Pore Space Structure Research Articles

Removal of ammoniacal nitrogen from Malaysian palm oil mill effluent (POME) using optimized operating parameters of peat soil as natural adsorbent

Nowadays, the use of natural absorbents to remove pollutants from POME has gained remarkable attention. The main objective of this study is to investigate the suitability and performance of modified peat soil as an adsorbent for the removal of NH3-N from POME. The chemical activation method was performed using readily available NaOH for the first time to improve the adsorption performance of naturally available low-cost peat soil. The physical properties of raw and modified peat soil were determined using water-holding capacity, moisture content, bulk density, porosity, and BET surface area. The adsorbents were also characterized by SEM and FTIR to investigate surface morphology and chemical composition. To optimize the experimental parameters namely adsorbent dosage, agitation rate, and contact time for removal of NH3-N from POME, response surface methodology (RSM) was employed in this study with two different activation ratios. Substantial improvement of physical properties was attained after the modification of raw peat soil. The SEM images of modified peat soil showed a more porous space structure with larger voids while the FT-IR demonstrated the distinctive functional groups in the raw and modified peat soil. At optimized conditions of 5.71 g/L adsorbent dosage, 50 rpm agitation rate, and 38.96 min contact time predicted removal efficiency of NH3-N has been revealed 64.06 and 58.74 % at 1:20 and 1:30 activation ratios, respectively. The experimental investigation using optimized parameters showed 69.12 ± 2.5 and 61.57 ± 4.3 % removal of NH3-N. The experimental and predicted results showed good agreement. The rapid removal of NH3-N (69.1 % within 39 min) was achieved by chemically modified peat soil in this study compared to previously reported studies. Nevertheless, the raw and modified peat soil showed good stability up to three cycles of reusability.

Study on microscopic pores and permeability changes of coal frozen by liquid nitrogen based on CT scanning

ABSTRACT Liquid nitrogen freezing has a certain promoting effect on improving the permeability of coal samples. In order to study the quantitative changes in the pore structure and permeability of coal samples after liquid nitrogen freezing, this paper carried out a three-dimensional reconstruction of the pore space structure of coal samples based on CT scanning experiments, and based on this, the porosity, connected pore volume, the equivalent pore radius, pore coordination number and permeability were studied based on the reconstruction model. The results show that the porosity of the coal samples in group B is 42.02% higher than that in group A after freezing with liquid nitrogen, the average value of the total connected pore volume, pore equivalent radius and coordination number of coal samples in group B are greater than those in group A, and they have increased by 16.5%, 2.95% and 14.8% respectively; the permeability in group B is 26.86% higher than that of group A, indicating that the pore connectivity and permeability of the coal samples in the liquid nitrogen freezing group have been significantly improved.

Regulating Catalytic Oxidation Enantiomers Behavior by Imparting Chiral Microenvironment in Zr-Based Metal-Organic Frameworks.

Chiral inversions of enantiomers have significantly different biological activities, so it is important to develop simple and effective methods to efficiently identify optically pure compounds. Inspired by enzyme catalysis, the construction of chiral microenvironments resembling enzyme pockets in the pore space structure of metal-organic frameworks (MOFs) to achieve asymmetric enantioselective recognition and catalysis has become a new research hotspot. Here, a super-stable porphyrin-containing material PCN-224 is constructed by solvothermal method and a chiral microenvironment around the existing catalytic site of the material is created by post-synthesis modifications of the histidine (His) enantiomers. Experimental and theoretical calculations results show that the modulation of chiral ligands around Zr oxide clusters produces different spatial site resistances, which can greatly affect the adsorption and catalytic level of the enantiomeric molecules of tryptophan guests, resulting in a good enantioselective property of the material. It provides new ideas and possibilities for future chiral recognition and asymmetric catalysis.

TECHNOLOGICAL COMPLICATIONS (FORMATION DAMAGE) DURING CO2 INJECTION FOR ENHANCED OIL RECOVERY. Part 1. GEOCHEMICAL PROCESSES INVOLVING ROCK MINERALS, CHANGE OF PETROPHYSICAL AND GEOMECHANICAL ROCK PROPERTIES

Decrease in permeability, porosity, change in wettability of oil-bearing formations during field development are defined by a general term - formation damage, which occur at various stages of field development, including drilling, production, application of enhanced oil recovery methods, well stimulation technologies with acid compositions, hydraulic fracturing and well workover. Reservoir damage leads to a reduction in the oil and gas content of reservoirs and in the economic efficiency of operation. In this regard, it is important to understand and prevent formation damage based on experimental and analytical methods, the applicationof which will minimize damage to the oil and gas bearing reservoir. The review considers anthropogenic processes that cause damage to oil and gas reservoir when CO2 is injected by various methods to enhance oil recovery. The processes of interaction of CO2 with formation rock are considered in detail. The main geochemical transformations of rock minerals are given, which lead to changes in the structure of pore space, permeability and porosity, decrease of geomechanical properties. Secondary sedimentation processes and risks of rock particles removal into the borehole are discussed.

Multiscale modeling of reactive flow in heterogeneous porous microstructures

This paper presents a multiscale reactive flow model to simulate in-situ leaching of copper in heterogeneous porous microstructures. The introduced workflow combines fluid flow simulation with advection-diffusion-reaction simulation, both required to model reactive flow. The proposed workflow can include the fluid flow in resolved and unresolved pore structures and utilizes required parameters from molecular simulation (ionic diffusivity) and reaction databases (reaction rate parameters). The modeling approach is validated by comparing results to other open-source codes for a model calcite dissolution on acid injection. This model is applied to copper mining by leaching to analyze the reactive flow through a fractured digital rock model of a subsurface sample. Results are analyzed by tracking the concentration distribution along the pore space structure and calculating the outlet concentration of copper to conform the leaching path. Several sensitivity studies are performed to show the robustness of the modeling framework as well as to investigate the importance of each of these parameters on copper production. The complexity of the model is systematically increased from a single scale surface reaction model, to consider the influence of competitive bulk solution reactions, and finally to include flow through porous media to model multiscale reactive flow. This study shows that a multi-scale flow model with homogeneous bulk and heterogeneous surface reactions is required to accurately model copper leaching.

Influence of Reservoir Microstructure on the State of Residual Oil According to Nuclear Magnetic Resonance (NMR) Spectroscopy

The influence of core properties on the state of residual oil in the process of oil displacement by water at the micro level is investigated. The pore size distribution, core permeability, dynamics and morphology of residual oil were studied. The analysis of the available experimental approaches to the study of the properties of the core and residual oil in the core samples showed that the existing methods do not provide complete information about the studied parameters. To solve these problems, it is proposed to use a combination of innovative relaxation-diffusion spectroscopy technology of nuclear magnetic resonance with traditional technology. A combination of mercury injection and nuclear magnetic resonance is used to measure the pore size distribution. The core permeability was determined using the nuclear magnetic resonance method. Two-dimensional nuclear magnetic resonance spectroscopy makes it possible to study the microscopic state of residual oil in an undisturbed core during the displacement process. With the help of the proposed methodology, a core study of the Shengli deposit in China was carried out. Pore size distributions were obtained, permeability and residual oil saturation at different stages of displacement were studied. Four types of residual oil are distinguished: strip-shaped (island), film, mesh, continuous. The influence of permeability on the fraction content of different types of residual oil in the process of displacement is shown. The research results demonstrate the influence of the pore space structure and wettability on the state of residual oil.

Predicting carbonate rock dissolution using multi-scale residual neural networks with prior knowledge

The factors that affect carbonate dissolution are complex, and it is crucial to acquire efficient and accurate knowledge of carbonate dissolution characteristics for CO2 capture and storage (CCS) projects. In current research, the most precise outcomes can be achieved through experimental or simulation techniques, but they are frequently computationally demanding and time-consuming. Data-driven machine learning methods can efficiently perform regression prediction tasks. In this paper, we propose a multi-scale hierarchical regression model for the dissolution problem based on residual neural networks, incorporating prior knowledge. We have developed new equations for carbonate rock dissolution and have incorporated the factors that influence this process into 3D image data by introducing Dissolution Degree (Dd) parameters. This allows the image data to include both the pore space structure and dissolution information with physical meaning. We utilize the pore phase and matrix phase grayscale thresholds (Pt, Mt) to eliminate voxel noise in the characteristic maps obtained from the model. This ensures that the predicted characteristics of carbonate rock dissolution are consistent with practical physics knowledge. We selected a total of 5 core samples to test the model. Among them, three samples are from the test set, and the additional two core samples selected have strong and weak correlations with the training set samples, respectively. The predictions were evaluated using semantic segmentation evaluation parameters, porosity, geometrical and topological structure parameters, Péclet and Damköhler numbers, porous media flow field simulations, and absolute permeability. The results of both visual comparisons and quantitative analyses demonstrated a high degree of consistency between predicted and experimental results, and the trained multi-scale hierarchical regression residual neural network with prior knowledge (MSR-Net) demonstrates good accuracy and generalization ability. The results of this study demonstrate that model based on MSR-Net can be utilized to predict the dissolution properties of the pore space in the formation where the core was extracted, along with the related formation.

Freeze-thaw effects on pore space and hydraulic properties of compacted soil and potential consequences with climate change

Freezing and thawing affect the pore-space structure in agricultural soils with implications for soil hydraulic properties and water flow. Previous studies have focused on the upper few centimeters of the tilled topsoil, where most freeze-thaw (FT) cycles occur, even though deeper soil layers are also subject to freezing and thawing in cold climates. Thus, little is known about how freezing and thawing affect untilled soil layers, which often show high bulk densities that restrict vertical water movement. Furthermore, it remains unclear how shifts in FT patterns with climate change may change the pore-space structure and water flow through these soil layers. Here we investigated the effects of freezing and thawing on X-ray imaged pore-space characteristics, water retention and near-saturated hydraulic conductivity (K) in untilled soil directly below plough depth. Intact cores were sampled at two sites in central Sweden under the same long-term reduced tillage management. The two soils, a silt loam and a silty clay loam, were subjected to three FT scenarios in a laboratory environment intended to represent FT patterns that are considered likely under current and future winter conditions for this region. The latter scenario was characterised by more FT cycles and a lower freezing temperature. Freezing and thawing increased K in the near-saturated range in both soils, which we attribute to observed small (<0.01 mm3 mm−3) increases in the volume of pores of diameters close to the X-ray resolution limit. Concomitant increases in pore network connectivity and critical pore diameter, especially in the denser silty clay loam soil, probably contributed to this increase in K. The water retention data suggested that changes in pore-space characteristics below X-ray resolution also occurred in both soils. Furthermore, our results indicate that both soils may show higher drainage rates due to shifts in FT patterns in the future, although longer-term changes in pore-space structure with an increasing number of FT cycles would mostly be limited to soils with relatively high clay contents. These soils are often more compacted below plough depth and, thus, benefits from improvements in soil structure such as improved root growth and plant water supply are also expected to be larger.

Study of structural characteristics of hydrocarbon reservoir pore space based on X-ray computed tomography images

Digital studies of pore space and internal structure of hydrocarbon reservoir were conducted on the basis of multiscale X-ray computed tomography images and the analysis of heterogeneities, cavernosity, fracturing and bedding in the rock. Main results. 3D models of rock pore space were created on the basis of computed tomography images through segmentation. Porosity estimation based on the digital approach was performed. It was shown that the digitally obtained data are in good agreement with the results of laboratory measurements. Analysis and visualization of the structure of the main filtration channels in the rock were performed. Pore size distributions in the specimen were obtained, and 3D visualization of the largest pore size was shown. Conclusions. The pore space characteristics obtained on the basis of tomographic approach are valuable data for filling reservoir models and can be used in solving the problems of permeability reduction during different kinds of reservoir impacts. Application of the obtained results in combination with geomechanical tests of rocks is intended to expand existing approaches to complex analysis of core material of reservoirs, as well as to supplement and refine mathematical and operational models of the studied objects.

Dependence of pore space structure and characteristics of SiC-based ceramic materials on the morphology of the initial components

Ultrafine silicon carbide powders of two types were used as fillers for synthesis of porous ceramics. The first powder was obtained by the furnace method (SiCF), the second sample was synthesized using the SHS technology (SiCSHS). The fillers had identical average particle size, but different morphology of their surface. It is established that with the same size, the morphology of initial powder components determined structural parameters and characteristics of the synthesized porous ceramics. It determines effective applicability of various materials for ultrafiltration or catalysis processes.

Цеолитовая минерализация пород-коллекторов севера Западной Сибири: литолого-геофизические аспекты и особенности разработки

As the hydrocarbon production tends to decline, formations with a complex geological structure and various secondary mineral formation types of reservoir rocks gain a considerable attention. The importance of secondary minerals for formation of pore and void space structure in hydrocarbon reservoirs is extremely high. The physical and chemical properties of these minerals should be considered during exploration works, calculation of reserves, reservoir engineering, wellwork planning. This article highlights the methodological study approach of mountain rocks with zeolitization based on the results of modern lithological, analytical, and laboratory research. The implementation of the approach allowed for recommendations for rapid quantitative assessment of zeolite content in the Lower Cretaceous sediments of the Bolshekhetskaya Depression.

FILTRATION EQUATIONS FOR PORE AND CAPILLARY SYSTEM TAKING INTO ACCOUNT PRESSURE DIFFUSION

Biological media are characterized by a complex system of pores and capillaries, the interaction between which leads to features in the transport of biological fluids. At low flow velocities, the mutual influence of convection and diffusion becomes important, as well as the influence of pressure gradient on diffusion. To take into account the complex structure of porous space, models of fractured porous media, models of media with double and triple porosity, are known in the literature. In this paper, we propose a model of a medium with double porosity in which, in addition to diffusion and filtration, barodiffusion is taken into account. Definitive relations follow from thermodynamics of irreversible processes. We consider particular versions of the equations: for a medium with predominant convection in both pore systems; for media with predominantly diffusion transport mechanism, typical for nanoporous materials; and for a medium in which convection prevails in one pore system and diffusion in the second.

Rate-Controlled Mercury Injection Experiments to Characterize Pore Space Geometry of Berea Sandstone

Interpretation of the relationship between heterogeneity and the flow in porous media is very important in increasing the recovery factor for an oil or gas reservoir. Capillarity for instance, controls fluids static distribution in a reservoir prior to production and remaining hydrocarbons after production commences. Therefore, capillary pressure data are used by petroleum engineers, geologists, and petrophysicists to evaluate production characteristics of petroleum accumulations. Conventional pressure-controlled mercury porosimetry produces an overall capillary pressure curve and pore throat size distribution data that provide little information about the porous medium structure and pore geometry. The present study provides information on three capillary pressure curves obtained from rate-controlled mercury injection porosimetry; one describes the larger pore spaces or pore bodies of a rock, another describes the smaller pores or pore throats that connect the larger pores, and a final curve which corresponds to the overall capillary pressure curve obtained from the conventional pressure-controlled mercury injection. An experimental constant-rate mercury injection apparatus was constructed that consists of a piston displacement pump, a computer controlled stepper motor drive and a core sample cell designed to minimize dead volume. The apparatus was placed in a glass chamber and subjected to an air bath to maintain a constant temperature of 27o C throughout the experiments. Then constant rate mercury injection experiments were performed on three Berea Sandstone core plugs. Results show that volume-controlled or rate-controlled porosimetry provides considerably more detailed data and information on heterogeneity and the statistical nature of pore space structure than the conventional pressure-controlled porosimetry as pressure fluctuations with time reveal menisci locations in pore bodies and pore throats. Moreover, pore size distributions based on volume-accessed pores and pore radii were obtained from the pressure versus saturation relationship.

STUDY ON THE EVOLUTION LAW OF PORE STRUCTURE AND MECHANICAL PROPERTIES OF MUDSTONE UNDER THE EFFECT OF WATER-ROCK CHEMISTRY

The influence of different pH and concentration of water chemical solutions on the mechanical properties of mudstone is studied. The triaxial compression test and nuclear magnetic resonance (NMR) test of mudstone are carried out, and the root cause of the deterioration of mechanical properties of mudstone during the hydration damage process is explored, combining macroscopic and microscopic. The results show that hydrolysis and chemical ion exchange are responsible for the deterioration of mudstone shear strength parameters. The essence of mudstone hydration damage is that water chemistry changes the original pore space structure and pore size distribution inside. Part of the minerals dissolve and fall off under the influence of the water chemical solution, which expands the pore size and increases the porosity. The connection force between mineral particles decreases, macroscopically, the mudstone undergoes a softening evolution from brittleness to ductility, and the shear strength parameters deteriorate. The results show that mudstone is more sensitive to acidic solution than neutral and alkaline solution. The higher the pH of the alkaline solution or the higher the concentration of the neutral solution, the more significant the deterioration of mudstone. Under the influence of hydrochemical solution, the fractal dimension of mudstone gradually tends to 2 from 3, which indicates that the process of hydration damage reduces the complexity of mudstone pore structure. On this basis, the damage variable D&lt;sub&gt;n&lt;/sub&gt; defined based on the change of porosity before and after hydration damage of mudstone, to a certain extent, quantitatively reflects the law of mudstone shear strength parameters accompanied by microscopic pore structure evolution. The shear strength parameters of mudstone decrease significantly with the increase of damage variable D&lt;sub&gt;n&lt;/sub&gt;. The test analyzes the root cause of the deterioration of the macroscopic mechanical properties of mudstone during the hydration damage process from a microscopic point of view, and the conclusions obtained provide a good reference for the quantitative study of the effect of water chemistry on the mechanical properties of mudstone.

Predicting the permeability of the near-bottomhole zone during wave impact

The research reveals that during selection of a method to increase oil recovery it is necessary to take into account rheological features of fluid movement through the formation, effect of capillary forces and heterogeneity of reservoir properties of the productive formation in thickness and along the bedding. Low-frequency wave impact, which is used to increase production in oil fields, is considered. At low-frequency impact new fractures appear and existing fractures in rocks increase in size. The greatest increase in porosity and permeability of rocks occurs at an impact frequency up to 10 Hz. Dynamics of oscillation amplitude during wave's movement in saturated porous medium is studied in the paper: essential attenuation of amplitude occurs at distance up to 1 m from borehole axis. With increase of frequency from 1 to 10 Hz the intensity of amplitude's attenuation decreases. The technology was tested on a well in Perm region (Russia). The actual permeability value was 50 % higher than the predicted value. According to the results of hydrodynamic investigations processing, it was noted that the greatest increase of permeability took place near the wellbore, while away from the wellbore axis permeability remained almost unchanged. In order to refine the mathematical model for prediction of wave impact on rock permeability it is necessary to take into account interconnection of pore space structure, change of adhesion layer, as well as to study transfer of particles during vibration.

Pore-scale modeling of seepage behaviors and permeability evolution in heterogeneous hydrate-bearing sediments and its implications for the permeability model

Permeability is one of the key factors determining the recovery of gas resources from natural gas hydrate (NGH) reservoirs. The heterogeneous distribution of hydrates induced by random nucleation and growth in the pore space of hydrate-bearing sediments (HBS) inevitably results in pore space structure change, thereby significantly affecting fluid flow and permeability. In this paper, the seepage behaviors in a series of two-dimensional (2D) idealized HBS models were simulated based on the pore-scale computational fluid dynamics (CFD) modeling to obtain permeability and pore-scale seepage field. The 2D hydrate heterogeneity degree coefficient (DH) was proposed to quantitatively characterize the hydrate distribution heterogeneity. The pore-throat evolution characteristics were quantified by average pore-throat size and pore-throat size distribution. The results show that the occurrence and growth of hydrates within pores lead to the reconstruction and evolution of pore space structure and the formation of new fluid migration channels. The main reason for the reduction of HBS permeability is that with the increase of hydrate saturation, pores and throats with small sizes gradually become dominant, pore space connectivity is weakened, and the tortuosity for fluid flow increases. Additionally, the evolution of flow path and flow channel morphology caused by the growth of hydrates with different pore habits leads to the difference in pore-scale seepage behaviors and permeability variations in the homogeneous model. However, the effect of hydrate pore habits on permeability is no longer obvious due to the spatial heterogeneity of sediment grains and gas hydrates in the heterogeneous model. The effective flow path for pore fluid controlled by overall hydrate distribution and pore-throat characteristics would be critical. The comparison of calculated permeability results reveals that the accuracy of reported permeability reduction models is limited due to the ignorance of the HBS heterogeneity, the actual hydrate pore habits and morphology, and the pore structure geometry. It is hoped that the findings of this study can provide some insights into the pore-scale seepage characteristics of HBS, providing important implications for the development of the permeability model that can be easily implemented in the numerical simulators for field-scale gas production optimization of hydrate reservoir.

Factoring Permeability Anisotropy in Complex Carbonate Reservoirs in Selecting an Optimum Field Development Strategy

Current methods of oil and gas field development design rely on reservoir simulation modeling. A reservoir simulation model is a tool to reproduce field development processes and forecast production data. Reservoir permeability is one of the basic properties that determines fluid flow. From existing approaches, the porosity and permeability values should be consistent with petrophysical correlations obtained from core sample tests in the course of development of an absolute permeability cube in the reservoir simulation model. For carbonate reservoirs with complex pore space structure and fractures, the petrophysical correlations are often unstable. To factor in the fluid flow in a fractured rock system, dual-medium models are developed, allowing for matrix and fracture components. Yet in this case, the degree of uncertainty only increases with the introduction of a new parameter: a cross-flow index of fluid migration from matrix to fracture, which is only determined indirectly by results of fluid flow studies conducted in the initial development period, and therefore most often is adaptive. Clearly, for well-studied fields there is an extensive data pool drawn on research findings: core studies, well logging, well flow testing, flowmetry, special well-logging methods (FMI, Sonic Scanner, etc.); the dual-medium model development for such reservoirs is fairly well-founded and supported by actual studies. However, at the start of the field development, the data are incomplete, which renders qualitative dual-medium modeling impossible. This paper proposes an approach to factor in the target’s permeability anisotropy at an early development stage through the integration of well, core and 3D seismic surveys. The reservoir was classified into pore space types, to which different petrophysical correlations were assigned to develop a permeability array, and relative phase permeabilities were studied. The fluid flow model was history-matched with allowance for permeability anisotropy and rock types. Comparative calculations were conducted on the resulting model to select the optimum development strategy for the target.

Evolution Law of Micro-Pore Structure of Cement-Emulsified Asphalt Mortar Based on NMR

Cement emulsified asphalt mortar (CA) is widely used as the cushion of two types of ballastless track (CRTS I and CRTS II) in high-speed railways. Nowadays, the lack of durability of CA mortar has severely affected the quality of high-speed railways, failing to meet the requirements of sustainability. Since CA mortar is a kind of porous material, its performance can be significantly affected by its microstructures, which means that revealing the evolution law of its microstructures can provide the basis for improving its durability. Therefore, CA mortar species with different asphalt-cement ratio under different curing ages were prepared based on the requirements of CRTS II in this research and the pore structures were determined based on SEM and NMR methods. Then, a fractal model of CA mortar pore volume was proposed based on the concept of box fractal dimension, and the fractal dimension of pore volume was calculated. The relationship between fractal dimensions and mechanical property was analyzed based on Pearson correlation coefficient and regression analysis. The results suggested that the overall microstructure of CA mortar shows a loose porous space structure with cement hydration products being the continuous phase and asphalt being the dispersed phase. With the increase in A/C ratio, the hydration products produced by cement hydration decrease, and the total porosity and average porosity of CA mortar gradually increase due to the increase of asphalt hindering the hydration process of the cement. With the increase in curing age, the pore structure of CA mortar becomes more compact. However, the evolution law of CA mortar pore structure with age is not consistent under different A/C ratios due to the influence of asphalt. The pore structure of CA mortar was proved to have obvious fractal characteristics based on the concept of box fractal dimension and the experimental data of NMR. In addition, the correlation analysis proves that the fractal dimension of pore structure has an obvious positive correlation with the compressive and flexural strength, which suggests that the fractal dimension of pore volume can be a bridge for connecting the macro-property and micro-structures of CA mortar.

In-situ Electrochemical Diagnostics for Morphological Study of CO2 Reduction Electrodes

Electrochemical CO2 reduction (CO2R) devices have immense potential to capture the effluent CO2 in hard-to-decarbonize sectors and convert them to valuable chemicals like CO, C2H4, CH4, alcohols etc. Inside these devices, CO2R occurs inside gas diffusion electrodes (GDE). The reaction rate strongly depends on the local environment at the catalyst-electrolyte interface like ionomer binders, pH, electrolyte cations etc[1]. The transport of reactants and products to and from the catalyst-electrolyte interface depends on the pore-space structure of the GDE, which comprises mostly of micro and smaller mesopores. Ionomer binders used in these GDEs also affect the Faradaic efficiencies (FE) of the CO2R products. Moreover, experimental results indicate that the KOH fed as the anolyte in alkaline CO2 electrolyzers impact the performance of CO2R at the cathode [2]. At present, there is a lack of simple experimental methods in the literature to systematically study the local electrochemical environments present in real decices and identify critical limiting phenomena.We have developed a novel setup to study the morphological aspects of CO2 electrodes at the electrode level without the complexities due to water splitting at the anode. A stable reference electrode, an ion-exchange membrane, and the CO2R cathode are integrated together to form a membrane electrode assembly (MEA) for the purpose of precise and reproducible electrochemical experimentation. AC impedance spectroscopy (EIS) is used to measure capacitance and ion-transport resistance of the CO2R electrodes. A novel MEA setup, previously developed in this group to study oxygen mass transport resistance (MTR) in non-Platinum group metal fuel cells electrodes, is used to measure MTR of CO2 in the CO2R electrodes [3]. We vary the experimental conditions used in the CO2R experiments, like feed gas RH, KOH flow rate etc., and measure the above-mentioned properties. In addition, we also used these diagnostic methods to study the role of ionomer, specifically the ionomer-catalyst interaction in these electrodes. Experiments done by our group members indicate that a suitable electrode ink recipe (catalyst and ionomer loading, organic solvent etc.) is required to optimize the performance of CO2R inside these electrodes. Overall, these techniques can be used to understand the CO2R trends of various electrodes and to identify key design parameters for more efficient CO2 reduction electrodes.Important references: Bui et al., Engineering Catalyst–Electrolyte Microenvironments to Optimize the Activity and Selectivity for the Electrochemical Reduction of CO2 on Cu and Ag; Acc. Chem. Res. 2022, 55, 484−494.Dinh et al., CO2 electroreduction to ethylene via hydroxide-mediated copper catalysis at an abrupt interface; Science, (2018), 783-787, 360(6390).Star et a., Mass transport characterization of platinum group metal-free polymer electrolyte fuel cell electrodes using a differential cell with an integrated electrochemical sensor; Journal of Power Sources, (2020), 227655, 450.

Non-Darcy flows in layered porous media (LPMs) with contrasting pore space structures

Compared to single layer porous media, fluid flow through layered porous media (LPMs) with contrasting pore space structures is more complex. This study constructed three-dimensional (3-D) pore-scale LPMs with different grain size ratios of 1.20, 1.47, and 1.76. The flow behavior in the constructed LPMs and single layer porous media was numerically investigated. A total of 178 numerical experimental data were collected in LPMs and single layer porous media. In all cases, two different flow regimes (i.e., Darcy and Non-Darcy) were observed. The influence of the interface of layers on Non-Darcy flow behavior in LPMs was analyzed based pore-scale flow data. It was found that the available correlations based on single layer porous media fail to predict the flow behavior in LPMs, especially for LPM with large grain size ratio. The effective permeability, which incorporated the influence of the interface is more accurate than the Kozeny-Carman equation for estimating the Darcy permeability of LPMs. The inertial pressure loss in LPMs, which determines the onset of the Non-Darcy flow, was underestimated when using a power law expression of mean grain size. The constant B, an empirical value in the classical Ergun equation, typically equals 1.75. The inertial pressure loss in LPMs can be significantly different from it in single lager porous media. For Non-Darcy flow in LPMs, it is necessary to consider a modified larger constant B to improve the accuracy of the Ergun empirical equation.