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The high-pressure structures of alkaline earth metal hydride-fluorides (AHFs) (A = Ca, Sr, Ba) were investigated up to 8 GPa. While AHF adopts the fluorite-type structure (Fm3¯m) at ambient pressure without anion ordering, the PbCl2-type (cotunnite-type) structure (Pnma) is formed by pressurization, with a declining trend of critical pressure as the ionic radius of the A2+ cation increases. In contrast to PbCl2-type LaHO and LaOF whose anions are fully ordered, the H−/F− anions in the high-pressure polymorph of SrHF and BaHF are partially ordered, with a preferential occupation of H− at the square-pyramidal site (vs. tetrahedral site). First-principles calculations partially support the preferential anion occupation and suggest occupation switching at higher pressure. These results provide a strategy for controlling the anion ordering and local structure in mixed-anion compounds. [ABSTRACT FROM AUTHOR]

Early transition metal-based intermetallic compounds, such as ZrV 2 , ZrMn 2 , and ZrCr 2 , can reversibly absorb large amounts of hydrogen and are of great interest for hydrogen storage. The dissociative hydrogen chemisorption can proceed easily on the surface, allowing the rapid formation of intermetallic hydrides. In this study, we present the results of initial NH 3 activity tests conducted on various Zr-based AB 2 -type intermetallic compounds, free of precious transition metals and rare earth metals. A dissociative hydrogen chemisorption together with nitrogen storage proceeds on AB 2 -type Laves phase intermetallic compounds accompanied by a lattice expansion. The formed intermetallic nitride hydride ZrCr 2 N 0.4 H 1.4 exhibits stable catalytic activity as an ammonia synthesis catalyst. In this study, we found a dissociative hydrogen chemisorption together with nitrogen storage proceed on AB 2 -type Laves phase intermetallic compounds, allowing the rapid formation of intermetallic nitride hydrides. The cell volume expansion upon hydrogenation facilitates nitrogen adsorption and dissociation. The formed intermetallic nitride hydride ZrCr 2 N 0.4 H 1.4 exhibits stable catalytic activity as an ammonia synthesis catalyst. [Display omitted] • A hydrogen adsorption together with nitrogen storage in Laves phase intermetallic compounds. • The lattice expansion accompanied by H intercalation could help the insertion of N. • The formed intermetallic nitride hydride exhibits stable catalytic activity for ammonia synthesis. [ABSTRACT FROM AUTHOR]

Optimally increasing the catalytic activity of Co3O4‐based materials is crucial for promoting their practical applications for acetone detection; however, this still remains challenging. Herein, a strategy is proposed in this work to increase the catalytic activity of Co3O4 toward the oxidation of acetone through the synergistic effect of boron doping and chemical reduction, which can substantially improve the sensing performance for acetone detection. The characterization results confirm that the present strategy facilitates the formation of more oxygen vacancies and increases the content of Co2+ ions serving as active sites. As expected, the optimal sensor yields a higher response. To extend the practical application to the auxiliary diagnosis of diabetes through exhaled breath, the optimal sensors distinguished between acetone concentrations in the breath of healthy individuals and in the simulated breath of patients with diabetes. Detailed gas‐sensing measurements reveal that the enhanced acetone sensing performance is attributed to the increased catalytic activity of materials for oxidation of acetone by the Mars–van Krevelen, Langmuir–Hinshelwood, and Eley–Rideal mechanisms. This study provides new insights into the fabrication of high‐performance metal oxide‐based gas sensors by improving the catalytic activity of sensing materials. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide (rGO)-based materials are deemed as promising candidates for fabrication of room-temperature gas sensors, while a tougher challenge is to develop an effective strategy for improving gas responses. Here, a noble metal decoration strategy is developed to enhance NO2 responses of α-Fe2O3/SnO2–rGO hybrids. Noble metal decorated α-Fe2O3/SnO2–rGO hybrids were prepared by depositing noble metals onto α-Fe2O3/SnO2–rGO hybrids through reduction of noble metal ions by NaBH4. Most importantly, Pt modified α-Fe2O3/SnO2–rGO hybrids (designated as Pt-FSR) exhibit the highest response value of 21.3 toward 5 ppm NO2, which is much higher than that of α-Fe2O3/SnO2–rGO (8.8). Combined characterization studies indicate that the enhanced NO2 response of Pt-FSR is attributed to the narrow band gap of Pt-FSR, small particle size and excellent catalytic activity of Pt. The NO2 sensing mechanism is also investigated by FT-IR spectroscopy. The findings proposed in this work not only broaden the study of room-temperature gas sensors, but also provide suggestions for discovering the gas sensing mechanism. [ABSTRACT FROM AUTHOR]

In this study, we investigate the phase behavior in Ln HO (Ln = Nd, Gd, and Er) at external pressures up to 5 GPa. In contrast to LaHO, we observed a direct phase transformation from the fluorite-type structure to the anti-Fe 2 P-type structure in all the compounds examined. In the high-pressure anti-Fe 2 P-type structure above 3 GPa, the H− and O2− anions are coordinated four-fold and five-fold, respectively, as observed in LaHO. The absence of the PbCl 2 -type structure by chemical pressure (i.e., smaller Ln 3+ substitution) is supported by DFT calculations. We further found a tendency for the fluorite-type structure to stabilize toward the higher-pressure side as the Ln ion becomes smaller; in ErHO and GdHO, the fluorite-type structure survives at the secondary phase even at 5 GPa. This suggests that chemical pressure plays a different role in the structural stabilization than physical pressure. The unexpected observation is interpreted in terms of entropy stabilization since, unlike LaHO and NdHO, the fluorite-type ErHO and GdHO compounds are anion disordered. We have performed high-pressure synthesis of Ln HO (Ln = Nd, Gd, and Er), and observed that the fluorite-structure directly transforms to the anti-Fe 2 P-type structure, without forming the PbCl 2 -type structure as in LaHO. The unexpected expansion of the fluorite phase toward high pressure for smaller Ln 3+ is derived from entropy stabilization. [Display omitted] • A phase diagram for the synthesis pressure of Ln HO is obtained. • NdHO, GdHO, and ErHO transform directly from the fluorite structure to anti-Fe 2 P structure under pressure. • The fluorite phase space is extended to higher pressures due to entropy stabilization. • Anion order/disorder gives a crucial influence on the phase transformation. [ABSTRACT FROM AUTHOR]

Toluene is widely used as a solvent and reactant in a wide range of industrial fields; however, gaseous toluene is toxic to humans, causing severe acute respiratory effects. In this case, Co3O4-based chemiresistive gas sensors are promising candidates for monitoring toluene. However, it is challenging to prepare Co3O4-based sensing materials with good toluene sensing performances on a large-scale. In this study, oxygen vacancy-rich Co3O4 materials were successfully synthesized via the reduction of commercial Co3O4 using NaBH4 as the reducing agent (designated as Co3O4-R), and the oxygen vacancy concentrations in Co3O4-R materials were effectively modulated by regulating the NaBH4 concentration. With an increase in oxygen vacancies, the optimal Co3O4-R-5 samples displayed better sensing performances toward 100 ppm toluene at 190 °C than that of the pristine commercial Co3O4, including an enhanced response value of 3.18 (vs. 1.22 for commercial Co3O4) and fast response time of 48 s and recovery time of 38 s. The combination of band structure analysis and chemisorption analysis indicated that the enhanced toluene sensing performances of Co3O4-R is attributed to the synergistic effect of reducing the band gap and activating the surface oxygen species. This work demonstrates the first utilization of commercial Co3O4 for toluene sensing applications, providing a universal and high-throughput preparation method to prepare gas sensing materials using commercial metal oxides. [ABSTRACT FROM AUTHOR]

Development of room-temperature gas sensors with excellent sensing performances for detection of dimethyl methylphosphonate (DMMP, a simulant of organophosphate) has aroused considerable attention. However, the weak adsorption ability of sensing materials toward DMMP molecules causes poor sensing performances. In this work, a multisite strategy for enhancing sensitivity was proposed by introduction of both N-doped carbon nanoparticles (N-CNPs) and copper ions onto the surface of rGO (designated as GNC). Impressively, optimal GNC-3 exhibits the response value of 10.2% toward 100 ppm DMMP, which is 5.3 times higher than that of pristine rGO. This mechanism for multisite-assisted enhanced DMMP sensing performances was investigated by combined characterizations of Fourier-transform infrared spectra, UV-Vis spectra, photoluminescence spectra and Mott-Schottky curves. Besides the construction of multisite, improvement of hydrogen bonding interactions between DMMP molecules and N-CNPs in hybrids assisted by copper ions, and decrease of conduction band potential by formation of ternary hybrids also contribute to enhance the sensitivity of DMMP sensors. These findings not only provided new insights into designing high-performance room-temperature gas sensors, but also promoted the fundamental research on sensing mechanism for room-temperature gas sensors. • A multisite strategy for enhancing sensitivity was proposed by constructing three kinds of DMMP adsorption active sites. • GNC hybrids demonstrate 5.3-fold improvement in response to 100 ppm DMMP compared to pristine rGO hybrids. • This mechanism for multisite-assisted enhanced DMMP sensing performances was confirmed by the spectroscopy. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Pd-SR-V O is fabricated by Pd nanoparticles and oxygen vacancy to modulate SnO 2 modified RGO. • Impressively, the response value of Pd-SR-V O for 1 ppm NO 2 at room temperature reaches to 9.8. • Notably, the response even could reach to 3.0 in 100 ppb NO 2 at room temperature. • The improvement of sensitivity is attributed to the synergy of Pd NPs and oxygen vacancies. Reduced graphene oxides (RGO)-based materials exhibit high carrier mobility and selective recognition ability to NO 2 , making them constitute promising platform for room-temperature NO 2 detection. However, the low sensitivity becomes the main bottleneck for their further development. Here, we demonstrate that synergy of Pd nanoparticles (NPs) and oxygen vacancies can modulate the surface active sites over SnO 2 NPs modified RGO hybrids (labeled as SR), leading to improving the sensitivity of room-temperature NO 2 sensors. Experimentally, a wet-chemical method was used to introduce oxygen vacancies onto SR, leading to forming SR with rich oxygen vacancies (labeled as SR-Vo), which were subsequently deposited with Pd NPs, resulting in preparing Pd NPs loaded SR-Vo hybrids (labeled as Pd-SR-Vo). Impressively, the response value to 1 ppm NO 2 of Pd-SR-Vo hybrids reaches to 9.8, which is much higher than that of R-Vo hybrids (5.6) and SR hybrids (3.3). The improvement of sensitivity toward NO 2 for Pd-SR-Vo hybrids is attributed to the synergy effect of Pd NPs and oxygen vacancies, including shortening the band gap of Pd-SR-Vo hybrids with raising conduction band level, widening the width of electron depletion layer between SnO 2 -Vo and RGO, introducing Schottky contact between Pd and SnO 2 -Vo, improving efficiency for gas sensing reaction. This work not only provides an efficient approach to fabricate high-performance NO 2 sensors, but also opens a new avenue for sensing materials design and modification. [ABSTRACT FROM AUTHOR]

The hydrogen bonding interactions are potentially employed to fabricate high-performance room-temperature gas sensors for detection of organophosphorus. Nevertheless, the low response toward target gases of conventional sensing materials hinders their further applications. Herein, an isolated Cu-N 5 sites engineering strategy is reported to improve sensing performances for polypyrrole-reduced graphene oxide hybrids (PPy-rGO)-based room-temperature dimethyl methyl phosphate (DMMP) sensors. The isolated Cu-N 5 sites were simply constructed by adsorption of Cu2+ ions with PPy-rGO hybrids owing to strong metal-support interactions. X-ray absorption fine structure analysis indicates that Cux+ ions with mean chemical valence of + 1.07 nearly atomically distributed on support with coordination structure of Cu-N 5. Benefiting from the structure regulation by Cux+ ions, as-constructed DMMP sensor demonstrated 4.5-fold improvement in response to 100 ppm DMMP and 2.5-fold improvement in limit of detection, compared to PPy-rGO hybrids. The density functional theory, spectroscopic characterizations and quartz crystal microbalance tests prove that the construction of Cu-N 5 sites not only heightens hydrogen bonding interactions between N H bonds and DMMP molecules induced by newly formed coordination interactions between Cux+ ions and N H bonds, but also serves as new active sites for adsorption of DMMP molecules. This work offers a new avenue for developing high-performance room-temperature gas sensors by heightening hydrogen bonding interactions. • Isolated Cu-N 5 sites-assisted heightening hydrogen bonds strategy is proposed to construct room-temperature DMMP sensors. • Cux+-PPy-rGO hybrids demonstrate 4.5-fold improvement in response to 100 ppm DMMP compared to PPy-rGO hybrids. • The limit of detection of the Cux+-PPy-rGO based sensor is 2 ppm. [ABSTRACT FROM AUTHOR]

A gathering pipeline in a gas field in Northeast China transporting mainly natural gas and also some water and sands was welded using two 20G pipes with different wall thicknesses. The internal corrosion of this pipeline was inhomogeneous. The unequal wall thickness welded joint suffered more serious corrosion damage than did other parts of the pipe and was found to fail during routine maintenance. In this paper, the corrosion damage at this joint was studied based on inhomogeneity. Internal and external factors affecting corrosion, such as the mechanical and electrochemical properties of materials, stress distribution at the joint, and the flow condition in the pipe, and their combined action were investigated. Failure attribution was performed on this basis. Specifically, a hardness test was conducted on different zones of the joint, including the base metal (BM), heat-affected zone (HAZ) and weld metal (WM), to investigate the abrasive wear resistance at the joint. Microstructures of the three zones were characterized by optical microscopy. The morphology and composition of the corrosion film covering the inner surface of the welded joint were characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and X-ray powder diffraction (XRD). Potentiodynamic polarization experiments and electrochemical impedance spectroscopy (EIS) were conducted on samples from the three zones to investigate their electrochemical performances. Moreover, a computational fluid dynamics (CFD) analysis was performed to obtain the flow condition near the joint, and a finite element method (FEM) was used to calculate the stress distribution at the joint. The results showed that the internal corrosion mechanism of the pipeline was CO 2 corrosion accelerated by detrimental Cl − . The geometric discontinuity of the welded joint was the main cause of the accelerated corrosion damage at the joint. The change in wall thickness of the welded pipe not only produced gas vortices but also led to stress concentration. Both of these conditions can further accelerate corrosion by destroying the protectiveness of the corrosion film. It is suggested that the corrosion can be prevented by eliminating the inhomogeneities of fluid flow and stress distribution. [ABSTRACT FROM AUTHOR]