Porous Network Research Articles

Synergistic Electrocatalyst-Cathode Architecture for Stable Long-Term Cycling Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are a promising candidate for next-generation energy storage owing to the high theoretical capacity of sulfur (1,675 mAh g−1). However, the intrinsically low electrical conductivity of sulfur and complex multistep electrolyte-mediated redox reactions involving soluble lithium polysulfide intermediates engender critical challenges toward practical realization. Specifically, migration and diffusion of higher-order lithium polysulfides provokes continuous loss of active sulfur species, yielding premature capacity fade. Electrochemical kinetics also remain sluggish due to the insulating nature of sulfur cathodes, which require engineering designs to accelerate charge transfer.Rational morphological and compositional cathode tuning represents a compelling strategy for addressing fundamental Li-S limitations. Herein, we develop an extended cathode architecture composed of a porous carbon nanotube network decorated with homogenously dispersed nanocatalysts. Electron microscopy and spectroscopy analysis verify platinum group metals are well-incorporated both within internal channels and external surface sites of conductive carbon nanotubes. The composite framework affords multifaceted functionality arising from synergistic chemical and structural attributes of components. Nanocatalyst sites demonstrate a pronounced chemical affinity toward soluble polysulfide intermediates, effectively localizing them within cathode, minimizing diffusional losses toward the anode. This anchoring phenomenon is complemented by the inherent microporosity of the high-surface-area nanotube network, further obstructing polysulfide migration through a confinement effects. Concurrently, noble metal nanoparticles facilitate the redox conversion of trapped higher-order polysulfides into solid Li2S alleviating the precipitation of electrically insulating discharge products. The excellent electrical conductivity of CNTs ensures efficient charge transport to all incorporated sulfur active materials, further maximizing reversible utilization.As a result of complementary polysulfide confinement and electrocatalytic conversion functionalities, Li-S coin cells exhibit enhanced reversible capacities exceeding 900 mAh g−1 for over 500 cycles at 0.558 A g−1. Notably, over 500 cycles, minimal capacity decay of 0.018% per cycle and 92% retention of the initial capacity are obtained at moderate sulfur loadings highlighting the exceptional cycling stability enabled by engineered cathodes. Outstanding rate performance is also demonstrated with the delivery of 854 mAh g−1 capacity at a very high current density of 1.675 A g−1. Our rationally designed cathode architecture provides critical mechanistic insight toward addressing fundamental bottlenecks to progress Li-S technologies.

Molecularly Imprinted Polymer Modified Laser-Engraved Graphene Electrode for the Ultra-Sensitive and Specific Detection of Ascorbic Acid

Sensitive and accurate detection of small molecule targets is critical for a variety of applications, including environmental monitoring, food safety and medical diagnostics. Electrochemical sensors with the advantages of high sensitivity, accuracy, convenience and low-cost make them well suited for these applications. Moreover, the combination of electrochemical sensors with micro-and nanofabrication technology offers the possibility of integrated and intelligent sensing systems.Figure 1. (a) The SEM characterization of PPD/LEG electrode, (b) the FT-IR of LEG and PPD/LEG electrode, (c) the Nyquist plots of LEG and PPD/LEG electrode, (d) the specificity, (e) linear relationship and (f) sensitivity of integrated electrochemical microsensor.In general, the ultimate performance of an electrochemical sensor relies on the high efficiency of bio/chemical reactions as well as transport of the analytes by diffusion onto the electrode. Accordingly, the desired electrode materials should permit very fast mass transport rates and possess the capability of specific capture of target analytes. Laser-etched graphene (LEG) electrodes featured with the advantages of porous three-dimensional network structure, large specific surface area, and high conductivity, are considered as an ideal sensing element for sensitive molecules detection, but cannot recognize specific targets. Molecularly imprinted polymers (MIPs) are low-cost and easy to modify on electrochemical sensing surfaces. It can be used to form molecular recognition sites by synthesizing target templates in polymers, giving the modified electrodes the ability to specifically recognize target molecules, which is an ideal modification material for electrochemical sensor platforms.Herein, we propose an integrated electrochemical microsensor sensing ultra-low concentration of ascorbic acid (AA) molecules by using MIP modified LEG as electrode material. The main characteristics of the detection system are as follows: 1) LEG electrode enables electrochemical sensing strategy with simple preparation and high sensitivity, 2) MIP poly-o-phenylenediamine (PPD) membrane on the surface of graphene provides the desirable property for highly selective AA molecular recognition, 3) the integrated PPD/LEG electrode allows to detect AA molecules in a ultra-low concentration range which is superior than that of other electrochemical detection techniques.The surface morphology of PPD/LEG electrode is characterized by using scanning electron microscopy (SEM, shown in Figure 1a), from which LEG shows three-dimensional network porous structure and the nature of graphene. In addition, the electropolymerized PPD membrane exhibits a rough and porous surface which would provide the large surface area for the adsorption of target AA molecules at the modified electrode. The formation of PPD/LEG electrode is further examined by Fourier Transform Infrared Spectroscopy (FT-IR Spectrometer) in Figure 1b. The polymerization of PPD membrane on the surface of the LEG electrode is confirmed by the appearance of two absorption peaks at 3385 cm-1 and 3360 cm-1, which are related to the stretching vibration of the -NH2 from the PPD. As shown in the Nyquist plots (Figure 1c), the semicircle in the high-frequency region is described as an intrinsic electron-transfer resistance in the electrode materials. The identical semicircles at high-frequency region of two electrodes indicate nearly equal electron transfer resistance (Rct) of LEG and PPD/LEG. The low-frequency region of the Nyquist plot is described as surface diffusion control, and the increase in the linear slope represents an enhanced surface diffusion control process at the electrodes demonstrating the lower impedance of the PPD/LEG electrode. Figure 1d verifies the specific recognition of AA molecules by the PPD/LEG electrode in PBS mixed with 1 mM of AA, dopamine (DA), uric acid (UA) and acetaminophen (AP) molecules. It can be seen that compared with the LEG electrode, the DPV response of the PPD/LEG electrode to DA, UA and AP molecules is significantly reduced, while the response to AA molecules is significantly enhanced. Furthermore, the ability of the integrated electrochemical microsensor to detect ultra-low concentrations of AA molecules in the 10 nM to 100 nM range is shown in Figure 1e, with a LOD of 2 nM (Figure 1f).In conclusion, we present an integrated electrochemical microsensor that can specifically detect AA molecules with ultra-high sensitivity. The LEG electrode with the modification of PPD membrane can effectively realize the specific recognition and accurate detection of AA molecules in mixed solutions. This integrated electrochemical sensing method is expected to be applied to the selective detection of multiple small molecule targets in complex environments.Key words: Laser-engraved Graphene Electrodes, Molecularly Imprinted Polymers, Integrated Electrochemical Microsensor, Ultra Sensitivity Detection. Figure 1

(Digital Presentation) Multiscale Modeling of Two-Phase Transport in the Membrane Electrode Assembly of Polymer Electrolyte Membrane Fuel Cells: Effect of Relative Humidity and Temperature

Water management plays an important role in the performance and durability of polymer electrolyte membrane fuel cells (PEMFCs). Achieving enhanced water removal at high current density without membrane dehydration requires an optimal design of the membrane electrode assembly (MEA) and MEA-channel interaction depending on operating conditions. The analysis of two-phase transport is challenged by the wide range of pore sizes found in porous layer assemblies, varying from 1-100 nm in the catalyst layer (CL), 50-1000 nm in the microporous layer (MPL) and 10 µm in the gas diffusion layer (GDL), up to the millimeter-sized channel. In this work, a hybrid multiscale model is presented to describe two-phase transport and performance of a representative unit cell as a function of relative humidity (RH) and temperature [1-3]. A control volume (CV) decomposition is used to represent the multiscale pore space of the GDL, MPL and CL in terms of local effective transport properties (porosity, effective diffusivity, permeability, thermal/electrical conductivity and entry capillary pressure) [4]. The model incorporates a macroscopic continuum formulation for gas flow and species, energy, liquid-phase pressure, water dissolved in ionomer, and electronic and ionic potentials [5]. Liquid water transport is modeled by means of a multi-cluster invasion-percolation algorithm, which is coupled to the macroscopic continuum formulation by the phase-change source term of water (evaporation/condensation). Water clusters with a net condensation rate grow by invading the adjacent dry CV with the lowest entry capillary pressure, while clusters with a net evaporation rate shrink by drying the wet CV of the cluster with the lowest entry capillary pressure. An all-or-nothing invasion law is adopted for saturation in the GDL (one pore per CV), while a macroscopic description in terms of capillary pressure curve at the representative elementary volume scale (REV) is used for the MPL and the GDL (thousands to millions of pores per CV). An example of the saturation distribution in the cathode MEA is shown in Figure 1. Local saturation remains between 0.1-0.4 in REVs of the CL and the MPL, increasing up to 1 in macropores of the GDL. Water condenses preferentially under the ribs and transport by capillary action to the GDL/channel interface, where the water flow is released to the channel. The channel saturation remains low, around 0.1, due to the large gas flow velocity used in the differential cell.[1] P.A. García-Salaberri, Modeling diffusion and convection in thin porous transport layers using a composite continuum-network model: Application to gas diffusion layers in polymer electrolyte fuel cells, 167 (2021) 120824.[2] D. Zapardiel, P.A. García-Salaberri, Modeling the interplay between water capillary transport and species diffusion in gas diffusion layers of proton exchange fuel cells using a hybrid computational fluid dynamics formulation, J. Power Sources 520 (2022) 230735.[3] P.A. García-Salaberri, Effect of thickness and outlet area fraction of macroporous gas diffusion layers on oxygen transport resistance in water injection simulations, Transp. Porous Media 145 (2022) 413-440.[4] P.A. García-Salaberri, I.V. Zenyuk, A General-Purpose Tool for Modeling Multifunctional Thin Porous Media (POREnet): From Pore Network To Effective Property Tensors, Heliyon (2023), submitted.[5] P.A. García-Salaberri, A. Sánchez-Ramos, A numerical analysis of the effect of layer-scale and microscopic parameters of membrane electrode assembly in proton exchange fuel cells under two-phase conditions, J. Power Sources (2023), accepted. Figure 1. Saturation distribution in the cathode MEA of a PEMFC operated at 70 oC and RH=0.95 at high stoichiometric conditions. The current density is I=0.5 A cm-2.- Figure 1

(Invited) Engineering Porous Electrodes for Redox Flow Batteries – Leveraging Computational and Synthetic Platforms

Porous electrodes are critical components in redox flow batteries where they are responsible for multiple critical functions in the cell, such as providing surfaces for electrochemical reactions, an open structure for fluid flow and mass transport, and the conductive scaffold for electronic and thermal conduction. However, our current portfolio of materials is limited to carbon-fiber-based electrodes which are assembled using various mechanical methods (e.g., paper making, weaving, hydro-entangling) resulting in distinct structures such as papers, cloths, and felts (1). These fabrication methods involve multiple complex subprocessing steps impacting the final product cost and limiting the achievable range of electrode properties, which ultimately restricts device performance (2). Thus, there is a need to develop new material sets with precise control over microstructure and surface composition while employing synthetic methods that are compatible with large-scale manufacturing.In this lecture, I will discuss our efforts to design tailored electrodes for redox flow batteries, which hold promise for long-duration stationary energy storage (3). First, I will introduce a pore network modeling framework that captures electrochemical performance in complex microstructures with low computational requirements (4), and then show the coupling of this framework with a genetic algorithm to enable bottom-up electrode design (5). In our most recent effort, we are building topology optimization models of porous electrodes using multi-scale modeling of redox flow batteries, coupling computational macro- and meso-scale models of transport processes constructed using finite element and finite volume methods. We then couple these approaches with upscaling strategies that enable manufacturability of the structures. Second, I will describe a new approach to synthesizing porous electrodes based on non-solvent induced phase separation (NIPS) (6). NIPS is a simple and versatile fabrication method that can be used to synthesize morphologically-diverse electrode microstructures (e.g., isoporous, pore-size gradients, and multimodal porosity) by tuning simple parameters in the polymer solution, such as polymer concentration, solvent type, and temperature. Using a suite of microscopic, spectroscopic, and electrochemical diagnostic tools, I will present synthesis-property-performance relationships of the NIPS electrodes (7). Third and finally, I will highlight our efforts to functionalize porous electrode interfaces with organic molecules to impart targeted functional properties including hydrophilicity, kinetic activity (8), and selectivity (e.g. H2 evolution suppression). References A. Forner-Cuenca, F. R. Brushett, Curr. Opin. Electrochem. 18, 113–122 (2019).C. Minke, U. Kunz, T. Turek, J. Power Sources. 342, 116–124 (2017).M. L. Perry, K. E. Rodby, F. R. Brushett, ACS Energy Lett. 7, 659–667 (2022).M. van der Heijden, R. van Gorp, M. A. Sadeghi, J. Gostick, A. Forner-Cuenca, J. Electrochem. Soc. 169, 040505 (2022).R. van Gorp, M. van der Heijden, M. A. Sadeghi, J. Gostick, A. Forner-Cuenca, Chem. Eng. J. 455, 139947 (2023).C. T. Wan et al., Adv. Mater. 33, 2006716 (2021).R. R. Jacquemond et al., Cell Reports Phys. Sci. 3, 100943 (2022).E. B. Boz, P. Boillat, A. Forner-Cuenca, ACS Appl. Mater. Interfaces. 14, 41883–41895 (2022).

Durability Investigation of Low Pt-Loaded PEM Fuel Cells with Different Catalyst Layer Morphologies

Low-temperature Polymer Electrolyte Membrane Fuel Cells (PEMFCs) emerge as the most promising fuel cell technology for transportation. Despite the growing interest in fuel cell electric vehicles (FCEVs) motivated by their rapid refueling, high power density, and long-range, their commercialization lags behind that of battery electric vehicles (BEVs) and internal combustion engine vehicles (ICVs). Apart from the lack of hydrogen infrastructure, other primary bottleneck lies in the cost-intensive production of essential components, particularly the dependence on noble metals such as platinum (Pt) to achieve high catalytic activity in the catalyst layer (CL). Simultaneously, meeting durability requirements for long-term performance and stability proposes another challenge. Therefore, enhancing the durability of PEM fuel cell systems without compromising performance and cost presents a significant challenge which stems from the trade-off relationships among these factors. The current target set by the U.S. Department of Energy (DOE) is achieving a durability of 8,000 hours of operation time, meaning 15,000 miles of driving, with less than 10% performance degradation using a 0.1 mg/cm2 Pt-loaded catalyst.The CL is a complex, heterogeneous structure composed of multiple components with different functionalities, and the electrochemical reaction takes place at the interfaces of the components. Several requirements are essential for the CL, including the presence of highly-dispersed Pt sites with high catalytic activity, a continuous path for efficient proton transport and electron conduction, and a through-connected pore network facilitating gas transport and water removal. Extensive research has been directed toward reducing Pt loading in the CL , motivated by the high cost and limited availability of Pt. At low Pt-loadings, researchers detailed the increased oxygen transport resistance within the CL, which is attributed to the reduction of active sites, as well as the heightened flux of reactants near each active site [1]. Therefore, optimizing the CL, both in terms of mass transport and reaction rate, as well as meeting economic and technical requirements, poses a significant challenge. While the impact of CL compositions on the cell performance is studied previously [2][3], systematic investigations are necessary to reveal the effect of CL characteristics on the electrode degradation. The understanding of performance losses during degradation processes is necessary for optimizing the CL for long-term operation and reducing Pt-loading in the cathode without compromising cell durability.This work aims on tailoring the impact of CL characteristics on electrode degradation for low Pt-loaded cells. To achieve this, five different samples with distinct CL features including Pt-loading, CL thickness, Pt/C ratio, and dilution ratio are fabricated. The samples are fabricated using the catalyst-coated membrane approach to suppress interfacial resistances between the membrane and the ionomer in the CL. In addition, a novel ultrasonic deposition method is employed to develop uniform and ultra-thin CLs enabling precise control of the CL thickness. With the use of an accelerated stress test (AST) ranging within 0.6-1 V in an air/H2 environment, the performance loss of the samples at the beginning-of-life (BOL), end-of-life (EOL) and at different stages during the applied AST is investigated. This experimental study serves as a foundational exploration into comprehending the individual impacts of CL compositions on electrode degradation and establishes the framework for the design of durable low Pt-loaded PEM fuel cells.

Using Micrometer Scale X-Ray CT and Pore Network Modeling to Assess High-Energy Bi-Layer Li-Ion Battery Cathode Structures

The optimization of cathode pore space is pivotal for enhancing the rate capability of lithium-ion battery electrodes. Previous studies on simulated cathodes have highlighted the importance of achieving an optimal porosity gradient, with a gradual increase from the current collector side to the separator side to accommodate the growing demand for ion transport in that direction [1]–[3]. In this research, we address this requirement by introducing and investigating bi-layer NCM 811 cathodes. These cathodes consist of a slurry-coated dense bottom layer and a spray-coated highly porous top layer with varying relative thickness to approximate the desired porosity gradient. Employing Micrometer-scale X-ray CT characterization and pore network modeling, we evaluate the structural features, demonstrating the effectiveness of the design, and quantify essential parameters such as porosity and tortuosity. Furthermore, the cathodes are integrated into lithium anode half-cells and subjected to electrochemical cycling at different rates to assess ion transport and rate capability. Our findings reveal that to achieve the highest discharge spatial energy density above 1C for cathodes approximately 100μm thick, the compressed bottom layer with 30% porosity should have a thickness of 60μm, while the highly porous top layer with around 47% porosity should be 40μm thick.Reference:[1] A. Shodiev et al., “Deconvoluting the benefits of porosity distribution in layered electrodes on the electrochemical performance of Li-ion batteries,” Energy Storage Mater., vol. 47, pp. 462–471, May 2022, doi: 10.1016/j.ensm.2022.01.058.[2] X. Lu et al., “3D microstructure design of lithium-ion battery electrodes assisted by X-ray nano-computed tomography and modelling,” Nat. Commun., vol. 11, no. 1, p. 2079, Apr. 2020, doi: 10.1038/s41467-020-15811-x.[3] K. Song, C. Zhang, N. Hu, X. Wu, and L. Zhang, “High performance thick cathodes enabled by gradient porosity,” Electrochimica Acta, vol. 377, p. 138105, May 2021, doi: 10.1016/j.electacta.2021.138105.

Measurement of Li-Ion Self-Diffusion in Laser Structured Electrodes

It is generally stated that a limiting factor in fast charging and high-power discharging of lithium-ion batteries (LiB) stems from the diffusion kinetics of Li+ in the electrode pore network. Numerous approaches in enabling fast charging of LiBs include active material development, electrolytes with high ionic conductivity and the management of the charging and discharging temperature. Another promising method is laser micro structuring to modify the electrode architecture regarding an enhanced lithium-ion diffusion kinetics. An increased high-rate capability and boost in cell lifetime have been demonstrated with such 3D electrodes [1, 2] but the related mechanisms leading to a substantial impact to diffusion kinetics are still poorly understood. Furthermore, it is imperative to find an optimal ablation pattern with regard to the desired application scenario that minimizes active mass loss in order to create the economic basis for efficient upscaling of the process.Nuclear Magnetic Resonance (NMR) measurements of longitudinal (T1) and transverse relaxation times (T2), as well as the T2/T2 exchange, are routinely used for the identification of different molecular species. The exchange NMR experiment is a well-known technique for studying local environments of nuclei such as liquids in pores and approximating their shapes and sizes [3]. The evolution of the transverse relaxation rate (T2) of a probed nuclei allows to determine if the specie is confined (shorter T2) or in liquid bulk (longer T2). In this work, so-called Exchange Nuclear Magnetic Resonance (T2/T2 exchange or EXSY), is conceptualized to study the impact of laser generated 3D patterns in pore self-diffusion of electrolyte species.Exchange NMR and T1 and T2 measurements were realized at various soaking times and electrolyte amounts for the following electrolyte species: Li+, PF6 -, ethyl carbonate (EC), and ethyl methyl carbonate (EMC), using laser structured, graphite-based electrodes casted on non-metallic substrates (to reduce RF interference). 2D exchange maps show the presence of confined species as well as the approximation of the diffusion properties. Using isotope exchange experiments with 6Li enriched electrolyte, concentration maps revealed the rate of 6LiPF6 intrusion into 7LiPF6 rich pre-soaked electrodes. The impact of laser generated 3D patterns in pore diffusion will be discussed in detail.[1]. Zheng, Y. et al. 3D silicon/graphite composite electrodes for high-energy lithium-ion batteries. Electrochim. Acta 317, 502–508 (2019).[2]. Smyrek, P., Pröll, J., Rakebrandt, J.-H., Seifert, H. J. & Pfleging, W. Manufacturing of advanced Li(NiMnCo)O2 electrodes for lithium-ion batteries . Laser-based Micro- Nanoprocessing IX 9351, 93511D (2015).[3]. Mitchell, J. et al. Validation of NMR relaxation exchange time measurements in porous media. J. Chem. Phys. 127, (2007).

(Invited) Novel Brush Design for Post CMP Cleans

Chemical Mechanical Polishing (CMP) process is one of the key processes in semiconductor wafer processing. A sub 10nm wafer fabrication process may require more than 40 dielectric and metal CMP steps. As CMP process requirements get more stringent, CMP slurries are formulated with smaller and smaller metal oxide abrasive particles. The abrasive particles may also be surface modified or doped with other metal oxides. Post CMP cleaning chemistry formulations are designed to remove polish byproducts, pad residues and abrasive particles from wafer surface. Chemical composition and PH are tuned for modulating wafer surface-particle interactions so brushes can mechanically “sweep” them off the surface. PVA brushes, used of post CMP cleans, are a highly porous network of crosslinked polyvinyl acetate with pore size in the range of 30 – 100 um and 80% - 90% porosity, depending on the type of brush being used. While PVA brushes have largely met the process capability requirements, they have limitations for advanced cleans such as nano-particle removal. As CMP process continues to expand to new dielectric and metal films for different process steps in wafer fabrication, there is a need for customized brush material and surface design for optimal cleaning efficiency.We discuss a new engineered post CMP brush design that shows high efficiency in nano-particle cleans and allows high level of material tunability. New brush design is an engineered composite with an open cell microporous core, overlaid with engineered fibers in form of loops. Brush design is compatible with existing post CMP cleans. Figure 1(a) shows the new design, where in DIW enters the brush through the center of microporous core and flows outwards to the surface. As water exits the surface, it flows over and across the loops and contacts the wafer surface. Flow resistance through core and loops can be independently tuned, which allows better fluid distribution and more effective cleans. Figure 1(b) show a close-up schematic of interaction between loop and particle. Flexing of the loops on brush surface provides improved contact as well as cleaning ability Brush design can be optimized for chemical and mechanical properties with choice of fiber material, fiber diameter and loop height. Figure 2 shows the Zeta potential of PVA and different loop materials. The fiber material maybe selected such that zeta potential of the loops can enhance mechanical action in removing particle. Mechanical action of the Loops can be modeled as a cantilever and force on the particle is exerted by flexing of the loops.Deflection of loops can be approximated with flexure stiffness of rods with point load at free end. For initial purposed loop is approximated as single element. The equation can be rewritten to calculate cleaning force P at the free end for given loop deflection (Y), P = 3EIY/L3 (1)Where E is elastic modulus, I = moment, L = length of fiber and for rod shapes; I = Pi*(r4/4)The adhesion of particles on the surface is due to the effect of van der Waals and electrostatic forces. The total adhesion force on the surface can be written as: F=F vdw + F edl (2) where Ft is total adhesion force, Fvdw is the van der Waals force, and Fedl is the electrostatic force.Fvdw = AR/6r2 (3)Where A is the Hamaker constant, R is particle radius, r is the separation distanceFor effective removal of particles, P >/= F (4)Flex force and adhesion force were modeled based on equation (1) and (3) and are shown in Figure 3. New brush design was used for post CMP cleaning of silicon dioxide wafers polished with ceria slurry. Two different brush designs were tested for cleaning efficiency. Modeling data and comparison with experimental results is presented. Figure 1

High-Density, Low-Tortuosity Sulfur Electrodes for High Energy Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries have attracted significant attention due to their promising theoretical energy and cost-effectiveness.[1] While recently studies have predominantly focused on increasing sulfur mass loading and utilization rate for high specific energy, there remains a noticeable gap in addressing the intrinsic challenge of improving volumetric energy density.[2] This challenge arises as many Li-S investigations rely on highly porous electrodes.[3] Here, we employ a shear-rolling approach to prepare free-standing electrodes characterized by high density (porosity<15%), low tortuosity, and substantial S content (>70%). The incorporation of a vascular-like porous network, facilitated by a pore soft template, plays a pivotal role in achieving high sulfur utilization (>1000 mAh g-1) in high-loading electrodes (>4 mg cm-2) under lean electrolyte condition (E/S 4 mL g-1). This approach results in an extraordinarily high volumetric energy density (668 Wh L-1 of dry cell) when applied to practical Li–S pouch cells. Our study underscores that realizing high volumetric energy in Li–S cell can be achieved by rationalizing the dense electrode architecture. Furthermore, the shear-rolling approach holds broad applicability for fabricating high-energy electrodes using porous or nanoparticle materials with desirable structures. Details of the progress will be discussed at the conference.

Graphene Supported Silicon Nanocomposites As Anode for Lithium-Ion Batteries

This work indicates Silicon/Grphene (Si/G) nanocomposites anode on the performance in lithium-ion batteries (LIBs).The self-assembled graphene aerogel and silicon (Si/G) anode materials with some surface defects have been successfully prpared by hydrothermal synthesis using chemically modified graphene oxide and commercial Si nanopowder (about 50 nm) as precursor. The morphologies and textural properties of as-obtained Si/G were investigated by scanning electron microscopy, X-ray photoelectron spectroscopy, and other sturucture techniques. The surface defects and electrical conductivities of Si/G can be controlled by adjusting the amount of Si nanopowder. The results indicate that Si/G with Si amount of half exhibits excellent stability and reversible capacity and superior rate capability with excellent cycling stability. It is demonstrated that the 3D porous network with increased defect density, as well as the considerable electrical conductivity, results in the excellent electrochemical performance of the as-made Si/G anodes in LIBs.

Mangenese Copper Selenide Nanosheet Arrays Derived from Metal-Organic Frameworks for Efficient Solid-State Asymmetric Supercapacitors

Metal chalcogenide nanostructures, particularly metal selenides, have unique properties, such as high electrical conductivity, large specific surface area, exclusive porous networks, and exceptional electrochemical properties compared to traditional nanostructures.1 2 A novel strategy is proposed to design and fabricate hierarchical Manganese copper selenide nanosheet (MnCuSe NS) arrays from metal-organic frameworks (MOFs). The hierarchical MnCuSe NS arrays can deliver enriched electroactive sites and shorten the ion/electron diffusion pathways. When evaluated as positive electrodes for supercapacitor (SC), the MnCuSe NS electrode displayed remarkable electrochemical properties with ultra-high specific capacity of ≈350.4 mA h g− 1 and an areal capacity of ≈0.94 mA h cm− 2 at a current density of 3 mA cm− 2, exceptional rate capability (≈79.5% of the capacity retention at a higher current density of 50 mA cm− 2), and outstanding cyclic stability (≈95.4 % of capacity retention after 10 000 cycles). Most importantly, the assembled MnCuSe NS//FeMnO/NG solid-state asymmetric SC exhibited a wide operating potential window of 1.6 V with an ultra-high volumetric capacity of ≈2.4 mA h cm− 3 at a current density of 3 mA cm− 2, an excellent energy density of ≈71.6 Wh Kg− 1 at a power density of ≈794 W Kg− 1, and ultra-long cycle life (≈93.4 % of capacity retention after 10 000 cycles). This proposed method provides a general protocol to design and fabricate metal selenide nanosheet arrays with superior electrochemical energy storage properties and exceptional cyclic stability, holding significant potential for future energy storage devices in commercial aspects. Keywords: Hierarchical, Metal-organic frameworks, Metal chalcogenide, Energy density, Asymmetric supercapacitorsReference:(1) Han, J. H.; Kwak, M.; Kim, Y.; Cheon, J. Recent Advances in the Solution-Based Preparation of Two-Dimensional Layered Transition Metal Chalcogenide Nanostructures. Chem. Rev. 2018, 118 (13), 6151–6188. https://doi.org/10.1021/acs.chemrev.8b00264.(2) Karuppasamy, K.; Vikraman, D.; Hussain, S.; Kumar Veerasubramani, G.; Santhoshkumar, P.; Lee, S.-H.; Bose, R.; Kathalingam, A.; Kim, H.-S. Unveiling a Binary Metal Selenide Composite of CuSe Polyhedrons/CoSe2 Nanorods Decorated Graphene Oxide as an Active Electrode Material for High-Performance Hybrid Supercapacitors. Chemical Engineering Journal 2022, 427, 131535. https://doi.org/10.1016/j.cej.2021.131535.

(Digital Presentation) In-Situ Growth of CNT and Macroporous ZIF on Bacterial Cellulose for High Frequency Electrochemical Capacitor

High frequency electrochemical capacitors (HF-ECs) represent a class of devices characterized by their high capacitive density and operational capability within the hundreds or kilohertz range. As electronic devices continue to undergo downsizing trends, HF-ECs emerge as promising alternatives to bulky aluminum electrolytic capacitors (AECs), which are constrained by their limited working frequency of approximately 1 Hz and slow charge-discharge rates. The designing of electrodes of HF-ECs combines large surface area for capacitive density along with open porous network to facilitate rapid ion transport. In this study, we synthesized nickel coordinated ZIF-8 (Zeolitic Imidazole Framework-8) cages on bacterial cellulose (BC). The samples underwent rapid carbonization in the presence of dicyandiamide at ~950˚C for 20 minutes, during which the zinc centers inside the MOF cages evaporated forming macroporous structures, while the nickel particles gave rise to carbon nanotube (CNT) growth through tip growth mechanism. The uniform coverage of BC with macroporous ZIF cages reduces the microporous effect, while the CNT growth also imparts higher electronic conductivity via graphitic nitrogen groups. The HF-ECs made with these electrodes and 6M KOH aqueous electrolyte gave a capacitive density of ~3.4 mFcm-2 and a phase angle of -81.3˚. The electrodes were stacked in pairs of 2 and 3 to achieve higher capacitance of 6.3 mFcm-2 and 8.9 mFcm-2 respectively. The HF-ECs were also assembled with 1 M TEABF4 in acetonitrile to show higher working voltage of these electrodes. The device maintained a capacitance just above 3 mFcm-2 and a phase angle over -80˚. The cells show an excellent working capability at higher discharge rates of 100 mAcm-2, where they retained ~70% of the initial capacitance. Figure 1

Tandem Solid-Solution Phase Post-Synthetic Modification of Porous Molecular Crystals for In-Situ Generation of Fluorophores.

Conventional synthetic methods of organic luminescent molecules often involve labor-intensive solution-phase organic synthesis, which violate the principles of atom-economic transformation. Post-synthetic modification (PSM) offers a promising alternative, allowing direct transformation from one fluorophore to another. Although PSM is commonly implemented in extended frameworks, its application in porous molecular crystals remains challenging. Herein, we focus on utilizing porous molecular crystals, specifically tetraphenylethylene-cored frameworks, as versatile platforms for tandem PSM reactions to customize organic fluorophores. The tailored skeleton design ensures both the formation of porous structures and the occurrence of tandem solid-solution phase reactions while maintaining the solid state of reactants and products in each step. The inherent non-covalent bonding nature of the frameworks facilitates processing and characterization, offering unparalleled advantages for porous networks. The accompanying solid-state fluorescence transition from green to blue and then to green (or yellow) enables real-time monitoring of tandem reactions and provides intuitive mechanistic insights. This phenomenon is exploited for the facile construction of a dynamic information encryption system using fluorescent quick response codes.

Thermal Modeling of Li-Ion Cylindrical Cells at Scale

The electric vehicle industry has created a demand for batteries with higher power densities. The current design choice for low-weight lithium-ion battery packs for electric vehicles is to create stacks arranged in parallel or series configurations to match the power demands. The individual cells are separated and placed in a cooling duct to pull heat away from the longitudinal surface convective. The amount of cooling is dependent on the internal temperature of batteries core. The current design of the cylindrical cell is to roll the cathode, anode, and separators into a jelly roll together and attach a tab to the cathode and anode at opposite corners of the sheet. The tabs connect to the positive and negative terminals of the cell to draw current away from the cell. The tabs may act as an agent for drawing heat away from the center of the battery. Currently, commonly used cylindrical cells have a form factor of 18650, 21700, or 26650. The thermal, geometrical, and electrical properties of 18650 and 21700 cylindrical cells are studied and it is found that the 21700 cells showed additional degradation and stronger heating. Recently, companies like Tesla have produced cylindrical cells with a 4680-form factor, which is a decent way to increase the ratio of active material vs. inactive material in a cylindrical cell. However, large diameter thick cylindrical cells suffer from thermal issues. Even large format pouch cells suffer through heat trapped within the stack.Since the thermal conductivity of the anode and cathode electrodes is often near 1 W/m-K, it becomes difficult for the heat to be extracted from the center of a large-diameter cylindrical cell without forming a considerable thermal gradient. PyBaMM, an open-source mathematical modeling software written in Python programming language, has the capability to simulate different electrochemical models such as the Doyle-Fuller-Newman (DFN), Single particle model (SPM), and SPMe, and varying chemistry. The software provides easy access to the cell parameters modification and graphical user interface capabilities. The PyBaMM framework also allows to simulation lumped, isothermal, and base thermal models which are electrochemically coupled. PyBaMM uses CasADi (computer algebra systems algorithmic differentiation). The thermal gradient and heat dynamics within a porous electrode are modeled using PoreSpy and openpnm, two open-source Python libraries used to design porous networks and model physical equations such as governing heat flow, concentration gradient, and movement of water/oil through porous shale media.We have explored and combined heat dynamic models for Li-Ion cylindrical cells at both cell and electrode levels with reduced-order Doyle-Fuller-Newman electro-chemical model frameworks implemented in the PyBaMM python library. Radial temperature gradient at cell and electrode levels were both generated from simulations with a distributed parameter model as a function of electrolyte and separator thickness and thermodynamic properties. Figure 1

Achieving Remarkable Specific Mechanical Strength and Energy Absorption Capacity in SiC Nanowire Networks through Graded Structural Design.

Lightweight porous ceramics with a unique combination of superior mechanical strength and damage tolerance are in significant demand in many fields such as energy absorption, aerospace vehicles, and chemical engineering; however, it is difficult to meet these mechanical requirements with conventional porous ceramics. Here, we report a graded structure design strategy to fabricate porous ceramic nanowire networks that simultaneously possess excellent mechanical strength and energy absorption capacity. Our optimized graded nanowire networks show a compressive strength of up to 35.6 MPa at a low density of 540 mg·cm-3, giving rise to a high specific compressive strength of 65.7 kN·m·kg-1 and a high energy absorption capacity of 17.1 kJ·kg-1, owing to a homogeneous distribution of stress upon loading. These values are top performance compared to other porous ceramics, giving our materials significant potential in various engineering fields.

Experimental Study on CO2 Flooding Characteristic in Low-Permeability Sandstone Considering the Influence of In-Situ Stress

Summary The pore network controlled by in-situ stress significantly influences the CO2 flooding in low-permeability reservoirs. In this study, the CO2/oil distribution and response of pore structure were monitored online using low-field nuclear magnetic resonance (LF-NMR), and the in-situ stress dependence of oil recovery was analyzed. The results show that the pore structure consists of adsorption pore (AP &amp;lt; 1 millisecond), percolation pore (1 millisecond &amp;lt; PP &amp;lt; 10 milliseconds), and migration pore (10 milliseconds &amp;lt; MP). Oil recovery was primarily influenced by AP and MP at lower in-situ stress, while PP and MP are the main contributors at higher in-situ stress. The matrix experienced compression deformation, microfracture generation, and shrinkage of pore, combined with an increase and followed by a decrease in oil recovery, responding to the increase of in-situ stress from 5 MPa to 15 MPa and from 15 MPa to 20 MPa. The reduction in gas channels promotes a piston-like advancement of oil displacement, resulting in an initial increase in oil recovery, while subsequent decline is linked to heightened pore heterogeneity caused by high in-situ stress. Increased heterogeneity reduces gas displacement stability, hampers CO2 sweep efficiency, and results in a granular distribution of residual oil. The findings provide insight on CO2-enhanced oil recovery (EOR) in low-permeability reservoirs.

Induced polarization of clay-rich materials — Part 5: Influence of hyperalkalinity in bentonites

A total of 54 new core samples were built by mixing smectite-rich MX80-bentonite and Fontainebleau (silica) sand to study the effect of a hyperalkaline pore solution (including the presence of potassium) on the induced polarization properties of these mixtures. Two types of experiments were performed. In the first set of experiments, we performed induced polarization measurements 10 minutes after the preparation of the core samples (static experiments) for a broad variety of water contents and saturations. The second set of experiments was performed for over 1000 hours to study the potential effect of illitization upon the induced polarization properties (time-lapse experiments). Indeed, in the presence of potassium in the hyperalkaline pore solution favors the transformation of smectite into illite. Furthermore, we expect cation replacement (sodium replaced by calcium and potassium) in the smectite interfoliar pore network. For the static experiments, the relationships developed in the previous papers of this series regarding the dependence of the in-phase and quadrature conductivities on the water content and saturation remain valid. For the time-lapse experiments, we observed a decrease of the in-phase and quadrature conductivities over time. These trends can be fitted by a decaying exponential function. This behaviour is explained by the kinetics of the illitization process and its effect on the cation exchange capacity of the material. Induced polarization appears therefore as a promising technique to monitor the effect of hyperalkaline solutions associated with the leaching of concrete and permeating a bentonite seal in Deep Geologic Disposal facilities that could be potentially used for high-level and long-lived radioactive wastes.

Preparation and properties of alkali-activated fly ash-waste brick porous building materials

This study explores the development of sustainable porous building materials through the alkali-activation of fly ash and waste clay brick powder. Utilizing Class F fly ash and brick powder from demolished buildings, a series of alkali-activated mortars with varying brick powder replacements (0 % to 50 % by mass) were formulated and analyzed. The results reveal that a 10 % brick powder replacement optimizes the compressive strength, reaching 73 MPa at 28 days, attributed to enhanced nucleation and calcium-rich gel formation. However, higher brick content reduces strength due to the dilution of key reactive materials, with a 50 % replacement leading to a strength of 27 MPa. Porosity increases proportionally with brick content, achieving a maximum of 42 % at 50 % replacement, suggesting potential applications in insulation-centric scenarios. Microstructural analysis confirms the formation of a porous network and identifies the phase compositions and reaction products. This research demonstrates the potential of repurposing construction waste into efficient and environmentally friendly building materials, contributing to waste reduction and offering a greener alternative to traditional practices.

Investigation of self-desiccating cement-based materials for dihydrogen sequestration: Interactions between γ-MnO2/Ag2CO3 getter and the cement matrix

Mitigating the release of dihydrogen resulting from metal corrosion or water radiolysis is an important issue for the disposal of certain types of cemented radwaste packages. The approach investigated in this work consists in adding an oxide getter (γ-MnO2/Ag2CO3) to the cement matrix. Since the efficiency of the getter decreases under wet environment, two self-desiccating binders (calcium sulfo-aluminate and magnesium potassium phosphate cements), are used to obtain significant desaturation of the pore network by the sole hydration reactions. The getter slightly influences the rate of cement hydration at early age, but has no effect afterwards. Sorption of ions released by dissolution of cement phases onto γ-MnO2 is evidenced, as well as partial or total destabilization of silver carbonate. Nevertheless, the getter still enables to reduce strongly the outgassing of dihydrogen from mortars encapsulating Al-metal, which opens new perspectives to improve the conditioning of waste producing H2 in a cement matrix.

Preparation and electrochemical properties of flexible self-supported graphene/silicon/carbon nanotube composite electrode for lithium-ion battery

To meet the demand of flexible devices, it was urgent to develop flexible high-capacity electrodes for lithium-ion batteries (LIBs). Silicon (Si) as an active material would effectively elevate the specific capacity of LIBs, but the drastic volume changes and low intrinsic conductivity seriously affected its electrochemical performance during the charge-discharge process. In this research, a new type of composite was designed using two-dimensional reduced graphene oxide (rGO), one-dimensional carbon nanotubes (CNTs), and silicon nanoparticles (Si NPs) as raw materials. The prepared rGO/Si/CNTs composite had an intricate and intersecting porous network structure inside, with rGO as the substrate, CNTs as a bridge, and Si NPs as the active material. The rGO would provide abundant attachment sites for Si NPs, improve electrode conductivity, and alleviate the volume change of electrode. CNTs can effectively suppress the stacking of rGO layers and generate more voids for the reaction, and also serve as a bridge for electron transfer between rGO layers. Furthermore, the interaction between each other also heightened the flexibility and strength of electrodes. Compared to the other composites, rGO/Si/CNTs=2:2:1 electrodes presented the superior electrochemical performance. When cycled at 200 mA g−1, its discharge capacity was 2217.2 mAh g−1 after 200 cycles. As the current density increasing to 1000 and 5000 mA g−1, the discharge capacity maintained at 1877.2 and 534.8 mAh g−1 for 1000th cycle, and it also demonstrated superior rate performance. Besides, the assembled flexible battery maintained a good current output under various bending conditions, and was expected to be widely used in the flexible wearable energy storage devices.