NiM (Sb, Sn)/N-doped hollow carbon tube as high-rate and high-capacity anode for lithium-ion batteries.

Alloy-type materials are regarded as prospective anode replacements for lithium-ion batteries (LIBs) owing to their attractive theoretical capacity. However, the drastic volume expansion leads to structural collapse and pulverization, resulting in rapid capacity decay during cycling. Here, a simple and scalable approach to prepare NiM (M: Sb, Sn)/nitrogen-doped hollow carbon tubes (NiMC) via template and substitution reactions is proposed. The nanosized NiM particles are uniformly anchored in the robust hollow N-doped carbon tubes via NiNC coordination bonds, which not only provides a buffer for volume expansion but also avoids agglomerating of the reactive material and ensures the integrity of the conductive network and structural framework during lithiation/delithiation. As a result, NiSbC and NiSnC exhibit high reversible capacities (1259 and 1342 mAh/g after 100 cycles at 0.1 A/g) and fascinating rate performance (627 and 721 mAh/g at 2 A/g), respectively, when employed as anodes of LIBs. The electrochemical kinetic analysis reveals that the dominant lithium storage behavior of NiMC electrodes varies from capacitive contribution to diffusion contribution during the cycling corresponding to the activation of the electrode exposing more NiM sites. Meanwhile, M (Sb, Sn) is gradually transformed into stable NiM during the de-lithium process, making the NiMC structure more stable and reversible in the electrochemical reaction. This work brings a novel thought to construct high-performance alloy-based anode materials.

Azadipyrromethene Dye-Assisted Defect Passivation for Efficient and Stable Perovskite Solar Cells.

Organic-inorganic perovskite solar cells (PSCs) provide one of the most outstanding photovoltaic (PV) technologies, yet their efficiency, stability, and defect passivation engineering still remain challenging. We demonstrate the use of low-cost, eco-friendly, and multi-functional aza-dipyrromethene (Aza-DIPY) dye molecules to promote the power conversion efficiency (PCE) and the operating stability of PSC devices. The Aza-DIPY dye was meticulously synthesized and incorporated into PSC devices via a one-step solution processing approach. The pyrrole, benzene ring, and chlorine functional groups on the dye have intense interactions with perovskite to passivate surface defects and obtain high-quality perovskite absorbers, resulting in the lengthened carrier recombination time and enhanced fill factor of PSCs. Additionally, the hydrophobic phenyl and halogen functional groups on the Aza-DIPY perform as a protecting barrier against moisture and ameliorate the stability of PSCs. As a consequence, the PV performance of PSCs is considerably improved, with the average PCE increased from 16.71% to 19.71%, and the champion device with Aza-DIPY shows a PCE of 20.46%. The unencapsulated PSC devices with multi-functional molecular Aza-DIPY maintains 89.06% of their beginning PCEs after storage in ambient air (25-30 °C, 50-70% relative humidity) under dark conditions for 100 h, exhibiting a significantly enhanced ambient stability compared with the case of the reference cells without the dye. Furthermore, the Aza-DIPY-modified PSC devices exhibit strong and reversible photoresponses, with a high responsivity of 0.739 mA/W to near-infrared (NIR) laser beams. Our results highlight the potential of synthesizing multi-functional Aza-DIPY dyes-incorporated PSC devices with sensitive NIR/visible light responses, high PV efficiency, and stability.

Improved SERS activity of non-stoichiometric copper sulfide nanostructures related to charge-transfer resonance.

The low enhancement factor of semiconductor SERS substrates is a major obstacle for their practical application. Therefore, there is a need to explore the facile synthesis of new SERS substrates and reveal the SERS enhancement mechanism. Here, we develop a simple, facile and low-cost two-step method to synthesize copper sulfide based nanostructures with different Cu7.2S4 contents. The as-synthesized sample is composed of nanosheets with the CuS phase structure. With the increase of the annealing temperature to 300 °C, the CuS content gradually decreases and disappears, and the content of Cu7.2S4 and CuSO4 appears and gradually increases. At the annealing temperature of 350 °C, only CuSO4 exists. Compared with pure CuS or pure CuSO4, the detection limit of R6G molecules is the lowest for the composite sample with a higher content of Cu7.2S4, indicating that the introduction of non-stoichiometric Cu7.2S4 can improve the SERS performance and the higher content of Cu7.2S4 leads to a higher SERS activity. Furthermore, to investigate the SERS mechanism, the energy band structures and energy-level diagrams of different probe molecules over CuS, Cu7.2S4 and CuxS are studied by DFT calculations. Theoretical calculations indicate that the excellent SERS behavior depends on charge transfer resonance. Our work provides a general approach for the construction of excellent metal compound semiconductor SERS active substrates.