Enhancement of Photocatalytic Effect By Hydroxyapatite Coating on Titanium Dioxide Electrode

Abstract

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 withstand two hours of photopotential measurements.In the photopotential measurement, the prepared HAp-coated titanium dioxide electrode showed an apparent improvement in photopotential characteristics compared to the electrode with only titanium dioxide. In order to verify this effect, photopotential measurements were carried out on an electrode coated only with HAp. The relationship between the heat treatment temperature of HAp and the photocatalytic effect will be investigated in the later experiment.The current titanium dioxide electrodes do not adsorb dyes and can only utilize the photon energy of ultraviolet region. In the future, we aim to improve the electrode properties by adsorbing ruthenium dyes on the titanium dioxide and HAp layers to make the electrode capable of utilizing energy in the visible light region. In the meeting, it will be considered for use as an electrode in dye-sensitized solar cells.