Electrochemically Induced Phase Transformation in Vanadium Oxide Boosts Zn-Ion Intercalation.

Vanadium oxides are excellent cathode materials with large storage capacities for aqueous zinc-ion batteries, but their further development has been hampered by their low electronic conductivity and slow Zn2+ diffusion. Here, an electrochemically induced phase transformation strategy is proposed to mitigate and overcome these barriers. In situ X-ray diffraction analysis confirms the complete transformation of tunnel-like structural V6O13 into layered V5O12·6H2O during the initial electrochemical charging process. Theoretical calculations reveal that the phase transformation is crucial to reducing the Zn2+ migration energy barrier and facilitating fast charge storage kinetics. The calculated band structures indicate that the bandgap of V5O12·6H2O (0.0006 eV) is lower than that of V6O13 (0.5010 eV), which enhanced the excitation of charge carriers to the conduction band, favoring electron transfer in redox reactions. As a result, the transformed V5O12·6H2O delivers a high capacity of 609 mA h g-1 at 0.1 A g-1, superior rate performance (300 mA h g-1 at 20 A g-1), fast-charging capability (<7 min charging for 465 mA h g-1), and excellent cycling stability with a reversible capacity of 346 mA h g-1 at 5 A g-1 after 5000 cycles.

Characterization of Regional Combustion Efficiency using ΔXCO: ΔXCO2 Observed by a Portable Fourier-Transform Spectrometer at an Urban Site in Beijing.

Measurements of column-averaged dry-air mole fractions of carbon dioxide and carbon monoxide, CO2 (XCO2) and CO (XCO), were performed throughout 2019 at an urban site in Beijing using a compact Fourier Transform Spectrometer (FTS) EM27/SUN. This data set is used to assess the characteristics of combustion-related CO2 emissions of urban Beijing by analyzing the correlated daily anomalies of XCO and XCO2 (e.g., ΔXCO and ΔXCO2). The EM27/SUN measurements were calibrated to a 125HR-FTS at the Xianghe station by an extra EM27/SUN instrument transferred between two sites. The ratio of ΔXCO over ΔXCO2 (ΔXCO:ΔXCO2) is used to estimate the combustion efficiency in the Beijing region. A high correlation coefficient (0.86) between ΔXCO and ΔXCO2 is observed. The CO:CO2 emission ratio estimated from inventories is higher than the observed ΔXCO:ΔXCO2 (10.46 ± 0.11 ppb ppm-1) by 42.54%-101.15%, indicating an underestimation in combustion efficiency in the inventories. Daily ΔXCO:ΔXCO2 are influenced by transportation governed by weather conditions, except for days in summer when the correlation is low due to the terrestrial biotic activity. By convolving the column footprint [ppm (µmol m-2 s-1)-1] generated by the Weather Research and Forecasting-X-Stochastic Time-Inverted Lagrangian Transport models (WRF-X-STILT) with two fossil-fuel emission inventories (the Multi-resolution Emission Inventory for China (MEIC) and the Peking University (PKU) inventory), the observed enhancements of CO2 and CO were used to evaluate the regional emissions. The CO2 emissions appear to be underestimated by 11% and 49% for the MEIC and PKU inventories, respectively, while CO emissions were overestimated by MEIC (30%) and PKU (35%) in the Beijing area.

Impacts of Oxygen Vacancies on Zinc Ion Intercalation in VO2.

The aqueous zinc ion battery has emerged as a promising alternative technology for large-scale energy storage due to its low cost, natural abundance, and high safety features. However, the sluggish kinetics stemming from the strong electrostatic interaction of divalent zinc ions in the host crystal structure is one of challenges for highly efficient energy storage. Oxygen vacancies (VO••), in the present work, lead to a larger tunnel structure along the b axis, which improves the reactive kinetics and enhances Zn-ion storage capability in VO2 (B) cathode. DFT calculations further support that VO•• in VO2 (B) result in a narrower bandgap and lower Zn ion diffusion energy barrier compared to those of pristine VO2 (B). VO••-rich VO2 (B) achieves a specific capacity of 375 mAh g-1 at a current density of 100 mA g-1 and long-term cyclic stability with retained specific capacity of 175 mAh g-1 at 5 A g-1 over 2000 cycles (85% capacity retention), higher than that of VO2 (B) nanobelts (280 mAh g-1 at 100 mA g-1 and 120 mAh g-1 at 5 A g-1, 65% capacity retention).

Influence of the type of carrier on ferromagnetism in a Si semiconductor implanted with Cu ions.

Silicon semiconductor samples implanted with Cu ions and samples co-implanted with Cu- and N-ions were prepared by MEVVA and the Kaufman technique. None of the samples showed evidence of secondary phases. The initially n-type Si matrix, when implanted with Cu ions, changed to a p-type semiconductor, and the Cu ions existed as local Cu2+ cations in the p-type environment. As a result, none of the Cu-implanted samples were ferromagnetic at room temperature. The co-implanted samples, on the other hand, showed room-temperature ferromagnetism because the introduction of N ions made the carrier type change from p-type to n-type which is favorable for the appearance of Cu2+. First principles calculations were applied to understand the experimental phenomena. The formation energy was reduced by implanting N ions, and was decreased effectively with the increase in ratio of N to Cu ions. The density of states and spin density of states indicated that the hybridization of s, p and d electrons induced ferromagnetism at 0 K. Particularly, we proposed possible exchange interactions between the Cu2+-N-(N4+)-Cu2+ ions to explain the ferromagnetism mechanism.

Role of an external electric field on hybrid halide perovskite CH3NH3PbI3 band gaps.

The organic-inorganic perovskite CH3NH3PbI3 has attracted much attention due to their power conversion efficiency as a potential photovoltaic material, but the role of an external electric field has not been well understood. Based on first-principles calculations, the effects of an external electric field (E) applied along the [111] direction of the orthorhombic perovskite, CH3NH3PbI3, on its electronic structure and optical properties are investigated. Our results indicate that the electric field strength affects the band gap (Eg) of CH3NH3PbI3 (MAPbI3, MA = CH3NH3). The energy difference between the two peaks closest to the Fermi level in the density of states diagram decreases with increasing applied electric field strength along the [111] direction, indicating that the covalent character increases between A-sites cations and I-sites anions. Both the cell volume and the final energy show the same increasing trend. The absorption peaks move toward the visible-frequency range, with the optimal band gap of 1.1-1.45 eV and E = 0.04-0.06 eV/Å/e. In particular, the non-linear change of the second-order Stark effect causes a non-linear change in the band gap.