Influence Of Surface Structure Research Articles

Numerical analysis on influence of surface structures of cathode catalyst layers on performance of polymer electrolyte fuel cells

AbstractBecause it is time‐consuming to optimize the design of a cathode catalyst layer (CCL), a numerical simulation to predict the reaction and mass transport characteristics without trial and error is desirable. This study used numerical analysis to investigate how the mass transport occurring in CCLs with flat and three‐dimensional (3D) structures influenced the performance. The simulations included the reconstruction of the CCLs and their electrochemical calculation using our multi‐block model. The simulation results showed the reduction of the proton resistance in the ionomer was a factor in improving the performance in the 3D structure in comparison with the flat structure. An increasing aspect ratio of the 3D structure improved the cell performance and decreased the proton resistance in the ionomer. These results were due to the shortened conductive path of the protons from the polymer electrolyte membrane to the gas diffusion layer side surface in the 3D structure. Finally, the cell performance with an increase in the ionomer content was predicted. This numerical analysis made it possible to understand the reaction of the 3D structure and mass transport and predict ways to optimize the structural design to improve cell performance.

C2H2 semi-hydrogenation: Engineering the surface structure of Pt-based bimetallic catalysts to adjust catalytic performance

Engineering the catalyst surface structure is an effective method to adjust the catalytic performance. This work designs a series of Pt-M (M = Au, Ag and Cu) catalysts with different atomic arrangements of surface structure, including the PtxMy IMCs, PtnL@PtxMy(n = 1–3), PtnL@M, and the subsurface Pt1L-M, aiming at illustrating the influence of surface structure on C2H4 activity and selectivity in C2H2 semi-hydrogenation using DFT calculations and microkinetic modeling. The results showed that adjusting surface structure effectively alters catalytic performance, which markedly depend on the ensemble size of active site and electronic properties. The d-band center of Pt-M catalysts is proposed as a good descriptor to efficiently evaluate C2H4 activity. Among the considered Pt-M catalysts, PtCu3 IMC is screened out to be the most suitable catalyst to present excellent C2H4 selectivity, better activity, and good stability under the optimized experimental conditions of 520 K and the pH2: pC2H2 ratio of 10: 1, which resulted from the smaller ensemble size of active site and moderate d-band center.

Influence of laser surface structuring of steel sheets on the mechanical properties of electrodeposited ZnNi coatings

The influence of laser surface structuring on the formation and the internal strength of electrodeposited ZnNi coatings on steel sheets was investigated. Surface structuring by extended direct laser interference patterning (xDLIP) was used to modify the cohesive strength in the ZnNi layer. An SEM analysis of the crystal structures shows perpendicular nucleation during ZnNi layer formation and areas of crosslinked crystalline structures, which results in an interlocking of crystal structures within the layer. The interlocked crystalline structure leads to an increase of the cohesive strength in the ZnNi layer, which was observed in roller peel tests according to DIN 1464 for adhesively bonded joints.

Halogen and structure sensitivity of halobenzene adsorption on copper surfaces.

The adsorption orientation of molecules on surfaces influences their reactivity, but it is still challenging to tailor the interactions that govern their orientation. Here, we investigate how the substituent and the surface structure alter the adsorption orientation of halogenated benzene molecules from parallel to tilted relative to the surface plane. The deviation of the parallel orientation of bromo-, chloro-, and fluorobenzene molecules adsorbed on Cu(111) and Cu(110) surfaces is determined, utilising the surface selection rule in reflection-absorption infrared spectroscopy. On Cu(111), all three halogenated molecules are adsorbed with their molecular plane almost parallel to the surface at low coverages. However, they are tilted at higher coverages; yet, the threshold coverages differ. On Cu(110), merely bromo- and chlorobenzene follow this trend, albeit with a lower threshold for both. In contrast, fluorobenzene molecules are tilted already at low coverages. The substantial influence of the halogen atom and the surface structure on the adsorption orientation, resulting from an interplay of molecule-molecule and molecule-surface interactions, is highly relevant for reactivity confined to two dimensions.

Influence of Surface Structure on Performance of Inkjet Printed Cathode Catalyst Layers for Polymer Electrolyte Fuel Cells

Abstract The structure of the cathode catalyst layer (CCL) is critically important for improving the performance, durability, and stability of polymer electrolyte fuel cells (PEFCs). In this study, we designed CCLs with a three-dimensional (3D) structure that could increase the surface area of the CCLs to decrease their oxygen transfer resistance. The CCLs were fabricated using an inkjet printing method, and the electrochemical performance of the CCLs in a membrane electrode assembly was evaluated using an actual cell. The results showed that at high Pt loadings, the performance of the CCL with the 3D structure was superior to that of the flat structure. In particular, at a high current density, which is related to mass transport resistance, the two structures exhibited a significant difference in performance. At a Pt loading of 0.3 mg/cm2, the CCL with the 3D structure showed the highest maximum power density among all the CCLs investigated in this study. This indicates that the 3D structure decreases the oxygen transfer resistance of the CCL. Overall, the 3D structure provided improved morphological and microstructural characteristics to the CCL for fuel cell applications.

Influence of surface structure and morphology of PEDOT: PSS on its optical and electrophysical characteristics

This paper presents the results of a study of the effect of modification of the structure of the PEDOT: PSS polymer with hole conductivity on the optical and electrophysical properties of an organic solar cell. It was found that the modification of a polymer film with ethyl and isopropyl alcohols leads to a change in the morphology and roughness of the film surface. It has been determined that annealing of films in alcohol vapor promotes the formation of more uniform films. It is shown that upon modification of the PEDOT: PSS film in alcohol vapor the absorption spectrum shifts the absorption maximum of PEDOT to the short-wavelength region of the spectrum, the absorption of the aromatic PSS fragment decrease. X-ray phase analysis showed that after surface modification with alcohol vapor, the PEDOT and PSS chains change their structure. It is shown that the structural features of the surface morphology of PEDOT: PSS affect the electrophysical parameters of the films, such as the effective extraction rate and the effective time of flight of charge carriers. It was found that the modification of the surface of the PEDOT: PSS film leads to an improvement in the electrical transport properties of the films.

Facet-Dependent selectivity of CeO2 nanoparticles in 2-Propanol conversion

CeO2 nanoshapes, cubes with dominant (100) facets and octahedra with dominant (111) facets, were synthesized to investigate the influence of surface structure on acid-base properties. An optimization of calcination temperatures, coupled with Raman and TEM, was employed to minimize the intrinsic (Frenkel-type) defect sites and their potential complications on the facet studies involved in this work. The acid-base properties of these CeO2 nanoshapes were characterized with in situ pyridine and CO2 adsorption using infrared spectroscopy and quantified using pyridine, ammonia, and CO2 temperature-programmed desorption (TPD). The (100) facet displayed weaker acid sites with lower site density than the (111) facet which had a similar density of base sites but those on the (100) facet were stronger. A strong correlation was observed between 2-propanol conversion and each facet’s acid-base properties. CeO2 cubes exhibited greater base-site catalyzed dehydrogenation to acetone while the more acidic CeO2 octahedra were more active in dehydration to propene.

Local Ordering of Molten Salts at NiO Crystal Interfaces Promotes High‐Index Faceting

AbstractGiven the strong influence of surface structure on the reactivity of heterogeneous catalysts, understanding the mechanisms that control crystal morphology is an important component of designing catalytic materials with targeted shape and functionality. Herein, we employ density functional theory to examine the impact of growth media on NiO crystal faceting in line with experimental findings, showing that molten‐salt synthesis in alkali chlorides (KCl, LiCl, and NaCl) imposes shape selectivity on NiO particles. We find that the production of NiO octahedra is attributed to the dissociative adsorption of H2O, whereas the formation of trapezohedral particles is associated with the control of the growth kinetics exerted by ordered salt structures on high‐index facets. To our knowledge, this is the first observation that growth inhibition of metal‐oxide facets occurs by a localized ordering of molten salts at the crystal–solvent interface. These findings provide new molecular‐level insight on kinetics and thermodynamics of molten‐salt synthesis as a predictive route to shape‐engineer metal‐oxide crystals.

Influence of surface structure on D retention and erosion behaviours of RAFM steel with D-plasma exposure

As the first wall candidate material in the future fusion device, Reduced Activation Ferritic/Martensitic (RAFM) steel represented by CLF-1 steel was further investigated on the deuterium (D) erosion and retention behaviours. The influences of the surface conditions, including surface morphology, W-enriched structure and the original surface roughness, of the surface conditions including the sample temperature, W-enriched structure and the original surface roughness are mainly discussed. The results showed that with the increase of the sample temperature of CLF-1 steel during D-plasma exposure, the surface morphology changed obviously, and the grooves/pits formed by the erosion on the sample surface are deepened and the boundary becomes obvious. Then, the granular nanostructures appeared at the erosion edges and covered the grooves, eventually forming the nanoclusters structure on the surface. At the same time, TEM results showed that the thickness and content of W atoms on the surface increased. Under the combined action of the above surface conditions, both the sputtering rate and total D retention amount of CLF-1 steel decrease. Under the current experimental parameters, with the increase of the initial surface roughness, the sputtering morphology and the surface roughness of CLF-1 steel changed to different degrees after erosion of D, which eventually led to the slightly increase of the sputtering rate. The effect of incident D-plasma angle on the sputtering and redeposition behaviour of the material may explain this phenomenon. Besides, both the specific surface area of the contact plasma and the erosion behaviour of the material by D-plasma increased with the original surface roughness. The D releasing peak, thermal desorption temperature and total D retention amount of CLF-1 steel samples decrease with the original roughness of CLF-1 steel, which is mainly caused by the increase of D diffusion on the surface. At present, it can be found that the W-enriched surface behaviour induced by D-plasma exposure as well as the change of roughness and morphology lead to the decrease of the sputtering rate of RAFM steel with fluence, energy and sample temperature.

Influence of surface structures on wettability

Wettability of solid surfaces is a key parameter for many industrial applications of solid materials. The wettability is influenced not only by the nature of the material but also by the existence of surface structures. Crucial influence of the oriented surface structures on the shape of liquid drop was observed in this study. Observed differences in value of contact angle measured on the metal surface at two perpendicular directions were 19° for water and 23° for diiodomethane. These surface structures can significantly influence liquid and heat transfer on structured surfaces.

The Influence of Surface Structure of RhPt Bimetallic Nanoparticles on the Hydrogenation of Aromatic Compounds

The Influence of Surface Structure of RhPt Bimetallic Nanoparticles on the Hydrogenation of Aromatic Compounds

Structural dependent Cr(VI) adsorption and reduction of biochar: hydrochar versus pyrochar

Hydrochar and pyrochar are two typical biochars, and possess different intrinsic structures and chemical properties as well as pollutant removal abilities. However, their structural dependent pollutant removal performances and the related mechanisms are far less studied. In this study, we systematically compared the Cr(VI) removal processes of hydrochar and pyrochar in dark and under simulated sunlight at pH 5.7 ± 0.1, aiming to clarify the structural dependent Cr(VI) removal of biochar. In dark, hydrochar could remove 19.0% of Cr(VI) only via adsorption within 8 h, less than that (23.5%) of pyrochar via both adsorption and indirect solution •O2− reduction pathway. Although simulated sunlight irradiation could significantly promote the Cr(VI) reduction performances of both hydrochar and pyrochar, the Cr(VI) reduction percentage (88.1%) of hydrochar via both direct surface electron reduction and indirect solution •O2− reduction pathways, was much higher than that (30.2%) of pyrochar only via indirect solution •O2− reduction pathway. This different Cr(VI) reduction pathway of hydrochar and pyrochar was arisen from their structural dependent Cr(VI) adsorption models, as revealed by ATR-FTIR characterization and DFT calculation. More phenolic -OH group on hydrochar surface provided abundant sites for Cr(VI) chemical adsorption to form a strong inner-sphere complex, favoring the interfacial electron transfer for the direct surface Cr(VI) reduction. In contrast, more micropores in pyrochar were responsible for the Cr(VI) physical adsorption via intra-particle and boundary layer diffusion, which hampered the surface Cr(VI) direct reduction because of the weak interfacial interaction between Cr(VI) and pyrochar. This study clarifies the influence of surface structure on the Cr(VI) adsorption and reduction pathways of biochar, and also provides an efficient Cr(VI) removal strategy with sunlight and hydrochar.

Recent Advances of Oxygen Carriers for Chemical Looping Reforming of Methane

AbstractThis review discussed recent advances of oxygen carriers (OCs) for chemical looping reforming (CLR) of CH4 which aims to generate high‐quality syngas, an important chemical intermediate for the synthesis of chemicals and fuels. We firstly introduced CLR and that combined with CO2 and H2O splitting as well as clarified their advantages over conventional reforming processes. Then we reviewed the latest advances of metal‐based OCs, composite OCs including perovskites and hexaaluminates, and catalytic OCs, namely oxygen‐containing materials with catalytically metal sites, during the past five years. Specific discussion focused on the influence of composition, surface, and bulk structure of these OCs on conversion, selectivity, and lattice oxygen reactivity to summarize design and optimization strategies of the tailored OCs. Finally, a brief summary and an outlook on some of the scientific challenges and suggestions for future investigations on the development of outstanding OCs for CLR of CH4 are given.

Influence of surface structure on the performance of mono-like Si PERC solar cell

Mono-like Si wafers were textured by both alkaline solution and metal-assisted chemical etching (MACE) process. The influences of surface textures on the diffusion process, surface passivation, electrical property and performance of solar cells were investigated. The results show that the pyramid-like structures obtained by alkaline texturing facilitates a higher surface doping concentration, larger junction depth after diffusion and better passivation effect, compared with the honeycomb-like structures generated by MACE texturing. In the same wafer textured by alkaline solution or MACE, the mono-crystalline region exhibits a higher quantum efficiency than the multi-crystalline region. By combining the MACE and alkaline texturing processes, the honeycomb- and pyramid-like structures were generated on the surface of mono-like Si wafer, resulting in a conversion efficiency of 21.39% that is higher than that of the individually MACE or alkaline-textured solar cells by 0.4% and 0.02%, respectively.

Tribology of an assembly of hairs: Influence of multiscale surface chemistry and structure on sensorial tactile properties.

Hair fibers may be either oriented in a common direction or randomly arranged. Fiber arrangement as well as cosmetic treatment control the sensorial perception. The present study explores the respective influence of these two aspects by predicting the product performance in terms of tactile perception. Friction forces between hair swatches of different curl patterns using a finger-like probe have been measured to better mimic real-life hair/finger contact. Measurements of fiber alignment, hair diameter (thickness), and compression tests were performed on natural and treated swatches to assess the respective weight of these parameters. Conditioned hair exhibit an adhesive behavior measured at the start of the frictional movement. Conversely, natural hair is influenced by fiber reorientation. After a few seconds, friction-related signals stabilize. Thus, the averaged friction forces do not only depend on hair thickness, but increase with a decreased alignment of the fibers. Intrinsic (diameter/curliness) and external (orientation/ friction/compression) characteristics allow to define a model of "macroscopic" roughness linked to the sensorial characterization. As friction of hair swatches depends upon fiber alignment and coating, this combined approach is potentially a very useful in vitro test, as an alternative or complementary method to sensory tests.

STUDY OF HYDROPHOBICITY AND TEXTURE OF THE GRAVITY TRAY SURFACES TO IMPROVE THEIR TRANSFER CAPACITY

The article reveals a study of open trays transporting water and gravity. The study focuses on a new design patented small-size hydraulic benches, which allow investigating of the hydrophobicity degree of the materials intended for manufacture of open trays, as well as the efficiency of the tray internal surface textures to increase the transporting capacity of the streams containing solid inclusions. The wetting of protective coatings in dynamic conditions has been studied on a small hydraulic bench by creating a mini-flow and registering its characteristics with photo and video equipment. The study results on the liquid transfer in the trays of small-sized installations are given for two modes: single-phase (water) and two-phase (water with mineral inclusions). Exploratory studies have been performed to fix the vortex formation in the flow based on the chiaroscuro effect, when the filling has been made according to the tray surface corrugated texture, in a wide range of water flow velocities, as well as well as at calculated fillings corresponding to the actual operating conditions of trays and pipelines. The article estimates the pipeline surface structure influence on formation of the turbulence zones in different points of the obstacles. There were texture roughness characteristics given, which provide the most effective fluid flow transfer capacity by the mass of dispersed inclusions of various granulometric composition (sand-based) have been revealed. The velocity increasing ranges (below self-cleaning velocities), which provide the transfer capacity of the trays due to the textured surfaces, were established.

Influence of surface structures on torque of VT6 alloy cortical screws

The paper investigated the effect of the surface structure of VT6 alloy cortical screws after various modes of vacuum ion-plasma treatment on the magnitude of the torque when they are screwed and twisted into the threaded holes of titanium plates for bone osteosynthesis. It was shown that nitriding of the screw heads increases the surface hardness by 2 times, and the formation of the nitride layer-by 3 times. It was found that the maximum decrease in torque when unscrewing is observed for nitride coated screws.

Insights into the shape effect of H2 self-selective Ni catalysts for efficient acetone hydrogenation

The shape-function relationship for designing catalysts is always a focus to study. This article describes the influence of Ni catalysts surface structure on acetone hydrogenation. We report H2 as a morphology-directing agent to selectively synthesize branched Ni (Ni-BN), which exposes substantial stepped Ni(322) facet (~99%) that has elegant activity for acetone hydrogenation. In contrary, Ni nanoparticle (Ni-NP) prepared without H2 mainly exposes flat Ni(111) and Ni(100) facets and these facets perform less activity for acetone hydrogenation to isopropanol. Subsequently, DFT studies of reaction mechanism on different facets reveal that the step site in Ni(322) facet displays lower activation barriers than that of Ni(111) and Ni(100) facets. With help of kinetic growth model and microkinetics study, quantitative shape-function relationship of Ni-BN for acetone hydrogenation to isopropanol can be further established. This work not only clarifies the catalytic activity of Ni on acetone hydrogenation but also provides a method accessing the intrinsic kinetics of the reaction.

Bioinspired Surface with Superwettability for Controllable Liquid Dynamics

AbstractLiquid dynamics on a solid surface, i.e., the impact, flow, or overflow, are ubiquitous in nature and cause multifaceted problems that affect daily life. Recent studies on the role of surface superwettability in controlling liquid dynamics have attracted much attention. The role of particular surface morphologies and surface chemical compositions in manipulating the liquid impact or transport dynamics has garnered diverse scientific interests and has encouraged the widespread use of surface wettabilities in practical applications. Herein, the recent progress according to the interaction method between the liquid and solid is classified and summarized. The crucial influence of surface wettabilities and structures on liquid dynamic behaviors and a critical survey of the mechanism behind these behaviors, along with emerging applications, challenges, and perspectives, are presented.

The mechanism of Li2O2-film formation and reoxidation – Influence of electrode roughness and single crystal surface structure

In this work, the role of the electrode surface structure on oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in lithium ion containing dimethyl sulfoxide (DMSO) was elucidated for Pt single crystal electrodes and deliberately roughened polycrystalline gold and platinum electrodes. Both rotating ring disk electrode (RRDE) measurements and results obtained by differential electrochemical mass spectrometry (DEMS) show that the amount of insoluble Li 2 O 2 formed is proportional to the roughness factor and corresponds to one or two monolayers if referenced to the true surface area. The amount of soluble LiO 2 is independent of roughness, although the formation of the passivating Li 2 O 2 layer takes longer. On gold electrodes less side products are formed as compared to platinum electrodes. It was furthermore found that ORR on single crystalline Pt(100) leads to two monolayers of Li 2 O 2 , while in case of Pt(111)/Pt(pc) only one monolayer was reoxidized. The shape of the reoxidation peaks in the anodic potential scan is independent of roughness, but it depends not only on the electrode material (Au or Pt) but also on the atomic surface structure. Since Tafelslopes cannot be determined directly by usual methods for such surface confined reactions, we used ac voltammetry to determine the apparent transfer coefficient ( α′ ) and gain some insight into the reoxidation mechanism; the obtained α ′ of 0.3 hints to a rate determining first charge transfer. This agrees well with the detection of superoxide during oxidation of Li 2 O 2 on the surface. • Strong effect of electrode surface structure on electrochemistry in Li + -containing DMSO. • Superoxide as intermediate during lithium peroxide oxidation in DMSO. • Apparent transfer coefficient of lithium peroxide oxidation in Li + -containing DMSO. • Direct correlation of lithium peroxide formation and surface roughness.