Reduced graphene oxide/SnO2@Au heterostructure for enhanced ammonia gas sensing

Is Soft Carbon a More Suitable Match for SiOx in Li-Ion Battery Anodes?

Silicon oxide (SiOx ), inheriting the high-capacity characteristic of silicon-based materials but possessing superior cycling stability, is a promising anode material for next-generation Li-ion batteries. SiOx is typically applied in combination with graphite (Gr), but the limited cycling durability of the SiOx /Gr composites curtails large-scale applications. In this work, this limited durability is demonstrated in part related to the presence of a bidirectional diffusion at the SiOx /Gr interface, which is driven by their intrinsic working potential differences and the concentration gradients. When Li on the Li-rich surface of SiOx is captured by Gr, the SiOx surface shrinks, hindering further lithiation. The use of soft carbon (SC) instead of Gr can prevent such instability is further demonstrated. The higher working potential of SC avoids bidirectional diffusion and surface compression thus allowing further lithiation. In this scenario, the evolution of the Li concentration gradient in SiOx conforms to its spontaneous lithiation process, benefiting the electrochemical performance. These results highlight the focus on the working potential of carbon as a strategy for rational optimization of SiOx /C composites toward improved battery performance.

Flexible Electronic Systems via Electrohydrodynamic Jet Printing: A MnSe@rGO Cathode for Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (ZIBs) are promising candidates to power flexible integrated functional systems because they are safe and environmentally friendly. Among the numerous cathode materials proposed, Mn-based compounds, particularly MnO₂, have attracted special attention because of their high energy density, nontoxicity, and low cost. However, the cathode materials reported so far are characterized by sluggish Zn²⁺ storage kinetics and moderate stabilities. Herein, a ZIB cathode based on reduced graphene oxide (rGO)-coated MnSe nanoparticles (MnSe@rGO) is proposed. After MnSe was activated to α-MnO₂, the ZIB exhibits a specific capacity of up to 290 mAh g^-1. The mechanism underlying the improvement in the electrochemical performance of the MnSe@rGO based electrode is investigated using a series of electrochemical tests and first-principles calculations. Additionally, in situ Raman spectroscopy is used to track the phase transition of the MnSe@rGO cathodes during the initial activation, proving the structural evolution from the LO to MO₆ mode. Because of the high mechanical stability of MnSe@rGO, flexible miniaturized energy storage devices can be successfully printed using a high-precision electrohydrodynamic (EHD) jet printer and integrated with a touch-controlled light-emitting diode array system, demonstrating the application of flexible EHD jet-printed microbatteries.

Focusing on the Subsequent Coulombic Efficiencies of SiOx: Initial High-Temperature Charge after Over-Capacity Prelithiation for High-Efficiency SiOx-Based Full-Cell Battery

SiO_x-based anode materials are considered to be promising and have been gradually commercialized due to their high specific capacity as well as the acceptable volume change during lithiation/delithiation and preferable cycling stability compared to that of Si. Nevertheless, their inherently low Coulombic efficiency hinders the large-scale application. Up to now, researchers have paid much attention to the initial Coulombic efficiency and developed a series of effective prelithiation strategies. However, the subsequent cycles (focusing on the 2nd to 10th), during which the SiO_x anode suffers great lithium consumption as well, have received scarcely any concerns. In this work, a strategy of high-temperature (50 °C) initial charge after an overcapacity prelithiation for a SiO_x-based full-cell battery is proposed. As high temperature can promote the reaction between lithium and the SiO₂ matrix of SiO_x, SiO₂ will experience a one-step thorough reduction rather than gradual conversion in subsequent cycles, improving the subsequent Coulombic efficiencies (SCEs) accordingly. Overcapacity prelithiation can be achieved safely at 50 °C without Li metal depositon, just enough to meet the more initial lithium demand of anode at 50 °C. Furthermore, the initial deeper reduction of SiO₂ will release extra Si, improving the reversible capacity consequently. With the 50 °C initial charge after an overcapacity prelithiation, the full-cell battery exhibits considerable capacity retention as expected. This work raises concerns on SCEs of SiO_x-based anode innovatively, providing a feasible avenue for improving the capacity retention of a SiO_x-based full-cell battery.

Gas sensing materials roadmap

Gas sensor technology is widely utilized in various areas ranging from home security, environment and air pollution, to industrial production. It also hold great promise in non-invasive exhaled breath detection and an essential device in future internet of things. The past decade has witnessed giant advance in both fundamental research and industrial development of gas sensors, yet current efforts are being explored to achieve better selectivity, higher sensitivity and lower power consumption. The sensing layer in gas sensors have attracted dominant attention in the past research. In addition to the conventional metal oxide semiconductors, emerging nanocomposites and graphene-like two-dimensional materials also have drawn considerable research interest. This inspires us to organize this comprehensive 2020 gas sensing materials roadmap to discuss the current status, state-of-the-art progress, and present and future challenges in various materials that is potentially useful for gas sensors.

Quantitative analysis of the synergistic effect of Au nanoparticles on SnO2-rGO nanocomposites for room temperature hydrogen sensing

Hydrogen detection devices based on gold-tin oxide/reduced graphene oxide (Au-SnO2/rGO) nanohybrids were fabricated by combining a hydrothermal method with sputter coating. The gas sensing performance of the Au-SnO2/rGO sensor was investigated under different concentrations of hydrogen from 0.04% to 1% at room temperature, which indicated a notable sensitive response even for 0.04% hydrogen. The activation energies of hydrogen adsorption/desorption were extracted via Arrhenius analysis which revealed the acceleration effect of gold dopants. This acceleration led to a faster response and recovery during hydrogen sensing. The activation energy analysis provided a more comprehensive understanding on the gas sensing mechanism. A hydrogen detection handheld device is demonstrated by integrating the sensor chip with a portable digital meter for direct readout of test results.

Organic Heterojunction Devices Based on Phthalocyanines: A New Approach to Gas Chemosensing

Organic heterostructures have emerged as highly promising transducers to realize high performance gas sensors. The key reason for such a huge interest in these devices is the associated organic heterojunction effect in which opposite free charges are accumulated at the interface making it highly conducting, which can be exploited in producing highly sensitive and faster response kinetics gas sensors. Metal phthalocyanines (MPc) have been extensively studied to fabricate organic heterostructures because of the large possibilities of structural engineering which are correlated with their bulk thin film properties. Accordingly, in this review, we have performed a comprehensive literature survey of the recent researches reported about MPc based organic heterostructures and their application in gas sensors. These heterostructures were used in Organic Field-Effect Transistor and Molecular Semiconductor-Doped Insulator sensing device configurations, in which change in their electrical properties such as field-effect mobility and saturation current in the former and current at a fixed bias in the latter under redox gases exposure were assessed to determine the chemosensing performances. These sensing devices have shown very high sensitivity to redox gases like nitrogen dioxide (NO2), ozone and ammonia (NH3), which monitoring is indispensable for implementing environmental guidelines. Some of these sensors exhibited ultrahigh sensitivity to NH3 demonstrated by a detection limit of 140 ppb and excellent signal stability under variable humidity, making them among the best NH3 sensors.

Comparison of Gas Sensing Properties of Reduced Graphene Oxide Obtained by Two Different Methods

In this study, the sensitivity of reduced graphene oxide structures (rGO) to the action of selected gases (especially hydrogen, but also nitrogen dioxide and ammonia) was examined. Two sensing structures, based on rGO structures, obtained by different methods of oxidation (the modified Hummers, and the modified Tour’s method respectively), were investigated. We show here that the method used for the oxidation of rGO influences the sensitivity of the sensing structure during contact with various gaseous atmospheres. We performed our experiments in the atmosphere, containing hydrogen in a concentration range from 0 to 4% in nitrogen or synthetic air, both in dry and wet conditions. The temperature range was from 50 °C to 190 °C. Finally, we checked how the resistance of the samples changes when the other gases (NO₂, NH₃) appear in tested gas mixtures. The gas investigations were supplemented by the characterization of rGOs materials using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and N₂ sorption method.