A unique approach for the synthesis of nonstoichiometric, mesoporous molybdenum oxide (MoO 3-x ) with nanosized crystalline walls by using a soft template (PEO-b -PS) synthesis method is introduced. The as-synthesized mesoporous MoO 3-x is very active and stable (durability > 12 h) for the electrochemical hydrogen evolution reaction (HER) under both acidic and alkaline conditions. The intrinsic MoO 3 serves as an HER electrocatalyst without the assistance of carbon materials, noble metals, or MoS 2 materials. The results from transmission electron microscopy and N 2 sorption techniques show that the as-synthesized mesoporous MoO 3-x has large accessible pores (20-40 nm), which are able to facilitate mass transport and charge transfer during HER. In terms of X-ray diffraction, X-ray photoelectron spectroscopy, temperature-programmed oxidation, and diffusive refl ectance UV-vis spectroscopy, the mesoporous MoO 3-x exhibits mixed oxidation states (Mo 5+ , Mo 6+ ) and an oxygen-defi cient structure. The as-synthesized MoO 3-x only requires a low overpotential (≈0.14 V) to achieve a 10 mA cm −2 current density in 0.1 M KOH and the Tafel slope is as low as 56 mV dec −1 . Density functional theory calculations demonstrate a change of electronic structure and the possible reaction pathway of HER. Oxygen vacancies and mesoporosity serve as key factors for excellent performance.

The development of high-performance silicon anodes for the next generation of lithium ion batteries (LIBs) evokes increasing interest in studying its lithiated counterpart-lithium silicide (LiSi). In this paper we report a systematic study of three thermodynamically stable phases of LiSi (x = 4.4, 3.75, and 2.33) plus nitride-protected LiSi, which are synthesized via the high-energy ball-milling technique. All three LiSi phases show improved performance over that of unmodified Si, where LiSi demonstrates optimum performance with a discharging capacity of 3306 (mA h)/g initially and maintains above 2100 (mA h)/g for over 30 cycles and above 1200 (mA h)/g for over 60 cycles at the current density of 358 mA/g of Si. A fundamental question studied is whether different electrochemical paradigms, that is, delithiation first or lithiation first, influence the electrode performance. No significant difference in electrode performance is observed. When a nitride layer (LiNSi) is created on the surface of LiSi, the cyclability is improved to retain the capacity above 1200 (mA h)/g for more than 80 cycles. By increasing the nitridation extent, the capacity retention is improved significantly from the average decrease of 1.06% per cycle to 0.15% per cycle, while the initial discharge capacity decreases due to the inactivity of Si in the LiNSi layer. Moreover, the Coulombic efficiencies of all LiSi-based electrodes in the first cycle are significantly higher than that of a Si electrode (∼90% vs 40-70%).

Lithium silicide (LixSi) is the lithiated form of silicon, one of the most promising anode materials for the next generation of lithium-ion batteries (LIBs). In contrast to silicon, LixSi has not been well studied. Herein we report a facile high-energy ball-milling-based synthesis of four phase-pure LixSi (x = 4.4, 3.75, 3.25, and 2.33), using hexane as the lubricant. Surprisingly, the obtained Li3.75Si phase shows significant downward shifts in all X-ray diffraction peak positions, compared with the standard. Our interpretation is that the high-energy ball-mill-synthesized Li3.75Si presents smaller internal pressures and larger lattice constants. The chemical-stability study reveals that only surface reactions occur after Li4.4Si and Li3.75Si are immersed in several battery-assembly-related chemicals. The thermal-stability study shows that Li4.4Si is stable up to 350 °C and Li3.75Si is stable up to 200 °C. This remarkable thermal stability of Li3.75Si is in stark contrast to the long-observed metastability for electrochemically synthesized Li3.75Si. The carbon encapsulation of Li4.4Si has also been studied for its potential applications in LIBs.

N-Bromosuccinimide based bromination is proven to be an effective and mild intermediate step to produce surface functionalized, red-emitting, colloidal SiQDs.

A one-step hydrothermal method, followed by calcination at 300 °C in an argon atmosphere, has been developed to synthesize TiO2-B nanoparticles/double-walled nanotubes (NP/DWNT) and TiO2-B nanoparticles/multiple-walled nanotubes (NP/MWNT). To the best of our knowledge, this is the first synthesis of TiO2-B NP/NT hierarchical structures. Both NP/DWNT and NP/MWNT show high performance as anode materials for lithium-ion batteries, superior to their counterparts of DWNT and MWNT, respectively. Among all the four materials studied herein, NP/DWNT demonstrates the highest discharge-charge capacity, rate capability, and cycling stability. The enhancement due to the NP loading results from the increased surface areas, the improved kinetics, and the decreased transport distance for both electrons and Li ions. The charge capacity at high rates lies in the intercalation pseudocapacitance originating from fast Li-ion transport through the infinite channels in TiO2-B. The superiority of DWNT materials versus MWNT materials is ascribed to the thinner walls, which provide a shorter distance for Li-ion transport through the radial direction.