We have developed a gold recovery method utilizing the thiosulfate leaching and cementation onto silicon (Si) powder. In this process, copper (oxidizing agent for gold dissolution) was also recovered after gold recovery. In this work, we tried to monitor the recovery behavior in order to improve selectivity of metals. For experimentation, an ammonium thiosulfate solution containing 1 mM (M: mol dm⁻³) sodium gold(I) sulfite and 5 mM copper(II) sulfate was prepared (pH 13). We immersed a gold wire in the solution and measured the rest potential during the recovery process using Si powder. The potential of gold wire shifted to negative direction at the start and end of gold and copper recovery. We discussed the potential shift by measuring polarization curves of gold wire in the ammonium thiosulfate solution under various conditions. The efficient recovery of high-purity gold would be achieved by monitoring the potential of gold.

This study focused on Wadsley–Roth phase Ti₂Nb₁₀O₂₉ as a negative electrode material for lithium-ion batteries. We investigated the effect of a network consisting of corner-sharing octahedra, which form a conduction pathway for Li⁺, on the electrode properties. Charge/discharge cycle tests show that the capacity of Ti₂Nb₁₀O₂₉ is significantly reduced by ball milling. Because the treatment broadens the Bragg peaks in the diffraction pattern, the poor electrode properties of the ball-milled sample are considered to be due to the disordered atomic configuration. To investigate the structural disorder in more detail, we performed total scattering and X-ray absorption fine structure measurements and analyzed the intermediate-range structure. The results reveal that ball milling significantly disrupts the octahedral network, indicating a disordered conduction pathway for Li⁺. It is also demonstrated that the subsequent heat treatment after ball milling alleviates the disorder in the intermediate-range structure and improves the electrode properties.

Zinc-air batteries are anticipated to be next-generation energy storage devices because of their high capacities compared with conventional secondary batteries. However, the growth of zinc dendrites and electrolyte decomposition can compromise battery performance. To solve those problems, a thorough understanding of electrolyte and electrode behavior is paramount. Therefore, this study employs operando X-ray transmission imaging to observe electrolyte and electrode behavior during charging and discharging, aiming to elucidate their influence on battery performance. Operando X-ray transmission imaging successfully captures bubble generation and zinc deposition in the zinc-air battery. During discharge, bubbles form on the zinc electrode surface through a reduction reaction, while the battery current is suppressed by hindering ion transportation and electrode surface reactions. During charging, a change in the zinc deposition mode is observed from dense deposition to dendrite deposition. This deposition mode change is dependent on the charging current density and zinc ion concentration in the electrolyte. With an increase in the current density and a decrease in the zinc ion concentration, the deposition mode rapidly changes. Through experiments altering both the current density and initial zinc ion concentration in the electrolyte, we effectively determined the operating conditions that hinder zinc dendrite formation.

Electrodes coated with poly(4-vinylpyridine) (PVP) shift the oxidation peak potential of N-hydroxyphthalimide (NHPI) in acetonitrile to a less positive direction compared with that at the uncoated electrodes, which promotes proton-coupled electron transfer reaction. Adding a trace amount of poly(acrylic acid) to acetonitrile stabilizes the oxidation products at the electrodes. The formed products were identified to be N-oxyl radical from thin-layer spectroelectrochemical measurements using optically transparent PVP-coated Pt minigrid electrodes. The formal redox potential of the NHPI oxidation at the PVP-coated electrodes was evaluated by Nernstian analysis of the electronic absorption spectra after the higher-order derivative conversion.

A citric acid was added to the electrolyte as an capping agent to effectively enhance the reflectance of the Ag deposition-based electrochromic (EC) cells. The electrochemical properties of EC electrolytes containing different concentrations of citric acid were compared and the surface morphology of Ag deposited in these electrolytes were also analyzed. The redox potential of Ag⁺/Ag was not changed in the presence of citric acid, but the rate of consumption of Ag⁺ in the deposition was significantly affected by the citric acid especially in case of high concentration. As adding citric acid, the increasing of reflectance of Ag deposits in total wavelength region is increased, typical at the [Silver nitrate] : [Citric acid] is 1 : 2, the reflectance in the wavelength range (400–580 nm) is increased more, it is leading to specular mirror appearance. The mechanism for enhancement of the reflectance was discussed in terms of surface morphology of the Ag deposits and deposition behavior of the Ag nanoparticle.

To investigate the feasibility of the electrorefining process for aluminum (Al) upgrade recycling, Al electrodeposition employing an ionic liquid consisting of anhydrous aluminum chloride (AlCl₃) and 1-ethyl-3-methylimidazolium chloride (EMIC) was conducted. The effects of the operating temperature on the current efficiency, specific energy consumption, deposit properties, and deposition rate were investigated using the AlCl₃-EMIC bath containing 1,10-phenanthroline anhydride (OP) as an additive at the current density of 100 mA cm⁻². A constant-current electrodeposition showed that the specific energy consumption decreased to 5605 kWh t⁻¹ at 80 °C with increasing the operating temperature in the OP-added bath and the current efficiency was over 90 % at the operating temperatures of 60–80 °C, but decreased to below 90 % at 90–100 °C. The cross-sectional ultra-low accelerating voltage scanning electron microscope (ULV-SEM) images showed the smoothness of the deposit obtained from the OP-added bath at 70 °C, but not at 90 °C. The XRD patterns of the Al deposits obtained from the OP-added bath showed a preferential orientation to the {100} plane at 60–80 °C, but almost no preferential orientation at 90–100 °C. It has been revealed that the improvement in the specific energy consumption requires an increase in the operating temperature, and that the surface roughness of the Al deposit must be improved by preferentially orienting the {100} plane in the texture to prevent any Al deposit from dropping out in order to improve the current efficiency at the cathode, which implies Al recovery.

In this study, effects of NaCl concentration on galvanic corrosion behavior of zinc and A1050 couple was investigated by means of corrosion potential and galvanic current measurements, surface observation, electrochemical impedance measurements, and polarization tests. Corrosion potential and galvanic currents were measured for 72 hours during immersion in 0.01 to 2 mol L⁻¹ NaCl solutions. During the galvanic corrosion tests, the corrosion potential of the couples remained nearly constant, except in the early stage of immersion, and became more negative as the NaCl concentration increased. During the immersion test, the galvanic current always flowed in the direction of the zinc being the anode. However, the galvanic current changed with immersion time. That is, in the early stage of immersion, the galvanic currents were higher at higher NaCl concentrations, but over time, these values decreased, and after 72 hours, they decreased to much lower values and were almost independent of the NaCl concentration. Surface observations, electrochemical impedance measurements, and polarization curve measurements revealed that a decrease in the cathodic reaction rate on the A1050 surface with immersion time. Finally, the corrosion mechanisms that explain the galvanic corrosion of zinc and A1050 were discussed.