Effect Of Capillary Condensation Research Articles

Utilization of Pt Nanoparticle Catalysts during Capillary Condensation Phenomenon in PEMFC: A Lattice DFT Simulation Based on 3D Reconstruction of TEM Images

The use of porous carbon support particles in Cathode Catalyst Layer (CCL) of Polymer Electrolyte Membrane Fuel Cell (PEMFC) has gained significant interest due to their ability to enable proper dispersion of Platinum (Pt) nanoparticles [1]. This offers a key advantage of avoiding the Pt nanoparticles from potential poisoning by sulfonate anion functional groups in the ionomer that is deposited on the surface of the support particles [2]. Furthermore, the presence of condensed liquid water is essential for effective utilization of the Pt nanoparticles that are dispersed both inside and outside of the porous carbon support particles. This is because water plays a crucial role as a proton pathway for hydrogen ions during the electrochemical reaction, thus a requisite amount of condensed liquid water is also needed to promote efficient catalytic activity and maximize the performance of Pt nanoparticle catalysts. It has been demonstrated that the microstructure characteristics of the porous carbon support particles have a significant impact on the performance of Pt utilization, which is attributed to the varying behavior of water condensation [2]. Microstructure properties such as pore size, surface area, and wettability properties, can influence the distribution of condensed liquid water, thereby affecting the electrochemical performance of Pt nanoparticles in the catalyst layer of PEMFC. Understanding the effect of capillary water condensation in the porous carbon support particles is therefore crucial for maximizing the utilization and catalytic activity of Pt nanoparticles in fuel cell systems.To investigate the behavior of water condensation in the CCL particles of PEMFC, we conducted simulations based on reconstructed structural data obtained from Transmission Electron Microscopy (TEM) images, as shown in Figure 1. The CCL particle used in this study is taken from the Toyota MIRAI Gen 2 model, an emerging commercial PEMFC-based vehicle in Japan. Here, we used the lattice Density Functional Theory (DFT) to simulate the process of capillary water condensation within the pore network of the particle. The lattice DFT method, which is based on the mean-field lattice gas model, can be interpreted as a coarse-grained equivalent of the conventional DFT [3]. The significant advantage of using lattice DFT is to provide a simple model and computationally efficient approach for studying the behavior of capillary water condensation. To validate the parameters used in our lattice DFT simulations, we compared the isotherm curve obtained from our simulation results with experimental data. Through this comparison, we were able to fine-tune the parameters of the lattice DFT simulation to fit the simulated isotherm curve with that of the experiment. When the parameters are optimized, the resulting water distribution obtained from the lattice DFT simulation, as illustrated in Figure 1, serves as a crucial input to investigate the utilization/activation of Pt nanoparticles within and outside the carbon support particle under varying relative humidity (RH) conditions. Since the resulting water distribution depends on RH, we expect that the utilization/activation of Pt nanoparticles also depend on RH. In this study, we defined utilization/activation of Pt nanoparticle when there is a continuous path of condensed water connecting the Pt nanoparticle to the surface of the carbon support particle. This criterion is similar to the case when we assume that the ionomer is distributed uniformly on the surface of the carbon support particle. Our investigation shows that the utilization/activation behavior of Pt nanoparticles follows closely the isotherm curve of the capillary water condensation.The complex internal structure of CCL particles in PEMFC makes it challenging to visualize and understand their workings through experiments alone. Therefore, our approach of using lattice DFT simulations offers valuable insights to the role of capillary water condensation behavior in the utilization/activation of Pt nanoparticles. This approach may also pave the way for future research in optimization strategies for PEMFC, ultimately contributing to the advancement of clean energy technologies.This work was supported by the New Energy and Industrial Technology Development Organization (NEDO) of Japan (Grant number JPNP20003).[1] Islam, M.N., et al. (2022), Nat. Commun. 13, 6157.[2] Ramaswamy, N., et al. (2020) J. Electrochem. Soc. 167 064515.[3] Monson, P. (2012) Micropor. Mesopor. Mater. 160, 47–66.Figure 1. Reconstructed structural data obtained from TEM images of a PEMFC CCL particle used in Toyota MIRAI Gen 2 model, with visualization of condensed water obtained from a sample lattice DFT simulation. Figure 1

Time Dependence of the Graphene Surface Adhesion Force of the Sphere-Plane Contact at Different Relative Humidities.

Graphene has a promising application prospect in integrated circuits and microelectromechanical systems, and sphere-plane contacts are their common contact types. At present, it is difficult to explain the time dependence of the adhesion force of the sphere-plane contact by conventional theory. Therefore, a single rough peak of sphere-plane contact adhesion force model based on variable water contact angle theory and Bradley contact theory was established; the aim is to reveal the changing law of graphene adhesion force. Then, the time dependence of the graphene surface adhesion force at different humidity levels was investigated by using an atomic force microscopy spherical probe. Finally, a quantitative comparative analysis of the theory and experiment was performed. The results show that the theoretical adhesion force was in good agreement with the experimental measurement results. The time dependence of graphene surface adhesion was not obvious within a relative humidity of 45-55%. When the relative humidity was greater than 65%, the graphene surface adhesion first increased and then decreased with dwell time and finally tended to be stable. Because of the increase in relative humidity, the capillary condensation effect increases, and then the adhesion force increases with the development of the meniscus. When the water film was generated on the sample surface, the adhesion force decreased until the meniscus achieved equilibrium.

Effect of ionomer swelling and capillary condensation of water on porous characteristics in cathode catalyst layers of polymer electrolyte membrane fuel cells under humidified conditions

Reducing oxygen diffusion resistance in the cathode catalyst layer of polymer electrolyte fuel cells under humidified conditions is essential for reducing the cost of expensive platinum catalysts. We designed an ionomer swelling model that reproduces isotherm adsorption and oxygen diffusion coefficient measurements, to elucidate the effect of pore blockage due to ionomer swelling and capillary condensation on the decrease in oxygen diffusivity. Coupled simulations of ionomer swelling, capillary condensation, and oxygen diffusion are performed using this model, and the water and swelled ionomer distributions at each relative humidity are elucidated. When the humidity is low, ionomer swelling is dominant for the oxygen diffusivity reduction, whereas when the humidity is high, both ionomer swelling and capillary condensation affect them.

Feasibility investigation of enhanced coalbed methane recovery by steam injection

Heat injection is an effective technique to enhance unconventional oil and gas recovery. As an excellent heat transfer medium, steam has a great potential for coalbed methane (CBM) recovery enhancement. To investigate the feasibility of enhanced CBM recovery by steam injection, infrared thermal imaging (ITI) and thermocouples were employed to study the heating efficiency of steam on three ranks of coal, and nuclear magnetic resonance (NMR) was applied to analyze water transport within the coal after steam treatment. The results showed that the internal temperature of the coal samples reached about 80 °C in 17 min of steam treatment and thermal cracking of coal were induced, hence steam injection could facilitate gas desorption and provide more channels for gas migration. NMR test results indicated that steam preferentially condensed in coal micropores due to the capillary condensation effect, hence steam might have the potential to displace methane. The T2 spectra of the coals after steam treatment exhibited only the first two peaks without the third peak, indicating that steam injection might not cause the water blocking effect. The outcomes of this study are expected to provide valuable insights into the field application of steam injection to enhance CBM production.

Influence of solid particles deposition on the initial atmospheric corrosion of 7B04 aluminum alloy

The influence of the deposition of three different particles (NaCl, C and SiO2) on the initial atmospheric corrosion of 7B04 aluminum alloy was investigated via laboratory exposure testing, environmental scanning electron microscope (E-SEM), energy dispersive X-ray spectroscopy (EDS), and scanning Kelvin probe (SKP). The results showed that the deposition of NaCl had a significant acceleration effect on the initial corrosion of 7B04 aluminum alloy and resulted in the occurrence of localized corrosion on sample surface. Because of its capillary condensation effect, SiO2 could absorb the vapor in humid environment to form a local water-rich area around the particles which could promote the corrosion of 7B04 aluminum alloy. C had basically no effect on the corrosion of 7B04 aluminum alloy.

Water vapor diffusion models in asphalt mortar considering adsorption and capillary condensation

Water vapor diffusion persistently and extensively existing in asphalt pavement is one of the important contributors to moisture-induced damage. Non-Fickian diffusion of water vapor in asphalt mortar has not been deeply understood due to the lack of quantitative characterization of water molecular transport in micropores affected by the adsorption and capillary condensation. The objective of this study is to establish diffusion models considering the effects of the adsorption and capillary condensation and quantitatively characterize the dependence of diffusion coefficient on the humidity and sample thickness. The diffusion characteristics of water vapor in asphalt mortar with various thicknesses under various humid conditions were investigated using a standard wet cup method. The results suggest that in the steady diffusion the measured mass loss of diffusive water vapor linearly increases with time. The apparent diffusion coefficients determined by the first Fick’s law demonstrate a nonlinear rapid reduction from 51.45×10–9 m2/s to 12.66×10–9 m2/s while the relative humidity varies from 22% to 95%. The diffusion coefficient nonlinearly decreases from 40.92×10–9 m2/s to 24.71×10–9 m2/s while the sample thickness increases from 3.62 mm to 16.34 mm. The molecular transports in gaseous flow, surface flow, and capillary condensate flow were introduced to formulate the effects of adsorption and capillary condensation. Combining the measured adsorption isotherm of water vapor in asphalt mortar, a diffusion model considering adsorption was derived and quantitatively characterizes the diffusion coefficients varying with the relative humidity. The dependence on relative humidity is attributed to the thickening of adsorbed water film in high humidity that changes the diffusivities in gaseous flow and surface flow. Another diffusion model considering capillary condensation was established to formulate the thickness-dependent diffusion coefficients in asphalt mortar. The dependence on the sample thickness is explained as the variable ratio of the diffusion in capillary condensate flow to the overall diffusion in a thick sample. This study provides a feasible approach to quantifying the environment-dependent diffusion characteristics and promotes the understanding of non-Fickian diffusion of water vapor in asphaltic materials.

Nanoporous Gold as a VOC Sensor, Based on Nanoscale Electrical Phenomena and Convolutional Neural Networks.

Volatile organic compounds (VOCs) are prevalent in daily life, from the lab environment to industrial applications, providing tremendous functionality but also posing significant health risk. Moreover, individual VOCs have individual risks associated with them, making classification and sensing of a broad range of VOCs important. This work details the application of electrochemically dealloyed nanoporous gold (NPG) as a VOC sensor through measurements of the complex electrical frequency response of NPG. By leveraging the effects of adsorption and capillary condensation on the electrical properties of NPG itself, classification and regression is possible. Due to the complex nonlinearities, classification and regression are done through the use of a convolutional neural network. This work also establishes key strategies for improving the performance of NPG, both in sensitivity and selectivity. This is achieved by tuning the electrochemical dealloying process through manipulations of the starting alloy and through functionalization with 1-dodecanethiol.

Solid polymer desiccants based on poly(acrylic acid-co-acrylamide) and Laponite RD: Adsorption isotherm and kinetics studies

This study investigates the potential application of superporous hydrogels (SPHs) and their composites with Laponite-RD (Lap-RD) for the adsorption of water vapors from humid air. Super-hydrogel composites (SPHCs) wee synthesized via gas blowing and foaming technique. Synthesized adsorbents were characterized using different techniques such as fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermos-gravimetric analysis (TGA). The incorporation of Lap-RD within the polymer matrix increased its thermal stability. Further, P(AA-co-AM) SPHs as well as SPHCs were used to adsorb water vapors from humid air. The adsorption of water vapors in both of these materials exhibited type-III isotherm with a maximum adsorption capacity of 1.03 and 1.24 gw/gads for P(AA-co-AM) SPH and SPHC at 25 °C, respectively. Higher adsorption capacity of SPHC was due to the combined effects of capillary condensation and the presence of hydrophilic Lap-RD particles within the polymer matrix. Adsorption isotherm for both materials followed Guggenheim, Anderson and Boer (GAB) model which suggested that the main driving force for water vapors adsorption was capillary condensation. The adsorption capacity of both materials decreased with increasing temperature. Furthermore, the adsorption capacity for these materials was quite low in the relative humidity range of 20–50 % which increased abruptly with increasing the relative humidity above 50 %. The isosteric heat of water vapors adsorption for P(AA-co-AM) SPHs and SPHC were found to be in the range of 59−48 and 57−49 kJ/mol, respectively. Adsorption kinetics followed linear driving force model and the diffusion of water molecules followed non-Fickian type diffusion mechanism. Finally, the synthesized adsorbents showed very good reusable efficiency and used successfully for ten cycles of adsorption.

Adsorption isotherm and kinetics of water vapors on novel superporous hydrogel composites

Abstract A promising and highly efficient new solid desiccant material composted of superporous hydrogel (SPHs) of polyacrylamide (PAM) and AQSOA-Z02 zeolite was fabricated to capture water vapor from moist air. The synthesis method of PAM-SPHs involved the gas blowing and foaming technique which insured a uniform distribution of zeolite particles throughout the polymer matrix. The presence of three dimensional porous structure, interconnected macropores in SPHs and the highly hydrophilic functional groups of AQSOA-Z02 particles enabled the synthesized SPHs composite to exhibit excellent water vapor adsorption capacity. The introduction of AQSOA-Z02 zeolite in the polymer matrix increased the water vapor adsorption capacity from 0.77 gw/gads to 0.89 gw/gads. Both materials exhibited type-III isotherm and followed Frenkel-Halsey-Hill and Guggenheim, Anderson and Boer (GAB) adsorption isotherm models. The high adsorption capacity was attributed to the combined effects of capillary condensation in interconnected macropores and the attachment of water molecules to the hydrophilic functional groups present in the zeolite structure. The water vapor adsorption capacity was found to decrease with increasing temperature. Adsorption kinetics studies suggested that the water vapor adsorption followed first-order kinetics models and the mechanism of water molecules diffusion into the internal structure of SPHs was case-II type of diffusion mechanism.

Highly Sensitive and Discriminative Detection of BTEX in the Vapor Phase: A Film-Based Fluorescent Approach.

BTEX (benzene, toluene, ethylbenzene, o-xylene, m-xylene, and p-xylene) represents a group of volatile organic compounds (VOCs) and constitutes a great threat to human health. However, sensitive, selective, and speedy detection of them on-site and in the vapor phase remains a challenge for years. Herein, we report a film-based fluorescent approach and a conceptual sensor, which shows unprecedented sensitivity, speed, and reversibility to the aromatic hydrocarbons in the vapor phase. In the studies, pentiptycene was employed to produce a nonplanar perylene bisimide (PBI) derivative, P-PBI. The compound was further utilized to fabricate the film. The novelty of the design is the combination of capillary condensation and solvent effect, which is expected to enrich the analytes from vapor phase and shows outputs at the same time. Importantly, the film permits instant response (∼3 s) and real-time identification (<1 min) of benzene and toluene from other aromatic hydrocarbons. The experimental detection limits (DLs) of the six analytes are lower than 9.2, 2.7, 1.9, 0.2, 0.4, and 0.4 ppm, which with the exception of benzene, are significantly lower than the NIOSH recommended long-term exposure limits. More importantly, the film is photochemically stable, and more than 300 repetitive tests showed no observable bleaching. In addition, the sensing is fully reversible. The superior performance of the film device is in support of the assumption that the combination of capillary condensation and solvation effect would constitute an effective way to design high-performance fluorescent films, especially for challenging chemical inert and photoelectronically inactive VOCs.

Dropwise condensation on hydrophobic bumps and dimples

Surface topography plays an important role in promoting or suppressing localized condensation. In this work, we study the growth of water droplets on hydrophobic convex surface textures such as bumps and concave surface textures such as dimples with a millimeter scale radius of curvature. We analyze the spatio-temporal droplet size distribution under a supersaturation condition created by keeping the uniform surface temperature below the dew point and show its relationship with the sign and magnitude of the surface curvature. In particular, in contrast to the well-known capillary condensation effect, we report an unexpectedly less favorable condensation on smaller, millimeter-scale dimples where the capillary condensation effect is negligible. To explain these experimental results, we numerically calculated the diffusion flux of water vapor around the surface textures, showing that its magnitude is higher on bumps and lower on dimples compared to a flat surface. We envision that our understanding of millimetric surface topography can be applied to improve the energy efficiency of condensation in applications such as water harvesting, heating, ventilation, and air conditioning systems for buildings and transportation, heat exchangers, thermal desalination plants, and fuel processing systems.

Experimental study and isotherm models of water vapor adsorption in shale rocks

The understanding of water vapor adsorption and equilibrium in the low permeability matrix of gas shale is crucial for predicting and optimizing gas productivity in shale gas reservoirs. In this study, water vapor adsorption isotherms for gas shale samples from the Lower Silurian Longmaxi Formation in Southern China were measured gravimetrically at two temperatures (30 °C and 50 °C) under the relative humidity ranging from 11.1% to 97.0%, and four different isotherm models were used to fit the experimental data and to analyze water vapor adsorption on shale rocks. The experimental results showed that water vapor adsorption for shale rocks followed a typeⅡsigmoid shape over the humidity range. At the lower humidity range, the monolayer-multilayer adsorption was the dominant process while capillary condensation and temperature effects became significant with relative humidity increasing. As the amount of total organic carbon increases, water adsorption weakens while calcite has an inhibitory effect. Through quantifying the average relative error (ARE), coefficient of determination (R2) and chi-square (χ2) of the isotherm models relative to data, the GAB isotherm model was identified to be the best-fitting isotherm to describe the water adsorption process in shale rocks. Moreover, the FHH plot was used to analyze and distinguish the states of water retention by adsorption and capillary condensation.

Effect of capillary condensation on gas transport properties in porous media.

We investigate the effect of capillary condensation on gas diffusivity in porous media composed of randomly packed spheres with moderate wettability. To simulate capillary phenomena at the pore scale while retaining complex pore networks of the porous media, we employ density functional theory (DFT) for coarse-grained lattice gas models. The lattice DFT simulations reveal that capillary condensations preferentially occur at confined pores surrounded by solid walls, leading to the occlusion of narrow pores. Consequently, the characteristic lengths of the partially wet structures are larger than those of the corresponding dry structures with the same porosities. Subsequent gas diffusion simulations exploiting the mean-square displacement method indicate that while the effective diffusion coefficients significantly decrease in the presence of partially condensed liquids, they are larger than those in the dry structures with the same porosities. Moreover, we find that the ratio of the porosity to the tortuosity factor, which is a crucial parameter that determines an effective diffusion coefficient, can be reasonably related to the porosity even for the partially wet porous media.

Densimetry for the Quantification of Sorption Phenomena on Nonporous Media Near the Dew Point of Fluid Mixtures

Phase equilibria of fluid mixtures are important in numerous industrial applications and are, thus, a major focus of thermophysical property research. Improved data, particularly along the dew line, are needed to improve model predictions. Here we present experimental results utilizing highly accurate densimetry to quantify the effects of sorption and capillary condensation, which exert a distorting influence on measured properties near the dew line. We investigate the (pressure, density, temperature, composition) behaviour of binary (CH4 + C3H8) and (Ar + CO2) mixtures over the temperature range from (248.15 to 273.15) K starting at low pressures and increasing in pressure towards the dew point along isotherms. Three distinct regions are observed: (1) minor sorption effects in micropores at low pressures; (2) capillary condensation followed by wetting in macro-scale surface scratches beginning approximately 2% below the dew-point pressure; (3) bulk condensation. We hypothesize that the true dew point lies within the second region.

Wet CO2/N2 permeation through a crosslinked thermally rearranged poly(benzoxazole-co-imide) (XTR-PBOI) hollow fiber membrane module for CO2 capture

Recently developed crosslinked-thermally rearranged (XTR) polymeric membranes, which show enhanced gas separation, are applicable for CO2 separation from post-combustion gases. Moreover, the resulting thermally rearranged polybenzoxazole (TR-PBO) structure that is thermally induced from hydroxyl-polyimides (HPI) provides high thermal and chemical resistance, which is favorable for gas separation applications containing condensable gases such as water vapor. Herein, the influence of water vapor on the CO2 capture efficiency was evaluated using XTR poly(benzoxazole-co-imide) (XTR-PBOI) hollow fiber membrane modules which were compared with crosslinked HPI (XHPI) in mixture gas and single gases for CO2 and N2. The results revealed that the permeate CO2 flow rate in the hydrophobic XTR-PBOI module showed enhanced separation performance, whereas the flow rate severely decreased in the relatively hydrophilic XHPI module, reflecting more significant capillary condensation effect in the XHPI membranes. Both membrane modules showed excellent plasticization resistance, and the XTR-PBOI hollow fiber membrane module presented reasonable long-term stability over 240h.

Versatile Reducing Reaction Field within Layered Polysilane for Efficient One‐Pot Synthesis of Metal Nanoparticles

AbstractMetal nanoparticles (MNPs) have received a great deal of attention in both scientific and industrial fields because of their special characteristics originating in the nanostructure. Herein, we developed a new synthesis strategy for MNPs based on the utilization of layered polysilane (Si6H6). The special arrangements of layers in this material allows the formation of an interlayer space with both suitable dimensions and surface chemistry characteristics for reducing metal ions to MNPs in a simple and efficient manner. The interlayer space assimilates a metal ion by a capillary condensation effect. These metal ions are subsequently reduced by the hydrosilyl groups on layered polysilane, thereby forming MNPs within the interlayer space. The synthesis strategies for MNPs presented in this paper can be utilized as a method for recovering and absorbing noble or toxic metal elements.

Effect of capillary condensation on gas transport properties in porous materials

Effect of capillary condensation on gas transport properties in porous materials

The effect of capillary condensation on the phase behavior of hydrocarbon mixtures in the organic nanopores

ABSTRACTIn nanoscale pores, the adsorption of gas is a multilayer adsorption process, and the conventional Langmuir model is no longer valid. In particular for the unconventional gas condensate reservoir, the adsorbed gas will become condensate once the pressure is above the critical condensate pressure at pore scale. In this study, considering the effect of adsorption (wetting) film, the multicomponent Kelvin equation is modified to computing the isotherm of capillary condensation. Then it is coupled with the multispace adsorption model and Peng-Robinson equation of state to investigate and represent the phase behavior of hydrocarbons in organic nanopores. Then, a prediction process for the behavior of a four-component mixture of methane, n-butane, n-pentane, n-hexane are performed. The actual Marcellus shale gas is also used to examine the performance of this model.

Effect of Capillary Condensation on Gas Transport in Shale: A Pore-Scale Model Study

SummaryThe condensation of the gas inside nanopores at pressures lower than the dewpoint pressure, or capillary condensation, is an important physical phenomenon affecting the gas flow/transport process in shale. This work investigates the underlying transport mechanism and governing factors for the gas transport at a pore scale associated with capillary condensation. We numerically simulate and compare the gas-transport process within pores for two cases, with and without capillary condensation, while Knudsen diffusion, wall slippage, and phase transition are included in the numerical model. In each case, the simulations are performed for two pore geometries corresponding to a single pore and two parallel-connected pores. The main objective is to determine whether capillary condensation blocks or enhances gas transport during production. The results show that the presence of the liquid phase in the pore throat initially enhances the gas flow rate to the outlet of the pore, but significantly reduces it later. This blockage depends on pore geometry and the properties of the oil and gas phases. The relatively low mobility of the condensed liquid in the pore throat is the main factor that reduces the mass transport along the pore. The reduction of overall mass transport in a single pore is more significant than that for the parallel pore geometry. Implications of this work for predicting large-scale gas transport in shale are also discussed.

Control of optical transport parameters of ‘porous medium – supercritical fluid’ systems

The possibility of controlling optical transport parameters (in particular, transport scattering coefficient) of porous systems based on polymer fibres, saturated with carbon dioxide in different phase states (gaseous, liquid and supercritical) has been experimentally studied. An increase in the pressure of the saturating medium leads to a rise of its refractive index and, correspondingly, the diffuse-transmission coefficient of the system due to the decrease in the transport scattering coefficient. It is shown that, in the case of subcritical saturating carbon dioxide, the small-angle diffuse transmission of probed porous layers at pressures close to the saturated vapour pressure is determined by the effect of capillary condensation in pores. The immersion effect in ‘porous medium –supercritical fluid’ systems, where the fluid pressure is used as a control parameter, is considered. The results of reconstructing the values of transport scattering coefficient of probed layers for different refractive indices of a saturating fluid are presented.