Effect of Accelerating Gas Flow on Pore Structure and Mass Transport Property of Vacuum Cold Sprayed TiO₂ Coatings Using Strengthened Nanostructured Powder

The pore structure in nano-porous TiO₂ coating influences the ion diffusion property and photovoltaic performance of dye-sensitized solar cells (DSC). In this paper, TiO₂ coatings were deposited by vacuum cold spray (VCS) using a strengthened nanostructured powder. The pore structure, ion diffusion and dye infiltration properties were examined to understand the deposition mechanism of the coating and the suitability of cold sprayed TiO₂ coating for DSC. It was interestingly found that the pores in the VCS TiO₂ coating presented a bimodal size distribution with two peaks at ~15 nm and ~50 nm, which contributed to a much higher ion diffusion coefficient comparing to that of the conventional unimodal-sized nano-porous coating. The dye infiltration and loading are beneficial from the bimodal size distribution of the pores. Based on the impact behavior of the spray powder, a deposition model was proposed to explain the deposition mechanism of the strengthened nanostructured powder during vacuum cold spray.