Improvement of electrochemical properties and hydrogen production by Ho-Eu-TiO2 nanotubes

Abstract

In this study, the electronic structure of TiO2 nanotubes (TNTs) was modified through holmium(Ho) doping and europium(Eu) photodeposition to enhance photoelectrochemical (PEC) water splitting performance. Ho doping introduced impurity energy levels (IEL) within the band gap, while Eu photodeposition generated oxygen vacancies whose concentration correlated with the Eu(II)/(Eu(II) + Eu(III)) ratio depending on the photodeposition time (30, 60, 90, and 120 min). Among the prepared samples, the one treated for 90 min (EH90-TNTs) exhibited the highest photoactivity, as verified by a series of electrochemical and optical analyses. PEC water splitting experiments revealed that the hydrogen evolution rate and photocurrent density of EH90-TNTs increased by 25.4% and 22.8%, respectively, compared with those of Ho-TNTs. This enhancement is attributed to the synergistic effect between IEL and oxygen vacancies, which suppresses photogenerated charge recombination and extends light absorption into the visible region. These findings demonstrate that the coexistence of lanthanideinduced IEL and oxygen vacancies provides an effective strategy for improving the efficiency of TiO2-based photoanodes.