Template-Induced Structuring and Tunable Polymorphism of Three-Dimensionally Ordered Mesoporous (3DOm) Metal Oxides

Convectively assembled colloidal crystal templates, composed of size-tunable (ca. 15-50 nm) silica (SiO₂) nanoparticles, enable versatile sacrificial templating of three-dimensionally ordered mesoporous (3DOm) metal oxides (MO_x) at both mesoscopic and microscopic size scales. Specifically, we show for titania (TiO₂) and zirconia (ZrO₂) how this approach not only enables the engineering of the mesopore size, pore volume, and surface area but can also be leveraged to tune the crystallite polymorphism of the resulting 3DOm metal oxides. Template-mediated volumetric (i.e., interstitial) effects and interfacial factors are shown to preserve the metastable crystalline polymorphs of each corresponding 3DOm oxide (i.e., anatase TiO₂ (A-TiO₂) and tetragonal ZrO₂ (t-ZrO₂)) during high-temperature calcination. Mechanistic investigations suggest that this polymorph stabilization is derived from the combined effects of the template-replica (MO_x/SiO₂) interface and simultaneous interstitial confinement that limit the degree of coarsening during high-temperature calcination of the template-replica composite. The result is the identification of a facile yet versatile templating strategy for realizing 3DOm oxides with (i) surface areas that are more than an order of magnitude larger than untemplated control samples, (ii) pore diameters and volumes that can be tuned across a continuum of size scales, and (iii) selectable polymorphism.

Walnut-like Porous Core/Shell TiO2 with Hybridized Phases Enabling Fast and Stable Lithium Storage

TiO₂ is a promising and safe anode material for lithium ion batteries (LIBs). However, its practical application has been plagued by its poor rate capability and cycling properties. Herein, we successfully demonstrate a novel structured TiO₂ anode with excellent rate capability and ultralong cycle life. The TiO₂ material reported here shows a walnut-like porous core/shell structure with hybridized anatase/amorphous phases. The effective synergy of the unique walnut-like porous core/shell structure, the phase hybridization with nanoscale coherent heterointerfaces, and the presence of minor carbon species endows the TiO₂ material with superior lithium storage properties in terms of high capacity (∼177 mA h g^-1 at 1 C, 1 C = 170 mA g^-1), good rate capability (62 mA h g^-1 at 100 C), and excellent cycling stability (∼83 mA h g^-1 was retained over 10 000 cycles at 10 C with a capacity decay of 0.002% per cycle).