Gas-solid Interface Research Articles

Identification of Halogen-Associated Active Sites on Bismuth-Based Perovskite Quantum Dots for Efficient and Selective CO2-to-CO Photoreduction.

All-inorganic Pb-free bismuth (Bi) halogen perovskite quantum dots (PQDs) with distinct structural and photoelectric properties provide plenty of room for selective photoreduction of CO2. However, the efficient conversion of CO2-to-CO with high selectivity on Bi-based PQDs driven by solar light remains unachieved, and the precise reaction path/mechanism promoted by the surface halogen-associated active sites is still poorly understood. Herein, we screen a series of nontoxic and stable Cs3Bi2X9 (X = Cl, Br, I) PQDs for selective photocatalytic reduction of CO2-to-CO at the gas-solid interface. Among all the reported pure-phase PQDs, the as-synthesized Cs3Bi2Br9 PQDs exhibited the highest CO2-to-CO conversion efficiency generating 134.76 μmol g-1 of CO yield with 98.7% selectivity under AM 1.5G simulated solar illumination. The surface halogen-associated active sites and reaction intermediates were dynamically monitored and precisely unraveled based on in situ DRIFTS investigation. In combination with the DFT calculation, it was revealed that the surface Br sites allow for optimizing the coordination modes of surface-bound intermediate species and reducing the reaction energy of the rate-limiting step of COOH- intermediate formation from •CO2-. This work presents a mechanistic insight into the halogen-involved catalytic reaction mechanism in solar fuel production.

Numerical investigation of slip flow phenomenon on performance characteristics of gas foil journal bearing

Gas foil bearings (GFBs) are often employed in turbomachinery, particularly in high-speed turbochargers and turboexpanders. These bearings operate at very high speed and under very low clearance. On account of very low clearance, velocity slip can be observed at the gas–solid-interface. This paper investigates the effect of slip on various performance characteristics of the GFB. A model is put forth to predict the pressure and film thickness of a Gas Foil Journal Bearing (GFJB) used in helium-liquefaction turboexpander operating at 240 krpm. The present model addresses the slip at the gas-foil interface. Modified Reynolds equation, assuming first-order slip, is used along with the structural equation, which illustrates the compliant property of the foil. A numerical model is developed by finite difference approximation and solved by an iterative method. Various performance parameters are assessed for the no-slip and slip flow phenomenon in GFJB. The results are compared and a considerable difference is seen between the two models. The conventional Reynolds equation overestimates the load by approximately 8% at 240 krpm. The load-carrying capacity at different values of Knudsen number is also shown.

A single-electron tunneling model: a theoretical analysis of a metal nanoparticle-doped epoxy resin to suppress surface charge accumulation on insulators subjected to DC voltages

In high-voltage direct current transmission systems, charges accumulate at the gas—solid interface, distorting the local field strength, causing a reduction in the flashover voltage, and threatening the safe and reliable operation of the power system. The latest research has found that doping metal nanoparticles into an epoxy resin effectively suppresses the surface charge accumulation on insulators and improves their flashover voltage. This paper further analyzes the microscopic mechanism of this phenomenon, establishes a single-electron tunneling mode, and draws two conclusions: when there is no agglomeration of the doped nanoparticles, a higher doping concentration can be achieved, which provides a better insulative performance. The optimal metal nanoparticle radius is several to tens of nanometers. This work provides theoretical guidance for the future improvement of insulating materials through metal nanoparticle doping and has good prospects in engineering applications.

A Correlation for Nusselt Number of Slip Gas Flow in Confined Porous Media

Abstract A clear understanding of flow and heat transfer at pore-scale level in microporous media is a topic of concern in microcooling/heating systems. In this work, a multiple-relaxation-time lattice Boltzmann method (LBM) is employed to study flow and heat transfer of gas in microporous media. Curved boundaries are treated using an effective boundary condition, which is formed by combining nonequilibrium extrapolation with counterextrapolation methods. The method also incorporates velocity slip and temperature jump on gas–solid interface. A two-dimensional (2D) porous domain composed of microcylinders, is considered from a representative element volume (REV) for the simulation. Porosity of the domain is variated by altering diameter of microcylinders. Nusselt number is calculated by varying Knudsen number (0.0–0.1), Reynolds number (5–50) and porosity (0.4–0.8). Based on the obtained numerical predictions, a new Nusselt number correlation is proposed for the first time in this work which can accurately predict the heat transfer for slip gas flow in confined porous media.

Visualisation of stabilising particles at the gas-solid interface of metal foams

In this article, we demonstrate a technique to visualise the stabilising particles at the gas-solid interface of metal foams by employing metallographic etching. This technique is easy to perform and can be applied on a relatively large sample size. The particles present at the gas-solid interface of five different types of foams were investigated. Information on the type of particles and the particle coverage could be obtained from this study.

Multifunctional marine bio-additive with synergistic effect for non-toxic flame-retardancy and anti-microbial performance

Flame-retardants and biocides are well-established functional additives that enhance key properties of polymer and porous materials. Conventional additives and their secondary emissions may render materials hazardous in the long-term, incrementing human exposure to a toxic load of persistent bio-cumulative substances in the indoor built environment. The present study developed a novel multifunctional green additive formulated for the optimization of thermoplastic-lignocellulose hybrid sheet materials engineered for indoor building applications. The compound was developed from two marine bio-materials, Kelp Macroalgae (Eklonia spp.) and Bivalve mollusc shells (Veneridae spp.), selected due to their exceptional properties for these functions, as result of the complex mixture of biogenic carbonate/halide/oxide inorganic phases intricately connected through a hierarchical structure. Oxidative flame propagation was investigated under fire conditions and thermal degradation coupled with gas analysis was investigated under inert gas purge for the temperature range 30–1300 °C. The microbial biomass was analysed with culture-dependent and independent methods. The marine panel prototypes exhibited superior flame-retardant characteristics as result of synergistic mechanisms occurring at the solid-gas interface through the disruption of volatiles flame reactions in the gas-phase, endothermic reactions, and self-catalytic activation. This resulted in self-extinguishing, flame-inhibition, slow-flame propagation rate; and the formation of hierarchically porous carbonaceous phase of high-adsorptive capacity. The biodegradation and ecotoxicity analyses indicated very low-moisture absorption and a possible inhibitory effect on microbial development due to the CaCO3/alginate destabilizing effect on the cell membrane. This promising result demonstrates that the synergistic effect of the marine additive has high-potential rendering the novel hybrid materials non-toxic, biodegradation resistant, whilst increasing the recyclability potential at their end-of-life.

Decomposition characteristics and marker products of C3F7CN/EP insulation system with long-term surface discharge

C3F7CN has the potential to replace SF6 in gas insulated equipment due to its excellent insulation properties and low GWP. In order to apply better use of C3F7CN gas in the future, it is of great significance to study the reaction products of C3F7CN and epoxy resin (EP) with discharge failure conditions for online monitoring and insulation evaluation. In this paper, the experiments of gas–solid interface discharge for 300 h were carried out. The gas decomposition products were tested by GC–MS, the elements and chemical bonds on the surface of EP before and after discharge were tested by FTIR and XPS. The results showed that the number of gas decomposition products increased with the increase of discharge time. The products mainly included saturated carbon–fluorine gas CF4, C3F8, and C6F14, unsaturated carbon–fluorine gas C3F6, C4F6, and C4F8, nitrile gas CF3CN, ester gas C12F7H17O2, among which C12F7H17O2 was the marker product of C3F7CN/EP. And the relative contents of CF4 and C3F8 increased linearly with the increase of discharge time. The growth rates of C4F10, C4F8, C3F6 and C6F14 increased firstly and then decreased. After discharging on the gas–solid insulating surface, F and N elements in the gas appeared on the EP surface in the form of CF bond and CN bond. Further analysis of the products, a mathematical model for the variation of product formation rate with discharge time was proposed. Finally, it was proposed that C12F7H17O2 was a marker product for diagnosing discharge decomposition of C3F7CN/EP resin insulation system.

Feasibility of C 3 F 7 CN/CO 2 gas mixtures in high‐voltage DC GIL: a review on recent advances

With the rise of renewable energy resources, especially offshore wind power plant, the DC transmission concept has attracted more and more attention. The selection of eco-friendly insulating gas, as most critical insulating part of gas-insulated equipment is top priority for developing highly reliable system. Moreover, it is acknowledged that eco-friendly C3F7CN/CO2 gas mixtures have become a potential alternative to SF6 gas due to its excellent performance. This study reviews the basic physical properties of C3F7CN gas/gas mixtures and insulation properties including the gas gap breakdown and surface flashover performance at DC, as well as lightning impulse voltage. Investigation about the gas stability is presented, including the compatibility of gas with solid materials in gas-insulated transmission line (GIL), and the decomposition characteristics under long-term electrical and thermal stresses. The important progress on the charge accumulation characteristics of gas–solid interface in the novel gas environment under DC voltage stress is analysed. Finally, the key issues that need to be paid attention to and further followed through regarding the application of this novel gas in GIL are summarised and put forward. This study hopefully can provide a complete reference for the development of eco-friendly DC gas insulation equipment with C3F7CN/CO2 gas mixtures.

Characterizing Complex Gas–Solid Interfaces with in Situ Spectroscopy: Oxygen Adsorption Behavior on Fe–N–C Catalysts

Electrocatalysts for the oxygen reduction reaction within polymer electrolyte membrane fuel cells based on iron, nitrogen, and carbon elements (Fe–N–C) have received significant research attention ...

Recent advances in methodologies and applications of cataluminescence sensing.

Cataluminescence (CTL), a kind of chemiluminescence emitted at the gas-solid interface during catalytic oxidation reactions, has been developed for many decades as a novel and promising gas sensing technique. In this review, we introduce the origin, basic principles, and mechanisms of CTL sensing systems and summarize the recent advances in CTL sensing, focusing on methodologies and extended applications such as in gas selective monitoring, recognition of complex mixture, evaluation for catalytic property and use in high-performance liquid chromatography, capillary electrophoresis and gas chromatography detectors. In addition, development prospects and some challenges facing CTL-based sensing are also discussed.

Catalytic flow with a coupled finite difference — Lattice Boltzmann scheme

Many catalyst devices employ flow through porous structures, which leads to a complex macroscopic mass and heat transport. To unravel the detailed dynamics of the reactive gas flow, we present an all-encompassing model, consisting of thermal lattice Boltzmann model by Kang et al., used to solve the heat and mass transport in the gas domain, coupled to a finite differences solver for the heat equation in the solid via thermal reactive boundary conditions for a consistent treatment of the reaction enthalpy. The chemical surface reactions are incorporated in a flexible fashion through flux boundary conditions at the gas–solid interface. We scrutinize the thermal FD-LBM by benchmarking the macroscopic transport in the gas domain as well as conservation of the enthalpy across the solid–gas interface. We exemplify the applicability of our model by simulating the reactive gas flow through a microporous material catalyzing the so-called water-gas-shift reaction.

Numerical simulations of onset and growth of Rayleigh–Taylor instability involving solids in converging geometry

Numerical simulation of Rayleigh–Taylor instabilities involving solids has been carried out in a spherically converging geometry. A solid shell is driven toward the center by high-pressure gas outside. Low-pressure gas inside the shell is then compressed, causing the solid shell to slow down and eventually bounce back. Simulation results show the absence of the onset condition unlike in the planar geometry equivalent. Results also show that disturbance growth seems to be strongly associated with the deformation direction instead of the acceleration direction. For example, when the interface is compressed in the cross-stream direction, the disturbance at the gas–solid interface grows even under the Rayleigh–Taylor stable situation.

Phase field approach for void dynamics with interface stresses at the nanoscale

In this paper, a thermodynamically consistent interface stress is derived for the solid-gas interface of nanovoids within the concept of the phase field approach and using the laws of thermodynamics. The Cahn-Hilliard (CH) equation describes the evolution of nanovoid concentration which varies between 0 for perfect solid to 1 for gas. Considering the gradient term of the nanovoid concentration in the deformed state results in an inelastic term in the stress tensor which depends only on and is along the gradient of the nanovoid concentration. Also, multiplying the free energy of mixing and the gradient energy by the ratio of mass densities in the undeformed and deformed states leads to an inelastic hydrostatic stress. The combination of the above inelastic stresses gives the correct inelastic interface stress. It is proved that for a stationary interface which does not support elastic stresses, the obtained interface stress reduces to the biaxial tension which coincides with a sharp-interface approach limit. The interface stress changes the total stress distribution and affects the elastic stress field. Thus, due to the significant effect of the elastic energy on void dynamics, it can indirectly affect the void nucleation and growth. The coupled CH and elasticity equations are solved using the finite element method and several examples of void evolution are studied consisting of thermal induced initiation and propagation of a planar void, thermal induced circular void growth, evolution of void nanostructure under biaxial compression and evolution of void nanostructure with an initially, randomly distributed void concentration. The obtained results show the significant effect of the interface stress on the total stress distribution and consequently, a different distribution of thermodynamic driving force which can affect the nanostructure evolution and deformation. The interface stress represents a promotive effect on the void growth which results in a faster void growth and a larger void concentration. Also, the results reveal a significant effect of temperature, elastic properties and sample size on the interface stress.

Bubble Consumption Dynamics in Electrochemical Oxygen Reduction

Electrochemical oxygen reduction reaction(ORR) is crucial for fuel cells and metal-air batteries, while the oxygen consumption dynamics study during ORR, which affects the ORR efficiency, is not as concerned as catalysts design does. Herein the consumption behavior of an individual oxygen bubble on Pt foils with different wettabilities during ORR was tracked by a real-time approach to reveal whether the surface wettability of electrode can influence the consumption dynamics and determine the reaction reactive zones of oxygen bubble consumption. The oxygen bubble underwent a “constant contact angle” dominant consumption model on aerophobic Pt foil, while an initial “constant radius” and the subsequent “constant contact angle” oxygen consumption models were observed on aero-philic Pt foil. Results here demonstrated that the current was proportional to the bottom contact area, rather than the three-phase contact line of the bubbles according to the fitting curves between individual bubble current and the con-sumption behavior parameters. This study highlights the important role of the gas-solid interface in influencing the efficiency of gas consumption electrochemical reactions, which shall benefit the understanding of reaction kinetics and the rational design of electrocatalysts.

Thermodynamics of the Contact Angle of a Sessile Bubble

Numerous experimental data are available on contact angles. However, the majority of them concern sessile droplets, although bubbles are more interesting from the point of view of colloid science, because a sessile bubble is distinguished by the existence of an equilibrium thin liquid film at a gas–solid interface. This paper presents the totality of modern thermodynamic equations necessary for describing the contact angle of a bubble of an arbitrary size. However, in view of their complexity, specific relationships are derived and analyzed for small although macroscopic bubbles. The dependences of a bubble contact angle on the temperature, pressure in a liquid, composition of a liquid phase, and roughness of a solid surface are considered. In the case of a pure liquid, when a gaseous phase consists of its vapor, the obtained relations are of significance for the cavitation theory. The study as a whole has a framework character, and so only the general basic results are presented. Their detailing is possible in combination with experimental data.

Opportunities in the Synthesis and Design of Radioactive Thin Films and Nanoparticles.

Studies of radioactive isotopes at the liquid-solid or gas-solid interface are enabling a detailed mechanistic understanding of the effects of radioactive decay on physical, biological, and chemical systems. In recent years, there has been a burgeoning interest in using radioactive isotopes for both imaging and therapeutic purposes by attaching them to the surface of colloidal nanoparticles. By merging the field of nanomedicine with the more mature field of internal radiation therapy, researchers are discovering new ways to diagnose and treat cancer. In this Perspective, we discuss state-of-the-art radioactive thin films as applied to both well-defined surfaces and more complex nanoparticles. We highlight the design considerations that are unique to radioactive films, which originate from the damaging and potentially self-destructive emissions produced during radioactive decay, and highlight future opportunities in the largely underexplored area between radioisotope chemistry and nanoscience.

Dehydration of methanol and ethanol over silica-supported heteropoly acids in the gas phase: Surface-type versus bulk-type catalysis mechanism

Dehydration of MeOH to dimethyl ether and EtOH to diethyl ether and ethene was studied at the gas-solid interface in the presence of bulk and SiO2-supported Keggin heteropoly acids (HPAs) H3PW12O40 (PW) and H4SiW12O40 (SiW) as catalysts. The catalysts were prepared by HPA impregnation from water and MeOH. Their acid strength, texture and structural integrity was characterised using NH3 adsorption calorimetry, BET, XRD and DRIFT spectroscopy. The strength of acid sites in HPA/SiO2 catalysts increased monotonously with HPA loading. In the dehydration of MeOH and EtOH, the turnover reaction rate for PW catalysts was higher than for SiW catalysts in agreement with their acid strength. HPA catalysts prepared from water and MeOH had a very close acid strength and showed similar activities in alcohol dehydration. The steady-state catalyst activity was found to correlate with the density of catalyst proton surface sites rather than with the HPA loading. This indicates that alcohol dehydration occurred via a mechanism of surface-type HPA catalysis at the gas-solid interface rather than a bulk-type (pseudo-homogeneous) catalysis.

Open-cell foams as catalysts support: A systematic analysis of the mass transfer limitations

• Systematic analysis of the mass transfer limitation in wash-coated open-cell foams. • CFD simulations on Kelvin’s cell by DNS. • Mass transfer correlation for low Reynolds number. • Practical criteria in terms of dimensionless numbers for rate limiting regimes. In this work, the analysis of the mass transfer phenomena in catalytic open-cell foams is carried out through the combination of computational fluid dynamics (CFD) simulations and experiments, using the CO oxidation on Pt(1%)/γ-Al 2 O 3 /foam as a model reaction. The influence of the local hydrodynamic effects on the diffusion-reaction phenomena occurring at the gas-solid interface of the open-cell solid foams are investigated by Direct Numerical Simulations assuming an infinitely fast reaction. A correlation for the Sherwood number as function of Reynolds -for low Re- is proposed. To validate this experimentally, aluminum foams coated with Pt(1%)/γ-Al 2 O 3 are tested at different reaction conditions for the CO oxidation. The obtained reaction rates and apparent activation energy show the presence of external mass transfer limitations. An analysis of the diffusion-reaction phenomena taking place in the wash-coated layer is presented in terms of dimensionless numbers. A practical criterion is developed in terms of the Thiele modulus ( ϕ w ) and the Biot number (Bi m ) for the identification of the reaction regimes: kinetic control ( ϕ w 2 / B i m < 0.1 ) , internal and/or external mass transfer limitations ( 0.1 < ϕ w 2 / B i m < 10 ) , and full mass transfer control ( ϕ w 2 / B i m > 10 ) .

Surface charge transport behavior and flashover mechanism on alumina/epoxy spacers coated by SiC/epoxy composites with varied SiC particle size

Charge accumulation phenomenon on gas–solid interface greatly restricts the development of HVDC energy transmission system. In this study, the surface charge transport behavior and flashover performance on alumina/epoxy spacer coated by SiC/epoxy composites are experimentally investigated under DC stress. SiC/epoxy composites with varied SiC particle size are fabricated and deposited on spacer surface. Nearly a charge free surface is achieved especially at smaller SiC particle size, even when metallic wires are adhered on spacer surface and connected to high voltage electrode. The DC flashover voltage increases with the decrease of SiC particle size. On the one hand, smaller SiC particle size exhibits more outstanding nonlinear conductivity characteristics, contributing to accelerating charge dissipation, whereas on the other hand, it would introduce plenty of shallow traps due to the increased interfacial regions between SiC particle and epoxy matrix, resulting in aggravating charge accumulation. A theoretical model is proposed to reveal the control mechanism of SiC/epoxy coating with different SiC particle size on flashover performance. The validity of this model can be confirmed based on the surface trap distribution, carrier mobility and our previous investigations on gas–solid interface flashover development process.

In situ oxidation studies of Cu thin films: Growth kinetics and oxide phase evolution

A comprehensive understanding of the oxidation of Cu thin films in the low-temperature regime is of fundamental interest and particularly relevant for applications in the fields of micro- and nanoelectronics, sensors, catalysis, and solar cells. The current study reports on the oxidation kinetics of PVD grown Cu thin films (20–150 nm thick) and the oxide phase evolution from Cu2O to CuO upon thermal oxidation in the temperature range of 100–450 °C. XRD investigations in the laboratory and at the synchrotron show that the oxide phase formation critically depends on the oxidation conditions such as temperature and oxygen partial pressure. The real-time synchrotron XRD measurements reveal that the formation of the CuO phase only starts after complete oxidation of the Cu films to Cu2O films. In situ resistance measurements were performed to follow the oxide growth rate of Cu2O on Cu films in the temperature range of 100–300 °C in air and in 10 mbar pO2. It is found that the oxidation kinetics of Cu films to Cu2O films follows the linear rate law, which is attributed to surface reaction controlled oxidation. The oxygen dissociation rate at the gas–solid interface is the rate-limiting process. A dramatic decrease in the linear oxidation rate is observed at low oxygen partial pressures. The fundamental differences between the oxidation rate-limiting processes of Cu as compared to other transition metal films are discussed.