Complete via-filling by conventional direct electroplating becomes difficult with increasing hole diameter and aspect ratio. To achieve complete filling, various stepwise current controls were evaluated using the copper electroplating bath in the presence of additives. We found that there were two important factors necessary to produce complete filling of the wide opened via holes with a high aspect ratio. One factor was the suppression of the preferential deposition around the open area at the top of the holes and the other one was to effectively carry the copper ions into the bottom of the holes. Complete filling was achieved by applying the high current density for several seconds at the onset. Next a low current was applied followed by a stepwise increase back to the original level. This method provided complete filling of the via-holes. In addition, the influence of additives on the copper deposition and the effectiveness of stepwise current control were evaluated by electrochemical measurements.
Carbon fiber (CF) was anodically oxidized and the resulting oxidized CF was modified with several organic compounds such as butyl bromide, benzoic anhydride, and β-cyclodextrin (CD) under electroreductive conditions. By using the resulting modified CFs as cathodes, the electroreduction of methyl cinnamate (1) was carried out in MeCN affording methyl 3,4-diphenylcyclopentanone-2-carboxylate (3), methyl 3-phenylpropionate (4), and trace amount of dimethyl 3,4-diphenyladipate (2), and the electrode effects on the reduction efficiency and the products selectivity were investigated. The use of the oxidized CF gave relatively high products selectivity (the products ratio 3/4=29.0) and slight increase of the reduction efficiency (62%) in comparison with the use of the untreated CF or the alkylated CF (the products ratio 3/4=9.4–9.6, the reduction efficiency=57–58%). In the electroreduction by using the modified CF having benzoate groups (Ph-modified CF) the yield of 3 and the reduction efficiency also increased (3/4=11.2, the reduction efficiency=67%). The use of the CD-modified CF afforded the highest yield of the hydromonomer 4 (15%) in MeCN–H2O mixed solvent. These electrode effects were explained by the interaction between the functional groups on the modified CFs and the substrate 1.
The performance of a novel DMFC that uses a porous carbon plate as a support was investigated. The novel DMFC is a passive type and generates power by sucking the methanol solution through the porous body by osmotic action and breathing air by natural diffusion and convection. The i-V performance measured at different methanol concentrations revealed a higher performance at methanol concentration as high as 17 M suggesting that the porous carbon plate provided a function of controlling the methanol crossover. Hence, the methanol crossover for MEA with the porous carbon plate was evaluated and was compared with that for the conventional MEA. It was confirmed that the methanol crossover was reduced by the porous carbon plate. Mass transport controlled by the porous plate was considered as a mechanism for the reduction in the methanol cross over.
A new method for the surface modification of carbon fiber by using electro-oxidation and -reduction sequential procedure has been exploited. The introduction of hydroxyl groups on carbon fiber was attained by the electrooxidation of the NO3 anion containing electrolyte using the carbon fiber as an anode, and the anodically introduced hydroxyl groups were successively transferred to the alkoxy groups by the electroreduction in the presence of alkyl halides using the oxidized carbon fiber as a cathode. The functional groups introduced on the carbon fiber were estimated by the X-ray photoelectron spectroscopy, the observation of the hydrophilicity of the carbon fibers, and also by using the carbon fibers as cathodes for the electroreduction of acetophenone (1). The diastereoselectivity of the reduced product, 2,3-diphenyl-2,3-butanediol (2), in the electroreduction of 1 indicated the interaction between the electrogenerated radical anion species of 1 with the hydroxyl groups on the carbon fiber surface, and the dl/meso ratio was found to increase with an increase in the content of the hydroxyl groups on the carbon fibers. The sequential modification method for carbon fibers in one-pot was successfully performed by using the MeCN–H2O (3:1) mixed solvent containing the mixed supporting electrolytes Bu4NNO3–Bu4NClO4 (1:1) and alternating the polarity of the electrodes to give the carbon fibers having high content of hydroxyl or alkoxy groups.
The aluminum-carbon nanotube composite (Al-CNT composite) much improves the properties of aluminum such as the toughness and the electrical conductivity. However, the manufacturing procedure for producing the Al-CNT composite requires multistage processes. We obtained electrolytically the Al-CNT composite coating from a 66.7 mol%AlCl3–33.3 mol%1-ethyl-3-methylimidazolium chloride bath containing CNT in a single process for the first time. We also visualized and clarified the process whereby solid particle such as CNT was co-deposited with the aluminum, and proved the co-depositing mechanism that previously had been understood only theoretically and conceptually. Namely, we show that the CNT was adsorbed on the cathode, and immediately seized by the initial depositing nucleus of the aluminum, then completely covered by both the grown nucleus and the newly generated initial depositing nuclei, and finally buried in the composite.
A detection method of low hydrolyzed-chlorine concentrations in chlorinated water using an electro-oxidation reaction has been studied at a platinum electrode. Owing the potential sweep measurement, the formation current of a Pt surface oxide was observed in the background solution; and interestingly, the current decreased with an increase in the hydrolyzed chlorine. The current-potential curves at various concentrations showed good reproducibility. Plots of the concentration vs. the current at fixed potentials showed a linear relationship with a negative slope. Moreover, potential-step chronocoulometry was successfully applied, and plots at a fixed time showed a good linear relationship in the low concentration range of 0.1∼1.0 mg dm−3. Based on these results, this technique can be used for the detection of low concentrations of hydrolyzed chlorine for practical purposes.