Unusual Mesoporous Titanium Niobium Oxides Realizing Sodium-Ion Batteries Operated at -40 °C.

Sodium-ion batteries (SIBs) are a promising candidate for grid-scale energy storage, however, the sluggish ion-diffusion kinetics brought by the large radius of Na+ seriously limits the performance of SIBs, let alone at low temperatures. Herein, a confined acid-base pair self-assembly strategy to synthesize unusual Ti0.88 Nb0.88 O4- x @C for high-performance SIBs operating at room and low temperatures is proposed. The confinement self-assembly of the acid-base pair around the micelles and confined crystallization by the carbon layer realize the formation of ordered and stoichiometric mesoporous frameworks with opened ion channels. Thus, the mesoporous Ti0.88 Nb0.88 O4- x @C exhibits rapid Na+ diffusion kinetics at 25 and -40 °C, which are one order higher than that of the nonporous one. A high reversible capacity of 233 mAh g-1 , excellent rate (a specific capacity of 103 mAh g-1 at 50 C), and cycling performances (<0.03% fading per cycle) can be observed at 25 °C. More importantly, even at -40 °C, the mesoporous Ti0.88 Nb0.88 O4- x @C can still deliver the 161 mAh g-1 capacity, a high initial Coulombic efficiency of 60% and outstanding cycling stability (99 mAh g-1 at 0.5 C after 500 cycles). It is believed this strategy opens a new avenue for constructing novel mesoporous electrode materials for low-temperature energy storage.

Monodisperse Ultrahigh Nitrogen-Containing Mesoporous Carbon Nanospheres from Melamine-Formaldehyde Resin.

An aqueous emulsion polymerization self-assembly approach is demonstrated for the first time to synthesize ultrahigh nitrogen containing mesoporous polymer nanospheres, using melamine-formaldehyde resin oligomers as precursors. In the synthesis, change from alkaline to acidic conditions is critical for the formation of monodisperse mesostructured polymer nanospheres. Owing to unique structure of triazine stabilized in the covalent polymeric networks during the pyrolysis process, the derived mesoporous carbon nanospheres possess an ultrahigh nitrogen content (up to 15.6 wt%) even after pyrolysis at 800 °C, which is the highest nitrogen content among mesoporous carbon nanospheres. Furthermore, these monodisperse mesoporous carbon nanospheres possess a high surface area (≈883 m2 g-1 ) and large pore size (≈8.1 nm). As an anode for sodium-ion batteries, the ultrahigh nitrogen-containing mesoporous carbon nanospheres exhibit superior rate capability (117 mAh g-1 at a high current density of 3 A g-1 ) and high reversible capacity (373 mAh g-1 at 0.06 A g-1 ), indicating a promising material for energy storage.

Sequential Chemistry Toward Core-Shell Structured Metal Sulfides as Stable and Highly Efficient Visible-Light Photocatalysts.

A universal sequential synthesis strategy in aqueous solution is presented for highly uniform core-shell structured photocatalysts, which consist of a metal sulfide light absorber core and a metal sulfide co-catalyst shell. We show that the sequential chemistry can drive the formation of unique core-shell structures controlled by the constant of solubility product of metal sulfides. A variety of metal sulfide core-shell structures have been demonstrated, including CdS@CoSx , CdS@MnSx , CdS@NiSx , CdS@ZnSx , CuS@CdS, and more complexed CdS@ZnSx @CoSx . The obtained strawberry-like CdS@CoSx core-shell structures exhibit a high photocatalytic H2 production activity of 3.92 mmol h-1 and an impressive apparent quantum efficiency of 67.3 % at 420 nm, which is much better than that of pure CdS nanoballs (0.28 mmol h-1 ), CdS/CoSx composites (0.57 mmol h-1 ), and 5 %wt Pt-loaded CdS photocatalysts (1.84 mmol h-1 ).

Highly Reversible and Durable Na Storage in Niobium Pentoxide through Optimizing Structure, Composition, and Nanoarchitecture.

Amorphous, hydrogenated, and self-ordered nanoporous Nb2 O5 films serve as an excellent binder-free electrode for sodium batteries, affording a high and sustainable capacity delivery and robust high-rate capability. This collaborative material engineering of structural order (amorphization), composition (hydrogenation), and architecture (ordered nanopore) opens up new possibilities to develop an energy storage solution that is more accessible, sustainable, and producible.