Showing papers in "Advanced Materials Interfaces in 2019"

Controlling Cell Behavior through the Design of Biomaterial Surfaces: A Focus on Surface Modification Techniques

Abstract: Surface interaction at the biomaterial–cell interface is essential for a variety of cellular functions, such as adhesion, proliferation, and differentiation. Nevertheless, changes in the biointerface enable to trigger specific cell signaling and result in different cellular responses. In order to manufacture biomaterials with higher functionality, biomaterials containing immobilized bioactive ligands have been widely introduced and employed for tissue engineering and regenerative medicine applications. Moreover, a number of physical and chemical strategies have been used to improve the functionality of biomaterials and specifically at the material interface. Here, the interactions between materials and cells at the interface levels are described. Then, the importance of surface properties in cell function is discussed and recent methods for surface modifications are systematically highlighted. Additionally, the impact of bulk material properties on the cellular responses is briefly reviewed.

Sulfur Redox Reactions at Working Interfaces in Lithium–Sulfur Batteries: A Perspective

Abstract: DOI: 10.1002/admi.201802046 of obstacles: a) the huge volume fluctuation of sulfur cathode during lithiation/ delithiation leads to the cracking and pulverization of electrodes; b) the insulating nature of sulfur and its discharged products (Li2S2/Li2S) induces a high redox overpotential and sluggish reaction kinetics; and c) lithium polysulfides (LPSs), soluble intermediates in liquid electrolytes, dissolve, diffuse, and decompose in electrolytes and/or at interfaces, leading to loss of active materials and interface destabilization. All above obstacles come together to render current Li–S batteries with low Coulombic efficiency, insufficient sulfur utilization, poor cycling stability, and severe anode corrosion.[3,4] In general, a typical Li–S battery is composed of a sulfur cathode, a lithium metal anode, and a suitable electrolyte either in liquid or solid state.[5] The electrochemical redox reactions of sulfur in aprotic liquid electrolytes (or gel polymer electrolytes containing a fraction of liquid solvents) include complicated multiphase evolution and multistep charge-transfer/nontransfer processes (S8 (s) ↔ Li2Sm (l) ↔ Li2Sn (l) ↔ Li2S2/Li2S (s), 4 ≤ n < m ≤ 8 while s and l refer to solid and liquid, respectively).[6] Although the chemical equilibria of soluble LPSs in electrolytes has a positive effect on improving sulfur conversion rates to Li2S product,[7] the formation of LPSs and their dissolution and migration in liquid electrolytes between cathodes and anodes, that is so-called shuttle effect, is clearly one of the greatest threats to cycle life and stability of Li–S batteries.[8–10] Considerable efforts have been paid to mitigate the shuttle of soluble LPSs via spatial confinement by porous hosts and chemical adsorption by polar materials.[11] However, the accumulation of soluble LPSs in catholyte always occurs and hence the shuttle driven by the concentration gradient can hardly be fully avoided. Therefore, enhancing conversion kinetics of soluble LPSs to alleviate the shuttle effect has attracted more attentions.[12–14] On one hand, promoting the transformation (liquid to liquid) from higher-order and highly soluble LPSs (Li2S8 and Li2S6) to lowerorder and relatively poorly soluble LPSs (Li2S4) can reduce the overall dissolution of LPSs in liquid electrolytes.[9] On the other hand, facilitating the conversion (liquid to solid) of LPSs to solid Li2S2/Li2S can reduce the bulk concentration of active species and, more importantly, shorten their retention time in electrolytes. To realize rapid redox kinetics of LPSs, electrocatalysis at the working solid (electrode)/liquid (electrolyte) interface plays a pivotal role. Lithium–sulfur (Li–S) batteries have been strongly considered as one of the most promising future energy storage systems because of ultrahigh theoretical energy density of 2600 Wh kg−1. The natural abundance, affordable cost, and environmental benignity of elemental sulfur constitute additional advantages. However, complicated reaction behaviors at working electrode/ electrolyte interfaces that involve multiphase conversion and multistep ion/electron diffusion during sulfur redox reactions have impeded the thorough understanding of Li–S chemistry and its practical applications. This perspective article highlights the influence of the ion/electron transport and reaction regulation through electrocatalysis or redox mediation at electrode/electrolyte interfaces on various interfacial sulfur redox reactions (liquid–liquid–solid interconversion between soluble lithium polysulfide with different chain lengths and insoluble lithium sulfides in liquid-electrolyte Li–S batteries and direct solid–solid conversion between sulfur and Li2S in all-solid-state Li–S batteries). The current status, existing challenges, and future directions are discussed and prospected, aiming at shedding fresh light on fundamental understanding of interfacial sulfur redox reactions and guiding the rational design of electrode/electrolyte interfaces for next-generation Li–S batteries with high energy density and long cycle life.

Graphene Modified Multifunctional Personal Protective Clothing.

Abstract: Personal protective clothing is intended to protect the wearer from various hazards (mechanical, biological, chemical, thermal, radiological, etc.) and inhospitable environmental conditions that may cause harm or even death. There are various types of personal protective clothing, manufactured with different materials based on hazards and end user requirements. Conventional protective clothing has impediments such as high weight, bulky nature, lack of mobility, heat stress, low heat dissipation, high physical stress, diminishing dexterity, diminishing scope of vision, lack of breathability, and reduced protection against pathogens and hazards. By virtue of the superlative properties of graphene, fabrics modified with this material can be an effective means to overcome these limitations and to improve properties such as mechanical strength, antibacterial activity, flame resistance, conductivity, and UV resistance. The limitations of conventional personal protective equipment are discussed, followed by necessary measures which might be taken to improve personal protective equipment (PPE), the unique properties of graphene, methods of graphene incorporation in fabrics, and the current research status and potential of graphene-modified performance textiles relevant to PPE.

2D SnO/In2O3 van der Waals Heterostructure Photodetector Based on Printed Oxide Skin of Liquid Metals

Abstract: Heterostructures assembled from atomically thin materials have led to a new paradigm in the development of the next-generation high-performing functional devices. However, the construction of the ultrathin van der Waals (vdW) heterostructures is challenging and/or limited to materials with layered crystal structures. Herein, liquid metal vdW transfer method is used to construct large area heterostructures of atomically thin metal oxides of p-SnO/n-In2O3 with ease. The heterostructure exhibits both outstanding photodetectivity of 5 x 10(9) Jones and photoresponsivity of 1047 A W-1 with fast response time of 1 ms under illumination of the 280 nm light. Such excellent performances are due to the formation of the narrow bandgap of the staggered gap at the p-n junction produced by the high-quality SnO/In2O3 heterostructure. The facile production of high-quality vdW heterostructures using the liquid metal-based method therefore provides a promising pathway for realizing future optoelectronic devices.

Evidence for Primal sp2 Defects at the Diamond Surface: Candidates for Electron Trapping and Noise Sources

Abstract: Many advanced applications of diamond materials are now being limited by unknown surface defects, including in the fields of high power/frequency electronics and quantum computing and quantum sensing Of acute interest to diamond researchers worldwide is the loss of quantum coherence in near-surface nitrogen-vacancy (NV) centers and the generation of associated magnetic noise at the diamond surface Here for the first time is presented the observation of a family of primal diamond surface defects, which is suggested as the leading cause of band-bending and Fermi-pinning phenomena in diamond devices A combination of density functional theory and synchrotron-based X-ray absorption spectroscopy is used to show that these defects introduce low-lying electronic trap states The effect of these states is modeled on band-bending into the diamond bulk and it is shown that the properties of the important NV defect centers are affected by these defects Due to the paramount importance of near-surface NV center properties in a growing number of fields, the density of these defects is further quantified at the surface of a variety of differently-treated device surfaces, consistent with best-practice processing techniques in the literature The identification and characterization of these defects has wide-ranging implications for diamond devices across many fields

Enabling High and Stable Electrocatalytic Activity of Iron-Based Perovskite Oxides for Water Splitting by Combined Bulk Doping and Morphology Designing

Abstract: The catalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are crucial for water splitting technology, and perovskite oxides have received tremendous attention as promising candidates due to the compositional flexibility and rich properties. Here, reported is the successful deployment of cost-effective iron-based perovskites into efficient water splitting catalysts with both high activity and stability by combined bulk and morphology tuning strategy. Through constructing 3D ordered macroporous (3DOM) structure of LaFeO perovskite, approximately twofold and approximately fourfold enhancement in activity for OER and HER, respectively were realized together with much improved OER durability. By a small amount of cobalt doping, both catalytic activity and stability were further improved with activity comparing favorably to or even outperforming Co-/Ni-rich perovskite catalysts. Enhanced performance is correlated with optimized Fe/O species, high surface area, and good charge/mass transport.

Trimetallic Metal–Organic Framework Derived Carbon-Based Nanoflower Electrocatalysts for Efficient Overall Water Splitting

Abstract: DOI: 10.1002/admi.201900290 limiting the whole reaction. At present, the practical application of electrocatalytic water splitting is largely limited by the high cost of conventional electrocatalysts, such as noble metal RuO2 and IrO2 for OER and Pt for HER.[3] In the past few decades, the inexpensive transition metal compounds have shown promising electrocatalytic activity.[4] Moreover, realization of HER and OER simultaneously based on the same catalyst and electrolyte in one electrochemical cell is highly important for practical overall water splitting.[5] The formation of multimetallic structures is a common strategy to improve the performance of electrocatalysts, as the interactions among different compositions can, in principle, lead to synergistic effects and well-tunable electronical activities.[6] For instance, Li et al. developed a strategy using bimetallic Prussian blue analogues to obtain superior Co1−xFex phosphide electrocatalysts.[7] Zhang et al. constructed FexNi1−x phosphide nanosheet arrays to optimize OER performance under both alkaline and neutral conditions.[8] Recently, there has been pioneering work revealing that the additional incorporation of a third metal into bimetallic component will lead to further enhancement in electrocatalytic activity and stability. For example, Li et al. reported that trimetallic metal–organic frameworks (MOFs) Fe/ Ni/Co(Mn)-MIL-53 could lead to superior electrocatalytic performance.[9] Huang and co-workers successfully fabricated the coralloid-like trimetallic W0.5Co0.5Fex oxyhydroxide sponge on nickel foam or carbon nanotubes which shows highly active and stable electrocatalytic performance.[10] On the other hand, it is well known that the electrocatalyst with unique nanostructure is an important factor to improve their electrocatalytic properties. Intricate novel nanostructures such as hollow structures,[11] nanocages,[12] core@shell structures,[13] 2D nanosheets,[14] and nanoflowers[15] have been proven to show ideal application value in the fields of catalysis, energy conversion, and storage. For instance, novel nickel-doped cobalt phosphide nanoflowers were successfully fabricated and exhibited remarkable electrocatalytic HER performance.[16] And the 3D hierarchical porous CoP nanoflowers were also shown to be a promising HER catalyst.[17] MOFs have been widely developed as promising precursors, which provide a proper template for the synthesis of nanomaterials with high porosity, high surface area, and distinctive Searching desirable cost-effective electrocatalysts for overall water splitting is of great importance for the hydrogen production industry. Here a facile synthesis of trimetallic carbon nanoflower electrocatalysts is reported which are derived from Co2+/Fe2+/Ni2+ ratio adjustable metal–organic frameworks (MOFs). The unique nanosheet-assembled multiscale nanoflower morphology can enlarge the catalyst/electrolyte contact area, and the synergistic electronic effects between trimetallic components endow the trimetallic carbon nanoflower electrocatalysts with more oxygen vacancies and a higher degree of graphitization of carbon, thus showing excellent activity. The optimized Co0.2Fe0.8Ni-OCNF reaches a current density of 10 mA cm−2 at low overpotential of 291 mV with a very small Tafel slope of 36.1 mV dec−1 and 1.65 V@10 mA cm−2 for a two-electrode water electrolysis in an alkaline solution, outperforming the commercial IrO2 electrocatalysts. The results may pave the way to the development of more efficient multicomponent nanosheetassembled multiscale nanomaterials for various catalytic applications.

Stick‐On Large‐Strain Sensors for Soft Robots

Abstract: DOI: 10.1002/admi.201900985 pneumatic and microfluidic structures,[1–8] dielectric elastomer actuators,[9–11] shape memory alloys,[12,13] responsive hydrogels,[14,15] and living cells.[16] Among them, soft pneumatic robots have attracted attention due to their complex motion, simple control input, and low-impedance interactions. For soft pneumatic robots, sensing techniques are important to improve accuracy and functionality when grasping or manipulating objects of different shapes and sizes. However, the limitations of existing sensing capabilities greatly restrict the applications for this type of soft robot. Traditional rigid sensing components on soft robots can limit the deformation and compliance of the underlying soft robotic structure. Existing strain sensors for soft robots mainly rely on stretchable electronic conductors, either in the form of 1) elastomeric conductors, which consist of elastomers embedded with conducting components such as silver nanowires, silver particles, carbon nanotubes, and graphene, or 2) liquid conductors, such as grease and liquid metal. The limitations of these sensors have been noted in previous studies. The conductivity of elastomeric conductors degrades due to contact defects between separated particles or liquid, especially under large deformation, as well as the resistance-strain hysteresis resulting from cyclic loading.[17] For liquid conductors like conductive paste, the localized plastic deformation resulting from ratcheting during cyclic loading accumulates and deteriorates conductivity as well.[18,19] The change in conductivity leads to signal drifts. In addition, liquid conductors are not biocompatible and need tight sealing to prevent oxidation and leakage, thus requiring additional technical effort. Soft actuators with integrated microchannels filled with conductive fluid have been fabricated via 3D printing.[20,21] But the intricate designs and complex manufacturing requirements dramatically increase the fabrication difficulty. It remains a major challenge to manufacture robust soft strain sensors for soft robots.[22–27] Compared to electronic conductors, ionically conductive hydrogels can be readily used as stretchable conductors,[28–30] and have recently enabled a new family of devices called hydrogel ionotronics.[31] Both the mechanical and electrical properties of hydrogels can be tuned on demand over a wide range. For example, hydrogels can be as soft as living tissues or as tough as natural rubber. As another example, the resistivity of hydrogels can vary from 18.2 MΩ m to 10−1 Ω m, depending on the type and concentration of salt.[32] In fact, hydrogels resemble ideal conductors, as their resistivity is a material Soft robots require sensors that are soft, stretchable, and conformable to preserve their adaptivity and safety. In this work, hydrogels are successfully applied as large-strain sensors for elastomeric structures such as soft robots. Following a simple surface preparation step based on silane chemistry, prefabricated sensors are strongly bonded to elastomers via a “stick-on” procedure. This method separates the construction of the soft robot’s structure and sensors, expanding the potential design space for soft robots that require integrated sensing. The adhesion strength is shown to exceed that of the hydrogel itself, and the sensor is characterized via quasi-static, fatigue, and dynamic response tests. The sensor exhibits exceptional electrical and mechanical properties: it can sense strains exceeding 400% without damage, maintain stable performance after 1500 loading cycles, and has a working bandwidth of at least 10 Hz, which is sufficient for rapidly-actuated soft robots. In addition, the hydrogel-based large-strain sensor is integrated into a soft pneumatic actuator, and the sensor effectively measures the actuator’s configuration while allowing it to freely deform. This work provides “stick-on” large-strain sensors for soft robots and will enable novel functionality for wearable robots, potentially serving as a “sensing skin” through stimuli-responsive hydrogels.