Exploiting defects in TiO₂ inverse opal for enhanced photoelectrochemical water splitting

Abstract

In this work, we report on defects generation in TiO₂ inverse opal (IO) nanostructures by electrochemical reduction in order to increase photocatalytic activity and improve photoelectrochemical (PEC) water splitting performance. Macroporous structures, such as inverse opals, have attracted a lot of attention for energy-related applications because of their large surface area, interconnected pores, and ability to enhance light-matter interaction. Photocurrent density of electrochemically reduced TiO₂-IO increased by almost 4 times, compared to pristine TiO₂-IO photoelectrodes. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses confirm the presence of oxygen vacancies in electrochemically reduced TiO₂-IO photoelectrodes. Oxygen vacancies extend the absorption of TiO₂ from the UV to visible region. The incident photon-to-current efficiency (IPCE) increased by almost 3 times in the absorption (UV) region of TiO₂ and slightly in the visible region. Impedance studies show improved electrical conductivity, longer photogenerated electron lifetime, and a negative shift of the flatband potential, which are attributed to oxygen vacancies acting as electron donors. The Fermi level shifts to be closer to the conduction band edge of TiO₂-IO.