Cu clusters supported on CeO2 nanorods (NRs) were found to exhibit significantly enhanced activity and thermal/hydrothermal durability for low-temperature CO oxidation when the catalyst was calcined at 800 °C in air prior to the catalytic measurements. The effect of calcination temperature and Cu loading on Cu-CeO2 catalysts was studied by the combination of powder X-ray diffraction (PXRD), Raman spectroscopy, H2-temperature program reduction (H2-TPR), ambient-pressure X-ray photoelectron spectroscopy (APXPS), synchrotron radiation photoelectron spectroscopy (SRPES), and X-ray absorption spectroscopy (XAS). Cu atoms were found to incorporate into the ceria lattice in air at below 500 °C, leading to the formation of a bulk Cu y Ce1–y O2–x solid solution. As the calcination temperature was raised to 800 °C, the solubility of Cu ions in bulk ceria was reduced sharply. Surface segregation of Cu atoms led to the formation of CuO x and a surface Cu-doped ceria thin layer, resulting in a much enhanced activity for CO oxidation. Moreover, the activities of calcined Cu-CeO2 catalysts did not increase with the Cu loading but exhibited an optimal activity at ∼2 wt % of Cu loading, where segregated CuO x species gave an average size in the sub-nanometer (sub-nm) range. Larger CuO x nanoparticles (NPs) on the Cu-doped ceria thin layer exhibited a lower activity toward CO oxidation. We believe the enhanced catalytic properties of the thermally aged Cu-CeO2 catalysts are attributed to the formation of an interface between sub-nm CuO x and the Cu-doped ceria thin layer. Our study thus sheds light on the nature of most active sites on Cu/CeO2 catalysts and facilitates the rational design of ceria-supported metal catalysts for oxidation reactions.

Liquid materials with the ability to transit between conductor and insulator are of great scientific and practical significance.

Nowadays, with the development of wearable devices, stretchable pressure sensors have been widely adopted in all kinds of areas. Most of the sensors aim to detect small pressure, such as fingertip tactile sensing, but only a few are focused on high-pressure sensing, such as foot pressure sensing during men’s walking. In this work, a liquid metal-based stretchable sensor for large-pressure measurement is investigated. This sensor is fully stretchable because it is made of soft materials. However, when the soft sensor is subjected to high pressure, the liquid metal easily leaks from microchannels because it maintains the liquid state at room temperature. We therefore propose to fabricate liquid metal-based leakage-free electrodes to handle the liquid-metal leak. Parametric studies are conducted to compare this sensor with liquid-metal-only electrodes and leakage-free electrodes. The leakage-free electrodes increase the measurement ranges from 0.18, 0.18, and 0.15 MPa to 0.44 MPa, with higher linearity and precision. The improvement in the liquid-metal electrode enables the sensors to work stably within 0.44 MPa pressure and 20% strain. In addition, we integrate two capacitors, namely, a working capacitor and a reference capacitor, into one sensor to reduce the influence of parasitic capacitance brought about by external interference. This stretchable capacitive sensor capable of working under a wide range of pressure with good repeatability, sensitivity, and linearity, exhibits great potential use for wearable electronics. Finally, the method for fabricating leakage-free electrodes shows great value for hyperelastic electronics manufacturing and micromachine technology.