Titanium Dioxide (TiO2) has been studied for its important photocatalytic semiconductor characteristics. Among many applicable areas of TiO2 photocatalysts, we have been studying to use as an anode electrode of the marine wet solar cells or marine microbial fuel cell. These studies include the analysis of TiO2 electrode prepared by the screen-printing method, and also the dye sensitizing effect on TiO2 electrode. In those studies, it was noticed that there is an open circuit potential that shifted to noble direction after TiO2 electrode was irradiated by the light source. This phenomenon usually occurred after a few minutes the electrode showed its photocatalytic characteristics. It is unclear which caused voltage loss during the measurement. In this study, we have been trying to understand the mechanism affecting the voltage decay of the TiO2 electrode and the factors influencing this. The TiO2 electrodes were prepared by screen printing method. Type 329J4L stainless steel which exhibits duel phase properties was used as a base substrate for the electrode. Firstly, the surface of the substrate was polished by sandpaper and the substrate was cleaned with acetone using the ultrasonic cleaner for 10 minutes. Then, the substrate was passivated with 10% nitric acid (HNO3) solution at 60 ºC for 30 minutes. After that, the substrate was screen printed with TiO2 paste followed by heat treating for 60 minutes and the first layer of TiO2 was formed. For the second layer forming, the substrate was again screen printed with TiO2 paste and heat treated for 30 minutes. With these processes, double-layered heterojunction TiO2 electrode was prepared. The electrode was then coated with insulating epoxy resins and prepared ready for the electrochemical measurements and analysis. The electrochemical measurements of TiO2 electrodes were performed in an artificial seawater used as an electrolyte. The irradiation was carried out on the electrodes using a calibrated xenon lamp with 150 W (wavelength ranging from 250 nm to 800 nm). The lamp was set to produce an output light intensity of 10.5 mW/cm2. The saturated calomel electrode (SCE) was used as the reference electrode. During the photo potential measurement, the potentials dropped as the electrodes were exposed to the light irradiation. But the potential values were ennobled after a few minutes the electrode was irradiated. Preliminary examinations showed that there is a relation between the ennobled potential values (open circuit voltage loss when coupled with a counter electrode) and the heat treatment temperatures of the electrodes. For example, the rebound rate of the photo-potentials of the electrode with heat treatment temperature of 150 ºC (second layer) was higher and longer compared to that of the electrode with 550 ºC (second layer). Detailed mechanism was yet under investigation. Those investigation includes the photopotential measurement and the electrochemical impedance spectroscopy (EIS). The surfaces of the electrodes before and after the measurements were compared and checked using scanning electron microscope (SEM). The X-ray powder diffraction (XRD) analysis and differential thermal analysis (DTA) were also included for analysis of the mechanism on the TiO2 electrode. The results of those analyses and the mechanism affecting the open circuit voltage degradation in the TiO2 electrode will be presented to the upcoming ECS conference.

Solar cells and panels are one of the applications by converting solar energy into electrical energy. However, there exist environmental impacts such as deforestation, microclimate change, soil quality deterioration and migration of wildlife animals when a large amount of land areas are used for solar power plants. One of the solutions to those issues is to build floating solar panels in dams and lakes. We still need to apply large water areas, i.e., oceanic areas for those floating solar cells. Our research group has been studying floating solar cells that are compatible and have the potential to be used in marine environments. This solar cell is made of titanium dioxide photoanode and copper oxides photocathode with seawater electrolyte. Titanium dioxide (TiO2) has been studied for its photocatalytic properties. In this study, the photocatalytic properties of screen printed TiO2 electrodes on stainless steel substrate prepared from different pastes of TiO2 were examined and analysed. Type 329J4L stainless steel with duplex phase structure (ferritic + austenitic) was used as a substrate for TiO2 electrode. At first, the surface of the substrate was polished by sandpaper of 60 grade to form a grid pattern on it. The substrate was then cleaned by acetone in ultrasonic cleaner for 10 minutes and rinsed with distilled water. After that, the substrate was treated with passivation treatment. In this treatment, the substrate was placed in 10 % nitric acid (HNO3) solution at 60 ºC for 30 minutes and then rinsed with distilled water. After passivation treatment, the substrate was printed with TiO2 paste and heat treated at 150 ºC for 60 minutes to form the first layer of TiO2 film on the substrate. The second layer of TiO2 film was formed by screen printing of TiO2 paste followed by heat treatment at 550 ºC for 30 minutes. Finally, the electrode was solder welded and coated with epoxy resin to get ready for the measurement. Different TiO2 pastes were prepared and used for printing on the substrate. The first one was using the purchased TiO2 paste (SP-100 Showa Denko, Japan). The other ones were prepared from TiO2 powder (Sigma-Aldrich). Those pastes were prepared using the certain ratios of TiO2 powder, nitric acid, acetic acid, tritonX-100, and polyethylene glycol. The potential and polarization measurement of the electrodes were carried out in artificial seawater. The irradiation measurement was conducted using a xenon lamp (150 W) with a calibrated wavelength range of 250 nm to 800 nm and output irradiation intensity of 10.5 mW/cm2. Saturated calomel electrode (SCE) was used as a reference electrode and the potentio-galvanostat (SDPS-511U, Japan) was used as the measuring device. Figure 1 shows the potential values over a 2 -hour irradiation testing of two TiO2 electrodes prepared from two different pastes. The optimized TiO2 paste showed higher photopotential performance over time than the merchandized one. The surface and microstructures of the electrodes before and after the measurement were examined by Scanning Electron Microscope (SEM) and the pastes were investigated by Thermogravimetry Differential Thermal Analysis (TG-DTA) and X-ray powder diffraction (XRD). The results are planned to be presented in the upcoming ECS conference meeting. Figure 1

Titanium dioxide (TiO₂) electrodes are used as anode electrodes in dye-sensitized solar cells, and when hydroxyapatite was coated on the TiO₂ layer to facilitate the dye-sensitizing such as ruthenium on TiO₂ electrodes, HAp itself was found to act as a photocatalyst to improve the electrode properties of TiO₂ electrodes. It was found that HAp itself acts as a photocatalyst to improve the electrode properties of TiO2 Therefore, before dye-sensitizing, the photocatalytic effect of HAp was tested to find the optimal coating method, and as a result, the electrode property of TiO₂ electrode was improved.Type 329J4L stainless steel was used as the base metal for the electrode; before coating the TiO₂ layer, the surface was cleaned and passivation treated with HNO3. The passivated substrate was coated with TiO₂ paste in two steps by screen printing method. The first layer was coated on the electrodes by screen printing method and heat treated at 150°C for 60 minutes. The second layer was coated by the screen-printing method like the first layer and then heat-treated at 550°C for 30 min. The HAP layer was coated in the same way. The HAp layer is prepared by processing the powdered HAp powder into a slurry, coating it on the TiO₂ layer by the screen-printing method, and then heat-treating it.The photopotential characteristics of the electrode are measured and compared with the electrochemical characteristics of the TiO₂ electrode coated with HAp. The photopotential was measured using a potentiostat. Artificial seawater was used as the electrolyte and a saturated calomel electrode (SCE) was used as the reference electrode. The light used in the experiment was a xenon lamp (150W, wavelength range 250~800nm), generating a light intensity of 10.5mW/cm². The potential was measured for 2 hours. The measurements were carried out in the dark for the first 3 minutes, followed by light illumination conditions.The photopotential of the TiO₂ electrode coated with HAp was more active than that of the TiO₂ electrode not coated with HAp. However, there is a problem that HAP is peeled off from the electrode surface during a photopotential measurement experiment using a xenon lamp and potentiometer for 2 hours. This issue was caused by the way the HAp paste was made. Initially, carboxymethyl cellulose (CMC) was used to make HAp paste due to its advantages of physical dispersibility and moderate viscosity. It was a good material that could take on viscosity and dispersibility, but it had durability problems. This was because CMC has a good affinity for water, so it contained the water in the electrolyte solution, causing the HAp layer to peel off from the TiO₂ layer. To make it clear this matter, we used nitric acid, acetylacetone, and Triton X-100, which are commonly used for making titanium dioxide slurries. Nitric acid and acetylacetone were used to improve the dispersibility of the HAP, while Triton X-100 was used as a surfactant.As a result, we could fabricate titanium dioxide and HAp layers as an electrode that were sufficient to w...

The photocatalytic n-type semiconductor characteristics of titanium dioxide (TiO2) has been under study for decades. We have studied the photocatalytic effect of titanium dioxide electrode such as the effect of impurities on TiO2, and the effect of heat treatment on TiO2. We also have studied the effect of dye sensitizing on TiO2 electrode with seawater as the electrolyte. In that study, we found that the hydroxyapatite (HAp) coating used for the purpose to increase the binding ability between dye and TiO2 improved the capability of TiO2 electrode. In order to clearly know the mechanism of HAp coating and to improve the effect of HAp coating on TiO2 electrode, this study is conducted by preparing different types of HAp paste for coating on TiO2 electrode. Screen printing method was used for TiO2 layer and both manual and screen printings were used for HAp (Ca10(PO4)6(OH)2) coating for comparison. Type 329J4L stainless steel was used as a substrate for TiO2 electrode. The surface of the substrate was cleaned with ultrasonic cleaner and then the surface was passivated with HNO3 solution for 30 minutes. Double layers of TiO2 were screen printed on the substrate. The first layer was screen printed and heat treated at 150 ºC for 60 minutes. The second one after printed was heat treated at 550 ºC for 30 minutes. HAp was coated on TiO2 doubled layer. HAp paste was heat treated after printed. HAp paste was prepared from HAp powder. The powder was mixed with carboxymethyl cellulose (CMC) in various ratios. Water and alcohols are added to the mixture and well stirred to get a paste. Different types of HAp paste were prepared by changing the ratios of the constituents of the paste. The finishing was performed to get the electrodes ready for measurements in artificial seawater. The potential measurement, polarization and power density measurements against platinum counter electrode were performed by a potentiostat in dark and irradiated conditions. The irradiation used for the experiments is a xenon lamp with 150 W and calibrated wavelength range from 250 nm to 800 nm. The lamp was calibrated so that the light intensity produced became approximately 10.5 mW/cm2. The surfaces of the electrodes before and after measurement were analysed and the microstructures of the electrodes were compared by scanning electron microscope (SEM). The photocatalytic effects of HAp were observed but the cause is still unclear. The study showed that screen printing of HAp on TiO2 electrode showed higher photopotentials than manual printing or without printing. The variations in HAp paste constituents also affected the performance of TiO2 electrodes. The power density output of TiO2 can be increased more than 2 times with HAp coating. Removal of HAp particles from the electrode surfaces were observed. Further study on new techniques for HAp paste preparation and film forming process is suggested.

Titanium Dioxide (TiO2) has been studied for its important photocatalytic semiconductor characteristics. Among many applicable areas of TiO2 photocatalysts, we have been studying to use as an anode electrode of the marine wet solar cells or marine microbial fuel cell. These studies include the analysis of TiO2 electrode prepared by the screen-printing method, and also the dye sensitizing effect on TiO2 electrode. In those studies, it was appeared that there is an open circuit potential that shifted to noble direction after TiO2 electrode was irradiated by the light source and measured its electrochemical properties. This phenomenon usually occurred after a few minutes the electrode showed its photocatalytic characteristics. It is unclear which caused the potential loss during the measurement. In this study, we have been trying to understand the mechanism affecting the potential degradation of the TiO2 electrode and the factors affecting that decay.The TiO2 electrodes were prepared by screen printing method. Type 329J4L stainless steel which exhibits duel phase properties was used as a base substrate for the electrode. Firstly, the surface of the substrate was polished and the substrate was cleaned with acetone using the ultrasonic cleaner for 10 minutes. Then, the substrate was passivated with 10% nitric acid (HNO3) solution at 60 ºC for 30 minutes. After that, the substrate was screen printed with TiO2 paste followed by heat treating for 60 minutes and the first layer of TiO2 was formed. For the second layer forming, the substrate was again screen printed with TiO2 paste and heat treated for 30 minutes. With these processes, double-layered heterojunction TiO2 electrode was prepared. The electrode was then coated with insulating epoxy resins and prepared ready for the electrochemical measurements and analysis.The electrochemical measurements of TiO2 electrodes were performed in an artificial seawater used as an electrolyte. The irradiation was carried out on the electrodes using a calibrated Xenon lamp with 150 W (wavelength ranging from 250 nm to 800 nm). The lamp was set to produce an output light intensity of 10.5 mW/cm2. The saturated calomel electrode (SCE) was used as the reference electrode. During the photopotential measurement, the potentials dropped to active direction as the electrodes were exposed to the light irradiation. But the potential values were ennobled rapidly after a few minutes the electrode was irradiated. Preliminary examinations showed that there is a relation between the rebounded potential values (open circuit potential loss) and the heat treatment temperatures of the electrodes. For example, the rebound rate of the electrode with second layer heat treatment temperature of 150 ºC was higher and longer compared to that of the electrode with 550 ºC one. Detailed mechanism was yet under investigation. Those investigation includes the photopotential measurement and the electrochemical impedance spectroscopy (EIS) analysis. The surfaces of the electrodes before and after the measurements ...