Preparation and properties of electrochemically assisted electroless Ni–P–TiO2–NG composite coatings

Inspired by NG/TiO₂ composite reinforcing particles in the Ni–P matrix, an electrochemically assisted electroless deposition method was used to deposit Ni–P–TiO₂–NG composite coatings on steel substrates in order to enhance their electrochemical and photocatalytic properties. The effects of current density on the microstructure, surface morphology and phase composition of the coatings were investigated. Statistical analysis based on multifractal formalism shows that the uniformity of the height distribution shows an increasing and then a decreasing trend as the current density increases. The results show that the average hardness reached a maximum value of 966 H_V0.1 for the optimum coating obtained at a current density of 4 A dm^–2, the corrosion current reached a minimum value of 2.041 × 10^–5 A cm^–2, with a maximum corrosion potential of –0.281 V vs. SCE. These improvements can be attributed to high phosphorus Ni–P composite coatings with smooth and dense morphology, TiO₂/NG nanocomposite impermeability and excellent mechanical properties. In addition, the photocatalytic activity of the Ni–P–TiO₂–NG coating gradually increases with increasing current density.