Steady‐State, Scalable Production of Mesoporous Rutile and Brookite Particles and Their Use in Energy Conversion and Storage Cells

Abstract Mesoporous TiO₂ rutile particles with a cauliflower‐like morphology and an internal structure of self‐assembled nanoneedles were synthesized in a novel Ti^IV chloride aqueous‐solution hydrolysis process. In an effort to make nanostructured rutile synthesis cost‐effective and green, the process was conducted at steady‐state in a continuously stirred tank reactor (CSTR) below 100 °C. High TiCl₄ concentration 0.5–1 m yielded rutile, while lowering the concentration to 0.1 m led to the crystallization of brookite nanoplatelets. Apart from phase control, specific surface area of rutile may be tuned via TiCl₄ concentration regulation from 85 to 500 m² g⁻¹. Investigation revealed that low pH/high Ti^IV concentration conditions favored direct nucleation of rutile nuclei during steady state that grow radially outward into nanoneedle structured cauliflower particles with nanoscale edgy surface. The unique steady‐state produced mesoporous rutile particles were shown to have excellent light scattering properties in a bi‐layer photoanode structure resulting in 42.5 % increase in photovoltaic efficiency. Brookite nanoplatelets were shown, in addition to their scattering properties, to exhibit stable Li‐ion intercalation functionality.