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Platinum reaches considerable activity and stability as an electrocatalyst but is not always capable of maintaining such performance under CO poisoning, particularly in CO residual fuels for practical proton-exchange membrane fuel cells (PEMFCs). In this work, we report that surface anions including a series of nonmetal elements on Pt nanoparticles result in outstanding CO tolerance for electrocatalysts in fuel cells. In particular, phosphorus surface-anion-modified Pt (denoted as P-Pt) possesses more than 10-fold enhancement of CO tolerance (only 8.4% decay) than commercial Pt/C, which can serve as a robust electrocatalyst both in CO poisoning half cells and full cells. Moreover, the general mechanism and principle were proposed, stating that surface anions should be selected preferentially to offer electron feedback to downshift the d-band center for the Pt surface, successfully weakening CO adsorption and leading to high-tolerance capability. We anticipate that surface anions on a Pt surface can bring robust electrocatalysts for practical PEMFCs and offer novel insights for high-performance Pt-based electrocatalysts.

Double-walled metal pipes are important components for heat exchange and liquid transportation. They can be manufactured by mechanical drawing of two concentric pipes. In this work, a mechanical model is developed to analyze the stress state evolution during the manufacturing process, and the criterion for forming the double-walled pipe was given under the ideal elastoplastic and thick-walled assumptions. The model also encompasses the results deduced under the thin-walled assumption. Numerical simulations confirmed that the accuracy of the analytical model was within 5%. The application on actual steel materials with various parameters varied, including the wall thickness and initial gap, was analyzed. This work can provide theoretical support to industrial manufacturing procedures and help to reduce costs by eliminating required test procedures.

Although short bamboo nodes function in mechanical support and fluid exchange for bamboo survival, their structures are not fully understood compared to unidirectional fibrous internodes. Here, we identify the spatial heterostructure of the bamboo node via multiscale imaging strategies and investigate its mechanical properties by multimodal mechanical tests. We find three kinds of hierarchical fiber reinforcement schemes that originate from the bamboo node, including spatially tightened interlocking, triaxial interconnected scaffolding and isotropic intertwining. These reinforcement schemes, built on porous vascular bundles, microfibers and more-refined twist-aligned nanofibers, govern the structural stability of the bamboo via hierarchical toughening. In addition, the spatial liquid transport associated with these multiscale fibers within the bamboo node is experimentally verified, which gives perceptible evidence for life-indispensable multidirectional fluid exchange. The functional integration of mechanical reinforcement and liquid transport reflects the fact that the bamboo node has opted for elaborate structural optimization rather than ingredient richness. This study will advance our understanding of biological materials and provide insight into the design of fiber-reinforced structures and biomass utilization.

Gas transport through nanochannels is ubiquitous in nature and also plays an important role in industry. The gas flow in this regime can be described by the Knudsen theory, which assumes that molecules diffusely reflect on the confining walls. However, with the emergence of low dimensional carbon-based materials such as graphene and carbon nanotubes, it has been evidenced that this assumption might not hold for some atomically smooth surfaces, resulting in an anomalous enhancement of gas flux. In this study, we meticulously investigated the gas transport through nanochannels constructed by two selected kinds of 2D materials, graphene and molybdenum disulfide (MoS2), and interpreted the remarkable difference in gas flux through these two nanochannels. We revealed the underlying mechanism as the surface morphological effect on the gas collision with solid walls. Even a subtle distinction of surface roughness results in specular scattering on graphene surfaces while diffuse scattering on MoS2 surfaces. We also found that the curvature effect could reduce the surface roughness of interaction potential surfaces, leading to an additional enhancement on the gas flow rate. These insights are expected to deepen the understanding of gas transport in nanochannels, paving a promising way in the gas permeation control.

Desalination can help to alleviate the fresh-water crisis facing the world. Thermally driven membrane distillation is a promising way to purify water from a variety of saline and polluted sources by utilizing low-grade heat. However, membrane distillation membranes suffer from limited permeance and wetting owing to the lack of precise structural control. Here, we report a strategy to fabricate membrane distillation membranes composed of vertically aligned channels with a hydrophilicity gradient by engineering defects in covalent organic framework films by the removal of imine bonds. Such functional variation in individual channels enables a selective water transport pathway and a precise liquid–vapour phase change interface. In addition to having anti-fouling and anti-wetting capability, the covalent organic framework membrane on a supporting layer shows a flux of 600 l m–2 h–1 with 85 °C feed at 16 kPa absolute pressure, which is nearly triple that of the state-of-the-art membrane distillation membrane for desalination. Our results may promote the development of gradient membranes for molecular sieving. Membrane distillation can use low-grade heat for salt water desalination, but the materials used can often suffer from limited permeance. Here, a strategy is proposed to construct a pore surface and size functionality gradient in a covalent organic framework, enabling a flux of 600 l m–2 h–1 with NaCl rejection of 99.99%.

Conventional strategies for modifying electrocatalysts for efficient CO2 reduction are mainly based on doping, defect/morphology engineering, substrate design and so on. In most cases, these methods can only tune their structures, electronic states and thereby catalytic properties in a gradual way. Here we report that the solid–liquid phase transition of Ga–Sn/Ga–In alloys can induce an instant and radical transformation of their atomic and electronic structures during electrocatalysis, which dramatically impacts their catalytic properties. The transition of Sn/In active components from phase-segregated clusters to dispersed single atoms during melting results in a unique electronic structure through further reduction of both metallic Sn/In and Ga. Such atomic/electronic structure transitions can correlate well with suppression of the hydrogen evolution reaction and an enhanced formate Faradaic efficiency from 95%. This two-state switching strategy may be extended to other catalytic reactions to determine correlations between their structures and catalytic properties. Common strategies for catalyst design explore ways of fine-tuning continuous structure–property relationships. Here, the abrupt solid–liquid transition of Ga–In and Ga–Sn alloys is shown to have a profound impact on the CO2 electroreduction performance, with the molten alloy achieving a Faradaic efficiency of 95% formate production.

Enhanced gas recovery (EGR) is believed to be a promising technology to improve the production of shale gas reservoirs and simultaneously reduce the emissions of greenhouse gas via the injection (s...

Disordered graphene networks (DGNs) can be regarded as the three-dimensional (3D) assembly of graphene-like fragments at the nanoscale, in which some intrinsic topological features are usually hidden in these formless fragments without clear understanding. Although some high-resolution structural patterns have been observed in pyrolytic carbons and flash graphene experimentally, it is still hard to characterize the topology and texture of DGNs considering continuous 3D connectivity. Toward this end, starting from the annealing process, we herein performed molecular dynamics simulations to investigate the formation and topological structure of DGNs. Three typical stages are found during the formation of DGNs, that is, the formation of polyaromatic fragments, formation of a disordered framework, and further graphitization. The topology of the obtained DGNs was then investigated, including topological defects, stacking behavior, and global curvature. Several typical in-plane and out-of-plane topological defects are found to connect the 3D network of graphene-like layers. The computed X-ray diffraction and angular defects demonstrate that a high-density DGN tends to form a randomly stacked structure with more connections, while a low-density DGN exhibits more bowl-shaped layers and a less distorted curvature. At low annealing temperatures, the local curvature of DGNs is highly distorted, and the structure seems to lack graphitization compared to high-temperature ones.

Undoubtedly humidity is a non-negligible and sensitive problem for cellulose, which is usually regarded as one disadvantage to cellulose-based materials because of the uncontrolled deformation and mechanical decline. But the lack of an in-depth understanding of the interfacial behavior of nanocellulose in particular makes it challenging to maintain anticipated performance for cellulose-based materials under varied relative humidity (RH). Starting from multiscale mechanics, we herein carry out first-principles calculations and large-scale molecular dynamics simulations to demonstrate the humidity-mediated interface in hierarchical cellulose nanocrystals (CNCs) and associated deformation modes. More intriguingly, the simulations and subsequent experiments reveal that water molecules (moisture) as the interfacial media can strengthen and toughen nanocellulose simultaneously within a suitable range of RH. From the perspective of interfacial design in materials, the anomalous mechanical behavior of nanocellulose with humidity-mediated interfaces indicates that flexible hydrogen bonds (HBs) play a pivotal role in the interfacial sliding. The difference between CNC-CNC HBs and CNC-water-CNC HBs triggers the humidity-mediated interfacial slipping in nanocellulose, resulting in the arising of a pronounced strain hardening stage and the suppression of strain localization during uniaxial tension. This inelastic deformation of nanocellulose with humidity-mediated interfaces is similar to the Velcro-like behavior of a wet wood cell wall. Our investigations give evidence that the humidity-mediated interface can promote the mechanical enhancement of nanocellulose, which would provide a promising strategy for the bottom-up design of cellulose-based materials with tailored mechanical properties.

Experiments showed that the fracture toughness of silicon carbide (SiC) ceramics can be enhanced by adding graphene-based fillers. To understand the toughening mechanism and thoroughly explore the toughening potential, we used a multiscale approach combined with molecular dynamics (MD) simulations to theoretically study the correlation between the toughening effect and the microstructure parameters of SiC/graphene lamellar composite. MD simulations demonstrated that the pull-out force can fluctuate periodically around a constant during the pull-out process and it will drop quickly to zero when the graphene sheet is pulled out from the SiC matrix entirely. The modified crack-bridging model revealed that the toughening enhancement of graphene/SiC composites can be improved with larger graphene size and volume fraction. The macroscopic fracture toughness and the atomistic level pull-out force are linked by the proposed multiscale crack-bridging model. We also found that the fewer-layer graphene sheets can better reinforce the fracture toughness than the more layer ones. These understandings may help the design and preparation of SiC/graphene lamellar composites toward better fracture toughness.

As the typical unconventional reservoir, shale gas is believed to be the most promising alternative for the conventional resources in future energy patterns, attracting more and more attention thro...

Purpose The purpose of this paper is to eliminate Part defects and enrich additive manufacturing of ceramics. Laser powder bed fusion (L-PBF) experiments were carried to investigate the effects of laser parameters and selective oxidation of Titanium (mixed with TiO2) on the microstructure, surface quality and melting state of Titania. The causes of several L-PBF parts defects were thoroughly analyzed. Design/methodology/approach Laser power and scanning speed were varied within a specific range (50–125 W and 170–200 mm/s, respectively). Furthermore, varying loads of Ti (1%, 3%, 5% and 15%) were mixed with TiO2, which was selectively oxidized with laser beam in the presence of oxygen environment. Findings Part defects such as cracks, pores and uneven grains growth were widely reduced in TiO2 L-PBF specimens. Increasing the laser power and decreasing the scanning speed shown significant improvements in the surface morphology of TiO2 ceramics. The amount of Ti material was fully melted and simultaneously changed into TiO2 by the application of the laser beam. The selective oxidation of Ti material also improved the melting condition, microstructure and surface quality of the specimens. Originality/value TiO2 ceramic specimens were produced through L-PBF process. Increasing the laser power and decreasing the scanning speed is an effective way to sufficiently melt the powders and reduce parts defects. Selective oxidation of Ti by a high power laser beam approach was used to improve the manufacturability of TiO2 specimens.

Multilayer two-dimensional (2D) material assemblies (MLMs) with a staggered architecture are widely applied to transfer exceptional properties of 2D materials into their 3D counterparts. However, the quantitative relation between interlayer shear and structural deformation, significant for the design of high-performance MLMs, has not been fully understood due to the inadequacy of existing theoretical model. Integrating the nonlinear shear-lag model and molecular dynamics (MD) simulations, we here investigate the intricate interplay between in-plane deformation and interlayer shear of multilayer assemblies of graphene, molybdenum disulfide (MoS2), and hexagonal boron nitride (h-BN). It demonstrates that the classical shear-lag model can well describe the in-plane deformation of multilayer MoS2 assembly, but fails for multilayer graphene and h-BN assemblies due to the edge effect induced by the interlayer van der Waals attraction. Then, a modified shear-lag model accounting for the edge effect is proposed to quantitatively reveal the respective contributions of the interlayer sliding, edge-effect shear stress and the elasticity of 2D material platelet on the deformation of MLMs. We find that, under the framework of shear-lag model, the inexplicit edge-effect shear stress can be described by two characteristic constants, extremely simplifying the expression of edge-effect shear stress in practical engineering applications.

Plenty of experiments have implied the possible role of moisture and especially pH variations in tailoring the mechanical properties of carbon-based composites. However, this effect of ambient aqueous environment remains elusive at the atomic level and was oft-overlooked in previous analytical studies upon (reduced) graphene oxide ((r)GO)-based binding systems. Here, using first-principles calculations with melamine as the representative organic molecule, we investigate the binding states between organic molecule and rGO in aqueous environment. We found that the solvent phase triggers the enhancement of noncovalent interactions and even a structural transition in the system. The bindings at rGO edge show excellent flexibilities in response to the pH-induced protonation and deprotonation, demonstrating their non-negligible importance in tuning the strength of organic molecule/rGO system, in sharp contrast to the relatively stable interfacial counterparts. Our insights provide a deepened understanding of the solvent-phase chemo-physical behavior, paving a promising way in tailoring (r)GO-based materials for aqueous-phase applications.

In recent years, since the fast mass transport emerges from some low-dimensional nanostructures (e.g., graphene and CNTs), the applicability of the continuous model (e.g., hydrodynamics) for descri...

Noble metal nanostructures have been widely explored as an effective method to increase photon absorption and charge separation in plasmonic photocatalysis. In this study, we integrated two differe...

In the past decades, shale gas has been recognized as the promising unconventional resource for global energy storage, and a clear understanding of the gas-transport characteristic within nonporous...

Summary Batch hydrothermal reactor is known as a closed system, and what happens in this “black box” is mysterious. Now, by using the tendency of graphene oxide (GO) to align along the flow and the fixation effect of thermoset resin, the hydrothermal annular convection can be inferred from the axisymmetric poloidal structure and GO-assembled annular distribution. Temperature difference and geometric symmetricity of the reactor account for the annular convection, which is also found to be affected by solution viscosity and reactor parameters. Numerical simulations reproduce the annular convection and are used to investigate the parameter space beyond experiments. Plume flows occur at the bottom of the reactor due to flow instability. Irregular and intensive flow is against the synthesis of high-aspect-ratio nanomaterials and monolithic gels. It is noteworthy that large-scale batch hydrothermal synthesis may not be feasible for some nanowires, nanosheets, and particularly gels due to the non-negligible flow influence.

Previous attempts to characterize shale gas transport in nanopores are not fully successful due to that the presence of water within shale reservoirs is generally overlooked. In addition, shale is ...