Influence of the Pd Oxidation State in PdNi Thin Films on Surface Acoustic Wave Hydrogen Sensing Performance.

PdNi alloy thin films demonstrate exceptional hydrogen sensing performance and exhibit significant potential for application in surface acoustic wave (SAW) hydrogen sensors. However, the long-term stability of SAW H2 sensors utilizing PdNi films as catalysts experiences a substantial decrease during operation. In this paper, X-ray photoelectron spectroscopy (XPS) is employed to investigate the failure mechanisms of PdNi thin films under operational conditions. The XPS analysis reveals that the formation of PdO species on PdNi thin films plays a crucial role in the failure of hydrogen sensing. Additionally, density functional theory (DFT) calculations indicate that hydrogen atoms encounter a diffusion energy barrier during the penetration process from the PdNiOx surface to the subsurface region. The identification of PdNi film failure mechanisms through XPS and DFT offers valuable insights into the development of gas sensors with enhanced long-term stability. Guided by these mechanisms, we propose a method to restore the hydrogen sensing response time and magnitude to a certain extent by reducing the partially oxidized surface of the PdNi alloy under a hydrogen atmosphere at 70 °C, thereby restoring Pd to its metallic state with zero valence.

Recent Progress in Flexible Surface Acoustic Wave Sensing Technologies.

In this work, the major methods for implementing flexible sensing technology-flexible surface acoustic wave (SAW) sensors-are summarized; the working principles and device characteristics of the flexible SAW sensors are introduced; and the latest achievements of the flexible SAW sensors in the selection of the substrate materials, the development of the piezoelectric thin films, and the structural design of the interdigital transducers are discussed. This paper focuses on analyzing the research status of physical flexible SAW sensors such as temperature, humidity, and ultraviolet radiation, including the sensing mechanism, bending strain performance, device performance parameters, advantages and disadvantages, etc. It also looks forward to the development of future chemical flexible SAW sensors for gases, the optimization of the direction of the overall device design, and systematic research on acoustic sensing theory under strain. This will enable the manufacturing of multifunctional and diverse sensors that better meet human needs.

Recent Advance in Co3O4 and Co3O4-Containing Electrode Materials for High-Performance Supercapacitors.

Among the popular electrochemical energy storage devices, supercapacitors (SCs) have attracted much attention due to their long cycle life, fast charge and discharge, safety, and reliability. Transition metal oxides are one of the most widely used electrode materials in SCs because of the high specific capacitance. Among various transition metal oxides, Co3O4 and related composites are widely reported in SCs electrodes. In this review, we introduce the synthetic methods of Co3O4, including the hydrothermal/solvothermal method, sol-gel method, thermal decomposition, chemical precipitation, electrodeposition, chemical bath deposition, and the template method. The recent progress of Co3O4-containing electrode materials is summarized in detail, involving Co3O4/carbon, Co3O4/conducting polymer, and Co3O4/metal compound composites. Finally, the current challenges and outlook of Co3O4 and Co3O4-containing composites are put forward.