Visible-light photocatalytic activity of TiOxNy thin films obtained by reactive multi-pulse High Power Impulse Magnetron Sputtering

Reactive High Power Impulse Magnetron Sputtering operated in multi-pulse mode (m-HiPIMS) of a pure Ti target in Ar/N2/O2 gas mixture (mass flow rates of 50, 2 and 0.16sccm, respectively) has been used for the deposition of titanium oxynitride (TiOxNy) thin films with variable content of nitrogen (from 0.6at.% to 24.2at.%). Increase of the nitrogen content in the deposited TiOxNy thin films determined a decrease of the optical bandgap energy and a corresponding increase of visible light adsorption. The photocatalytic activity for water molecule splitting of the films deposited on metallic substrate, which were used as the photo-anode in an electrochemical cell, has been investigated by measurements of photoelectrochemical current intensity versus biasing voltage during on/off cycles of visible light irradiation (sun light simulated by a xenon lamp). The as-deposited films have a short range order corresponding to rutile and anatase structures and showed very weak photocatalytic activity and chemical instability in the electrolyte of the photoelectrochemical cell. However, a post-deposition annealing treatment of the film with low content of nitrogen (0.6at.%) improved considerably the visible-light photocatalytic activity, the film crystalline order and chemical stability. •TiOxNy thin films were synthesized by multi-pulse High Power Impulse Magnetron Sputtering (m-HiPIMS) depositions.•The content of N atoms in the deposited films was changed from 0.6at.% to 24.2at.% by the HiPIMS pulsing frequency.•The energy bandgap decreased with the content of nitrogen from 3.18eV to 1.09eV.•Post deposition annealing of the films improved noticeably the crystalline order and photocatalytic activity.•The annealed TiOxNy film with low content of N showed the best crystalline order and photocatalytic activity.