This article describes our recent researches on the tailor-designed nanoparticles-based electrocatalysts with controllable size and crystallographic orientation, including the fabrication and characterization of chemically/electrochemically-prepared metallic nanoparticles (e.g. Au) and metal oxide nanostructures (e.g. manganese oxide) onto various substrates and their applications to electrocatalysts for some reactions, e.g., oxygen reduction and evolution reactions as well as biosensors for reactive species of biological importance, e.g., superoxide anion and dopamine.
Three-volt lithium-ion batteries consisting of Li[Li1/3Ti5/3]O4 and Li[Ni1/2Mn3/2]O4 were constructed and examined in terms of their intermittent charge and discharge consisting of a 5 s current on and 15 s off at high rate (9.3 mA cm−2) together with the continuous charge and discharge at low rate (0.17 mA cm−2) for 100 cycles. To monitor the polarization voltages of the positive and negative electrodes, an auxiliary lithium electrode was placed around the electrodes in the battery. The auxiliary lithium electrode worked well for monitoring voltage balance in the battery. The continuous 100-cycle test of the battery operated in the voltage range of 1.5 to 3.5 V showed an excellent capacity retention, i.e., more than 97% of the initial capacity after 100 cycles. Based on these results, the polarization measurements of the lithium insertion electrodes are discussed, through which the electrode kinetics of the lithium insertion materials can be developed and the battery materials can also be improved for high-power applications.
Dielectric properties of crystalline anodic barrier films formed on aluminum by multiple step anodizing were evaluated with focusing on the effects of each processing stage and electrolytes species. An aluminum sheet was first immersed in a boiling water to form a hydrated oxide and subsequently anodized up to 350 V in a mixture of boric acid—sodium borate solution or ammonium adipate solution. After the first anodizing, the leakage current of the film formed in borate was much higher than that of the film formed in adipate. After the subsequent heating in air at 500°C, the leakage current of the film formed in borate showed few change although that of adipate remarkably increased. These results suggest that the degree of crystallization accompanied by defects formation after the first anodizing of the film formed in adipate is lower than that in borate. The leakage current after the second anodizing of both films in the borate was effectively suppressed; however, it is still high in the film formed in borate. TEM observation indicated that the film formed in adipate was thinner than the other; despite their same withstand voltage, suggesting higher permittivity of the film formed in adipate. In accordance to that, the capacitance of the film formed in adipate was higher than that of borate. These differences in dielectric properties between the films would be attributed to the difference in anion incorporation depth into the films, particularly incorporation depth of borate.
During the electrodeposition of a multilayer film, the thickness of each layer can be obtained accurately by controlling not only the potential but also the extent of the chemical reaction. The extent of the chemical reaction is usually controlled with the electrodeposition time. However, it is an approximate measure and not very precise. When a multilayer film is electrodeposited by the pulse potential technique, the fluctuation of current is unavoidable. Therefore, the deposition rate is unstable. As a solution to this problem, we have developed a “coulomb controller” that controls the quantity of electricity. The coulomb controller has been designed such that it can be used for monolayer electrodeposition. The circuit of the coulomb controller has been newly developed in order to detect the moment when the quantity of electricity reaches a target value. The coulomb controller has been assembled and used in a trial operation. The result of this operation has confirmed that the accuracy of the coulomb controller is suitable for the specification that is determined beforehand. Thus, it is confirmed that the coulomb controller can be installed in general electrochemical systems and can be used for monolayer electrodeposition.