(Invited) Zinc Oxide and Titanium Oxide Photocatalysts Fabricated By Electrochemical Methods and Boron Doped Diamond Electrochemistry
Authors: Yoshihara Sachio 
Published: December 2024

Photocatalytic Properties of Transparent ZnO Films Prepared by Anodization of Zinc Plate

Transparent zinc oxide films were prepared by anodizing of zinc plate when the electrolyte was kept at low temperature（＜10℃）in low concentration of alkaline solution and under high bias voltage，Obtained transparent film was uniform，and it showed transparency even if it might be thick．Thus obtained transparent film is confirmed to be a pure zinc oxide，and its absorption edge is 380nm，which corresponds to the optical band gap energy of 3.2 eV，Moreover，it had high photocatalytic activity which was superior to the one prepared under no cooling. We have already reported that the photocatalytic properties were closely correlated with their orientation preference of（1010）. In this case，thus obtained transparent film also showed preferred orientation of the（1010），

Effects of Electrolytic Condition to Photocatalytic Activity for Cathodically Deposited ZnO Films.

Zinc oxide film was prepared easily by cathodic deposition from zinc nitrate aqueous solutions. Deposited film was evaluated as photocatalytic film under different deposition conditions. The Photocatalytic activity was evaluated by measuring acetaldehyde gas degradation. Film prepared in dilute solutions of Zn (NO3)2 showed superior photocatalysis activity. Film prepared under high current density showed superior photocatalysis. We monitored mass changes during cathodic deposition and confirmed that ZnO was completely deposited under the above conditions and that additional reactions took place under other preparation conditions. These additional reaction deactivated photocatalytic activity.

Photocatalytic Properties of Titanium Oxide Film Prepared by Electrophoretic Sol－Gel Deposition

Electrophoretic Sol-Gel Deposition was introduced to immobilize the TiO2 photocatalysis．Thus prepared coatings showed quite high－photocalytic activities without successive heat treatment．It is suggested that Non-heated coating showed high photocalytic activity because it responds effectively for light，which is attributed to the nano-structure of the deposited coating．

Fabrication and Characterization of Diamond Quartz Crystal Microbalance Electrode

Boron-doped diamond film on a quartz crystal electrode was prepared by a reflow technique. The mass sensitivity of this diamond-quartz crystal microbalance (QCM) sensor was determined by performing Fe electrodeposition. This novel electrochemical QCM sensor was quite stable under several electrochemical experimental conditions. Its wide potential window and significantly low background current are just the same as the performance of a diamond electrode. We also showed that the fabricated diamond-QCM electrode worked satisfactorily as a useful tool for electrochemical microgravimetry by examining hydrogen evolution, oxygen evolution, and oxidation of the diamond surface in acidic solutions. It was found that evolved H2 inserted into the bulk of as-grown diamond with a storage volume of 0.06 mol/dm3 in 0.5 mol/dm3 HCl solution, after sweeping the potential from 0 to -2.3 V at a scan rate of 10 mV/s, in contrast to O-terminated diamond-QCM, which inhibited hydrogen intercalation.

Oxygen reduction on Au nanoparticle deposited boron-doped diamond films

Nanoparticle Au was deposited on as grown boron-doped diamond (BDD). The coverage and the morphology of the deposited Au particles were investigated by means of the linear sweep voltammetry and scanning electron microscopy (SEM). From SEM, the gold electrodeposited randomly as small spherical particles with an average diameter of 60nm. The applications of the as grown BDD film deposited by Au for electrocatalytic reduction of the oxygen in acidic solution were investigated. The catalytic efficiency of the Au deposited as grown BDD with the coverage of 0.06 is near 20 times larger than that of polycrystalline gold. The mechanism of the highly electrocatalytic active was investigated by ac impedance and hydrodynamic voltammetric methods.

Photoelectrodeposition of Copper on Boron-Doped Diamond Films: Application of Conductive Pattern Formation on Diamond. The Photographic Diamond Surface Phenomenon

The photoelectrodeposition of copper on semiconducting B-doped diamond films was investigated. There were clear morphology differences between photoelectrodeposited and electrodeposited copper. Photoelectrodeposition proceeded by a uniform two-dimensional growth process, whereas electrodeposition involved isolated random deposition. By applying this effect we have succeeded in forming a conductive copper pattern on semiconducting B-doped diamond with the aid of a photo-mask. Interestingly, it was further found that changes occurring on the diamond surface during photoelectrochemical polarization in the absence of copper in solution facilitate subsequent copper electrodeposition in the dark, possibly due to the formation of subsurface hydrogen. We refer to this as the `photographic diamond surface phenomenon'.