Cathode Support Research Articles

A cathode support structure for use in a magnetron oscillator experiment

AbstractA low temperature co‐fired ceramic (LTCC) material system has been used to develop a protype field emission cathode structure for use in an experimental magnetron oscillator. The structure is designed for used with 30 gated field emission array (GFEA) die electrically connected through silver metal traces and electrical vias. To approximate a cylinder, the cathode structure (48 mm long and 13.7 mm in diameter) is comprised of 10 faceted plates which cover the GFEA dies. Slits in the facet plates allow electron injection. The GFEA die (3 mm × 8 mm) are placed in axial columns of 3 and spaced azimuthally around a cylindrical support structure in a staggered configuration resulting in 10 azimuthal locations. LTCC manufacturing techniques were developed in order to fabricate the newly designed cathode with seven layers wrapped to form the cylinder with electrical traces and vias. Two different cathode wrapping techniques and two different via filling techniques were studied and compared. Two different facet plate manufacturing techniques were studied. Finally, four different support stand configurations for firing the cylindrical structure were also compared with a square post stand having the best circularity and linearity measurements of the fired structure.

Inward growth of superthin TiC skin on carbon nanotube framework as stable cathode support for Li–O2 batteries

The rational design and synthetic route to fabricate stable air cathode supports, which combine high electron conductivity and desirable superoxide anion radical species (O2−)-against stability, remain critical but still challenging for sustainable Li–O2 batteries. Herein, a method of inward vapor-solid growth is proposed to prepare superthin TiC skin on multi-walled carbon nanotubes framework (MWNTs) as stable support (TiC/MWNTs) for air cathodes. By adjusting reaction temperature and time, the sp2-hybrid carbon walls of MWNTs are transformed into dense TiC skins layer by layer from outside to inside. The thickness of the transformed TiC skin can be controlled at a superthin nanosized magnitude of 3 ​nm. Benefiting from the seamless TiC surface layer, the TiC/MWNTs possesses both the advantages of MWNTs framework (light mass and high electronic conductivity) and TiC skin (excellent O2--against stability). Besides, by loading the catalyst of Ru nanoparticles on the obtained TiC/MWNTs support, the Li–O2 battery exhibits long-term cyclability (90 cycles) with little by-products (Li2CO3). The inward growth method is demonstrated to be also effective for graphene sheets and the conventional carbon blacks of Ketjenblack (KB). This achievement provides a new approach for surface enhancement of carbon electrodes from universal electrolyte corrosion problems.

Na3V2(PO4)3‐Supported Electrospun Carbon Nanofiber Nonwoven Fabric as Self‐Standing Na‐Ion Cell Cathode

AbstractSodium‐ion technology is a reliable alternative to lithium‐ion for large‐scale energy storage because of the abundance of sodium sources and related low cost. In this work, we report about a simple fabrication of self‐standing electrodes based on electrospun carbon nanofiber (CNF) loaded with Na3V2(PO4)3 with NASICON framework, which is a promising cathode material that has shown good electrochemical performance when its electrical conductivity is enhanced by a conductive medium. The proposed method is simple, low cost, potentially scalable to fabricate and load cathode support with active materials. The electrochemical tests confirmed the stable cycling performances and the high C‐rate capability of the NVP/CNFs composites, with hundreds of cycles without major degradation of performances. Our work demonstrates that stable, self‐supported, long‐term performing NIB electrodes, ready to use without addition of any performance enhancer, can be obtained by using fast and cost‐efficient procedures suitable to be scaled‐up at an industrial level.

Electron Gun Thermal Depended Properties’ Analysis of a High-Power ${W}$ -Band Sheet Beam Extended Oscillator

The studies of thermal-dependent properties, including the high-efficiency heater, thermal deformation of the cathode and focusing electrode (FE), and the associated beamforming problems of a sheet beam gun (SBG) for a ${W}$ -band sheet beam extended interaction oscillator (W-SBEIO), are presented. A simple but efficient method is proposed to complete the 3-D thermal simulations of SBG, including the contact thermal resistance. The heater efficiency is greatly improved by a three-layer folded cathode supporter. Almost 50% reduction in heating power (31.6–15.9W) is achieved at 1100 °C cathode temperature. The corresponding test was conducted on the optimized structure, and the experiment results validated its effectiveness. Besides, the axial thermal expansion is decreased by 38.9% and 47% for the cathode and the FE separately. The sheet beamforming deterioration caused by thermal deformation is studied by 3-D simulations. The prepositioning of cathode and bias potential of FE is applied to keep ideal beamforming with a 45-kV 2-A and 6.8 mm $\times0.36$ mm sheet beam.

One-pot conversion of carbon dioxide to CNT-grafted graphene bifunctional for sulfur cathode and thin interlayer of Li–S battery

Gaseous carbon dioxide (CO2) was converted into few-layered graphene sheets grafted by carbon nanofibers (G-CNFs) at the atmospheric pressure. The synthesis was performed in a one-pot route by the thermal Mg-aided reduction of CO2 in the presence of nickel nanoparticles that have a crucial role in the growth of carbon nanofibers. The produced G-CNF was bifunctionally applied as a cathode supporter for elemental sulfur and a thin interlayer for the separator in the Li–S battery. The graphene layers exfoliated by the carbon nanofibers enabled the formation of semi-freestanding membrane through sonication in a surfactant solution. They were attached on the separator to be used as a several micron-thick interlayer. The G-CNF employed as both cathode and interlayer materials enhanced the charge-discharge capacity and stability due to its low electrical resistivity and its role as a barrier to the polysulfides shuttle. As a result, a high capacity of 820 mAhg−1 and 640 mA h g−1 after 100 and 500 cycles were acquired at 0.5 C, respectively. The results suggest not only the facile one-step conversion of atmospheric CO2 to the exfoliated graphene grafted by carbon nanofibers, but also its outstanding electrochemical performance in the Li–S battery.

Three-dimensional twisted fiber composite as high-loading cathode support for lithium sulfur batteries

3D electrodes are widely researched for high sulfur loading, but still face challenges toward practical applications due to complex design, limited long cycling stability, and high volumetric changes. Herein, we report an efficient, facile, and cost-effective carbon-tungsten disulfide twisted cloth fibers (C/WS2-TCF/S) as a 3D cathode for Li–S battery. The C/WS2-TCF/S cathode combines the advantages of evenly-dispersed C/WS2 matrices and interconnected twisted cloth fiber networks which trap the polysulfide species, accommodate large active sulfur, and maintain the stable cycling performance even cycled at higher sulfur loading. In situ Raman spectroscopy further reveals the low shuttling effect observed with C/WS2-TCF/S cathode. With sulfur loadings of 2 mg cm−2, 3.5 mg cm−2, and 5 mg cm−2, C/WS2-TCF/S cathode shows high specific capacities at 1C. Moreover, for a sulfur loading of 4.5 mg cm−2, an initial discharge capacity of 722 mA h g−1 is delivered with capacity decay of 0.06% per cycle over 500 cycles at 0.5C. This work is valuable for the efficient design and preparation of high-loading cathode of lithium-sulfur batteries.

Comparing the electrocatalytic reduction of CO2 to CO on gold cathodes in batch and continuous flow electrochemical cells

The electrocatalytic reduction of CO2 on gold cathodes was found to differ significantly between a standard batch electrochemical cell and a flow cell incorporating a porous gold cathode. While the well-known influence of KHCO3 concentration on product selectivity was observed in the batch cell, the selectivity of the CO2 reduction reaction was shown to be independent of KHCO3 concentration in the flow cell. The Faradaic efficiency for CO production was found to be 80–90% regardless of the KHCO3 concentration whereas in the batch cell it decreased from 75% to 35% as the KHCO3 concentration is increased from 0.05 to 0.5 mol L−1. The current density was found to be independent of the KHCO3 concentration and similar in both cells (−4 to −10 mA cm−2 at −1.3 V vs Ag|AgCl). As the KHCO3 concentration effect is normally attributed to changes in the local pH at the cathode–electrolyte interface brought about by the buffering action of the electrolyte, the results found in this work suggest that pH buffering can be suppressed or manipulated in some cell/electrode configurations. In the flow cell used in this work, it is suggested that poor transport of the KHCO3 through the porous cathode support to the active surface results in higher local pH than that found at the surface of a cathode immersed in a traditional batch cell.

Size-Dependent Charge Storage Behavior of Mesoporous Hollow Carbon Spheres for High-Performance Li–Se Batteries

Hollow carbon spheres (HCSs) synthesized by a template-assisted hydrothermal carbonization approach have been evaluated as selenium cathode support in rechargeable lithium–selenium batteries. Homogenously formed hollow carbon microspheres upon selenium impregnation perform exceedingly well in lithium–selenium battery with a specific capacity of 500 mAh/g for 200 cycles. The unique carbon framework is capable of performing as a conducting medium as well as a polyselenide mediator, especially during charge/discharge cycles, owing to inherent benefits, such as a high surface area and porous nature. More importantly, the hollow nature of the carbon spheres is beneficial in reducing the volume expansion-related issues, resulting in good rate capability. Postcycling structural stability has been demonstrated by ex situ transmission electron microscopy studies of Se@HCS composite microsphere cathode, wherein no significant change has been noticed even after 200 cycles, thus substantiating the excellent electroch...

Magnetic circuit for mm-waveband magnetron with axial cathode support

Magnetic circuit for mm-waveband magnetron with axial cathode support

Catalytic CeO2 washcoat over microchanneled supporting cathodes of solid oxide electrolysis cells for efficient and stable CO2 reduction

Infiltration is an effective way to improve porous electrode performance of solid oxide cells while the preparation procedure and catalyst stability still remain challenging. The microchannel structure of cathodes enables the implementation of catalysts into conventional Ni-based cathode supports of solid oxide electrolysis cells via the infiltration process to accelerate CO2 electrolysis. Infiltrating a CeO2 colloid precursor to prepare catalytic washcoat has been demonstrated as a more efficient catalyst preparation and resulted in a more stable CO2 electrolysis performance, compared with infiltrating conventional nitrate precursors. The catalytic CeO2 washcoat possesses a uniform particle size distribution and strong adhesion to the cathode scaffold surface. The optimization of the infiltration process results in a remarkable stability of CO2 electrolysis performance during cell operation for 334 h owing to the stable catalyst microstructure.

3D‐Printed MOF‐Derived Hierarchically Porous Frameworks for Practical High‐Energy Density Li–O2 Batteries

AbstractAprotic Li–O2 batteries are promising candidates for next‐generation energy storage technologies owing to their high theoretical energy densities. However, their practically achievable specific energy is largely limited by the need for porous conducting matrices as cathode support and the passivation of cathode surface by the insulating Li2O2 product. Herein, a self‐standing and hierarchically porous carbon framework is reported with Co nanoparticles embedded within developed by 3D‐printing of cobalt‐based metal–organic framework (Co‐MOF) using an extrusion‐based printer, followed by appropriate annealing. The novel self‐standing framework possesses good conductivity and necessary mechanical stability, so that it can act as a porous conducting matrix. Moreover, the porous framework consists of abundant micrometer‐sized pores formed between Co‐MOF‐derived carbon flakes and meso‐ and micropores formed within the flakes, which together significantly benefit the efficient deposition of Li2O2 particles and facilitate their decomposition due to the confinement of insulating Li2O2 within the pores and the presence of Co electrocatalysts. Therefore, the self‐standing porous architecture significantly enhances the cell's practical specific energy, achieving a high value of 798 Wh kg−1cell. This study provides an effective approach to increase the practical specific energy for Li–O2 batteries by constructing 3D‐printed framework cathodes.

SDC-Infiltrated Microporous Silver Membrane with Superior Resistance to Thermal Agglomeration for Cathode-Supported Solid Oxide Fuel Cells

This work presents a microporous silver cathode membrane reinforced with infiltration of samarium-doped ceria (SDC). The ion-conducting SDC effectively confines the surface of a porous silver membrane to maintain microporous structure and prevents the electrode agglomeration. SDC precursor solution is fired together with silver membrane at 700 °C for 2 h and formed as a nanocrystalline SDC on the silver pore surface. The SDC-infiltrated microporous silver membrane shows superior resistance to agglomeration without noticeable change in microstructures even at 900 °C for 12 h, which makes it promising for the application of solid oxide fuel cells as a cathode support.

Effect of NiO/YSZ cathode support pore structure on CO2 electrolysis via solid oxide electrolysis cells

Gas diffusion within supporting cathodes of solid oxide electrolysis cells (SOECs) plays an important role in CO2 electrolysis process. This study has investigated the effect of cathode pore structure on gas diffusion during CO2 electrolysis. The cathode pore structure was adjusted by applying the different amounts of pore former during cathode preparation. The more pore former added produced the higher porosity of cathode and the higher limiting current density. High limiting current densities are beneficial to diminish or even eliminate gas diffusion limitation in practical applications, where the electrolysis is expected to be operated at low CO2 concentrations to increase CO2 conversion. An advanced impedance spectroscopy study is performed to confirm the limiting current density measured according to current-voltage curves. It was revealed that CO2 electrolysis performance is greatly affected by gas diffusion, which is determined by the employed cathode pore structure.

Investigation of proper external air flow path for tubular fuel cell stacks with an anode support feature

Although solid oxide fuel cell (SOFC) stacks are generally considered promising devices due to their many unique advantages, there are very few experiments and reports on anode support-type SOFC stacks with tubular (T-) designs, since it is quite difficult to determine a proper external air flow path design to support proper air and heat distribution qualities compared with cathode support T-SOFC stacks. In this paper, a large-scale 3D multiphysics model for the external air flow path of a convenient anode support T-SOFC stack is developed for the first time to investigate the general flow distribution characteristics of the external air flow paths. A novel external air flow path for an anode support T-stack is achieved by modifying the main and sub inlet/outlet manifolds, feed/exhaust headers structures and cross-section parameters. This new design is proven to greatly increase the air supply qualities among the tubes and over each tube surface and decrease the temperature gradients in the entire stack. The design could be the proper basic form used for anode support for T-SOFC stacks to achieve good stack performance and duration time in the near future.

Electrochemical conversion of CO2 over microchanneled cathode supports of solid oxide electrolysis cells

This study has demonstrated that microchanneled cathode supports of solid oxide electrolysis cells were developed to improve CO2 electrolysis performance. Through numerous channels embedded within the support, gas species can diffuse quickly to/from the reaction zone near the cathode/electrolyte interface, and efficient catalyst delivery to the reaction zone can also be achieved. The effect of channel size on CO2 electrolysis was investigated, and the smaller channel size results in the faster gas diffusion and the lower cell resistance. Therefore, this study reports a new strategy to improve CO2 electrolysis performance via refining the microchannel structure during a mesh-templating phase-inversion process.

Tuning the Adsorption of Polysulfides(Li2Sx) in Lithium-Sulfur Batteries with Metal-Organic Frameworks(MOFs)

The dissolution of polysulfide (PS) intermediates during discharge is a well-known obstacle to achieving long cycle-life in lithium-sulfur batteries. Prior work has shown that PS dissolution can be partially suppressed via physical encapsulation of sulfur and PS within a porous cathode support. Metal-organic frameworks (MOFs) are crystalline, nanoporous materials with extremely high surface areas, whose structure and composition can be varied extensively. MOFs are promising cathode support materials because the encapsulation afforded by MOF pores can be augmented by chemical adsorption of PS onto coordinately unsaturated metal sites (CUS). Here we demonstrate that this additive approach – restricting PS dissolution by combining encapsulation and adsorption within a MOF – can be tuned to maximize PS anchoring via metal substitution on the CUS. Optimal MOF compositions are pinpointed by computationally screening 16 metal-substituted variants of M2(dobdc) (MOF-74) for their ability to chemically anchor prototypical species (S8, Li2S4, and Li2S) present during the cycling of Li-S batteries. Ti2, Ni2, and Mo2(dobdc) are identified as the compositions with the largest affinities for Li2S4 and Li2S. As Ni2(dobdc) has been synthesized previously, this MOF is proposed as a promising cathode support for Li-S batteries. [1] R. Demir-Cakan et al., J. Am. Chem. Soc., 133, 16154 (2011) [2] J. Zheng et al., Nano Lett., 14, 2345 (2014). [3] H. Park and D. J. Siegel, Chem. Mater., 29(11), 4932 (2017)

Performance, Interactions, and Degradation of Polymer Electrolyte Fuel Cell Cathode Catalysts, Supports, and Ionomers

Over the past decade, the intrinsic oxygen reduction reaction (ORR) activity of platinum-based nanoparticle catalysts for polymer electrolyte fuel cells (PEFCs) has been improved by over an order of magnitude, with numerous catalysts now exceeding the catalytic activity target (>0.44 A/mg-Pt) established for the automotive propulsion power application.1-3 However, the majority of catalysts meeting the activity targets are unable to achieve the current densities at low catalyst loadings (cathode loading: 0.1 mg-Pt/cm²) necessary to meet the automotive performance and cost targets simultaneously.2 Many of the high activity catalysts also rapidly lose activity during voltage cycling in the PEFC environment.2,4 Research focus in recent years has broadened beyond catalyst activity improvement to the understanding the sources and mechanisms of activity and performance loss and using that knowledge to mitigate the losses. For example, the major source of electrochemically-active surface area (ECA) loss for platinum nanoparticles is dissolution of particles of <~4 nm, leading to the development of catalysts with larger as-prepared mean diameters .5,6 It has also been determined that base metal is rapidly lost from platinum-base alloy nanoparticles during electrode preparation and during voltage cycling in the fuel cell environment, leading to development of catalysts with lower initial base metal content and “pre-leaching” of base metal.4 In state-of-the-art catalysts, the platinum or platinum alloy nanoparticles are supported on high-surface-area carbon powders, such as Vulcan XC72R, Ketjen black, or graphitized carbon blacks. These inexpensive supports fulfill the necessary functions of electron conduction and dispersing and anchoring the catalyst particles. However, they are prone to oxidation and have weak interaction with the Pt nanoparticles. These shortcomings allow the nanoparticles to migrate and coalesce during fuel cell operation and to become disconnected from the support due to oxidation, leading to ECA loss, with support oxidation also causing loss of catalyst layer porosity.7 There have been extensive alternative support development efforts aimed at addressing these issues while maintaining the electrical conductivity of carbon (~2 S/cm).8 A wide array of alternative supports have been developed, including doped oxides, carbides,9,10 and nitrides, to name a few, but most lack the requisite high surface area and/or high electrical conductivity.8 While a improved materials are the ultimate solution to the carbon support instability issues, automotive fuel cell system developers have designed system-level mitigation strategies to allow the existing carbon supports to achieve the lifetime targets. A more recently-studied support issue is the impact of support structure on catalyst utilization.11 While the higher surface area carbon supports are desirable in terms of their ability to disperse the catalyst nanoparticles, they contain internal porosity. A significant portion of the catalyst nanoparticles can be buried in the pores.12 Limited proton conductivity in the pores leads to under-utilization of the buried catalyst particles at high current densities and, especially, under low humidity conditions.11 To overcome this limitation, recent efforts focus on catalyst deposition methods or carbon supports that can limit catalyst deposition to the external surface of the support.11,13 This presentation will give an overview of the current understanding of catalyst and catalyst support performance and performance stability and the interactions between catalyst, support, and ionomer that define these properties. The impact of catalyst and support degradation on the ionomer properties will also be discussed. AcknowledgementsThis work was supported by the U.S. Department of Energy (DOE), Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office under the auspices of the Fuel Cell Performance and Durability (FC-PAD) Consortium. Argonne National Laboratory is managed for the U.S. DOE by the University of Chicago Argonne, LLC, under contract DE-AC-02-06CH11357. References U.S. DOE FCTO Multi-Year Research, Development, and Demonstration Plan, 2016.A. Kongkanand et al., J. Phys. Chem. Lett., 7 (2016) 1127−1137.M. Debe, Nature, 486 (2012) 43–51.R. Mukundan, et al., 232nd Electrochemical Society Meeting, National Harbor, MD, Oct., 2017, 1681.J.A. Gilbert, et al., Electrochimica Acta, 173 (2015) 223-234.K. Yu, et al., Chemistry of Materials, 2014.L. Castanheira, et al., ACS Catal. 5 (2015) 2184–2194.Y. Shao, et al., J. Mater. Chem. 19 (2009) 46–59.M. Nie, et al., J. Power Sources, 162 (2006) 173-176.H. Chhina, et al, J. Power Sources, 179 (2008) 50-59.K. Shinozaki, et al., J. Electrochem. Soc., 158 (2011) B467-B475.K.L. More, “FC136 – FC-PAD: Components and Characterization”, 2017 DOE-FCTO Annual Merit Review and Peer Evaluation, June 6, 2017. https://www.hydrogen.energy.gov/pdfs/review17/fc136_more_2017_o.pdfA. Kongkanand, “FC144 – Highly-Accessible Catalysts for Durable High-Power Performance”, 2017 DOE-FCTO Annual Merit Review and Peer Evaluation, June 7, 2017. https://www.hydrogen.energy.gov/pdfs/review17/fc144_kongkanand_2017_o.pdf

Tailoring the pore structure of cathode supports for improving the electrochemical performance of solid oxide fuel cells

Two types of lanthanum doped strontium manganite (LSM)-yttria-stabilized zirconia (YSZ) composite cathodes were prepared, one with the finger-like straight open pores by the phase inversion tape casting, and the other with the randomly distributed tortuous pores by the conventional tape casting. A gas permeation flux of 42.5 × 105 Lm−2 h−1 was measured under a trans-membrane pressure of 0.6 bar for the former while only 10.6 × 105 Lm−2 h−1 for the latter. Fuel cells supported on the as-prepared LSM-YSZ composite cathodes were fabricated, comprising a 15 μm thick YSZ electrolyte layer and a 20 μm thick NiO-YSZ anode. The electrochemical performance of the fuel cells was measured using H2 as fuels and air as oxidants. The cell supported on the phase-inversion derived cathode showed a maximum power density of 362 mWcm−2 at 850 °C, while only 149 mWcm−2 for the cell supported on the cathode formed by the conventional method. The difference in the electrochemical performance between the two cells can be attributed to the pore structure of the cathode supports. It is concluded that the phase inversion tape casting provides a simple and effective approach for tailoring the pore structure of the cathode support and thus enhancing the electrochemical performance.

3D Pd/Co core-shell nanoneedle arrays as a high-performance cathode catalyst layer for AAEMFCs.

A novel cathode architecture using vertically aligned Co nanoneedle arrays as an ordered support for application in alkaline anion-exchange membrane fuel cells (AAEMFCs) has been developed. The Co nanoneedle arrays were directly grown on a stainless steel sheet via a hydrothermal reaction and then a Pd layer was deposited on the surface of the Co nanoneedle arrays using a vacuum sputter-deposition method to form Pd/Co nanoneedle arrays. After transferring the Pd/Co nanoneedle arrays to an AAEM, a cathode catalyst layer was formed. Without the use of an alkaline ionomer, the AAEMFC with the prepared cathode catalyst layer showed an enhanced performance with ultra-low Pd loading of down to 33.5 μg cm−2, which is much higher than the conventionally used cathode electrode with a Pt loading of 100 μg cm−2. This is the first report where three-dimensional Co nanoneedle arrays have been used as the cathode support in an AAEMFC, which is able to deliver a higher power density without an alkaline ionomer than that of conventional membrane electrode assembly (MEA).

A nanocatalyst network for electrochemical reduction of CO2 over microchanneled solid oxide electrolysis cells

A nanocatalyst network has been successfully prepared over the internal surface of Ni-based cathode support with a microchanneled structure via an impregnation process. Through numerous microchannels within the cathode support, a catalyst precursor solution was effectively delivered to the interface between cathode and electrolyte, resulting in the formation of the nanocatalyst network in the cathode reaction zone and therefore decreased degradation rate during CO2 electrolysis. After four coatings, the robust nanocatalyst network was formed to produce the least degradation, and further catalyst coatings caused concentration polarization.