Nano Materials Science最新文献

Multifunctional and flexible wearable devices play a crucial role in a wide range of applications, such as heath monitoring, intelligent skins, and human-machine interactions. Developing flexible and conductive materials for multifunctional wearable devices with low-cost and high efficiency methods are highly desirable. Here, a conductive graphene/microsphere/bamboo fiber (GMB) nanocomposite paper with hierarchical surface microstructures is successfully fabricated through a simple vacuum-assisted filtration followed by thermo-foaming process. The as-prepared microstructured GMB nanocomposite paper exhibits not only a high volume electrical conductivity of ∼45 ​S/m but also an excellent electrical stability (i.e., relative changes in resistance are less than 3% under stretching, folding, and compressing loadings) due to its unique structure features. With this microstructured nanocomposite paper as active sensing layer, microstructured pressure sensors with a high sensitivity (−4 ​kPa⁻¹), a wide sensing range (0–5 ​kPa), and a rapid response time (about 140 ​ms) are realized. In addition, benefitting from the outstanding electrical stability and mechanical flexibility, the microstructured nanocomposite paper is further demonstrated as a low-voltage Joule heating device. The surface temperature of the microstructured nanocomposite paper rapidly reaches over 80 ​°C when applying a relatively low voltage of 7 ​V, indicating its potential in human thermotherapy and thermal management.

Electrically conductive elastomer composites (CECs) with segregated networks of conductive nanofillers show high potential in stretchable strain sensors due to balanced mechanical and electrical properties, yet the sensitivity at low strain is generally insufficient for practical application. Herein, we report an easy and effective way to improve the resistive response to low strain for CECs with segregated network structure via adding stiff alumina into carbon nanostructures (CNS). The CEC containing 0.7 ​wt% CNS and 5 ​wt% Al₂O₃ almost sustains the same elasticity (elongation at break of ∼900%) and conductivity (0.8 ​S/m) as the control, while the piezoresistive sensitivity is significantly improved. Thermoplastic polyurethane (TPU) composites with a segregated network of hybrid nanofillers (CNS and Al₂O₃) show much higher strain sensitivity (Gauge factor, GF ​= ​566) at low strain (45% strain) due to a local stress concentration effect, this sensitivity is superior to that of TPU/CNS composites (GF ​= ​11). Such a local stress concentration effect depends on alumina content and its distribution at the TPU particle interface. In addition, CECs with hybrid fillers show better reproducibility in cyclic piezoresistive behavior testing than the control. This work offers an easy method for fabricating CECs with a segregated filler network offering stretchable strain sensors with a high strain sensitivity.

Since the discovery of mesoporous silica in 1990s, there have been numerous mesoporous silica-based nanomaterials developed for catalytic applications, aiming at enhanced catalytic activity and stability. Recently, there have also been considerable interests in endowing them with hierarchical porosities to overcome the diffusional limitation for those with long unimodal channels. Present processes of making mesoporous silica largely rely on chemical sources which are relatively expensive and impose environmental concerns on their processes. In this regard, it is desirable to develop hierarchical silica supports from natural minerals. Herein, we present a series of work on surface reconstruction, modification, and functionalization to produce diatomite-based catalysts with original morphology and macro-meso-micro porosities and to test their suitability as catalyst supports for both liquid- and gas-phase reactions. Two wet-chemical routes were developed to introduce mesoporosity to both amorphous and crystalline diatomites. Importantly, we have used computational modeling to affirm that the diatomite morphology can improve catalytic performance based on fluid dynamics simulations. Thus, one could obtain this type of catalysts from numerous natural diatoms that have inherently intricate morphologies and shapes in micrometer scale. In principle, such catalytic nanocomposites acting as miniaturized industrial catalysts could be employed in microfluidic reactors for process intensification.

The oxygen reduction reaction (ORR) electrocatalytic activity of Pt-based catalysts can be significantly improved by supporting Pt and its alloy nanoparticles (NPs) on a porous carbon support with large surface area. However, such catalysts are often obtained by constructing porous carbon support followed by depositing Pt and its alloy NPs inside the pores, in which the migration and agglomeration of Pt NPs are inevitable under harsh operating conditions owing to the relatively weak interaction between NPs and carbon support. Here we develop a facile electrospinning strategy to in-situ prepare small-sized PtZn NPs supported on porous nitrogen-doped carbon nanofibers. Electrochemical results demonstrate that the as-prepared PtZn alloy catalyst exhibits excellent initial ORR activity with a half-wave potential (E_1/2) of 0.911 ​V versus reversible hydrogen electrode (vs. RHE) and enhanced durability with only decreasing 11 ​mV after 30,000 potential cycles, compared to a more significant drop of 24 ​mV in E_1/2 of Pt/C catalysts (after 10,000 potential cycling). Such a desirable performance is ascribed to the created triple-phase reaction boundary assisted by the evaporation of Zn and strengthened interaction between nanoparticles and the carbon support, inhibiting the migration and aggregation of NPs during the ORR.

Electronic skin and flexible wearable devices have attracted tremendous attention in the fields of human-machine interaction, energy storage, and intelligent robots. As a prevailing flexible pressure sensor with high performance, the piezoresistive sensor is believed to be one of the fundamental components of intelligent tactile skin. Furthermore, graphene can be used as a building block for highly flexible and wearable piezoresistive sensors owing to its light weight, high electrical conductivity, and excellent mechanical. This review provides a comprehensive summary of recent advances in graphene-based piezoresistive sensors, which we systematically classify as various configurations including one-dimensional fiber, two-dimensional thin film, and three-dimensional foam geometries, followed by examples of practical applications for health monitoring, human motion sensing, multifunctional sensing, and system integration. We also present the sensing mechanisms and evaluation parameters of piezoresistive sensors. This review delivers broad insights on existing graphene-based piezoresistive sensors and challenges for the future generation of high-performance, multifunctional sensors in various applications.

The future intelligent era that will be brought about by 5G technology can be well predicted. For example, the connection between humans and smart wearable devices will become increasingly more intimate. Flexible wearable pressure sensors have received much attention as a part of this process. Nevertheless, there is a lack of complete and detailed discussion on the recent research status of capacitive pressure sensors composed of polymer composites. Therefore, this article will mainly discuss the key concepts, preparation methods and main performance of flexible wearable capacitive sensors. The concept of a processing “toolbox” is used to review the developmental status of the dielectric layer as revealed in highly cited literature from the past five years. The preparation methods are categorized into types of processing: primary and secondary. Using these categories, the preparation methods and structure of the dielectric layer are discussed. Their influence on the final capacitive sensing behavior is also addressed. Recent developments in the electrode layer are also systematically reviewed. Finally, the results of the above discussion are summarized and future development trends are discussed.

Improving catalytic activity and durabilty through the structural and compositional development of bifunctional electrocatalysts with low cost, high activity and stability is a challenging issue in electrochemical water splitting. Herein, we report the fabrication of heterostructured P-CoMoO₄@NiCoP on a Ni foam substrate through interface engineering, by adjusting its composition and architecture. Benefitting from the tailored electronic structure and exposed active sites, the heterostructured P-CoMoO₄@NiCoP/NF arrays can be coordinated to boost the overall water splitting. In addition, the superhydrophilic and superaerophobic properties of P-CoMoO₄@NiCoP/NF make it conducive to water dissociation and bubble separation in the electrocatalytic process. The heterostructured P-CoMoO₄@NiCoP/NF exhibits excellent bifunctional electrocatalysis activity with a low overpotential of 66 ​mV at 10 ​mA ​cm⁻² for HER and 252 ​mV at 100 ​mA ​cm⁻² for OER. Only 1.62 ​V potential is required to deliver 20 ​mA ​cm⁻² in a two-electrode electrolysis system, providing a decent overall water splitting performance. The rational construction of the heterostructure makes it possible to regulate the electronic structures and active sites of the electrocatalysts to promote their catalytic activity.

Bimetallic Pt-skin catalyst is a class of near-surface alloy (NSA) that owns a high degree of control over composition. Herein, density functional theory (DFT) is used to calculate the energetics of oxygen reduction reaction (ORR) on Pt-skin over Ir, Pd and Au substrates. A Brønsted-Evans-Polanyi (BEP) relationship can be determined for the oxygen molecule dissociation. The binding energy of both atomic oxygen and hydroxyl radical is found to correlate well with the d band center of Pt-skin atoms. Their catalytic activities show the volcano relationship as the positions of each substrate in the periodic table. The effect of surface strain, band structure and charge transfer on the d band center is well studied, and it can be found that the surface strain effect plays a dominant role for all Pt-skin catalysts. Ir substrate makes the d band center of Pt-skin go far away from the Fermi level, while Au substrate makes it move towards the Fermi level. Being different from both Ir and Au, Pd substrate makes the d band center of Pt-skin comparable with the monometallic Pt.