Photocatalytic Properties of TiO2 Electrodes on Stainless Steel Substrate Using Optimized TiO2 Pastes for Screen Printing
Authors: Wunn Htoo Nay , Motoda Shin-ichi , Morita Motoaki , Sakamoto Yutaro 
Published: November 2022

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