Electrode Design Research Articles

Application of metal oxide/porous carbon nanocomposites in electrochemical capacitors: A review

In the past decade, electrochemical capacitors (ECs) have emerged as innovative energy storage devices, attracting considerable interest from both industrial and academic sectors due to their prolonged cyclic stability and impressive power density. Recently, there has been a focus on advancing high-performance ECs by developing electrode material composed of metal oxide incorporated with porous carbon. Integrating metal oxides into a porous carbon structure enhances capacitance, charge storage, and cyclic stability. Furthermore, the porous structure inherent in carbon materials offers efficient ion diffusion and large surface area, thereby augmenting the overall effectiveness of the nanocomposites. Efficient electron and ion transport within the electrode's bulk is achieved through the interaction between electrodes and electrolytes occurring at the electrode-electrolyte interface, subsequently increasing the capacitance. This paper summarizes the latest developments in ECs, focusing on key performance metrics such as cyclic stability and capacitance. It also summarizes the recent advancements made in electrode materials, emphasizing the utilization of sustainable feedstocks. As the research landscape shifts towards more environmentally friendly solutions, the incorporation bio-materials into electrode design has gained significant attention. It particularly highlights underlying mechanisms governing the performance of metal oxides/porous carbon nanocomposites in ECs and outlines future research directions aimed at maximizing their potential for next-generation energy storage devices. Additionally, the paper delves into the possibilities and challenges associated with the preparation, and optimization of the structure of metal oxide electrodes incorporating porous carbon to improve energy storage performance in ECs.

Design and Characterization of Porous Electrodes for Redox Flow Batteries

The commercialization of redox flow batteries as large-scale energy storage systems depends on lowering the capital and operating costs which depend on achieving maximum power density. Optimizing electrode design parameters and flow field-electrode combinations is critical to minimize losses and maximize active material utilization. Modeling the current drawn from an electrode offers a means to interpret electrode structure based on the electrolyte distribution driven by internal design. However, direct imaging methods (such as in-situ fluorescence microscopy and X-ray tomography) and numerical methods for current to potential prediction (3D Lattice Boltzmann modeling) are specific to individual electrode structures and possess limited predictable value to obtain an ideal electrode design. In this work, we present an electrode impedance spectroscopy (EIS)-based approach for determining electrode design parameters and devise a general method for determination of effective diffusion layer thickness. Using COMSOL modeling we verified the development of slug flow behavior in highly randomized porous electrode systems, indicating that the mass transport properties are dictated by inter-fiber distance. An analytical model to predict current as a function of applied overpotential is presented which allows us to vary structural parameters of the porous electrodes to study the influence of surface area, inter-fiber distances and diffusion layer thickness on the RFB performance. This model is a highly flexible tool applicable to any electrochemical system using a porous electrode and identifies critical variables affecting electrode design to characterize optimal electrode structure to minimize mass transport losses and optimize operational parameters.

Electrochemical Hydrogenation in Action: Redefining the Production of Commodity and Fine Chemicals

Electrocatalytic hydrogenation reactions (ECH) are increasingly recognized as promising approaches for the reductive production of both commodity and fine chemicals. Particularly when powered by renewable energies, ECH offers a sustainable alternative, avoiding the need for gaseous hydrogen, high-pressure conditions, and stoichiometric reducing agents, which often lead to excessive waste formation. Moreover, ECH processes can be conducted under mild conditions near room temperature, utilizing environmentally friendly solvents like water as a proton source. This marks them as a sustainable process for the future.1 Here, we discuss our latest advancements and challenges in advancing electrochemical hydrogenations towards significant industrial applications. We focus on critical aspects such as catalyst selection, electrode design, and the suitability of reactor concepts, illustrated through selected unsaturated organic substrates that are used industrially on a large scale. Specifically, we explore the selective semi-hydrogenation of internal and terminal alkynes as well as (di)aldehydes. Each substrate presents unique challenges and opportunities, showcasing potential pitfalls, unexpected reaction pathways, and serving as a source of inspiration for future ventures in electroorganic synthesis.1-3

Elucidating the Electrochemical Impact of the Calendering Process on Three-Dimensional Designed Electrodes for Lithium-Ion Batteries

Significant advancements in battery technology are imperative to meet the ambitious demands for electromobility and stand-alone energy storage devices. This stems from the need to achieve operations with high energy and power density, coupled with stringent safety standards and extended lifespans, while reducing production and material costs. The preferred energy storage technology for the coming decade is anticipated to remain lithium-ion battery (LIB) technology. The focus on researching high-energy active materials to optimize this technology is paramount. In addition to optimizing materials, significant performance enhancements can be achieved by using electrodes with high mass loading and a multiscale tailored electrode design that can be scaled up to production level.The technological challenges of achieving a breakthrough in gaining simultaneously high energy and power density characteristics while maintaining high process and operational reliability with significant cost savings are the subject of current research and development in the field of LIB technology. To tackle this, the study explores the laser-assisted generation of three-dimensional (3D) electrode architectures and assesses its impact on battery performance and future integration into battery production. The advanced electrode design involves micro and sub-micron structures that can be tailored in various ways, leading to notable improvements in battery lifespan, battery safety, and fast charging and high-power operation capabilities compared to batteries with conventional two-dimensional (2D) electrodes. High-power ultrafast laser ablation emerges as a precise method for introducing such structures.Coordinating the production of 3D electrodes with laser assistance necessitates synchronization with established manufacturing steps in the battery production process. Notably, the calendering of electrodes holds significance due to its substantial influence on the microstructural properties of the electrode material, encompassing porosity, material density, and layer adhesion. The study investigates the impact of laser-induced structuring, encompassing micro-/nano-porosities and microtopography, on electrodes with varying mass loadings ranging from 2mAh/cm² to 6mAh/cm². Electrochemical characteristics such as high-rate capability, fast charging, and cycle lifetime are evaluated accordingly, employing cells with graphite anodes and lithium-nickel-manganese-cobalt oxide cathodes.

Microelectrode-Based Diffusivity Measurements of Hydrogen in Molten 2LiF-BeF2

Detailed knowledge of the mass transport behavior of hydrogen isotopes in molten 2LiF-BeF2 salt (FLiBe) is essential to the design of new nuclear fusion technologies that make use of this molten salt to breed tritium to fuel the fusion reaction. However, typical studies of hydrogen transport using macroelectrodes are limited to solely measuring the permeability of an analyte—a property defined as the product of concentration squared and diffusivity. This challenge necessitates the development of microelectrodes capable of dynamically measuring diffusion coefficients when concentrations are variable. Unlike macroelectrodes, microelectrodes can measure diffusivity and concentration independently due to a steady-state current proportional to the product of diffusivity and concentration captured in addition to the Cottrellian current response.This steady-state current is established due to a continuously expanding diffusion layer from the electrode that cannot expand indefinitely within finite experimental setups. Therefore, COMSOL Multiphysics simulations mirroring experimental conditions were performed to validate the analytical mass transport model based on the solution of Fick’s Second Law in radial coordinates. These simulations employed a 2D axisymmetric model to examine the conditions under which the infinite bulk solution approximation is valid, confirming that our electrode design would yield true steady-state current responses indicative of radial diffusion.Platinum microelectrodes developed in this study served a dual purpose: they not only addressed previous limitations in high-temperature molten salt experimentation but also enabled dynamic measurements of both the diffusion coefficient and concentration of hydrogen in molten FLiBe introduced by lithium hydride. Square wave voltammetry and chronoamperometry were performed on a three-electrode cell using a platinum working microelectrode, a tungsten counter electrode, and a Ni/Ni2+ thermodynamic reference electrode. The successful measurement of hydrogen diffusivity in these experiments not only offers essential insights into molten FLiBe behavior but also sets the stage for future investigations into the effects of redox conditions, impurities, and equilibration time on tritium within nuclear fusion reactors.

New Electrochemical Channel Flow Cell Design for Electrochemical Studies at Elevated Temperatures and Pressures

Temperature exerts a considerable influence on the efficiency of chemical and electrochemical processes, and it is expected that studies under wide temperature and pressure (T and p) conditions can significantly impact fields of technological interest such as energy storage and conversion, water treatment, waste conversion, metal recovery, and electrosynthesis, among others.1 The electrochemical studies conducted by Bard’s group in near-critical and supercritical aqueous solutions,2 as well as the contributions made by MacDonald’s and Lvov’s3,4 groups on corrosion and pH determination in hydrothermal systems, offer valuable insights into the effects of temperature and pressure on electrochemical reactions under extreme conditions and construction materials and electrode designs. Other studies in the field, though they did not reach such harsh conditions, made valuable contributions by proposing innovative hydrodynamic electrode systems, from channel cells for studies up to 110 oC,5 a rotating disc electrode for temperatures up to 150 oC,6 and even an imping jet electrode able to reach 210 oC.7 Unfortunately, these studies were rarely expanded to more than one or two systems.In this work, various hydrodynamic electrode configurations have been examined to conclude that the channel flow cell design presents several advantages over other systems for high T and P applications. These cells can provide consistent and reproducible mass transport conditions across a broad range of flow rates and allow channel dimension adjustments to tackle diverse technological challenges. Furthermore, this configuration aligns well with spectroscopic techniques like Raman/SERS (surface-enhanced Raman spectroscopy). COMSOL Multiphysics was used when designing the cell prototype, and validation of the model was carried out using data from previous studies.8 The high T,p cell uses disposable thin-film electrodes (TFEs) patterned onto sapphire wafers through nanofabrication methods; a significant amount of time has been invested in testing the performance of the TFEs up to at least 150°C. These results will also be presented along with experiments conducted with the new channel cell under ambient conditions. References (1) Giovanelli, D.; Lawrence, N. S.; Compton, R. G., Electroanalysis (New York, N.Y.) 2004, 16 (10), 789-810.(2) Liu, C.-y.; Snyder, S. R.; Bard, A. J. J. Phys. Chem.B 1997, 101 (7), 1180-1185.(3) Macdonald, D. D. Corrosion 2013, 34 (3), 75-84.(4) Balashov, V. N.; Fedkin, M. V.; Lvov, S. N., J. Electrochem. Soc. 2009, 156 (7), C209.(5) Wang, H.; Jusys, Z.; Behm, R. J.; Abruña, H. D., J. Electroanal. Chem. 2021, 896, 115251.(6) Fleige, M. J.; Wiberg, G. K.; Arenz, M., Rev Sci Instrum 2015, 86 (6), 064101.(7) Trevani, L. N.; Calvo, E.; Corti, H. R., Electrochem. Commun 2000, 2 (5), 312-316.(8) Moorcroft, M. J.; Lawrence, N. S.; Coles, B. A.; Compton, R. G.; Trevani, L. J. Electroanal. Chem. 2001, 506 (1), 28-33.

Lithium-Mediated Nitrogen Reduction in a Flow Electrolyzer Cell Using Gas Diffusion Electrodes with Carbon-Based Electrocatalysts

Due to the sluggish kinetics in activating the chemically stable dinitrogen (N2) and the competing hydrogen evolution reaction in aqueous media, recent attention in the field of direct ammonia (NH3) electrosynthesis has been increasingly drawn to the lithium-mediated N2 reduction reaction (LNRR) in tetrahydrofuran (THF)-based non-aqueous electrolyte. In particular, near 100% faradaic efficiency (FE) and/or a current density (j) of 100 mA cm-2 has been demonstrated with unique electrolyte (proton-shuttle additive) and/or electrode designs (expansive electrochemical surface area) in single-compartment cells at elevated N2 pressure (5 – 20 bar).[1,2]A submerged electrode leads to electrolyte flooding and restricts to N2 mass transfer to the electrode surface where electrodeposited Li as an electron mediator is available.[3] However, flow cell electrolyzers containing gas-diffusion electrodes can improve this technology to practical relevance, which features the LNRR on the cathode and hydrogen oxidation reaction (HOR) on the anode. Differing from single-compartment cells, the HOR supplements the ethanol additive (<1 vol%) as the proton source, which not only prevents the oxidative electrolyte degradation but also reduces the energy consumption due to a lower equilibrium anode potential (E0 = 0 VRHE). Gas-diffusion electrodes (GDEs) are used in the few LNRR studies with flow cell configurations, which are prepared by electro- or electroless depositing electrocatalysts (e.g., Pt [4] or PtAu alloy [5]) onto a porous substrate.In this work, carbon-based electrocatalysts (Vulcan XC72R carbon black, battery-grade conductive carbon SUPER C45, and graphitic carbon SFG6L) as low-cost alternatives to previously studied precious metals are assessed for their LNRR performance in flow cells using an HOR anode. In comparison to Vulcan-supported Pt, XC72R and C45 can obtain similar NH3 production rates (rNH3 )and FE at the same . Continuous LNRR at -3 mA cm-2 was demonstrated with linearly increased NH3 production for over 8 h without catalyst layer detachment, which was also verified with open circuit and Ar control experiments (Fig. 1). By presenting the LNRR activity with GDEs spray-coated with carbon-based electrocatalysts, opportunities for future research are suggested, such as novel carbon materials and porous substrates other than SSC for facile N2 mass transfer and Li deposition.

High-Performance Optimised Porosity Iron Electrode for Hybrid Battery Electrolyzer

The growing demand for efficient, cost-effective and sustainable energy systems has prompted significant research into the development of advanced electrochemical devices. Hybrid battery electrolyzer, integrating the capabilities of both battery and electrolyzer, is a groundbreaking technology aiming to enhance both energy conversion efficiency and storage capacity. [1] Iron with large earth-abundance, low-cost, robustness, and high capacity is a promising electrode material for such hybrid energy systems. [2-4]This study focuses on the design, fabrication, and performance evaluation of a novel porous iron electrode tailored for use in a hybrid battery electrolyzer system. The proposed electrode exhibits superior electrocatalytic activity, enhanced mass transport properties, and increased surface area, contributing to improved overall performance. The electrode's porosity and pore structure are tuned to facilitate efficient mass transport and electrolyte penetration, addressing common challenges associated with conventional electrodes. The electrochemical performance of the optimised porosity iron electrode is investigated through comprehensive characterization techniques, including scanning electron microscopy (SEM), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and charge-discharge cycling tests. Results indicate superior electrochemical properties, showcasing enhanced specific capacity, faster charge/discharge kinetics, and prolonged cycle life compared to conventional electrodes. The incorporation of conducting nanocarbon and sintering at optimized temperature of 800 ℃ led to the achievement of a stable and elevated capacity exceeding 500 mAh/g for these advanced iron electrodes. The iron electrodes exhibit outstanding porosity (65 - 70%), along with a pore size of 5-10 µm. This configuration results in exceptional current rate performance, achieving a discharge capacity of 350 mAh/cm2 at a current density of 35 mA/cm2 and 245 mAh/cm2 at 50 mA/cm2. Furthermore, the iron electrodes exhibit superior performance in high-current electrolysis, showcasing an HER potential of -1.25, -1.34, and -1.50 V (vs Hg/HgO) at a current density of 200, 500 and 1000 mA/cm2 respectively.These findings highlight the potential of optimised porosity iron electrodes as a key component in the development of high-performance and cost-effective hybrid battery electrolyzer systems. The integration of such advanced materials holds promise for unlocking new frontiers in energy storage and green hydrogen technology, contributing to the realization of efficient and sustainable energy systems.

Embedded Micro-Interdigitated Flow Fields for Efficient Intercalation-Based Desalination at Seawater Scale

During the past decade, intensifying water crises around the globe have motivated research in electrochemical desalination. Among such technologies, Faradaic deionization (FDI) has shown great promise for seawater desalination with the use of intercalation electrode materials that possess at least ten-fold higher charge storage concentration (~5 M) than seawater salinity (~0.5 M). Despite many efforts focused either on developing electrode materials or modifying flow-cell architectures, the promise of intercalative FDI was not previously realized experimentally. This work demonstrates for the first time salt removal approaching seawater-level salinity by using a flow cell containing symmetric cation intercalation electrodes separated by an anion-exchange membrane [Do et al., Energy Environ. Sci., 16, 3025–3039 (2023)]. We show removal of 96% of salt from ~500 mM NaCl feeds with ~50% water recovery at a thermodynamic energy efficiency (TEE) of 7%. In addition, the flow cell readily produces fresh water (< 0.017 M NaCl) from brackish water with 40% TEE and substantially lowered hypersaline brine concentration from 0.78 M down to 0.23 M at 11.7% TEE. We note that (1) scaling up the charge capacity of intercalation electrodes is crucial to improve salt removal in FDI and (2) rational design of flow-through electrodes is equally important to make FDI more energy-efficient by mitigating pumping energy consumption. Upscaling was achieved by using large-area electrodes with high areal loading of nickel hexacyanoferrate (NiHCF), up to 21 mg cm-2. Pumping energy was drastically reduced by embedding an interdigitated array of 70 µm wide channels into the NiHCF electrodes using laser micromaching to form novel embedded, micro-interdigitated flow fields (eµ-IDFFs). The dimensions of the eµ-IDFFs were tailored for our low-permeability electrodes based on analytical and numerical modeling, resulting in two orders of magnitude improvement in the apparent hydraulic permeability of these electrodes while minimizing active-material loss. Evidence of water transport between diluted and concentrated streams, as well as feed-concentration-dependent charge efficiency were reported, which potentially contributed to energy efficiency and water recovery losses, motivating their investigation to further improve FDI performance. In addition to their application toward desalination, the present eµ-IDFFs show promise for use in electrochemical energy storage and conversion processes that employ nanomaterials

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.

(Energy Technology Division Graduate Student Award sponsored by BioLogic) In-Situ, Non-Destructive, 3D Neutron Imaging of Lithium Plating Following Extreme Fast-Charging of Full-Cell Lithium-Ion Batteries

One of the primary challenges impeding extreme fast-charging (XFC) of current lithium-ion batteries (LIBs) for electric vehicles (EVs) within 10–15 minutes is the deposition of Li metal on graphite known as “Li plating”.1-2 After Li plates, it either re-intercalates into the graphite electrode or is stripped off during battery discharging to form “active Li”or becomes electronically disconnected resulting in “dead Li.” Previous studies have indicated that dead Li is the main contributor to the XFC-related capacity loss of LIBs. However, mechanistic understanding of the 3D morphological behavior and spatial heterogeneities of dead Li; and how they differ from those of plated and active Li during the XFC is not well understood.3-4 Here, we present an in-situ, non-destructive 3D characterization of the morphological behavior and spatial heterogeneities of plated, dead, and active Li on graphite electrodes in full-cell LIBs using high-resolution neutron micro-computed tomography. We performed neutron µCT5 (pixel size: ~ 5.74 µm; effective spatial resolution: ~10-15 µm) at the ICON beamline6 at the Swiss Spallation Neutron Source at the Paul Scherrer Institute. We imaged two batteries in the charged and discharged states: (1) after 4 cycles of 1C charging and (2) after 6 cycles of 6C charging.Our results show that Li plates at and around the edges of the graphite electrodes, indicating that graphite edges and the areas around these edges are the most susceptible to Li plating. However, certain edges and areas around these edges formed dead Li whereas others formed active Li, suggesting 3D spatial heterogeneities in the formation of dead and active Li at both 1C and 6C. Mainly, we discuss these heterogeneities at four regions: (1) near the Cu CC, (2) in the middle of the graphite electrode, (3) near the graphite-separator interface, and (4) in the separator. Specifically, we found that Li near the Cu CC remains active whereas most of the plated Li at the graphite-separator interface and in the separator becomes dead at both 1C and 6C.Morphologically, we observed porous nature of plated and dead Li at both 1C and 6C. Our 3D visualizations noticeably show nodules of varying densities of metallic Li. However, we observed different 3D behavior of Li plating at 1C and 6C. For example, tip-like Li deposits were seen laterally closer to the center of the graphite electrode, near the graphite-separator interface, and into the separator at 6C. In contrast, at 1C, no tip-like Li deposits were observed near the graphite-separator interface and into the separator. Based on our findings, we concluded that higher XFC-charging rate and cycling number (6 cycles of 6C charging) cause the formation of tip-like Li deposits as compared to the relatively slower XFC-charging rate and cycling number (4 cycles of 1C charging). We believe that insights derived from this work will guide the design of thick graphite electrodes with minimized-plating for fast-charged EVs.

Balancing the Mechanical and Electrochemical Properties of Multifunctional Composite Electrolyte for Structural Batteries

The pursuit of energy-efficient for electric vehicles and aircraft has driven the exploration of structural batteries. In the material-level design of structural batteries, electrode and electrolyte materials act as both load-bearing structures and energy storage elements. During these developments, carbon fibers with excellent mechanical and electrical conductive properties were used as electroactive materials and current collectors. However, most of these systems are combined with electrolytes without mechanical integrity (such as liquid or gel-type electrolytes), thus limiting the load-carrying performance of the battery. Currently the development of electrolytes for structural batteries remains challenging because the parameters enhancing electrochemical properties are often in contradiction with that for mechanical properties. In response to this challenge, the present study proposes a multifunctional composite electrolyte with balanced mechanical and electrochemical properties, which uses polyvinylidene fluoride (PVDF) as the matrix and metal-organic frameworks (MOF) modified glass fabric (MOF@GF) as the reinforcement. This study systematically investigates the following factors on mechanical and electrochemical properties of the composite electrolytes. Firstly, MOF with high specific surface areas and metal open sites onto the surface of glass fibers establishes a robust ion transporting network. With 20% MOF modified glass fiber and resin content 89%, the electrolyte exhibits high ion conductivity (1.74 × 10-3 S cm−1). In addition, by carefully controlling the resin content, a key parameter for fiber-reinforced composites, a delicate balance between mechanical strength and ionic conductivity can be achieved. Furthermore, interfaces were investigated, including glass fiber-MOF and MOF-PVDF interfaces, revealing the importance of effectively transfers stress and maintains structural integrity. Finally, these findings were combined to create a structural lithium metal battery that utilizes carbon fiber (CF) as the positive electrode and lithium metal as the anode. The resulting battery exhibits ultra-high tensile strength while maintaining a moderate capacity, ensuring normal operation under high voltage stress. This breakthrough discovery not only enhances the understanding of multifunctional composite electrolytes, but is also expected to promote further research and applications in the field of structural batteries. The promise of enhanced system electrolytes opens new avenues for lightweight design, space efficiency and expanded energy storage capabilities in electric vehicles and aircraft. Figure 1 . SEM images of (a) bare glass fiber. (b) MOF grown in-situ on glass fiber. (c) Single fiberglass within polymer matrix. (d) Cross section of the composite polymer electrolyte membrane. Figure 1

Finite Element Analysis of Flow-Electrode Capacitive Deionization

As access to freshwater diminishes due to climate change and population growth, drought-stricken regions across the globe continue to turn to groundwater and desalination. A largely untapped water resource in many parts of the world is brackish water - defined as water with total dissolved solids (TDS) in the range of 500 ppm to 10,000 ppm. Flow Capacitive Deionization (FCDI) is an electrochemical ion removal technology that is well-suited for the continuous desalination of brackish waters. Traditional Capacitive Deionization (CDI) consists of two fixed capacitive electrodes which are charged and discharged cyclically to capture ions from the solution being treated, and then regenerated to create a waste brine stream. During FCDI operation however, an applied potential drives ions out of a center water channel, typically through a pair of cation and anion exchange membranes (CEM/AEM), and into two flowing capacitive slurry electrodes (Figure 1). Because the electrodes are mobile, they can be moved into an adjacent cell for regeneration, thus enabling continuous operation of the desalination system without cyclical charge/discharge. The cathode and anode slurries typically consist of activated carbon suspended in a salt solution.Because the electrodes are flowing in FCDI, models describing this system must translate the Eulerian derivative to describe transient capacitive charge/discharge to a Lagrangian material derivative following the electrode material flowing through space. A flowing capacitive electrode is a significantly more complex system than a stationary porous and capacitive electrode matrix, incorporating the fluid dynamics of the slurries, ion transport within the slurry’s electrolyte medium, etc. Despite nearly a decade of research into FCDI, few researchers have probed the transient and spatially dependent mechanisms of ion transport and electro-adsoprtion within flow electrodes. While the overall electrodialytic contributions to ion capture within FCDI systems have been studied (1,2), the mechanism of competition between the electrodialysis and capacitive ion capture within the flow electrodes remains somewhat elusive. Additional analysis of the ion transport phenomena within these flow electrodes could bring forth insights into optimal design of FCDI devices and/or electrode formulations.In this study, an existing 2-dimensional mathematical model (3,4) for electrochemical flow capacitors is adapted to FCDI and solved via finite element analysis in COMSOL Multiphysics. Transport equations describing the advection of overpotential along with the flowing electrode are coupled with the Nernst-Planck equations which govern ion transport within the CEM/AEM, center water channel, and slurry electrolyte medium. This study investigates the effect of slurry flow velocity and sodium chloride concentration in the influent water on electrical potential profiles within an FCDI cell, and illustrates the active regions of capacitive electro-adsorption through the depth of the flow channel. Models of electrodialysis and FCDI are compared to understand the fundamental differences in driving forces for ion removal between the two technologies. The model shows agreement with experimental data through prediction of salt adsorption rate trends (mmol NaCl m-2 s-1) vs. influent sodium chloride concentrations. Through this analysis, it is shown that this model may serve as a valuable groundwork for expansion of FCDI modeling capabilities to include three dimensional cell geometries and subsequent optimization of operational parameters and cell dimensions. P. Nativ, Y. Badash, and Y. Gendel, Electrochem. Commun., 76, 24–28 (2017). J. Ma, C. He, C. Zhang, and T. D. Waite, Water Res., 144, 296–303 (2018). N. C. Hoyt, J. S. Wainright, and R. F. Savinell, J. Electrochem. Soc., 152, A652–A657 (2015). N. C. Hoyt, R. F. Savinell, and J. S. Wainright, Chem. Eng. Sci., 144, 288–297(2016). Figure 1

Synergy of Silicon-Graphene Anodes and Polymer-Ceramic Hybrid Separators for High Rate-Capable Lithium-Ion Batteries

With more and more electric vehicles (EV) hitting the market, the need for better and more robust energy storage system increases, and silicon has been a promising candidate for the next generation anode material to satisfy the high energy density and high-power requirements for electric vehicles because of its extremely high theoretical capacity. This has allowed the design of thinner electrodes to reduce the diffusion time scales and deliver a fast charge. However, at high charge and discharge rates, low electrical conductivity (~1.12 eV) of silicon hampers the battery performance. As a result, a lot of research has been conducted to improve the performance of silicon anodes using nanoscale carbon to increase the electrical conductivity. Graphene has been used to synthesize Si/Gr hybrid anodes due to its high conductivity.Graphene nanoribbons (GNRs) , a part of the graphene family, are one-dimensional graphene nanostructures which tune its electrical properties based on dimensional confinement. GNR has a higher conductivity than Graphene. It also has high aspect ratio and surface area to provide a strong conductive path along with mechanical strength to support the silicon anode. Due to presence of GNR, lithium-ion transport into silicon nanostructures was enhanced. As a result, 50% of graphene was replaced by 50% GNR with silicon nanoparticles to form anodes. Due to the highly conducting structure of GNR, capacity at high rates was significantly improved because of the improved silicon utilization. Since GNR’s dimensions are in nanometer range, connection with silicon nanoparticles is better. It not only improves silicon to silicon conductivity, but it also acts as a filler for better connection of graphene with silicon nanoparticles.Addition of graphene nanoribbons can improve the lithium-ion transport within the anode but to enhance the high charge transfer rate further, Si/GNR/Gr hybrid, high rate-capable anodes were paired with Polyimide (PI)/Polysilsesquioxane (PSSQ) hybrid separators which also shown to exhibit an improved charge transfer rate. At high rates such as 3C and 5C, the effect of separator on the cell performance becomes more prominent. While Celgard’s performance was very unstable at both 3C and 5C, at 3C, the cycling of hybrid separators did not get impacted, despite the relatively harsher conditions. This synergistic combination of high-rate capable silicon/graphene anode and hybrid separator outperformed the commercially used separator especially at high-rate cycling. Cells with Si/GNR/Gr anode paired with the PI/PSSQ separator delivered an impressive capacity of 1,000 mAh/g at high charge/discharge rates of 5C/5C.

Design and Additive Manufacturing of Electrodes for Electrochemical Energy Storage

Supercapacitors exhibit rapid charge/discharge times and have attracted considerable attention within the automotive, aerospace, and telecommunication industries. The high electrical conductivity and surface area of porous carbons have been attractive for supercapacitor electrodes. Fabricating thick electrodes is one strategy to further increase energy density due to a higher volume fraction of active material. However, thick electrodes suffer from sluggish charged species transport. In this work, we investigate the use of computational optimization and additive manufacturing to design and fabricate thick porous electrodes with improved performance. Electrode performance was maximized by designing their morphologies via topology optimization and printing by projection micro stereolithography (PµSL) using commercial resin (PR48). The PR48 resin was then pyrolyzed (PR48-P) to create the final conductive electrode. The optimized PR48-P electrodes exhibited 99% improvement in capacitance compared to control electrodes printed with cubic lattice morphologies. To further improve performance, we formulated a resin combining graphene oxide (GO) and trimethylolpropane triacrylate (TMPTA). Electrodes printed with 3 wt% GO in TMPTA exhibited improved capacitance retention after pyrolysis compared to the PR48-P electrodes. This work demonstrates the enormous potential of leveraging topology optimization and additive manufacturing to resolve many challenges in the electrochemical storage and renewable energy regimes. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. Lawrence Livermore National Security, LLC Figure 1

(Invited) Challenges and Opportunities in the Integration of CO2 Capture and Conversion

Over the past 15 years or so, the electroreduction of CO2 for the synthesis of intermediates for the chemical industry as well as for the synthesis of small molecule fuels has become a very active area of research. Activities span the whole value chain from electro-catalyst synthesis and characterization, to electrode and cell design and optimization, as well as studies on techno-economic feasibility and life cycle assessment of envisioned overall processes. In the vast majority of these studies, >98% pure CO2 is being used as the feed. In reality, CO2 feeds captured from industrial flue gasses or even those captured from air may not be close to 100% in CO2.This presentation will explore the integration of a nanomembrane-based CO2 capture method with different CO2 electrolysis approaches. The nano-membrane-based CO2 capture is based on work by Fujikawa and Selyanchyn (Polymer J. 2021, 53, 111), using polydimethylsiloxane-derived membranes that are preferentially permeable to CO2 over nitrogen. Multistage arrangement of modules comprised of arrays of membranes allows for efficient concentration of CO2 from air, from 420 ppm to tens of percent, using just vacuum pumps to drive the process. We explore the use of these concentrated CO2 streams that still contain nitrogen and some oxygen as the feed in subsequent CO2 electrolysis conversions to CO, to methane, or to other products, depending on catalyst choice. We study the effects of feed composition, catalyst chosen, and cell configuration on product speciation, conversion efficiency, etc.

(Invited) Insights from the Interplay of the Electrode Structure and the Microenvironment for Electrochemical CO2 Conversion

The electrochemical CO2 reduction reaction (CO2RR) represents a critical approach toward the carbon-neutral generation of hydrocarbons. However, despite intense research efforts, the need remains to increase the selectivity and activity of electrocatalysts for CO2RR. Thus, there has been increasing interest in optimizing the microenvironment to boost the activity and selectivity of electrocatalytic sites for CO2 conversion.This presentation discusses several strategies that are being pursued in my research group to optimize the microenvironment for CO2 conversion based on a detailed understanding of model systems for electrochemical CO2 conversion to C2+ products on Cu. Here, microenvironment-level insights from two model systems will be discussed: The effect of localization of Ag co-catalysts in Cu nanowire arraysThe impact of the 3D interface on the microenvironment within model Cu nanowire array cathodes to boost C2 product activity Overall, these insights can aid in the rational design of electrodes for electrochemical CO2 conversion. Figure 1

3D-Printed Hierarchical Electrodes for Ampere-Level Alkaline Water Electrolysis

In the realm of water electrolysis technology, Alkaline Electrolysis Cell (ALK) hydrogen production stands as a pivotal technology, playing a critical role in the pursuit of large-scale green hydrogen production and the achievement of the "dual carbon" objective. Despite its importance, the mass transfer efficiency of commercial porous nickel electrodes currently used in ALK systems is suboptimal. These electrodes, plagued by unstable catalyst loading, typically operate at current densities between 300-500 mA/cm², seldom reaching the desired threshold of 1 A/cm². This limitation hampers the potential of ALK hydrogen production to satisfy industrial-scale hydrogen production demands.In the quest to overcome these limitations, the concept of the Triple Periodic Minimum Surface (TPMS) structure, a cellular architecture mathematically defined and prevalent in natural biological forms such as butterfly wings and beetle shells, is introduced. The TPMS's unique geometry is adept at adapting to mechanical requirements for various applications, including structural and fluidic systems. It allows for versatile manipulation of geometric parameters like aperture size, porosity, and tortuosity, thereby substantially broadening the design possibilities for electrode structures and enhancing the efficiency of gas-liquid and electron transfer.To harness these benefits, we propose the creation of nickel/nickel-iron electrodes using 3D printing technology. These electrodes are characterized by their cross-scale porosity, ordered structure, and adjustable TPMS design. This innovative electrode design significantly augments bubble transport efficiency and mass transfer performance, while also providing additional anchor points for catalysts, thereby enhancing the electrochemical active surface area, intrinsic activity, and stability of the composite catalyst. As a result, these electrodes achieve ampere-level current densities in ALK electrolysis cells, enhancing electrolysis efficiency and reducing energy consumption.Our methodology involves the use of selective laser melting printing technology to fabricate multi-tier nickel/nickel-iron electrodes of varying specifications. These electrodes are then coated with MOOH catalysts using an electrochemical deposition process. Through rigorous testing and comparison of electrochemical performance parameters, we identified the optimal multi-stage nickel/nickel-iron electrode and its composite catalyst.Electrochemical performance tests reveal that, compared to traditional commercial porous nickel electrodes, our 3D printed electrodes decrease overpotential by 14% and improve electrolytic cell efficiency by 10% at a current density of 1 A/cm². Furthermore, these electrodes exhibit minimal degradation after a 500-hour durability test. The demonstrated efficiency and durability of these 3D-printed hierarchical electrodes indicate significant potential for their application in ampere-level alkaline water electrolysis. Figure 1

Operando Stress Evolution in Hard Carbon Anodes – Insight into the Mechanical Degradation Induced Failure Mode in Rechargeable Sodium Ion Batteries

Microstructural instabilities in electrodes arising from cycling induced stress is a primary failure mode in rechargeable batteries. Therefore, a quantitative knowledge of the cycling induced stress evolution in rechargeable battery electrodes is important for understanding the electrode microstructural instabilities during cycling that can potentially inform the electrode design to prolong battery cycle life. The cycling induced stress in electrodes typically arises from the volume changes associated with insertion/extraction of the electroactive species in the electrode matrix. For example, operando measurement of lithiation-delithiation induced stress in graphite electrodes that typically show 10% volume change has previously resulted in useful information that correlates well with the lithiation-delithiation mechanism in graphite anodes1. The size of the shuttling-electroactive species can be taken as an indicator of the cycling induced stress magnitude that drives the electrode microstructural instabilities. In this regard, quantification of the cycling induced stress in rechargeable Na-ion battery electrodes is warranted for understanding mechanical degradation induced failure modes owing to the larger size of the electroactive species, i.e., Na ions (vs. Li-ion).Hard carbons as potential anodes in rechargeable sodium ion batteries has gained considerable attention in the recent past due to their superior Na-ion storage capability (vs. graphite that is a canonical anode in rechargeable lithium-ion batteries). However, hard carbon anodes typically show significant capacity fade that can potentially arise from cycling induced mechanical degradation of the anodes. Operando stress measurements coupled with comprehensive electrode microstructural characterization will provide valuable insights in this context. Here we report on the operando stress evolution in hard carbon anodes in rechargeable sodium ion batteries as probed by Multiple Optical-beam Sensing (MOS) technique that basically involves monitoring the spacings among a group of laser spot (Fig. 1). Preliminary measurements have shown that the stress correlates with the potential with a maximum around 12 MPa in compression during sodiation and tensile stress of ~ 2MPa during desodiation. Operando stress measurements are performed in hard carbon anodes in two different electrode configurations – typical composite anodes (with binder and conductive agents) and hard carbon thin film anodes (without binder and conductive agents). The thin film configuration is considered to evaluate intrinsic stress response in hard carbon anodes in absence of any secondary phase. A comparison of operando stress response in these two types of hard carbon anodes along with comprehensive electrode microstructural characterization will be presented. Additionally, attempts will be made to shed light on the current debate in the mechanism of sodium storage in hard carbon anodes by comparing operando stress response of hard carbons from multiple sources along with their structural characterization (Raman, XPS, surface area etc.). V. A. Sethuraman, N. Van Winkle, D. P. Abraham, A. F. Bower, and P. R. Guduru, Journal of Power Sources, 206, 334–342 (2012). Figure 1

Electrocatalytic Reduction of Oxygen to Peroxide on a Microporous Carbon Layer in a Gas Diffusion Electrode: Implications for Scale-up

When coupled with renewables, the two-electron oxygen reduction reaction(O2RR) could be a valuable process to generate hydrogen peroxide (H2O2), a versatile and environmentally friendly oxidant[1]. While the electrocatalyst's nature determines the catalytic activity and selectivity (2e- vs. 4e- reduction), the O2 gas mass transport, electrolyte type (e.g., alkaline, neutral, or acidic) and its flow rate, and the electrode configuration (e.g., trickle-bed or gas diffusion (GDE) electrode) are also essential factors for scale-up[2-4]. Typically, operational current densities for O2RR are limited to less than 100 mA cm-2, which is inadequate for industrial applications. The porous gas diffusion electrode (GDE) assembly provides continuous O2 gas delivery at the catalyst/electrolyte interface by overcoming O2 mass transport limitations encountered in trickle-bed or dissolved gas (single-phase) configurations. While the GDE could enable the operation under industrially relevant current densities (i.e., > 100 mA cm-2), for two-phase flow processes, flooding imposes severe challenges in the GDE scale-up and the durability of the process. Here, we present that a microporous carbon-coated gas diffusion electrode could enable very high current density (> 500 mA cm-2) synthesis of alkaline peroxide in a flow reactor with more than 90% faradaic efficiency. The microporous carbon layer provides dual functionality, namely the catalytically active sites for the reaction and controlling the GDE flooding. In addition to the electrode design, the two-phase fluid flow dynamics and electrolyzer operation conditions are significant factors for long-term stability. Although the fluid flow effect on the trickle bed type electrolyzer has been studied [3], no study exists on the systematic investigation of the two-phase mass transfer effect in the GDE-based electrolyzer for peroxide generation with a catholyte layer. The experimental findings and mass transfer modeling highlight further improvements concerning the process scale-up.