Devising the Specification of a Solar Cell Utilizing TiO2 Photoanode and Copper Oxides Photocathode
Authors: Nay Wunn Htoo , Tanifuji Hiroya , Motoda Shinichi , Morita Motoaki 
Published: February 2020

We have been studied the performance of Marine Microbial Fuel Cell (MMFC) composed of Titanium dioxide anode and marine microbial film cathode. In order to improve the power density of MMFC, we have studied to improve the photocatalytic effects of TiO2 anode such as the effect of impurities on TiO2, double layer coating of TiO2, the effect of heat treatment on TiO2, and the effect of dye sensitizing on TiO2. On the other hand, the photocathodic effect of Copper oxides cathode has been studied such as the effect of heat treatment on Copper oxides. Based on the photocatalytic semiconductor effects of TiO2 and Copper oxides, we tried to develop a solar cell coupled with TiO2 photoanode and Copper oxides photocathode.
The base metal used for both electrodes was Type 329J4L stainless steel substrate. The surface cleaning and passivation treatment were performed to the substrate before coating of photoactive layers. To produce TiO2 electrode, the passivated substrate was coated with TiO2 first layer by screen printing method followed by 150 °C heat treatment for 60 minutes. The second layer of TiO2 was coated by screen printing and heat treatment was performed at 550 °C for 30 minutes. Besides, vacuum deposition method was used to the base substrate to produce Copper oxides cathode. A set of copper wires was evaporated and deposited on the substrate in vacuum evaporator. The copper-deposited substrate was then heat treated at 350 °C for 30 minutes to form Copper oxides film on the substrate. To compare the characteristics of electrodes, the passivated stainless steel was used as a cathode in couple with TiO2 electrode in the measurements. The electrolyte used for the measurement was artificial sea water (Aquamarine). The cell voltage measurement and power density measurement was performed by a potentiostat (Syrinx, SDPS- 501C, 511C).
Two types of cell was prepared; TiO2 anode vs Copper oxides cathode cell and TiO2 anode vs passivated stainless steel cathode cell. Firstly, the measurement of cell voltage for these cells were performed under light irradiation. The light used for these experiments was a xenon lamp with 150 W and calibrated wavelength range of 250 nm to 800 nm which produced a light intensity of 10.5 mW/cm2 (equivalent to approximately 1/10th of 1 sun) onto the test electrode. From the results of cell voltage measurement, power density measurement of the cell was performed in dark condition and under irradiated condition from open circuit cell voltage to short circuit cell voltage. The current densities at which the maximum power density from these cells was obtained and at at which the linear portion of the graph (Tafel gradient) was obtained were recorded for AC impedance measurement as the EIS analysis. The AC impedance measurement of these cells were performed at the current density points obtained from above under irradiated and dark conditions. As the EIS analysis, the Cole-Cole plot and the Bode plot was obtained, and the equivalent circuit was constructed.
The results from these experiments were compared and analysed. The results showed the open circuit cell voltage and maximum current density and hence maximum power density of the cell using TiO2 anode and Copper oxides cathode under light irradiation was increased compared to the cell without irradiation. This showed the photocatalytic effect of Copper oxides and Titanium dioxide. The performance of the cell with TiO2 anode vs Copper oxides cathode was increased compared to that of the cell with TiO2 anode and Stainless steel cathode. This is due to increased photocatalytic effect of copper oxide by vacuum deposition. By comparing AC impedance measurement results, the capacitive component of the impedance was reduced largely in the cell with TiO2-Copper oxides than TiO2-stainless steel cell. This leaded to a decrease of cell internal resistance by introducing Copper oxides cathode.