P2-type Ni/Mn-based layered oxides are promising cathode materials for sodium-ion batteries (SIBs). However, ground challenges, e.g., irreversible phase transition during cycling, moisture instability, and inferior electrochemical performance, greatly impede their practical applications. Herein, a series of Cu-substituted P2− Na 0.6 Ni 0.3−x Mn 0.7 Cu x O 2 (0 ≤ x ≤ 0.2) cathode materials for SIBs are fabricated and the mechanisms responsible for their improved electrochemical performances are comprehensively investigated. It is discovered that Cu dopants with strong electronegativity could stabilize the crystal structure by inhibiting the common P2−O2 phase transition, leading to improved cycling stability. The expanded interlayer spacing after Cu doping is facilitated for the charge transfer kinetics, which ensures excellent rate performance. In addition, all Ni, Mn, Cu, and O participate in the charge compensation upon sodiation and desodiation through reversible redox reactions. More importantly, Cu substitution improves the moisture stability of the cathode materials because the Cu 2+ /Cu 3+ redox couple increases the initial charging potential. This work provides a promising guidance for the design of low-cost, high-performance, and air-stable cathode materials with both cationic and anionic redox activities for SIBs.
further extended through well-designed SERS substrates. [5,6] Although many kinds of SERS substrates have been reported, extensive studies have mainly focused on enhancing the sensitivity by generating more SERS-active sites (commonly known as "hot spots") on the substrates using strategies such as colloidal assembly, lithography technique, and nanoimprinting. [7][8][9][10][11] Besides, the wetting properties of the SERS substrates have recently gained much attention. Typically, the SERS substrates that are covered with noble metals are naturally hydrophilic, which in turn restricts further applications such as trace analysis or single-molecule detection because of the low probability in locating the analyte molecules at SERS-active sites especially for highly diluted solutions. [12,13] To overcome the limitations, many strategies have been reported. For example, Yang et al. developed a method by aggregating target molecules and metal nanoparticles into small regions. [14] A slippery liquid-infused porous surface consisting of a Teflon membrane and a perfluorinated lubricant, which eliminates the adhesion of the droplets, was used. Such a surface was found to lead to a constant water contact angle (WCA) during the solvent evaporation process and enhance the aggregation efficiency of the gold nanoparticles (AuNPs) and the target molecules. In another example, Chen et al. demonstrated a strategy to achieve effective aggregation by applying the coffee ring effect using cellulose nanofibers (CNFs) and AuNPs. [15] Suspended analyte particles were carried and accumulated at the drop edges by the hydrodynamic flow, and eventually, formed ring-shape SERS sensitive regions. The CNF-AuNPs substrates were found to have a wider SERS detection zone (L D ≥ 300 µm) compared with the conventional method (L D ≤ 30 µm), which can be attributed to the unique surface properties. Park et al. also developed a facile protocol by placing the analyte molecules at the SERS-active nanogaps of the nanopillars to achieve high sensitivity. [16] By controlling the surface energy of plasmonic nanopillars through the selective removal process, a wide range of WCA from 165.8° (superhydrophobic surface) to 40.0° (hydrophilic surface) was obtained. Under the optimized wetting conditions, successful detection Surface properties are essential for substrates exhibiting high sensitivity in surface-enhanced Raman scattering (SERS) applications. In this work, novel SERS hybrid substrates using polystyrene-block-poly(methyl methacrylate) and anodic aluminum oxide templates is presented. The hybrid substrates not only possess hierarchical porous nanostructures but also exhibit superhydrophilic surface properties with the water contact angle ≈0°. Such surfaces play an important role in providing uniform enhanced intensities over large areas (relative standard deviation ≈10%); moreover, these substrates are found to be highly sensitive (limit of detection ≈10 −12 m for rhodamine 6G (R6G)). The results show that the hybrid SERS substrates can achieve the simu...
Regular arrays of anisotropic polymer nanomaterials have attracted great attention because of their unique properties and various applications such as solar cell devices, sensors, and supercapacitors. The control of the shape manipulation and tailored properties of individual polymer nanomaterials in arrays, however, remains a great challenging task. In this work, we demonstrate a versatile approach to fabricate elliptical and bent polymer nanorod arrays through laser-induced photo-fluidization of azobenzene-containing polymers (azopolymers). Ordered anodic aluminum oxide (AAO) membranes are used as templates for generating azopolymer nanorod arrays via a solvent vapor annealing-induced wetting method. After being released from the AAO templates and shone by linearly polarized lights, the nanorod arrays can be transformed into anisotropic nanostructures, driven by the trans-to-cis and cis-to-trans isomerization of the azobenzene groups in the azopolymers. Depending on whether the laser beam is shone at normal or tilt angles of incidence, elliptical or bent nanorod arrays can be prepared, respectively. The deformation degrees and water wettabilities of the nanorod arrays can be varied by changing the illumination times. This study reports a beneficial route to prepare ordered arrays of anisotropic polymer nanostructures for advanced applications.
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