Room-temperature conversion of ethane and the mechanism understanding over single iron atoms confined in graphene

Abstract(#br)The catalytic conversion of ethane to high value-added chemicals is significantly important for utilization of hydrocarbon resources. However, it is a great challenge due to the typically required high temperature (> 400 °C) conditions. Herein, a highly active catalytic conversion process of ethane at room temperature (25 °C) is reported on single iron atoms confined in graphene via the porphyrin-like N 4 -coordination structures. Combining with the operando time of flight mass spectrometer and density functional theory calculations, the reaction is identified as a radical mechanism, in which the C–H bonds of the same C atom are preferentially and sequentially activated, generating the value-added C 2 chemicals, simultaneously avoiding the over-oxidation of the products to CO 2 . The in-situ formed O–FeN 4 –O structure at the single iron atom serves as the active center for the reaction and facilitates the formation of ethyl radicals. This work deepens the understanding of alkane C–H activation on the FeN 4 center and provides the reference in development of efficient catalyst for selective oxidation of light alkane

Highly active and stable single iron site confined in graphene nanosheets for oxygen reduction reaction

Exploring high performance non-precious metal catalysts to substitute Pt for oxygen reduction reaction (ORR) has stimulated wide research interest recently, but it remains a great challenge. Herein, we report a single iron site confined in graphene catalyst via 4N atoms, forming flat FeN4 structure in the matrix of graphene. The optimized catalyst shows a high ORR activity, almost coming up to the activity of commercial 40% Pt/C catalyst, but a significantly higher stability and tolerance to SOx, NOx and methanol with respect to 40% Pt/C. This well-defined structure provides an ideal model to study the catalytic origin of iron-based catalysts. DFT calculations indicate that the high ORR activity origins from highly dispersed and high-density coordinatively unsaturated Fe centers, and the excellent stability origins from the unique confinement of the graphene matrix via 4N atoms. This reaction can proceed easily to H2O via a four electron transfer path way on the single iron site, which is further confirmed by the experiment. This experimental and theoretical study provides a further insight into the nature of the Fe/N/C catalyst and also introduces a reference for designing high efficient catalysts in electrocatalysis

Temporal and spatial changes in hydrological wet extremes of the largest river basin on the Tibetan Plateau

Global warming accelerates the rate of inter-regional hydrological cycles, leading to a significant increase in the frequency and intensity of hydrological wet extremes. The Tibetan Plateau (TP) has been experiencing a rapid warming and wetting trend for decades. This trend is especially strong for the upper Brahmaputra basin (UBB) in the southern TP. The UBB is the largest river on the TP, and these changes are likely to impact the water security of local and downstream inhabitants. This study explores the spatial-temporal variability of wet extremes in the UBB from 1981–2019 using a water- and energy-budget distributed hydrological model (WEB-DHM) to simulate river discharge. The simulated results were validated against observed discharge from the Ministry of Water Resources at a mid-stream location and our observations downstream. The major findings are as follows: (1) the WEB-DHM model adequately describes land-atmosphere interactions (slight underestimation of −0.26 K in simulated annual mean land surface temperature) and can accurately reproduce daily and monthly discharge (Nash-Sutcliffe efficiency is 0.662 and 0.796 respectively for Nuxia station); (2) although extreme discharge generally occurs in July and is concentrated in the southeastern TP, extreme wet events in the UBB are becoming increasingly frequent (after 1998, the number of extreme days per year increased by 13% compared to before) and intense (maximum daily discharge increased with a significant trend of 444 (m ^3 s ^−1 ) yr ^−1 ), and are occurring across a wider region; (3) Precipitation is more likely to affect the intensity and spatial distribution of wet extremes, while the air temperature is more correlated with the frequency. Our wet extreme analysis in the UBB provides valuable insight into strategies to manage regional water resources and prevent hydrological disasters

Multiscale structural and electronic control of molybdenum disulfide foam for highly efficient hydrogen production

AbstractHydrogen production through water splitting has been considered as a green, pure and high-efficient technique. As an important half-reaction involved, hydrogen evolution reaction is a complex electrochemical process involving liquid-solid-gas three-phase interface behaviour. Therefore, new concepts and strategies of material design are needed to smooth each pivotal step. Here we report a multiscale structural and electronic control of molybdenum disulfide foam to synergistically promote the hydrogen evolution process. The optimized three-dimensional molybdenum disulfide foam with uniform mesopores, vertically aligned two-dimensional layers and cobalt atoms doping demonstrated a high hydrogen evolution activity and stability. In addition, density functional theory calculations indicate that molybdenum disulfide with moderate cobalt doping content possesses the optimal activity. This study demonstrates the validity of multiscale control in molybdenum disulfide via overall consideration of the mass transport, and the accessibility, quantity and capability of active sites towards electrocatalytic hydrogen evolution, which may also be extended to other energy-related processes.</jats:p

Reaction Mechanisms of Well-Defined Metal-N-4 Sites in Electrocatalytic CO2 Reduction

Electrocatalytic CO2 reduction to CO emerges as a potential route of utilizing emitted CO2. Metal-N-C hybrid structures have shown unique activities, however, the active centers and reaction mechanisms remain unclear because of the ambiguity in true atomic structures for the prepared catalysts. Herein, combining density-functional theory calculations and experimental studies, the reaction mechanisms for well-defined metal-N-4 sites were explored using metal phthalocyanines as model catalysts. The theoretical calculations reveal that cobalt phthalocyanine exhibits the optimum activity for CO2 reduction to CO because of the moderate *CO binding energy at the Co site, which accommodates the *COOH formation and the *CO desorption. It is further confirmed by experimental studies, where cobalt phthalocyanine delivers the best performance, with a maximal CO Faradaic efficiency reaching 99%, and maintains stable performance for over 60 hours

Abnormal fertility, acrosome formation, IFT20 expression and localization in conditional Gmap210 knockout mice

GMAP210 (TRIP11) is a cis-Golgi network-associated protein and a Golgi membrane receptor for IFT20, an intraflagellar transport component essential for male fertility and spermiogenesis in mice. To investigate the role of GMAP210 in male fertility and spermatogenesis, floxed Gmap210 mice were bred with Stra8-iCre mice so that the Gmap210 gene is disrupted in spermatocytes and spermatids in this study. The Gmap210(flox/flox): Stra8-iCre mutant mice showed no gross abnormalities and survived to adulthood. In adult males, testis and body weights showed no difference between controls and mutant mice. Low-magnification histological examination of the testes revealed normal seminiferous tubule structure, but sperm counts and fertility were significantly reduced in mutant mice compared with controls. Higher resolution examination of the mutant seminiferous epithelium showed that nearly all sperm had more oblong, abnormally shaped heads, while the sperm tails appeared to have normal morphology. Electron microscopy also revealed abnormally shaped sperm heads but normal axoneme core structure; some sperm showed membrane defects in the midpiece. In mutant mice, expression levels of IFT20 and other selective acrosomal proteins were significantly reduced, and their localization was also affected. Peanut-lectin, an acrosome maker, was almost absent in the spermatids and epididymal sperm. Mitochondrion staining was highly concentrated in the heads of sperm, suggesting that the midpieces were coiling around or aggregating near the heads. Defects in acrosome biogenesis were further confirmed by electron microscopy. Collectively, our findings suggest that GMAP210 is essential for acrosome biogenesis, normal mitochondrial sheath formation, and male fertility, and it determines expression levels and acrosomal localization of IFT20 and other acrosomal proteins

Room-temperature electrochemical water-gas shift reaction for high purity hydrogen production

Traditional water-gas shift reaction provides one primary route for industrial production of clean-energy hydrogen. However, this process operates at high temperatures and pressures, and requires additional separation of H-2 from products containing CO2, CH4 and residual CO. Herein, we report a room-temperature electrochemical water-gas shift process for direct production of high purity hydrogen (over 99.99%) with a faradaic efficiency of approximately 100%. Through rational design of anode structure to facilitate CO diffusion and PtCu catalyst to optimize CO adsorption, the anodic onset potential is lowered to almost 0 volts versus the reversible hydrogen electrode at room temperature and atmospheric pressure. The optimized PtCu catalyst achieves a current density of 70.0 mA cm(-2) at 0.6 volts which is over 12 times that of commercial Pt/C (40 wt.%) catalyst, and remains stable for even more than 475 h. This study opens a new and promising route of producing high purity hydrogen

Probing subwavelength in-plane anisotropy with antenna-assisted infrared nano-spectroscopy.

Infrared nano-spectroscopy based on scattering-type scanning near-field optical microscopy (s-SNOM) is commonly employed to probe the vibrational fingerprints of materials at the nanometer length scale. However, due to the elongated and axisymmetric tip shank, s-SNOM is less sensitive to the in-plane sample anisotropy in general. In this article, we report an easy-to-implement method to probe the in-plane dielectric responses of materials with the assistance of a metallic disk micro-antenna. As a proof-of-concept demonstration, we investigate here the in-plane phonon responses of two prototypical samples, i.e. in (100) sapphire and x-cut lithium niobate (LiNbO3). In particular, the sapphire in-plane vibrations between 350 cm-1 to 800 cm-1 that correspond to LO phonon modes along the&nbsp;crystal b- and c-axis are determined with a spatial resolution of &lt; λ/10, without needing any fitting parameters. In LiNbO3, we identify the in-plane orientation of its optical axis via the phonon modes, demonstrating that our method can be applied without prior knowledge of the crystal orientation. Our method can be elegantly adapted to retrieve the in-plane anisotropic response of a broad range of materials, i.e. subwavelength microcrystals, van-der-Waals materials, or topological insulators