The development of wearable strain sensors with simultaneous large stretchability (strain >55%) and high sensitivity (gauge factor >100) remains a grand challenge to this day. Drawing on inspiration from nature, nacre has demonstrated outstanding mechanical properties, especially combining high strength and toughness, which is due in part to its delicate hierarchical layered architecture with rich interfacial interactions. We demonstrate that strain sensors based on this nacre-mimetic microscale “brick-and-mortar” architecture can simultaneously achieve ultrahigh sensitivity and large stretchability while performing well in linearity, reliability, long-term durability, and monotonicity. The bioinspired sensor demonstrated a gauge factor >200 over a range of working strains up to 83% and achieved a high gauge factor exceeding 8700 in the strain region of 76–83%. This successful combination of high sensitivity and large stretchability is attributed to (1) the microscale hierarchical architecture derived from the amalgamation of 2D titanium carbide (MXene) Ti3C2T x /1D silver nanowire “brick” and poly(dopamine)/Ni2+ “mortar” and (2) the synergistic toughing effects from interfacial interactions of hydrogen and coordination bonding, layer slippage, and molecular chain stretching. The synergistic behavior of the “brick” and “mortar” allows for controlled crack generation for high sensitivity but can also dissipate considerable loading energy to promote the stepwise propagation of cracks while stretching, guaranteeing the significant comprehensive sensing performance. Moreover, this bioinspired strain sensor is employed to monitor human activities under different motion states to demonstrate its feasibility for wearable, full-spectrum human health and motion monitoring systems.
MXene, a new class of two-dimensional materials, offers a unique combination of metallic conductivity and hydrophilicity. This material has shown great promise in numerous applications including electromagnetic interference shielding, sensing, energy storage, and catalysis. In this paper, we report on the fabrication of transparent, conductive, and flexible MXene/silver nanowire (AgNW) hybrid films, resulting in the highest figure of merit (162.49) in the reported literature to date regarding an MXene-based transparent electrode. The hybrid films, prepared via a simple and scalable solution-processed method, exhibit good electrical conductivity, high transmittance, low roughness, work function matching, and robust mechanical performance. Following film fabrication, the hybrid electrodes were demonstrated to function as transparent electrodes in fullerene molecule PTB7-Th:PC71BM and nonfullerene molecule PBDB-T:ITIC organic photovoltaics (OPVs). In an effort to further improve the performance of flexible OPVs, a ternary structure of PBDB-T:ITIC:PC71BM was demonstrated, resulting in a power conversion efficiency (PCE) of 8.30%. Mechanical properties were also quantified, with the flexible ternary organic solar cells capable of retaining 84.6% of the original PCE after 1000 bending and unbending cycles to a 5 mm bending radius. These optoelectronic and mechanical performance metrics represent a breakthrough in the field of flexible optoelectronics.
Oxidative dispersion has been widely used in regeneration of sintered metal catalysts and fabrication of single atom catalysts, which is attributed to an oxidation-induced dispersion mechanism. However, the interplay of gas-metal-support interaction in the dispersion processes, especially the gas-metal interaction has not been well illustrated. Here, we show dynamic dispersion of silver nanostructures on silicon nitride surface under reducing/oxidizing conditions and during carbon monoxide oxidation reaction. Utilizing environmental scanning (transmission) electron microscopy and near-ambient pressure photoelectron spectroscopy/photoemission electron microscopy, we unravel a new adsorption-induced dispersion mechanism in such a typical oxidative dispersion process. The strong gas-metal interaction achieved by chemisorption of oxygen on nearly-metallic silver nanoclusters is the internal driving force for dispersion. In situ observations show that the dispersed nearly-metallic silver nanoclusters are oxidized upon cooling in oxygen atmosphere, which could mislead to the understanding of oxidation-induced dispersion. We further understand the oxidative dispersion mechanism from the view of dynamic equilibrium taking temperature and gas pressure into account, which should be applied to many other metals such as gold, copper, palladium, etc. and other reaction conditions.
To promote silver nanowire (AgNW) as a viable commercial alternative for transparent electrodes, it is necessary to further develop industrially scalable, high‐performance yielding and cost‐efficient methods of purifying large quantities of as‐prepared AgNW suspensions. In this work, a facile, effective, and mass scalable purification method that employs a novel dynamic agitation‐induced centrifugal filtration concept to obtain highly purified and printable AgNW solutions. This unique dynamic filtration system, which amalgamates the advantages of membrane filtration, centrifugal filtration and “cross‐flow” filtration, is effective at (1) removing nanoparticles, short nanorods and organic additives from as‐prepared AgNW suspensions without producing aggregation; (2) concentrating purified AgNW suspensions to a desirable concentration; and (3) formulating printable AgNW suspensions with suitable solvents. The resulting purified, polyol‐method synthesized AgNW with a modest aspect ratio of ≈1000 and narrowed length distribution, can be coated into flexible transparent electrodes to yield a transmittance of 99.2% and 95.2% at 230 and 29.6 ohm sq‐1 respectively. These performance metrics are comparable or exceed that of most transparent electrodes made from AgNW with larger aspect ratio (>2000) but purified through conventional purification methods. To maximize the dynamic purification efficiency, a model is also developed to describe and predict this dynamic filtration process.
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