Ni-Doped Titanium Dioxide Films Obtained by Plasma Electrolytic Oxidation in Refrigerated Electrolytes

• Published in: Surfaces
• Main Authors: Hamed Arab, Gian Luca Chiarello, Elena Selli, Giacomo Bomboi, Alberto Calloni, Gianlorenzo Bussetti, Guglielmo Albani, Massimiliano Bestetti, Silvia Franz
• Format: Article
• Language: English
• Published: MDPI AG 2020-04-01
• Subjects: titanium dioxide; plasma electrolytic oxidation; Ni-doping; S-doping; photocurrent; IPCE
• Online Access: https://www.mdpi.com/2571-9637/3/2/13

Porous crystalline Ni-doped TiO₂ films were produced using DC plasma electrolytic oxidation in refrigerated H₂SO₄ aqueous solutions containing NiSO₄. The crystalline phase structure consisted of a mixture of anatase and rutile, ranging from ~30 to ~80 wt % rutile. The oxide films obtained at low NiSO₄ concentration showed the highest photocurrent values under monochromatic irradiation in the UV-vis range, outperforming pure TiO₂. By increasing NiSO₄ concentration above a threshold value, the photoelectrochemical activity of the films decreased below that of undoped TiO₂. Similar results were obtained using cyclic voltammetry upon polychromatic UV-vis irradiation. Glow discharge optical emission spectrometry (GD-OES) analysis evidenced a sulfur signal peaking at the TiO₂/Ti interface. XPS spectra revealed that oxidized Ni²⁺, S⁴⁺ and S⁶⁺ ions were included in the oxide films. In agreement with photocurrent measurements, photoluminescence (PL) spectra confirmed that less intense PL emission, i.e., a lower electron-hole recombination rate, was observed for Ni-doped samples, though overdoping was detrimental.