ag rolled alloy, cooled by ice salt, are the highest. This can be attributed to its largest specific surface area, which promotes the contact between the anode and electrolyte.

Properties of Al/conductive coating/α-PbO2-CeO2-TiO2/β-PbO2-WC-ZrO2 composite anode for zinc electrowinning

The properties of Al/conductive coating/α-PbO2-CeO2-TiO2/β-PbO2-WC-ZrO2 composite anode for zinc electrowinning were investigated. The electrochemical performance was studied by Tafel polarization curves (Tafel), electrochemical impedance spectroscopy (EIS) and corrosion rate obtained in an acidic zinc sulfate electrolyte solution. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive X-ray spectroscopy (EDXS) were used to observe the microstructural features of coating. Anodes of Al/conductive coating/α-PbO2-CeO2-TiO2/β-PbO2, Al/conductive coating/α-PbO2-CeO2-TiO2/β-PbO2- WC, Al/conductive coating/α-PbO2-CeO2-TiO2/β-PbO2-ZrO2, and Pb-1%Ag anodes were also researched. The results indicated that the Al/conductive coating/α-PbO2-CeO2-TiO2/β-PbO2-WC-ZrO2 showed the best catalytic activity and corrosion resistant performance; the intensity of diffraction peak exhibited the highest value as well as a new PbWO4 phase; the content of WC and ZrO2 in coating showed the highest value as well as the finest grain size.