Synthesis, Shape Control, and Methanol Electro-oxidation Properties of Pt–Zn Alloy and Pt₃Zn Intermetallic Nanocrystals

We report the first synthesis of highly monodisperse Pt₃Zn nanocrystals (NCs). Shape-controlled synthesis generates cubic and spherical Pt–Zn NCs. Reaction temperature is the key to incorporate Zn into Pt, even in the absence of a strong reducing agent. The Pt–Zn NCs are active toward methanol oxidation, with the spherical NCs exhibiting higher activity than the cubic NCs. The Pt–Zn alloy phase can be transformed into the Pt₃Zn intermetallic phase, upon annealing. The intermetallic Pt₃Zn shows better performance than the alloy phase Pt–Zn. Besides the activity toward methanol oxidation, Pt–Zn NCs show excellent poisoning tolerance. With activities comparable to the commercial Pt catalyst, enhanced poisoning tolerance and lower cost, Pt–Zn and Pt₃Zn NCs are a promising new family of catalysts for direct methanol fuel cells

Biaxial Stretchability and Transparency of Ag Nanowire 2D Mass-Spring Networks Prepared by Floating Compression

Networks of silver nanowires (Ag NWs) have been considered as promising materials for stretchable and transparent conductors. Despite various improvements of their optoelectronic and electromechanical properties over the past few years, Ag NW networks with a sufficient stretchability in multiple directions that is essential for the accommodation of the multidirectional strains of human movement have seldom been reported. For this paper, biaxially stretchable, transparent conductors were developed based on 2D mass-spring networks of wavy Ag NWs. Inspired by the traditional papermaking process, the 2D wavy networks were produced by floating Ag NW networks on the surface of water and subsequently applying biaxial compression to them. It was demonstrated that this floating-compression process can reduce the friction between the Ag NW–water interfaces, providing a uniform and isotropic in-plane waviness for the networks without buckling or cracking. The resulting Ag NW networks that were transferred onto elastomeric substrates successfully acted as conductors with an excellent transparency, conductivity, and electromechanical stability under a biaxial strain of 30%. The strain sensors that are based on the prepared conductors demonstrated a great potential for the enhanced performances of future wearable devices

Reversibly Stretchable, Optically Transparent Radio-Frequency Antennas Based on Wavy Ag Nanowire Networks

We report a facile approach for producing reversibly stretchable, optically transparent radio-frequency antennas based on wavy Ag nanowire (NW) networks. The wavy configuration of Ag NWs is obtained by floating the NW networks on the surface of water, followed by compression. Stretchable antennas are prepared by transferring the compressed NW networks onto elastomeric substrates. The resulting antennas show excellent performance under mechanical deformation due to the wavy configuration, which allows the release of stress applied to the NWs and an increase in the contact area between NWs. The antennas formed from the wavy NW networks exhibit a smaller return loss and a higher radiation efficiency when strained than the antennas formed from the straight NW networks, as well as an improved stability in cyclic deformation tests. Moreover, the wavy NW antennas require a relatively small quantity of NWs, which leads to low production costs and provides an optical transparency. These results demonstrate the potential of these wavy Ag NW antennas in applications of wireless communications for wearable systems

Chemically Designed Metallic/Insulating Hybrid Nanostructures with Silver Nanocrystals for Highly Sensitive Wearable Pressure Sensors

With the increase in interest in wearable tactile pressure sensors for e-skin, researches to make nanostructures to achieve high sensitivity have been actively conducted. However, limitations such as complex fabrication processes using expensive equipment still exist. Herein, simple lithography-free techniques to develop pyramid-like metal/insulator hybrid nanostructures utilizing nanocrystals (NCs) are demonstrated. Ligand-exchanged and unexchanged silver NC thin films are used as metallic and insulating components, respectively. The interfaces of each NC layer are chemically engineered to create discontinuous insulating layers, i.e., spacers for improved sensitivity, and eventually to realize fully solution-processed pressure sensors. Device performance analysis with structural, chemical, and electronic characterization and conductive atomic force microscopy study reveals that hybrid nanostructure based pressure sensor shows an enhanced sensitivity of higher than 500 kPa^–1, reliability, and low power consumption with a wide range of pressure sensing. Nano-/micro-hierarchical structures are also designed by combining hybrid nanostructures with conventional microstructures, exhibiting further enhanced sensing range and achieving a record sensitivity of 2.72 × 10⁴ kPa^–1. Finally, all-solution-processed pressure sensor arrays with high pixel density, capable of detecting delicate signals with high spatial selectivity much better than the human tactile threshold, are introduced