High-power Na-ion batteries have tremendous potential in various large-scale applications. However, conventional charge storage through ion intercalation or double-layer formation cannot satisfy the requirements of such applications owing to the slow kinetics of ion intercalation and the small capacitance of the double layer. The present work demonstrates that the pseudocapacitance of the nanosheet compound MXene Ti2C achieves a higher specific capacity relative to double-layer capacitor electrodes and a higher rate capability relative to ion intercalation electrodes. By utilizing the pseudocapacitance as a negative electrode, the prototype Na-ion full cell consisting of an alluaudite Na2Fe2(SO4)3 positive electrode and an MXene Ti2C negative electrode operates at a relatively high voltage of 2.4 V and delivers 90 and 40 mAh g−1 at 1.0 and 5.0 A g−1 (based on the weight of the negative electrode), respectively, which are not attainable by conventional electrochemical energy storage systems.

The development of high-performance Na-ion intercalation electrodes has been required recently because Na-ion batteries hold much promise for inexpensive and efficient energy storage, which can be deployed in a power grid. For both optimization and better understanding of the electrode materials, it is indispensable to clarify the relationship between the electronic state and electrochemical properties systematically. In this work, we studied the electrochemical properties of P2−Na 2/3 Mn y Co 1−y O 2 in detail. A series of the P2 phases was successfully synthesized by the conventional solidstate reaction. The solid solution P2 compounds showed that the redox potential of Co 4+ /Co 3+ and Mn 4+ /Mn 3+ shifts systematically by the transitionmetal substitution. The charge−discharge cycle tests revealed that with increasing y the initial specific capacity increases while the cycle stability degrades. The origin for the cycle degradation was analyzed by the electrochemical impedance spectroscopy, which evidenced that the substitution of Co for Mn accelerates the formation of the passivating layer at the electrode surface.

Na-ion batteries have been the subjects of intensive studies for grid-scale energy storage recently. O3-type NaFeO2 is a promising candidate for the Na-ion cathode materials, though the irreversibility during Na-ion extraction/insertion seriously hinders its practical application. The present work demonstrates that partial replacement of Fe in O3-NaFeO2 with Ni leads to the significant improvement of the electrochemical properties. The 57Fe Mössbauer and X-ray absorption spectra show that O3-type NaFeO2–NaNiO2 solid solution forms hybridized frontier orbital of a Fe–O–Ni bond via ligand-to-metal charge transfer, which plays a dominant role in the charge–discharge process. The resulting O3-NaFe0.3Ni0.7O2 delivers an initial discharge capacity of 135 mA·h·g–1, most of which is in a high-voltage region of 2.5–3.8 V, with a high initial Coulombic efficiency of 93%, and shows enhanced cycle stability.

Bulk quantities of hexagonal boron nitride (h-BN) nanosheets have been synthesized via a simple template- and catalyst-free chemical vapor deposition process at 1100−1300 °C. Adjusting the synthesis and chemical reaction parameters, the thickness of the BN nanosheets can be tuned in a range of 25−50 nm. Fourier transform infrared spectra and electron energy loss spectra reveal the typical nature of sp2-hybridization for the BN nanosheets. It shows an onset oxidation temperature of 850 °C for BN nanosheets compared with only about 400 °C for that of carbon nanotubes under the same conditions. It reveals a strong and narrow cathodoluminescence emission in the ultraviolet range from the h-BN nanosheets, displaying strong ultraviolet lasing behavior. The fact that this luminescence response would be rather insensitive to size makes the BN nanosheets ideal candidates for lasing optical devices in the UV regime. The h-BN nanosheets are also better candidates for composite materials in high-temperature and hazardous environments.

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An easy chemical route for the synthesis of (γ-Fe 2 O 3 @SiO 2 ) n @TiO 2 functional hybrid nanoparticles is reported in this paper. The hybrid nanoparticles are composed of spherical nanoparticles about 100 nm in diameter, with several γ-Fe 2 O 3 fine particles about 15 nm in diameter as cores distributing within the titania matrix and silica as coatings and barrier layers between the magnetic cores and titania shells. The (γ-Fe 2 O 3 @SiO 2 ) n @TiO 2 hybrid nanoparticles show good magnetic response and got together within 20 s in a magnetic field. Photodegradation examination of the magnetic hybrid nanoparticles was carried out in methylene blue solutions illuminated under UV light in a photochemical reactor. It is shown that the (γ-Fe 2 O 3 @SiO 2 ) n @TiO 2 functional hybrid nanoparticles are photocatalytically actived. About 80% of methylene blue decomposed in 80 min in the presence of magnetic hybrid nanoparticles under illumination of UV light. The synthesized magnetic hybrid nanoparticles display high photocatalytic efficiency and will find potential applications for cleaning polluted water with the help of magnetic separation.

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Tailoring cathode materials with cations enables an improved hydration ability and proton migration, leading to a high fuel cell performance.