Porous Electrode Structure Research Articles

Electrochemical CO2 Reduction Using Porous Cu Electrodes with Polymer Addition

Greenhouse gas emissions and following global climate change problems are the most important human-being facing issues. The electrochemical CO2 reduction reaction (CO2RR) is one of the most promising processes to obtain value-added hydrocarbons from carbon dioxide (CO2) and water (H2O), and the process is being actively investigated as an alternative way to conventional hydrocarbon production by fossil resources. Among the electrocatalysts for CO2RR, copper (Cu) species are unique and most studied material group because of their capability of producing C2+ species, such as ethylene (C2H4), ethanol (C2H5OH) and propanol, through forming C-C bonding. Especially C2H4 is the most highly demanded and profitable product[1]. Porous structure of electrodes is reported to be advantageous to CO2RR because it enables enrichment of reactants, CO2 molecules, and intermediates[2–5]. Polytetrafluoroethylene (PTFE), a hydrophobic polymer, has been reported to be beneficial to increase the FE towards C2+ products[6] and suppressing competitive reaction, hydrogen production[7,8]. In this study, we prepared PTFE modified porous Cu electrodes and investigated the influence of each factor and their synergistic effect on CO2RR activity. As a result, the introduction of porous structure increased FE to C2H4 (FE(C2H4)) and suppressed both carbon monoxide (CO) and methane (CH4) production. Further modification by PTFE enhanced FE(C2H4) and improved durability significantly. Porous Cu electrode was prepared by de-alloying process[9]. First, Cu and Al metals were co-sputtered to form CuAl alloy on gas-diffusion layer (GDL, MFK-A, Mitsubishi Chemical) coated with micro porous layer (MPL). The samples were etched using 5 wt.% hydrochloric acid for approximately 20 minutes to remove Al from the alloy and obtained porous Cu electrodes. CO2RR test was carried out in flow cell with gas-diffusion electrode (GDE), the electrocatalyst coated GDL, as a cathode under applied current density of 300 mA cm-2. Both gas phase products and liquidous products were quantified by gas chromatography (GC). Structural characterizations using scanning electron microscope (SEM) confirmed that porous Cu structure was successfully formed, and porous Cu electrodes exhibited higher FE(C2H4) of 48%, and lower FE toward CO (FE(CO)) of 6% and FE toward CH4 (FE(CH4)) of less than detection limit, while smooth Cu electrode showed FE(C2H4) of 45%, FE(CO) of 12%, FE(CH4) of 0.6%, respectively. However, FE(C2H4) started to decrease 6 hours after the start of the reaction and decreased to 12% after 24 hours reaction. This could be caused by GDE soaking to electrolyte. To overcome these issues, we next investigated PTFE added porous Cu electrodes. PTFE was introduced into the porous Cu layer by electrostatic spray[10].The introduction of PTFE further improved FE(C2H4) from 48% to 55% and demonstrated over 80% of FE towards valuable C2+ products at 300 mA cm-2. PTFE introduction enhanced durability and resulted in FE(C2H4) of 55% for over 24 hours.

Tailored 3D Porous N-Doped Carbon Nanospheres for Bottom-up Electrode Design - Independent Pore and Particle Size Control for the Use in Model Electrodes

Design of porous carbon-based electrode materials and derived porous electrode structures is crucial for the performance of electrochemical energy storage and conversion devices. In that context carbon-based electrode material building blocks with well-defined properties are desired. Such properties include controlled morphology (preferably spherical), particle size, and intra-particle porosity along with controlled composition, surface chemistry, and processability. These factors influence the particle arrangement and electrode structure during processing, as well as electrolyte interaction, distribution, and mass transport phenomena within the electrode.In this work, we introduce a hard-templating method for producing highly uniform meso- and macroporous N-doped carbon nanospheres with independently tuneable pore and particle sizes, serving as a versatile material platform for the bottom-up design of 3D porous carbon electrodes. We could thereby customize the pore sizes between approximately 10 to 100 nm at a constant particle size, while particle sizes between 50 and 300 nm could be achieved for a constant pore size. Other physicochemical parameters such as chemical composition, graphitization, and surface functionalization remained constant across all samples, allowing for the exclusive investigation of pore and particle size effects independently from each other.We further used our different N-doped carbon nanospheres as building blocks for 3D porous electrodes and studied these in electrochemical double-layer capacitors with the aim to (i) showcase the versatility of our materials and (ii) examine pore and particle size effects on the performance. Indeed, electrochemical double-layer capacitors serve as an excellent model system for such investigations due to their sensitivity to carbon particle surface area, pore size, and mass transport phenomena within the 3D percolated structure of porous carbon electrodes.

Effect of Short-Chain Polymer Binders on Mechanical and Electrochemical Performance of Silicon Anodes

Polymer binders are crucial components in providing both mechanical support and chemical stability to the structure of porous Li-ion electrodes. Particularly in silicon anodes, active material undergoes substantial volume expansion of up to 280%. As is shown in Figure 1, due to the restriction of the current collector, these silicon materials tend to expand vertically and so this requires substantial rearrangement of particles and plastic deformation.However, conventional binders such as polyacrylic acid (PAA) and polyimide (PI), while providing satisfactory initial capacity, suffer from mechanical rigidity due to their long polymer chains, leading to diminished long-term performance.Our research attempts to address this limitation by exploring the use of short-chain polymer binders, which may offer improved flexibility to accommodate the substantial volume changes of silicon particles. Although our previous work indicated that shorter polymer chains might compromise the adhesion to the copper current collector, we have developed a multilayer anode (MLA) structure featuring an adhesion layer to mitigate this issue. As is shown in Figure 2, this adhesion layer, placed between the silicon-containing bulk layer and the copper current collector, is designed to enhance the interface stability without sacrificing the mechanical compliance provided by short-chain polymers.Our experiments demonstrate that cells combining both long and short-chain PAA binders outperformed those with conventional PAA alone, delivering initial capacity of 2200 mAh/g at a 0.1C rate, compared to 1700 mAh/g for pristine PAA cells. At the early stages of development of the MLA-style anode with an adhesion layer, there was not an observed increase in performance, though experiments are ongoing, and we will report on latest results.We believe that the introduction of a strategic blend of different molecular weight binders can offer a promising solution to some of the challenges faced by silicon-based anodes. Figure 1

(Invited) Edlc Characterization of Carbon Electrodes with Micro to Narrow Mesopores

The capacitance of carbon electrodes on electric double-layer capacitors (EDLCs) is improved by controlling the pore structure to increase the surface area where the electric double-layer can form. Porous carbon electrodes with micropores and narrow mesopores, through which bare electrolyte ions can invade, exhibit a high capacitance [1-3]. Because the electrolyte ions exist as a solvated state with solvent molecules in the electrolyte solution, a desolvation process in pores is required to improve EDLC performance. The desolvation of electrolyte ions spontaneously occurs in certain pore structures. The unique phenomena in nanopores, which are different from those in the bulk phase, were reported in the 1990s [4-6]. One of the representative phenomena is called as "quasi-pressure effect," in which molecules introduced into the pore behave as if they were in a high-pressure field [7-9]. The abnormality in the carbon pores is caused by the strong interaction between the molecules and ions introduced into the pores and the carbon atoms forming the pore walls. Such a strong interaction may be a trigger for desolvation. Accordingly, the pore structure of carbon electrodes must be carefully evaluated to design an ideal porous structure that maximizes EDLC capacitance. Gas adsorption isotherm analysis is one of the techniques used to clarify the porous structure of carbon electrodes. Many analytical methods to determine the specific surface area and pore size distribution (PSD) of adsorption isotherms have been reported. However, the calculated values differed based on analytical methods. The PSD depends on the calculation theories and pore structure models to determine the theoretical adsorption isotherms, whose fitting with the experimental adsorption isotherm provides the PSD of the target porous carbons. Simple pore structures such as slit and cylinder structures have been widely used as pore models. Recently, a set of realistic three-dimensional porous structures was proposed as a model pore structure for porous carbons [10]. Such a realistic model is expected to be effective for evaluating the pore structures of carbon electrodes with micropores and narrow mesopores. On the other hand, it is also considered effective to select Mg ions, which are multivalent ions, as carriers to enhance capacitance. However, Mg ions have a higher solvation energy than Li ions: it is necessary to determine a suitable pore structure for Mg ions. In this study, we designed optimal porous structures of carbon electrodes by clarifying the electric double-layer formation of Li and Mg ions on micro-mesoporous carbons using electrochemical quartz crystal microbalance (EQCM) measurements, while comparing various pore structure determination methods for adsorption isotherms. Reference: [1] J. Chmiola, G. Yushin, Y. Gogotsi, C. Portet, P. Simon, P. L. Taberna, Science, 313, 1760-1763 (2006). [2] K. Urita, N. Ide, H. Furukawa, I. Moriguchi, ACS Nano, 8, 3614-3619 (2014). [3] K. Urita, C. Urita, K. Fujita, K. Horio, M. Yoshida, I. Moriguchi, Nanoscale, 29, 15643-15649 (2017). [4] S. Granick, Science 1991, 253, 1374-1379. [5]T. Iiyama, K. Nishikawa, T. Ohba, K. Kaneko, J. Phys. Chem., 99, 10075-10076 (1995). [6]L. D. Gelb, K. E. Gubbins, Rep. Prog. Phys., 62, 1573-1660 (1999). [7] J. Imai, M. Souma, S. Ozeki, T. Suzuki, K. Kaneko, J. Phys. Chem., 95, 9955-9960 (1991). [8]K. Urita, T. Fujimori, H. Notohara, I. Moriguchi, ACS Appl. Energy Mater., 1, 807-813 (2018). [9]Y. Komine, K. Urita, H. Notohara, I. Moriguchi, Chem. Lett., 51, 118-120 (2022). [10]F. Vallejos-Burgos, C. de Tomas, N. J. Corrente, K. Urita, S. Wang, C. Urita, I. Moriguchi, I. Suarez-Martinez, N. Marks, M. H. Krohn, R. Kukobat, A. V. Neimark, Y. Gogotsi, and K. Kaneko, Carbon, 215, 118431 (2023).

(Invited) Microstructure Modeling of Computer-Generated Microstructures to Guide Design of Solid-State Electrolyte Architectures

Due to the ever-increasing interest in solid state batteries, there is a significant amount of ongoing research on developing novel fabrication approaches for creating a variety of solid electrolyte microstructures. This is done with the goal of meeting the multiple design requirements and overcoming fundamental challenges associated with solid electrolytes. Microstructure modeling can be a powerful tool to study and analyze electrolyte microstructures and guide design of improved microstructures. There have been a limited number of studies that have developed and utilized microstructure models to analyze solid electrolytes and solid-state batteries [1, 2]. These studies are typically limited to analyzing experimentally fabricated microstructures by using experimental imagery for generating the computational domain. While this is necessary for validating microstructure models against experimental data, this is not useful for discovering improved microstructures. There have been some past studies in the case of both traditional lithium-ion batteries and solid-state batteries where computer-generated microstructures are considered to inform architecture design [3, 4]. However, these studies typically assume highly idealized porous electrode structures that are not representative of the microstructures that can be fabricated using existing fabrication methods. In the present work, we study computer-generated lithium lanthanum zirconium oxide (LLZO) solid electrolyte microstructures informed by the microstructures that have been fabricated by scalable fabrication methods [4,5]. Although computer-generated microstructures being analyzed may lack some of the finer features of the fabricated microstructures, the type of computer-generated microstructures to be studied will be restricted based on their manufacturability using the state-of-the-art fabrication techniques [4,5]. The design parameters of the computer-generated microstructures (e.g., pore size, shape, and surface features) will be varied to explore the solid electrolyte design space to study tradeoffs associated with key design requirements such as gravimetric and volumetric energy density, rate capability, and mechanical properties. In the future, we will be fabricating microstructures informed by this analysis to validate the model predicted performance characteristics.

Kinetic Investigation of Electrode Reaction Processes on Ni-GDC Cermet Fuel Electrodes for Reversible Solid Oxide Cells

Introduction Reversible solid oxide cells (r-SOCs) are electrochemical energy devices that can reversibly switch between power generation by fuel cell operation (SOFC mode) and hydrogen production by steam electrolysis (SOEC mode). R-SOCs can adjust the demand and supply in renewable energy utilization. In order to design high performance and durable r-SOC electrodes for practical usage, it is essential to systematically understand the electrode reaction processes and electrode degradation factors in both SOFC and SOEC modes. Such fundamental information is also necessary for the analysis of electrode performance and the development of performance simulation models. The dependence of polarization resistance on electrode fabrication conditions and operating conditions has been investigated using steady-state polarization and impedance measurements for electrode materials used in either SOFCs or SOECs, and rate-determining reactions have also been discussed [1-5]. However, it is necessary to evaluate the electrode reaction mechanisms of electrode materials suitable for r-SOC operation in an integrated and detailed manner. Therefore, this study aims to systematically evaluate the similarities and differences in the fuel electrode reaction processes in both SOFC and SOEC modes from the viewpoint of dependence on operating conditions by using the distribution of relaxation times (DRT) analysis. Experimental As shown in Figure 1 (a), Ni-GDC cermet, a composite of Ni and mixed-conducting Gd0.9Ce0.1O2 (GDC), was used as the fuel electrode material, ScSZ as the electrolyte, and (La0.6Sr0.4)(Co0.2Fe0.8)O3 (LSCF) as the air electrode. GDC layer was inserted between the air electrode and the electrolyte plate as a buffer layer. Electrochemical impedance measurements were performed by supplying H2-H2O gas mixture to the fuel electrode of the fabricated cell, and varying operating temperature, H2-H2O ratio, and current density. Measurements were carried out in both SOFC and SOEC modes. The obtained impedance data were subjected to the DRT analysis to separate the polarization resistance components of the fuel electrode in the relaxation time domain of the electrode response. The area of each DRT peak corresponds to the resistance of each electrode process from which each peak originates. In this study, the dependence of the resistance of each DRT peak on the operating conditions was quantitatively investigated. As shown in Figure 1 (b), the microstructure of the electrodes was observed using FIB-SEM, confirming a porous electrode structure. Results and Discussion Figure 1 (c) shows the operating temperature dependence of the typical DRT peaks of the Ni-GDC cermet fuel electrode, in SOFC mode. In the range of 10-1 to 106 Hz where the frequency response was measured, three main DRT peaks appeared, P1: 10-1 to 100 Hz, P2: 100 to 102 Hz, and P3: 102 to 103 Hz, all DRT peak areas decreased with increasing operating temperature. In the presentation, the dependence of each DRT peak on operating parameters and the related electrode reaction processes will be discussed.

Mechano-Electro-Chemical Impedance Spectroscopy (MeIS): Concept, Theory and Experiment

Electrochemical impedance spectroscopy (EIS) is a widely used non-invasive method for characterizing and diagnosing lithium-ion batteries (LIBs)1. The key to utilizing EIS lies in interpreting the measured impedance spectrum. This involves fitting the experimental data to an impedance model to understand the internal states of the battery. However, due to the multiscale and multiphysical nature of LIBs, impedance models can be complex and have many parameters. As a result, there is a high risk of over-fitting the experimental data, making the interpretation of the EIS data challenging2. In addition to electrical signals, the mechanical responses of a LIB, such as pressure and thickness change during charge/discharge, provides valuable information for characterization and diagnosis3-5. Most existing analyses of mechanical signals focus on the time domain. Recently, von Kessel et al6 introduced Mechanical Impedance Spectroscopy (MIS) as a frequency-analyzing tool for characterizing LIBs. The MIS spectrum (the displacement response subject to a cyclic pressure trigger) turned out to vary with the state of the batteries, demonstrating the great potential of using mechanical responses in the frequency domain to characterize and diagnosis the LIBs. Nevertheless, measuring displacement for LIBs in real-world applications is challenging, as it requires a customized testing machine to measure the micrometer-level displacement while exerting a sinusoidal pressure input. This requirement for customized testing equipment limits the application scope of the MIS method.A free LIB cell cyclic changes its dimensions during charge/discharge. Under confinements where dimension change constricted, cyclic pressure change will be generated, which could be used for frequency analysis. This observation led us to propose a new method called mechano-electro-chemical impedance spectroscopy (MeIS). An MeIS spectrum is defined as the ratio of pressure perturbation to the input current, denoted as . Measurements can be obtained by perturbating the battery with sinusoidal current and recording the resulting pressure or displacement response. The basic transfer function for MeIS is derived from the electro-chemo-mechanical coupling of the porous electrode. The MeIS consists of two parts, the MIS term and an electrochemical term resulting from the insertion/extraction deformation of the electroactive particles. The great advantage of MeIS is that it requires only a pressure or displacement sensor and a charger capable of providing sinusoidal current, making it potentially applicable in in-field scenarios such as management of EV batteries or real-time monitoring of a battery-based energy storage facility. Sensitivity analysis reveals that MeIS is highly sensitive to changes in the structure of porous electrodes, thus providing valuable insights into the internal structural integrity and degradation of LIBs. In addition, the experimental design and demonstrational results are also provided. We believe that MeIS could serve as a convenient and useful complement to EIS, enhancing the non-invasive diagnostic toolbox for LIBs.Reference: K. Mc Carthy, H. Gullapalli, K. M. Ryan, and T. Kennedy, Journal of The Electrochemical Society, 168 (8), (2021).F. Ciucci, Current Opinion in Electrochemistry, 13 132-139 (2019).J. Zhu, T. Wierzbicki, and W. Li, Journal of Power Sources, 378 153-168 (2018).B. Rieger, S. Schlueter, S. V. Erhard, J. Schmalz, G. Reinhart, and A. Jossen, Journal of Energy Storage, 6 213-221 (2016).Z. J. Schiffer, J. Cannarella, and C. B. Arnold, Journal of The Electrochemical Society, 163 (3), A427-A433 (2015).O. von Kessel, T. Deich, S. Hahn, F. Brauchle, D. Vrankovic, T. Soczka-Guth, and K. P. Birke, Journal of Power Sources, 508 (2021). Figure 1

Thermo-Mechanical Properties and Benefits of Borosilicate Glass for SOEC Sealants

Boro-silicate glass materials have ideal properties for sealing oxidizing and reducing environments and electrically insulating solid oxide electrolysis cells (SOEC), while maintaining a glassy phase at high temperatures (750-900°C) to minimize chemo-mechanical degradation and gas permeability 1,2. Glass seals are typically applied as a slurry; hence, they are also expected to have non-wetting properties to prevent glass infiltration into the porous electrode structures during manufacturing 3. During the first startup, the initial temperature ramp serves to evaporate any binder in the slurry and to go through the glass transition phase, which cures the glass and increases hardness to improve resistance to creep. Typical glass materials operate in visco-plastic regimes (i.e., beyond the material’s glass transition temperature) and must be chemically stable while operating in steam-rich and oxygen-rich environments. To fully understand the performance of borosilicate glass seals, optimize the manufacturing, assembly, and maintenance of SOEC, we must be able to measure and analyze the glass material properties (i.e., glass transition temperature, coefficient of thermal expansion, modulus, creep, hardness) at the same operating conditions relevant for SOEC operation. In this work, we characterize the thermo-mechanical properties of borosilicate glass powder and sintered samples at various temperatures (ranging from ambient to 850°C), and at different aging conditions (i.e., atmosphere composition, temperature, and duration). The atmosphere composition is changed between air, steam-N2 mixtures, and H2-N2 mixtures to evaluate the chemical stability of borosilicate glass relating to the possible depletion of boron and silicon via the formation of boron hydroxide and silicon vapor when exposed to steam- and hydrogen-rich environments. The aging temperature and duration is varied to evaluate the crystallization kinetics, particle size growth, and its effect on mechanical properties. We employ a combination of Simultaneous Thermal Analysis - STA (i.e., combined Thermogravimetric Analysis - TGA, Differential Scanning Calorimetry - DSC, Fourier Transform Infrared - FT-IR spectroscopy, and Quadrupole Mass Spectroscopy - QMS), and nanoindentation as characterization techniques, while surface roughness is estimated with a 3D confocal optical microscope.Surface roughness varies between 0.83-1.38 𝜇m ± 1.1-1.76 𝜇m (Sa ± Sq). Both powder and solid samples are analyzed via STA with sequential temperature ramps (constant heating rate at 10 K/min in Ar atmosphere) up to 1500°C to estimate the effect of crystallization and particle size on the glass transition onset. For a sample aged at 850°C for 340 h, the first ramp shows typical DSC exothermic peaks (mW/mg) at around 800°C, with a midpoint glass transition occurring at 900°C. However, on the second ramps, peaks lower to around 500°C and the glass transition is estimated to be around 700°C. Subsequent tests consistently mirrored the trend of the second temperature ramp, showing minimal deviation and influence of crystallization and particle growth. Nanoindentation is performed between room temperature and 600°C to characterize both sintered glass samples “as-received” and aged at temperatures between 750-950°C for 340 h. Comparing a sample aged at 750°C with an “as-received” sample, the elastic moduli equally decreased from 100 GPa at room temperature to 40 GPa at 600°C, with comparable hardness values ranging from 10 GPa at room temperature to 0.5-0.9 GPa at 600°C, respectively. A.G. Sabato, G. Cempura, D. Montinaro, A. Chrysanthou, M. Salvo, E. Bernardo, M. Secco, F. Smeacetto, Journal of Power Sources, 328, 262-270 (2016)Dilshat U. Tulyaganov, Allu Amarnath Reddy, Vladislav V. Kharton, José M.F. Ferreira, Journal of Power Sources, 242, 486-502 (2013)S.-B. Sohn, S.-Y. Choi, G.-H. Kim, H.-S. Song, G.-D. Kim, Stable sealing glass for planar solid oxide fuel cell, J. Non. Cryst. Solids. 297 (2002) 103–112. doi:10.1016/S0022-3093(01)01042-0 Figure 1

Magnetized microcilia-based triboelectric nanogenerators with mechanoluminescence for energy harvesting and signal sensing

Flexible triboelectric nanogenerators with multimodal sensing capabilities have received considerable attention due to their potential for the development of wearable technology. However, the accurate and reliable display of motion trajectories represents a significant challenge. The structure design of the triboelectric nanogenerators yarn with magnetized microcilia and mechanoluminescence (MLY-TENG) was designed, which can be woven into the fabric of display force trajectories. The positive electrode is constructed by the braided yarn with a porous structure, consisting of polyurethane formed by wet spinning. Meanwhile, the flexible negative electrode is designed by the recombination of magnetized microcilia and the mechanoluminescent structure of polydimethylsiloxane, matching with the porous structure of the positive electrode, which enhances the electric transfer. At a compression depth of 100 %, compression frequency of 5 Hz, and magnetized powder of 50 wt%, the proposed MLY-TENG shows the triboelectric properties of 109.2 V and exhibits excellent cyclic stability. Furthermore, the magnetized microcilia on the luminescent magnetized microcilia (LMM) film with the polyurethane-copper-polyurethane (PWP)-based fabric (MLF-TENG) distinguishes the shape and area of object recognition with electrical signals and visual sensing of mechanoluminescence. The MLY-TENG offers the possibility of the development of advanced visualization techniques for wearable electronic devices.

High micropore‐utilization carbon aerogel with controlled nanostructures via adjusting aggregation state of polyacrylonitrile for energy storage systems

AbstractDesigning and optimizing the pore structure of porous carbon electrodes is essential for diverse energy storage systems. In this study, an innovative approach spray phase‐inversion strategy was developed for the rapid and efficient fabrication of controlled porous carbon aerogel. Moreover, the aggregation structure of polyacrylonitrile is controlled by adjusting the Hansen's solubility parameter, thereby regulating the electrode material structure. Furthermore, the theoretical analysis of the spray phase‐inversion process revealed that this regulation process is jointly regulated by solvent hydrodynamic diameter and phase‐inversion kinetics. Through optimization, a novel porous carbon material was obtained that exhibited excellent performance as an electrode material. When utilized in supercapacitors for energy storage, it demonstrated a high specific capacitance of 373.1 F g−1 in a 6 M KOH electrolyte solution. Simultaneously, it has been observed that the preparation strategy for porous electrodes offers notable advantages in terms of excellent designability, broad universality, simplicity, and high efficiency, thereby holding promise for large‐scale fabrication of diverse porous electrode materials and various types of electrodes for diverse energy storage applications.

Effects of foam cathode electrode structure on alkaline water electrolysis for hydrogen production

Hydrogen is widely recognized as a clean and sustainable energy source. One of the most promising methods for hydrogen production is alkaline water electrolysis. The efficiency and cost-effectiveness of this process heavily depend on the choice of a suitable porous electrode structure. This paper aims to investigate impact of the porous structure on the performance of alkaline electrolytic water through experiments and multi-physics field simulation. Specifically, the whole cell performance test and hydrogen-evolution reaction (HER) test of nickel foam were conducted in an electrolytic cell using 1 M KOH. Results revealed that various parameters of the electrode structure, such as specific surface area, pore density, thickness, and electronic conductivity, significantly influenced the hydrogen evolution. Increasing the specific surface area or pore density proved to enhance the hydrogen evolution under conventional voltage. Reducing the thickness has a similar effect. Additionally, materials with high conductivities increase the reaction rate. Based on experimental results, the optimal nickel foam cathode structure was 1000 μm thickness and 75 PPI pore density. The results of stability tests and electrolysis voltage efficiency analysis provide further support for the positive effect of this structure on hydrogen evolution. This study provides rational reference for designing efficient and stable porous electrode structures.

Manufacturing Free‐Standing, Porous Metallic Layers with Dynamic Hydrogen Bubble Templating

AbstractThe 3D structure (i.e., microstructure) of porous electrodes governs the performance of emerging electrochemical technologies such as fuel cells, electrolysis, and batteries. Sustaining electrochemical reactions and convective‐diffusive mass transport at high efficiency is complex and motivates the search for sophisticated microstructures with multimodal pore size distributions and pore size gradients. Here a new synthesis route for porous, metallic layers is presented that combines the characteristics of carbon structures (i.e., pore size, porosity) with the properties of metals (i.e., recyclability, conductivity). Building on the method of dynamic hydrogen bubble templating, a novel approach is engineered to manufacture thin, free‐standing layers using an electrochemical flow cell through the introduction of an intermediate layer and optimization of the synthesis parameters. Mechanically stable layers are created with thicknesses ranging from ≈50 to ≈200 µm comprising porous, dendritic structures, arranged to form a vascular network of larger pores with a gradient in radii from ≈5 µm at the bottom and up to ≈36 µm at the top of the material. Using X‐ray tomographic data, the morphology is analyzed, and the diffusive transport through the material as a function of liquid filling is simulated and compared to state‐of‐the‐art carbon fiber‐based electrodes, showing significantly higher mass transfer properties.

Local oxygen transport resistance in polymer electrolyte fuel cells: origin, dependencies and mitigation

Next-generation polymer electrolyte fuel cells (PEFCs) require an integral design of the porous structure of electrodes at different scales to improve performance and enlarge durability while reducing cost. One of today’s biggest challenges is the stable, high-performance operation at low Pt loading due to the detrimental effect of the local oxygen transport resistance caused by ionomer around catalyst sites. Hindered local oxygen transport arises from sluggish kinetics at the local reaction environment, that comprises adsorption at (wet) ionomer and Pt interfaces, and diffusivity of gas species in ionomer and water. Diverse factors affect oxygen transport, including operating conditions (relative humidity, temperature, and pressure), ionomer content and morphology, ionomer heterogeneity, porosity of carbon support, catalyst dispersity, and flooding. To attain performance and durability targets, it is essential to maximize the oxygen utilization of the catalyst layer by implementing enhanced membrane electrode assembly architectures. This involves employing advanced catalyst layer preparation techniques, including electrospraying, to generate optimized highly porous morphologies. Furthermore, achieving these targets necessitates the development of new materials with tailored properties, such as high permeability and porous ionomers, among other innovative strategies.

Application of Multistage Drying Profiles for Accelerated Production of Li‐Ion Battery Anodes Using Infrared Radiation: Validation with Electrochemical Performance and Structural Properties

The drying of solvent‐processed electrodes is a critical process step in the manufacturing of lithium‐ion batteries. The technology used to introduce the energy required for drying into the material, combined with the specified process parameters, significantly influences the resulting electrode properties. A major challenge is to counteract binder migration effects that may occur during drying of the porous electrode structure, causing a decrease in adhesion and electrochemical performance, especially for high drying rates. From this motivation, investigations on the influence of process design during near‐infrared drying of aqueous‐processed graphite anodes are carried out. A multistage drying design with varying parameters in specific drying sections with energy input by radiation is applied. The results show that the specific application of a three‐stage drying profile in combination with energy input by radiation enables a significant decrease in drying time by at least 60% while the electrode properties can be preserved. These findings indicate a beneficial development of binder distribution as a consequence of multistage NIR drying, evidenced by adhesion and electrochemical performance. Finally, the application of the multistage drying profile is theoretically transferred to an industrial‐scale roll‐to‐roll dryer, whereby the necessary dryer length can be reduced by 53%.

Synthesis of nanoporous solid polymer electrolyte AuNiCe/NC hydrogenation membrane electrode

In this study, using graphite fiber cloth as the support, gold-based solid polymer electrolyte (SPE) membrane electrodes were synthesized by high-vacuum ion beam sputtering, nitrogen doping of the support, combined electrochemical dealloying, and hot-pressing technology. The application of the SPE membrane electrode to couple hydrogen evolution and liquid organic hydrogen storage is of significant importance for sustainable hydrogen energy and efficient carbon dioxide conversion. Using various characterization techniques, we systematically analyzed the phase structure, surface morphology, porous structure, and electrocatalytic performance of the membrane electrode for the hydrogenation of cyclohexene. The results indicated that doping the carbonaceous support with nitrogen (NC), doping with cerium as catalyst promoter, and combined electrochemical dealloying can all enhance the activity of the catalyst. Cerium doping provides the catalyst with oxygen vacancies for accelerated electron transfer. After combined electrochemical dealloying, AuNiCe/NC formed a three-dimensional bicontinuous porous structure. The electrochemically active surface area increased by 23.94 times, the energy consumption of catalytic cyclohexene hydrogenation decreased by 35.7%, and current efficiency and the formation rate of cyclohexane increased by 54.9% and 29.4%, respectively.

Three-dimensional porous polyimide anode for high-rate lithium ion batteries

Polymeric electrode materials are widely used in many applications but still suffer from poor electrical conductivity and slow transport kinetics, especially poor performance at high current densities. Herein, a polyimide electrode structure with 3D-ordered interconnected gradient pores was developed to improve the lithium-ion transport efficiency. The homogeneous mixed PMTA-PMMA composite was prepared by a simple one-pot method, followed by removal of PMMA (polymethyl methacrylate) spherical porogenic agent during the synthesis of polyimide material at high temperatures to form a low curvature gradient-pore structure. The large pores in the electrode enhanced the ion transport ability and improved the electrolyte infiltration rate, while the small pores improved the active specific surface area and guided the deposition of lithium ions. As a result, a high specific capacity reaching 907 mAh/g was maintained even after 1000 cycles at 5 A/g, a value about 3-fold that of un-pored electrode materials. The experimental studies and DFT calculations were used to develop a 24Li storage mechanism of PMTA, and the active electrode material was fully electrochemically activated by the constructed three-dimensional porous electrode structure. Overall, the proposed porous material with a high active area and porosity looks potential for use as an ultra-fast charging and discharging electrode of lithium-ion batteries with high specific capacity and excellent cycling performance.

Synthesis of flower-type nanorods with Zn-doped manganese vanadate (Mn(VO3)2) and carbon nanofibers (CNFs) for enhanced performance in battery-type supercapacitors

Among the various novel electrode materials prepared to enhance the electrochemical performance of supercapacitors, ordered nanoarray structures stand out as highly promising candidates for use as binder-free electrodes. In this study, flower type nanorods of zinc manganese vanadate (MnZn3(VO4)2) grown on 3-D nickel foam, with additional incorporation of Carbon nanofibers (CNFs)(MZVC) by using a one-step hydrothermal method. The nanostructured MZVC electrode exhibited a specific capacitance of 469 Fg−1 at a current density of 0.5 Ag−1, surpassing the specific capacitance values of the pristine electrodes (ZV-304 Fg−1, MV-263 Fg−1) and MZV − 333 Fg−1) at the same current density. Remarkably, the MZVC composite electrode exhibited an exceptional retention rate of approximately 82.6 % even after 5000 charge–discharge cycles. All of the fabricated electrodes underwent comprehensive characterization utilizing different analytical techniques to assess their structural, and surface morphological attributes. Further, Electrochemical behavior was assessed for ZV, MV, MZV, and MZVC nanostructures through cyclic voltammetry (CV), galvanostatic charge /discharge (GCD), and electrochemical impedance spectroscopy (EIS). This 3D porous flower-type electrode structure offers an abundance of active sites for electrochemical reactions, enables efficient electron and ion transport, and mitigates the aggregation of MZVC flower structures throughout prolonged cycling.

Investigation of the catalyst ink compositions for a uniform microporous catalyst layer preparation via electrospray deposition technique and MEA assembling conditions in PEMFC specific

High utilization of catalyst and preserving evenly distributed pores for Proton Exchange Membrane Fuel Cell (PEMFC) electrodes were optimized using an in-house designed electrospray system. In order to hold the porous electrode structure prepared through the electrospray technique by varying ink compositions. Using optimized electrodes and commercially available Nafion-212 membrane, a series of membrane-electrode assemblies (MEAs) were fabricated by varying the hot-pressing parameters of pressure, temperature, and time for evaluating the performance at 60 °C to 80 °C with varying relative humidity. The MEAs were hot-pressed at 8 MPa for 390 s at a temperature of 150 °C generating a maximum peak power density of 903 mW cm−2 and current density of 1040 mA cm−2 at 0.6 V and calculated electrochemical surface area (ECSA) is 23.96 m2/gPt. In contrast, the MEAs hot-pressed for the same length of time at the same temperature but with a lower pressure of 2.67 MPa generated higher peak power density of 1130 mW cm−2, higher current density of 1320 mA cm−2 at 0.6 V, despite having a lower ECSA of 19.18 m2/gPt. Overall, results in this study present that low hot-pressing pressure and a high pressing temperature enable a negative effect on the porous structure of electrospray electrodes for producing the high achievement of MEA performance.

Spherical hard carbon/graphite anode for high performance lithium ion batteries.

The issue of long charging time for electric vehicles has been a matter of serious concern, and the problem is mainly stemmed from the graphite anode. The slow kinetics of pure graphite can lead to the formation of the lithium metal during fast charging, which triggers cycle degradation and safety issues of electric vehicles. In order to ameliorate the fast charging issue, a spherical hard carbon/graphite porous electrode is devised. Based on this, the discharge capacity ratio at 3C shows an improvement of about 40% at 25°C and at 1C shows an improvement of about 18% at 0°C. Additionally, the 300-cycle capacity retentions exhibit increases of 12% and 14% at temperature of 25°C and 50°C, respectively. Generally, the analysis shows that the spherical hard carbon/graphite porous electrode has more uniform porous structure, shorter transport path, less nano-scale powder and a certain voltage buffer ability compared to the pure graphite powder system, which enhance the ion transport kinetics, and reduce the side reactions under the high temperature, so as to effectively improve the fast charging performance and cycle life of the LIBs. It is also proved that the kinetics improvement is not only attributed to the high kinetics inherited from the instinct of hard carbon, but also the porous electrode structures constructed by the two-size powder system of graphite and hard carbon.

Development of Nanoporous Nickel Oxide Materials as Electrodes for Supercapacitors

As a potential electrochemical energy storage device, supercapacitor has been researched owing to its low weight, excellent power density, outstanding charging rate, and long durability. For the supercapacitor, the electrode material and its morphology determine its overall performance. Nickel oxide (NiO) is a promising material for the electrode because of its low cost, high specific capacitance, and eco-friendly manufacturing process. In this research, we developed a simple and cost-effective method to fabricate supercapacitor electrodes by electrospinning and thermal annealing, making porous nickel oxide nanofibers directly grow on 3D-nickel foam. The binder-free design and porous structure of electrodes enhance the ion transport and electron transfer in the supercapacitor. The crystal structure of NiO was identified by X-ray diffractometry (XRD). The morphological and microstructural characterization was analyzed by scanning electron microscopy (SEM). The electrochemical test was carried out in a three-electrode electrochemical cell with the obtained foamed NiO as the working electrode, the platinum sheet as the counter electrode, and the Ag/Cl electrode as the reference electrode. The electrochemical performance was evaluated by using cyclic voltammetry (CV), galvanostatic charge/discharge technique, and electrochemical impedance spectroscopy (EIS). Due to the large specific surface area and good electrical conductivity of the NiO electrode, the supercapacitor exhibited excellent electrochemical performance (591 F/g at 2 A/g). After 1500 cycles of charging and discharging at 10 A/g, the capacitance of the supercapacitor using the NiO electrode increased by 21.7% with excellent cycle stability.