An amperometric gas sensor based on electrolysis of CO gas has been developed by using gas permeable membrane modified by ion implantation technology. Expanded polytetrafluoroethylene (ePTFE) membrane has chemically stable nature and high permeability of gases without permeation of electrolytic solutions. Ion implantations of several kinds of ion into ePTFE membranes with fluenses of 1×1014∼5×1015 ions/cm2 was carried out to modify the gas permeable membranes. Gas permeable electrodes were prepared by Au coating on the ion-implanted ePTFE membranes. For CO detection, sensors constructed with the ion-implanted gas permeable electrode showed 5.5∼38 times higher sensitivity than that used non-ion-implanted one. Morphology change observed by SEM showed increase of effective surface area of the electrodes using ion implanted into ePTFE membrane. The increase of electrode surface area enhances sensor sensitivity, however, the enhancement depends on reactive gas species. For CO detection, the enhancement, response current ratio of sensor used ion-implanted membrane against that used non-ion-implanted, is remarkably high in comparison with that for the other gases such as H2S and NO except H2. In the case of CO detection, the modification of membranes brings active nature of electrode process of CO oxidation, which improves selectivity of CO. The surface modification of ePTFE will be useful method for development of a practical CO gas sensor.
Effect of surface treatment on F-doped tin oxide (FTO) coated conductive glass substrate was studied for electrodeposition of ZnO employing reduction of dissolved oxygen in ZnCl2 aqueous solution, through electrochemical analysis and observation of the products. Prolonged electrolysis for O2 reduction reaction (ORR) resulted in a gradual activation of the FTO to reach diffusion limited current, while the diffusion limit could not be reached by the substrates simply soaked in a 45 wt% nitric acid and that partially reduced to metallic Sn. Fitting of the profile of the chronoamperogram to the Scharifker-Hills model revealed instantaneous nucleation mechanism for electrodeposition of ZnO. The higher the electrode activity was, the higher the density of ZnO nucleus was reached to end up with a dense, flat and transparent ZnO thin film with its c-axis well oriented perpendicular to the substrate. Alternatively, transparent and dense film could also be obtained by applying a high overpotential for a short time to deposit particles of metallic Zn that served as nucleus for the growth of ZnO.
In order to investigate the growth processes of nanometric multilayers electrodeposited using the single bath technique, we have developed a system that provides high-speed and high-resolution measurement and analysis of long time current. An attempt was made to analyze the current during Co-Cu/Cu multilayer electrodeposition using this system. Multilayers were electrodeposited using the single bath technique under potential control with a coulomb controller, and the target thickness of each layer (5 nm) was controlled according to the quantity of electricity. During electrodeposition of approximately 25 min, the current was measured every 0.1 ms and analyzed. Cross-sectional observation by field emission-scanning electron microscopy (FE-SEM) showed a multilayered structure of which the layer thicknesses were close to 5 nm. The quantities of electricity used for each layer were controlled exactly; however, the deposition times used varied for each Cu layer. The deposition time for each of the Co-Cu layers was constant; however, the current during each Co-Cu layer deposition was found to increase slowly. During electrodeposition, current peaks caused by overshooting were observed at every switching of the substrate potential. The estimated non-faradaic current included in the peak was sufficiently small with respect to a 5 nm layer thickness.
We evaluated linear sulfones as an electrolyte solvent used for dye-sensitized solar cells (DSC). A comparison of the effects of the structure of linear sulfones found that ethylisopropylsulfone (EiPS), which has low viscosity and high relative permittivity, exhibits the highest conversion efficiency. Next, we studied the effects of LiI and N-methylbenzimidazole (NMBI), common additives, on EiPS electrolytic solutions. As a result, we found that, unlike nitrile-based or ionic liquid-based electrolytic solutions, EiPS electrolytic solutions exhibit a high open-circuit voltage (Voc) even when no basic additive is added. We also found that the addition of LiI causes the short-circuit current density (Jsc) to decrease. In other words, the optimum composition of an additive for a linear sulfone-based electrolytic solution differs from those for nitrile-based or ionic liquid-based electrolytic solutions. In addition, we found that EiPS electrolytic solutions without additives exhibit higher conversion efficiency than conventional electrolytic solutions with additives.
The iron oxide/polyaniline electrode was prepared from the photoanodic deposition of polyaniline film on the iron oxide electrode. The two linear relations of Mott-Schottky plots were obtained on the iron oxide/polyaniline electrode in HClO4 aqueous solution. This electrode showed a stable photoanodic current under visible light irradiation and also a linear dependence of photoanodic current on glycolic acid concentration.