A novel method of Ni recovery from the acid leaching solution of electroplating sludge through preparing Ni-Fe alloy with high Fe2+ content (i.e., 0.5 g/L) is proposed in this paper, and the corresponding electrodeposition process was studied using conventional electrochemical techniques and scanning electron microscopy. The obtained results showed that adding saccharin Na at concentrations from 0 to 14 g/L to the deposition bath increased the cathodic polarization potential of Ni-Fe co-deposition, with sensible grain refinement and disappearance of surface cracks observed after the addition of 14 g/L saccharin Na. Two different mathematical models of metal nucleation were tested, and the different morphologies of the deposits formed with and without saccharin Na suggested disparate nucleation mechanisms. The Ni-Fe deposition potential shifted positively in the presence of thiourea, and it should not be added together with saccharin Na during the nucleation stage for the grain refinement of the deposits. The iron contents in the deposits decreased with the increase of thiourea concentration ascribed to the thiourea complex which adsorbed on the cathodic surface preventing Fe2+electrodeposition from the electrolytes.
This paper reports the occurrence of electrochemical oscillations (EOs) in Cu electro-oxidation of phosphoric acid solution, and systematically investigated the effect of potential, electrolyte composition and concentration, temperature, stirring rate, and scanning speed on EOs. The mechanism of EOs occurred as a result of deposition and dissolution effects of CuH2PO4 through electro-oxidation of the Cu anode. The experimental result for amplitude and frequency can be explained by this simplified qualitative analysis, and further verified the previously speculated EO mechanism. This study provides insights into the relevance of micro-chemical mechanisms for the macroscopic non-equilibrium phenomenon and presents novel concepts for highly efficient electrodissolution in metallurgy.
Mechanical attrition (MA) is applied to assist the electroplating Ni-P coating on a magnesium alloy substrate. The influence of MA on the microstructure and electrochemical performance of the coating was studied with SEM, XRD, electrochemical impedance spectroscopy (EIS) and polarization curves. The results show that under MA, the Ni-P electroplating becomes compact and free of cracks and pores, leading to significant improvement in the coating corrosion resistance. MA promote transformation the coating from amorphous state to crystalline one and produce an obvious transition layer at the coating-substrate interface, which is beneficial to enhancing the coating adhesion strength and other mechanical properties.
The electrochemical behavior and specific adsorption of an ionic liquid, 1-butyl-3-methylimidazolium iodide, on a Au(111) electrode surface were investigated via voltammetric analyses, X-ray photoelectron spectroscopy (XPS), and scanning tunneling microscopy (STM). The electrochemical potential window and the reductive desorption of I adatoms were evaluated using voltammetric techniques. The XPS and STM results supported the specific adsorption of I adatoms on Au(111). Furthermore, high-resolution STM images revealed the formation of characteristic nanostructured rings consisting of imidazolium cations on I adatoms for the first time.
This headline article focuses on the oxygen reduction reaction (ORR), cathodic reaction of fuel cells, on well-defined high index planes of Pt and Pd for the elucidation of factors enhancing the activity for the ORR. The surfaces with (111) terrace edge have high activity for the ORR on Pt electrodes. Pt(331) = 3(111)-(111) gives the highest activity for the ORR in the stepped surfaces of Pt. Incorporation of one kink atom among eleven step atoms further enhances the activity of Pt(331). On single crystal electrodes of Pd, however, terrace edge deactivates the ORR and wide (100) terrace enhances the activity. Effects of Pt oxides (PtOH and PtO) on the ORR have been examined using vibrational spectroscopy. Infrared reflection absorption spectroscopy (IRAS) shows that PtOH prevents the ORR on Pt electrodes. Nanoparticle surface enhanced Raman spectroscopy (NPSERS) indicates that PtO also blocks the ORR on Pt(100) of which ORR activity is the lowest. The ORR activity of Pt is also enhanced by the modification of the surfaces by amines with long alkyl chains such as octylamine (OA) and amine with pyrene ring (PA). Modification by OA/PA increases the ORR activity on n(111)-(111) surfaces of Pt with terrace atomic rows more than 7. The activity of flat Pt(111) is enhanced most remarkably by OA/PA. However, the ORR of Pt(100), of which surface is also composed of flat terrace, is deactivated significantly.
An amorphous 80LiCoO2·20Li2SO4 (mol%; Li1.2Co0.8S0.2O2.4) thin film electrode is prepared by pulsed laser deposition (PLD). Although the Li1.2Co0.8S0.2O2.4 electrode material has been synthesized via mechanochemistry and includes a cubic LiCoO2 crystalline phase, amorphous Li1.2Co0.8S0.2O2.4 (without the cubic phase active material) is successfully obtained using the PLD method. The atomic ratio of Li/Co in the obtained film as determined by ICP-AES is identical to that of the milled powder. X-ray photoelectron spectroscopy reveals that the thin film mainly contains Co3+ and SO42−. The amorphous Li1.2Co0.8S0.2O2.4 thin film electrode is directly deposited on the 90Li3BO3·10Li2SO4 (mol%) oxide electrolyte to form closely-attached electrode-electrolyte interface. The fabricated all-solid-state cells shows a higher discharge capacity than the cell fabricated using the electrode derived from the mechanochemically prepared Li1.2Co0.8S0.2O2.4, which partially includes electrochemically-inactive cubic LiCoO2 nanoparticles. It is noted that complete amorphization of Li1.2Co0.8S0.2O2.4 is effective in increasing reversible capacities.
We investigated the oxygen reduction reaction (ORR) activity of several monolayer-thick Co-deposited Pt(111) model catalyst surfaces (n-monolayer(ML)-Co/Pt(111): n = 0.13–2.0) in 0.1 M KOH. Cobalt layer thicknesses of less than 0.25 ML enhance the ORR activity in contrast to clean Pt(111) surfaces. The maximum activity enhancement factor of 0.25 ML-Co/Pt(111) was ca. 1.7. The rotating ring–disk electrode measurements of n ML-Co/Pt(111) surfaces show an increase in the generation rates of HO2− at ∼0.8 V vs. reversible hydrogen electrode (RHE). This suggests that the deposited Co, in form of (hydro)oxide in 0.1 M KOH, functions as oxidation site and activates the Pt sites for the ORR. The results demonstrate that tuning the Pt and Co alloy compositions at the topmost surface is the key in developing highly active Pt-based alloy catalysts for the ORR, not only in acid but also in alkaline electrolytes.
The characteristics for 3,4,9,10-perylenetetracarboxylic-bisbenzimidazole (PTCBI, an n-type semiconductor) and 29H,31H-phthalocyanine (H2Pc, a p-type semiconductor) as organic p/n bilayer and bulk heterojunction (BHJ) photoelectrodes were studied for the photooxidation of thiol. Based on the analysis in their absorption spectra, a new absorption band in the longer wavelength (λ > 800 nm) for both bilayer and co-deposited photoelectrode suggested a formation of charge transfer complex. A photoanodic current was observed at λ ∼ 880 nm for the both bilayer and co-deposited electrodes, while no absorption and photocurrent for single layers of PTCBI and H2Pc. By assuming the Langmuir adsorption equilibrium at the solid/water interface, the kinetic parameters for the photoanodic current of thiol was analyzed for the longer wavelength of irradiation (λ ∼ 900 nm), and it was indicated that the rate of oxidation in the co-deposited was higher than that of the bilayer due efficient charge separation in the charge transfer complex.
Electrodeposition of cadmium (Cd) was investigated in a hydrophobic room-temperature ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) using CdCl2 as the source of Cd species in the presence of excess chloride ion. Raman spectroscopy and potentiometric measurement suggested formation of a cadmium tetrachlocomplex, [CdCl4]2−, in BMPCl/BMPTFSA. Cyclic voltammetry showed the possibility of electrochemical reduction from [CdCl4]2− to Cd(0) with interesting unusual electrochemical behavior, probably derived from the potential-dependent electric double layer structure typical to the ionic liquid. Electrodeposition of Cd was performed by potentiostatic electrolysis and the deposits were characterized by X-ray diffraction, energy dispersive X-ray analysis and scanning electron microscopy.
Structural effects on the activity for the oxygen reduction reaction (ORR) have been studied on single crystal electrodes of Pt modified with six aromatic organic molecules (AOMs). The AOMs examined affect the ORR activity slightly. However, the activity of the sites uncovered by AOMs increases after the modification: the ORR activity of uncovered Pt(111) area after the modification of phthalocyanine is 2.5 times as high as that of bare Pt(111). t-BuTAP and iron (II) phthalocyanine also enhance the ORR on Pt(997). These facts show that adsorbed AOMs can enhance the ORR activity of the uncovered active sites on Pt electrodes.