Investigation on the influence of pH on structure and photoelectrochemical properties of CdSe electrolytically deposited into TiO2 nanotube arrays

• There-dimensional CdSe-TiO2 multijunction was fabricated by electrochemical method.
• CdSe nanoparticles had a good bonding with the walls of TiO2 nanotube.
• pH value played an important role in the quality of CdSe-TiO2 interfaces.

In this work, we fabricated CdSe/TiO2 nanotube arrays (NTAs) by electrochemical method. In electrodeposition, the pH value of the electrolyte played an important role in formation of CdSe nanoparticles. As the pH value decreased, more CdSe deposited on TiO2 NTAs. Scanning electron microscopy and transmission electron microscopy characterization shows that the CdSe nanoparticles were uniformly deposited on and into TiO2 nanotubes when the pH value was 3, and this structure fully utilized the three-dimensional (3D) space of TiO2 nanotubes to form 3D multijunction heterostructures. According to the photoelectrochemical test, the CdSe/TiO2 NTAs sample prepared at pH = 3 exhibited maximum photocurrent and open circuit potential. This is because that the deposited CdSe nanoparticles had better bond with the walls of TiO2 nanotube than the samples deposited at other pH values, which facilitated the propagation and kinetic separation of photogenerated charges.