Effect of plasma power on the semiconducting behavior of low-frequency PECVD TiO 2 and nitrogen-doped TiO 2 anodic thin coatings: photo-electrochemical studies in a single compartment cell for hydrogen generation by solar water splitting

Previously optimized anatase and nitrogen-doped anatase TiO 2 coatings have been grown by low-frequency plasma-enhanced chemical vapor deposition (PECVD) on different kinds of substrates at low plasma power (64 W) and high plasma power (100 W) for photo-electrochemical studies. Nitrogen-doped TiO 2 layers exhibit better photoactivity and also higher electronic conductivity under UV and visible irradiations than non-doped materials. The main reason is that nitrogen introduction induces TiO 2 band gap tailoring towards higher wavelengths. In addition, films prepared at low plasma power present a ‘typical photo-material’ behavior (whose activity depends directly on the presence of light) while layers synthesized at higher plasma power contain an initial conductive phase giving them an activity that exists in the dark yet and can be slightly enhanced by illumination. Such conclusions are prominent in the field of photo-anodic thin films; indeed PECVD could constitute a promising approach for tailoring the efficiency of photo-electrochemical cells for hydrogen production under solar light. Graphical abstract