Takayuki Abe

Effect of underpotential deposition (UPD) of copper on oxygen reduction at Pt(111) surfaces

Abstract The influence of underpotentially deposited Cu adlayers on the electrocatalytic reduction of oxygen at Pt(111) has been studied in 0.05 M H2SO4 solutions using hanging meniscus rotating-disk (HMRD) voltammetry and electrochemical scanning tunneling microscopy (STM). Oxygen reduction at clean bare Pt(111) proceeds by a direct four-electron transfer with the formation of H2O as the primary reaction product. After the formation of the first underpotentially deposited Cu adlayer with (√3 × √3)R30° structure, the oxygen reduction current decreases to a steady-state value which is almost half that observed at bare Pt. This partial inhibition provided by the Cu adatoms can be explained by a change in the oxygen adsorption mechanism from the bridged orientation, favoring a four-electron transfer, to the end on orientation, favoring a two-electron transfer. The effect of coadsorbed halides on underpotential deposition (UPD) as well as the oxygen reduction reaction, has also been examined. Oxygen reduction at Cu-modified Pt(111) in the presence of chloride was completely inhibited after the first UPD process. Further, oxygen reduction in a pure H2SO4 solution on bare Pt(111) was carefully studied using HMRD voltammetry. The oxygen reduction current at 0.02 V was almost half the constant limiting current observed in the potential region between 0.5 and 0.3 V. This result can also be explained by a change in the oxygen adsorption mechanism from the bridged to the end-on orientation.

An ultramicroelectrode for determination of intracellular oxygen. Light-irradiation-induced change in oxygen concentration in an algal protoplast

Abstract An oxygen ultramicroelectrode was fabricated by pyrolysis of butane inside a glass capillary, followed by electrodeposition of Pt. The intracellular determination of oxygen in an algal protoplast (diameter, approx. 80 μm) with the ultramicroelectrode indicated that at a light intensity of 25 klx, the oxygen efflux from a single protoplast caused by the light reactions is approx. 5·10−13 mol/s and that corresponding to the dark reactions approx, 1 · 10−12 mol/s.

IN SITU CONDUCTANCE MEASUREMENT TO INVESTIGATE ROLES OF CONDUCTIVE ADDITIVES IN LITHIUM ION BATTERY ELECTRODES

Abstract Electrical dc conductance of a composite electrode for a lithium-ion battery was monitored in situ during successive charge/discharge cycles, in order to investigate functions of conductive additives. Such measurement was achieved by means of an interdigitated microarray electrode with a bipotentiostat. The composite films of mesocarbon microbeads (MCMBs) heat-treated at 1000°C were studied with conductive additives of acetylene black or a synthetic graphite in a 1 M LiClO 4 non-aqueous carbonate solution. The role of the conductive additives is discussed in connection with their type and content within the composites. In addition, we propose a modified preparation procedure for the composites having a high retention of conductance.