Built-in Electric Field-Assisted Surface-Amorphized Nanocrystals for High-Rate Lithium-Ion Battery

High-power batteries require fast charge/discharge rates and high capacity besides safe operation. TiO₂ has been investigated as a safer alternative candidate to the current graphite or incoming silicon anodes due to higher redox potentials in effectively preventing lithium deposition. However, its charge/discharge rates are reluctant to improve due to poor ion diffusion coefficients, and its capacity fades quickly with rate as only thinner surface layers can be effectively used in faster charge/discharge processes. Here, we demonstrate that surface-amorphized TiO₂ nanocrystals greatly improve lithium-ion rechargeable battery performance: 20 times rate and 340% capacity improvement over crystalline TiO₂ nanocrystals. This improvement is benefited from the built-in electric field within the nanocrystals that induces much lower lithium-ion diffusion resistance and facilitates its transport in both insertion and extraction processes. This concept thus offers an innovative and general approach toward designing battery materials with better performance

Converting CoMoO₄ into CoO/MoO_<i>x</i> for Overall Water Splitting by Hydrogenation

Special structures of materials often bring in unprecedented catalytic activities, which are critical in realizing large-scale hydrogen production by electrochemical water splitting. Herein, we report a CoO/MoO_<i>x</i> crystalline/amorphous structure as an effective bifunctional electrocatalyst for water splitting. Converted from CoMoO₄ by hydrogenation, the CoO/MoO_<i>x</i>, featured with crystalline CoO in amorphous MoO_<i>x</i> matrix, displays superior catalytic activities toward both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). It shows small onset overpotentials of 40 and 230 mV for the HER and OER in 1.0 M KOH, respectively, and overall water splitting starting at 1.53 V with a robust stability. The high catalytic activity of the CoO/MoO_<i>x</i> is benefited from the large defect-rich interface between CoO and MoO_<i>x</i>, along with the amorphous nature of MoO_<i>x</i>. Thus, this study demonstrates the effectiveness of structural manipulation in developing highly active electrocatalysts for overall electrochemical water splitting

Directional Heat Dissipation across the Interface in Anatase–Rutile Nanocomposites

Understanding the structures and properties of interfaces in (nano-)­composites helps to reveal their important influence on reactivity and overall performance. TiO₂ is a technologically important material, and anatase/rutile TiO₂ composites have been shown to display enhanced photocatalytic performance over pure anatase or rutile TiO₂. This has been attributed to a synergistic effect between the two phases, but the origin of this effect as well as the structure of the interface has not been established. Using Raman spectroscopy, here we provide evidence of distinct differences in the thermal properties of the anatase and rutile moieties in the composite, with anatase becoming effectively much warmer than the rutile phase under laser irradiation. With the help of first-principles calculations, we analyze the atomic structure and unique electronic properties of the composite and infer possible reasons for the directional heat dissipation across the interface