Reactive Spray Research Articles

Manufacturing of porous aluminum 2024 alloy samples with impressive compression properties

In the present work; nanocrystalline porous aluminum samples are manufactured using reactive spray atomization following an efficient procedure. The samples showed the best specific energy absorption density value in compression for aluminum on densification close to 0.06 MJ kg−1 at quasistatic loading, which is the best-recorded value for a bulk material according to authors knowledge. The reasons for such high compression plastic properties are due to a nano-sized intermetallic phase Al2Cu and nano stringers Al2O3 located on the walls of elliptical shape thick wall pores. The aforementioned structural features increased the strength for these samples and enabled absorption of high energy more than other materials. The high performance of the prepared samples and the cheapness of the present method can open new horizons for aerospace and automotive aluminum industries.

Tuning of WO3 Phase Transformation and Structural Modification by Reactive Spray Deposition Technology

Tuning of WO3 Phase Transformation and Structural Modification by Reactive Spray Deposition Technology

Nano-size IrOx catalyst of high activity and stability in PEM water electrolyzer with ultra-low iridium loading

The balance of catalyst loading, activity and stability remains a challenge for the anode of proton exchange membrane (PEM) water electrolyzers. Here we report a nano-size IrOx/Nafion® composite catalyst that exhibits both outstanding activity for oxygen evolution reaction (OER) and stability in a PEM water electrolyzer. The IrOx/Nafion® catalyst layer is fabricated using a flame-based cost-effect process, reactive spray deposition technology. The IrOx/Nafion® catalyst shows >10 times improvement in OER mass activity compared to IrOx nanoparticles synthesized using the wet chemistry method. The IrOx/Nafion® catalyst also achieved ∼4,500 h of stable operation in MEA electrolyzer at 1.8 A cm−2 and 80 °C with ultra-low iridium loading of 0.08 mg cm−2. Analysis of the IrOx structure and the electrochemical performance revealed three key factors for balancing high stability and activity: (1) high ratio of Ir (IV) to Ir (III) species and high content of hydroxide on the surface; (2) high anodic charge and surface area due to nano-size IrOx particles that are well-dispersed in the Nafion® ionomer electrolyte; (3) homogeneous anode catalyst layer morphology.

(Invited) Platinum Supported on Graphitized Carbon Cathode for PEMFC Fabricated with Reactive Spray Deposition Technology

Proton exchange membrane fuel cell (PEMFC) attracts huge attention as a new source of power generation for automotive applications. One key requirement for automotive applications is that the fuel cell must be tolerant of frequent start-stop cycling. It was found that the air/fuel boundary developed at the anode side after a fuel cell shut down or during its restart caused extremely quick degradation of the cathode [1, 2]. High potentials occur at the air cathode when hydrogen is introduced into the air on the anode [3]. These high overpotentials lead to platinum oxidation and dissolution and carbon corrosion at the air cathode [2]. The damage to the cathode catalyst layer causes severe irrecoverable performance decay [2]. To mitigate carbon corrosion from frequent start-stop cycling, graphitized carbon black (GCB) are used to replace the traditional carbon black support [4, 5]. GCB is usually prepared through thermal treatment at elevated temperatures in an inert environment [4]. Thus, it is structurally distinct from the traditional carbon black with respect to surface area, porosity, and surface homogeneity [6], which could change its interaction with ionomer and Pt nanoparticles. In addition, we propose the use of a new technology called reactive spray deposition technology (RSDT) to lower the manufacturing cost and improve the fuel cell performance especially for very low catalyst loadings. Therefore, it is important to have a comprehensive understanding on how graphitized carbon support affect the fuel cell performance at both beginning-of-test (BOT) and end-of-test (EOT). In this study, low Pt loading cathode electrodes using graphitized carbon support are fabricated with RSDT. RSDT is an open-atmosphere, cost-effective process that combines the catalyst synthesis and deposition into one step. It also allows for independent control of the catalyst, support and ionomer compositions in the electrode. A six-step method [7] is used to analyze the polarization losses for the Pt/GCB cathodes. Figure 1 shows a step-by-step correction of BOT polarization overpotentials for a Pt/GCB cathode with Nafion/carbon ratio of 0.3 and platinum loading of 0.1 mg cm-2. Furthermore, comparison of the polarization overpotentials is made with high-surface-area carbon black to elucidate the effect of carbon microstructure on the polarization losses. Additionally, the effect of Nafion/carbon ratio and various types of perfluorosulfonic acid (PFSA) ionomers are studied to optimize the Pt/GCB cathode performance.

(Invited) Study on the Degradation of PEM Water Electrolysis MEA after Long-Term Operation

Water electrolysis has the potential to become a key element in coupling the electricity, mobility, heating and chemical sector via power-to-liquids or power-to-gas in a future sustainable energy systems [1]. While proton exchange membrane (PEM) water electrolysis offer several advantages over traditional electrolysis technology, advances are still needed in catalyst stability against corrosion and fluctuated loads for PEM water electrolysis [2]. In particular, the anode requires improvement in the activity and stability of the catalyst due to the sluggish kinetics of oxygen evolution reaction (OER) and the corrosive environment due to high overpotentials. The state-of-the-art anode catalyst in conventional PEMWEs is iridium oxide. However, iridium suffers from dissolution at high anodic potentials [3] albeit being the most corrosion resistant metal known. The iridium dissolution in a MEA is evidenced by the iridium deposits in the electrolyte membrane [4, 5]. Furthermore, platinum degradation on the cathode has been reported where platinum nanoparticles were coarsened after long-term operation [6, 7]. Although the platinum coarsening is not directly related to the cell potential increase after long-term operation, the stability of the platinum nanoparticles is important in the context of reducing the platinum loading [6]. In this study, post mortem MEAs are analyzed with electron microscopy to investigate the degradation mechanisms and to provide guidance for future electrode design. The full MEA was fabricated by reactive spray deposition technology (RSDT) with ultra-low iridium and platinum loading. The anode catalyst is composed of IrOx nanoparticles embedded in Nafion ionomer with an iridium loading of 0.08 mg cm-2; while the cathode is platinum supported on carbon black with a platinum loading of 0.3 mg cm-2. These loadings are about 10% of the loadings that are currently used in state-of-the-art electrolyzers. The full RSDT-derived MEA successfully demonstrated a long-term operation of 4500 hours. Preliminary study on the anode catalyst degradation shows that the anode catalyst layer thickness is reduced by 15% due to compression and/or loss of iridium catalyst (Figure 1a, b). In addition, metallic iridium deposits are found in the electrolyte membrane adjacent to the anode catalyst for the post mortem MEA cross section (Figure 1c, d). EDX mapping of the deposits confirm the metallic state of iridium (Figure 1 e, f). Further analysis of the post mortem MEA cross section will elucidate through-plane catalyst loading distribution using high-resolution TEM and EDX analysis, for both anode and cathode.

One-step fabrication of binder-free three-dimensional Co3O4 electrodes by Reactive Spray Deposition Technology for application in high-performance supercapacitors

Abstract

Ternary Pt-Rh-SnO2 Catalyst Synthesized from Vapor Phase for Ethanol Oxidation

Ethanol is an ideal fuel for direct oxidation fuel cells for portable and mobile application as it offers multiple advantages over hydrogen and methanol. The most important of these are ease of transportation, storage and handling, and high energy density [1]. Platinum and palladium based catalyst are commonly used for ethanol oxidation. The major issue with current catalysts is their inability to cleave the C-C bond in ethanol [2] resulting in incomplete oxidation of ethanol [3]. As a result the fuel cell operates at low efficiency. Hence, bimetallic or trimetallic catalyst are developed to both promote the C-C bond cleavage and to stabilize the hydroxyl group for reducing CO poisoning [4]. In particular, the Pt-Rh-SnO2 catalyst showed predominant oxidation of ethanol to CO2. SnO2 provides hydroxyl species to oxidize the dissociated CO at Rh sites and Pt facilitate ethanol dehydrogenation. The electronic structure of Rh is modified to afford moderate bonding to ethanol, intermediates and products, promoting the C-C bond cleavage.[5,6] Preliminary results of Pt-Rh-SnO2 (3:1:3) catalyst synthesis via reactive spray deposition technology (RSDT) shows promising activity for ethanol oxidation (Figure 1a) and good fuel cell performance (Figure 1b). This can be attributed to the porous electrode morphology that provide high surface area for the gas diffusion electrode (Figure 1c). However, in-situ infrared reflection-adsorption spectroscopy (IRRAS) in the electrochemical cell suggests mixed products of carbon dioxide, acetic acid, and acetaldehyde, as shown in Figure 1d. This implies that the mixing between Pt, Rh, and SnO2 could be inhomogeneous and the interplay between the three components could be hindered.[6] This work focus on the optimization of the interface between three components by varying the relative atomic ratio of Pt, Rh, and Sn. Furthermore, the effect of RSDT process parameters, such as fuel and gas flow rate, precursor solubility, on the precursor mixing are investigated. The surface elemental components and chemical environment are characterized using X-ray photoelectron spectroscopy (XPS). In addition, high-resolution transmission electron microscopy (HRTEM) is employed to study the elemental distribution of the catalyst particles and investigate the phase separation of Pt, Rh, and SnO2. Figure 1. (a) Electrochemical measurement of ethanol oxidation with rotating disk electrode; (b) fuel cell performance Anode: RSDT deposited gas diffusion electrode of Pt-Rh-SnO2, Cathode 45 wt% Pt/C, 2 mg/cm2. Membrane: Nafion 115; (c) Surface morphology of Pt-Rh-SnO2 on gas diffusion electrode; (d) In situ IRRAS of ethanol oxidation at various potentials form -0.2 V to 0.55 V vs. Ag/AgCl. Acknowledgment This manuscript has been authored by employees of Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy. The publisher by accepting the manuscript for publication acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes.

Single-Step Deposition of Nanostructured Fe2O3 as Anode for Li-Ion Batteries

Alpha phase iron oxide has been investigated as active anode material for lithium ion batteries because of high theoretical specific capacity, low cost and eco-friendly nature. Porous nanostructured electrode materials directly deposited on current collectors effectively enhance the rate performance of Li-ion batteries. The unique structure provides open channels for electrolyte penetration and short diffusion pathways for Li ions and electrons. In addition, the open spaces can accommodate the large volume change from the repeated conversion reaction of α-Fe2O3 during cycling. A simple and economical manufacturing approach of the nanostructured electrodes is essential to the development and application of the next generation Li-ion batteries. In this study, nanostructured α-Fe2O3 electrodes are fabricated by reactive spray deposition technology (RSDT) which is a single-step flame combustion synthesis method. This process is continuous and scalable. The structure and morphology of as-prepared electrode are investigated by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Electrochemical properties of the nanostructured α-Fe2O3 electrodes are studied using cyclic voltammetry, galvanostatic charge/discharge cycling and electrochemical impedance spectroscopy in half-cell configuration.

IrOx/Nafion Catalyst for Oxygen Evolution: Effect of Surface Oxide on Activity and Stability

High catalyst loading is a major barrier for large-scale production of proton exchange membrane water electrolysis (PEMWE) despite its advantages over other electrolysis technologies. [1]. [2,3] Herein, a low iridium loading composite catalyst layer of iridium oxide/Nafion (IrOx/Nafion) is developed using reactive spray deposition technology (RSDT). In this process, the catalyst synthesis and catalyst-coated membrane (CCM) fabrication are combined into one step. The activity and stability for oxygen evolution reaction (OER) are tested through rotating disk electrode (RDE) measurements and membrane electrode assembly (MEA), respectively. The iridium particles has an average size of ~2 nm resulting in very high surface area and superior activity over planar and electrodeposited IrO2 thin films. In this study, two flame conditions (F-1 and F-2) are used for synthesizing the iridium particles and a correlation between the surface oxide layer and the electrochemical performance is observed. Based on preliminary results of X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM), we hypothesize that the iridium particles exhibit core-shell structure with a metallic iridium core and mixed iridium (IV and III) oxides shell. Higher flame temperature and longer residence time in the flame (F-2 condition) increases the amount of surface oxide and forms a thicker oxide layer. The oxide composition of the particle can be determined from XPS results (Figure 1 a and b) employing the fitting model proposed in reference [4]. The oxide composition for sample F-1 and F-2 are 54% and 90%, respectively. On the other hand, electron diffraction pattern from TEM analysis shows a metallic phase, which suggests the oxides may reside only on the surface since XPS is surface sensitive. Electrochemical measurements have shown that the iridium particles with higher oxide content improves the OER mass activity by ~3 fold over particles with lower oxide content. Furthermore, the catalyst stability in electrolysis test is improved from 250 hours to 4500 hours with the higher oxide content. Detailed surface analysis is carried out using XPS and high-resolution TEM to obtain the chemical state or change of iridium in particles synthesized under different flame conditions and to investigate the role of surface oxide in the enhancement of activity and stability. Figure 1. XPS of iridium particles synthesized in F-1 (a) and F-2 condition (b) fitted with asymmetric Doniach-Sunjic line shape.

Sensitivity to Acetone By Epsilon-Phase Tungsten Trioxide Films Produced By Reactive Spray Deposition Technology

Studies have shown that when an individual with diabetes has low insulin levels, the body is unable to burn glucose and converts those molecules into ketones, predominantly acetone. That acetone then transfers into the blood stream before being exhaled by an individual’s breath. Rather than using current methods to monitor diabetes, such as a blood test conducted by a finger prick, some researchers have suggested measuring the acetone in exhaled breath as a noninvasive method to monitor diabetes [1]. This noninvasive diabetes monitoring method is made possible by using resistive sensors that utilize a thin-film deposited on interdigitated electrodes. While healthy individuals will exhale 300-900ppb acetone, individuals suffering from diabetes may exhale up to 1800ppb acetone [2]. Recent studies have shown an ability of these sensors to reach the sensitivity required to sense acetone in these diabetic cases. When the sensor is heated, the conductivity of the film increases and allows for the flow of electrons between digits of the sensor. When acetone is present, the acetone adsorbs onto the acetone-sensitive material causing a noticeable change in resistance. As the concentration of acetone increases, the amount of acetone adsorbed on the film increases, causing a change in resistance which allows researchers to correlate acetone concentration with a sensor resistance. One acetone-sensitive material that researchers are studying is epsilon-phase tungsten trioxide. While other forms of tungsten trioxide, such as the gamma-phase, can also sense acetone, the specific structure and surface dipole of the epsilon-phase allows for a particular sensitivity to high dipole moment compounds such as acetone [2]. Unfortunately, this material is prohibitive to use, as the epsilon-phase tungsten trioxide is not the thermodynamically preferred structure at the operating temperature [1]. Some researchers have used dopants, such as silicon or chromium to stabilize the epsilon-phase. However, past research has shown that by using Reactive Spray Deposition Technology (RSDT), it is possible to directly deposit tungsten trioxide onto sensors and anneal the material to achieve the epsilon-phase [3]. Using these undoped epsilon-phase tungsten trioxide sensors, as seen in the scanning electron micrograph in Figure 1, we are able to achieve a sensitive and durable film which can be used to detect the concentrations of interest for diabetes monitoring. This work will examine the acetone sensitivity of the undoped epsilon-phase tungsten trioxide films developed using RSDT and compare them to other research.

Morphological and Electrochemical Optimization of Solid Oxide Fuel Cell (SOFC) Diffusion-Blocking Layer and Cathode Layer Fabricated By Reactive Spray Deposition Technology (RSDT)

SOFCs typically operate up to 1000ºC [1]. This temperature is notably higher than the temperatures at which other fuel cells, such as PEM fuel cells, run. This elevated temperature offers distinct advantages, such as greater efficiency due to faster reaction kinetics, flexibility to use fuels other than hydrogen, and relatively high resistance to impurities in the fuel [1]. When running hydrogen, the faster reaction kinetics also eliminate the need for noble metal catalysts, which are an inherent component of PEM fuel cells; instead the anode and cathode in SOFCs can be made of relatively inexpensive ceramics. The cost of SOFCs can be further reduced by decreasing the operating temperature to 500-650ºC [2]. In this temperature range LSCF (La0.6Sr0.4Co0.2Fe0.8O3-δ) is a commonly used cathode materials because of its good ionic and electronic conductivity [2]. A common electrolyte used in SOFCs is YSZ (Zr0.92Y0.08O2- δ), which reacts with LSCF to form SrZrO3 [2]. The presence of SrZrO3 leads to resistive losses in the cell. To mitigate this, a diffusion-blocking layer of GDC (Ce0.9Gd0.1O1.95) can be applied between the YSZ and LSCF. Previous work suggests that GDC blocking layers applied by RSDT lead to better cell performance than GDC applied using traditional screen-printing techniques [2,3]. This work focuses on optimizing the coating of a GDC blocking layer and LSCF cathode layer on SOFC half cells with NiO,YSZ anode support, NiO,YSZ anode functional layer, and YSZ electrolyte using RSDT. RSDT is an open-atmosphere, flame-based deposition process that uses inexpensive solvents and precursors (i.e. toluene and metal acetylacetonates) and performs a direct deposition of GDC and LSCF layers onto the cell [4]. By using RSDT, a dense GDC layer with good adhesion can be achieved at ~1000°C, which is a relatively low temperature compared to the ~1400°C at which GDC is traditionally processed. This lower temperature allows for reduced production costs and limits the inter-diffusion of the YSZ and GDC. Image (a) of the attached figure shows plan-view SEM of the RSDT-fabricated GDC layer on a half cell. This thin, dense GDC layer is expected to be transparent in SEM [2]; the large grains are the underlying YSZ. Energy Dispersive X-Ray Spectroscopy indicates the presence of cerium. Gadolinium is not detected, which is likely the result of its intended low mole ratio. The cathode is fabricated by simultaneously spraying a slurry of pre-synthesized LSCF nanoparticles and spraying LSCF nanoparticles synthesized directly in the flame. Preliminary testing shows that cells with the RSDT-fabricated cathode have less mass-transfer resistance at high current densities than cells with traditional LSCF cathodes (plot (b) of attached figure). These performance tests were conducted by FuelCell Energy at 750°C with humidified hydrogen on the anode and air on the cathode. To improve the performance of a cell with RSDT-fabricated GDC blocking layer and LSCF cathode, it is important to decrease the ohmic resistance of the cell. This can be achieved by increasing the ionic and electronic conductivity of the LSCF cathode and by increasing the area of the triple phase boundary (TPB). In this work, the LSCF cathode morphology is tailored to optimize its ionic and electronic conductivity, TPB, and mass transfer resistance. The surface morphology of the dense GDC is also adjusted to optimize TPB. As part of the optimization, the morphology of the deposited layers is analyzed by X-Ray Diffraction and Scanning Electron Microscopy. Additionally, performance testing and electrochemical testing is carried out on the cells. This establishes a correlation among RSDT processing parameters, cell morphology, and cell performance.

Performance of Metal-Supported Proton-Conducting Solid Oxide Fuel Cells By Reactive Spray Deposition Technology

In order to make solid oxide fuel cells (SOFCs) more economically feasible, researchers are studying how to reduce the cost to produce these fuel cells. One method that researchers are using to reduce that production cost is to reduce the operating temperature of the fuel cell from ~1000°C to 600°C. Producing SOFCs with proton-conducting materials leads to many advantages that can make the overall device more economical. One major benefit of using these materials is the ability to operate the fuel cell at lower temperatures with no significant negative impact on conductivity as a result of the perovskite structure of these materials[1]. By using the lower operating temperature, it is possible to utilize more inexpensive materials for the internal components of the SOFC. Rather than using ceramic supports or high temperature alloy materials which can increase the cost of the SOFC, it is possible to use more inexpensive steels as a support for the cell. With the lower operating temperature, these materials would not degrade as fast as in traditional SOFCs and will allow for a longer lifespan and less degradation of the fuel cell. In order to further decrease the cost of the cell production, it is also possible to incorporate internal reforming which can allow the use of methane as a fuel rather than hydrogen at the lower operating temperatures. In this work, we will examine the use of Reactive Spray Deposition Technology (RSDT) as a method to produce these metal-supported proton-conducting solid oxide fuel cells. Use of the RSDT process in the production of low-temperature SOFCs has been well-documented, as previous studies show that the RSDT was able to deposit porous electrodes as well as dense electrolytes with satisfactory electrochemical performance [2]. The RSDT process allows for a direct deposition of the desired electrode and electrolyte materials onto a stainless steel or Crofer 22 APU® support and subsequent layers. In an effort to prevent oxidation of the metal supports, previous work has examined using diffusion blocking layers to allow for to use of Crofer 22 APU® in an RSDT application [3]. This work will use the proton conducting material Ba(Zr0.4Ce0.4Y0.1Yb0.1)O3 (BZCYYb4411) as the electrolyte material. Previous studies using BZCYYb have shown excellent ionic conductivity below 750°C [4]. Data from Yang et al. shows that the ionic conductivity of BZCYYb is significantly greater than the conductivity of yttria-stabilized zirconia, a traditional oxygen anion conducting SOFC material, at the same temperature [4]. That BZCYYb electrolyte is deposited on a Ni-BZCYYb cermet anode with an La0.6Sr0.4Co0.2Fe0.8O3 (LSCF6428) cathode. Following each deposition, the deposited layers are examined using scanning electron microscopy to check that each RSDT-deposited layer has the desired morphology, as shown in Figure 1. This work examines those cells and demonstrates the electrochemical performance given by the RSDT-produced metal-supported proton-conducting SOFCs.

Electrochemical and Spectroscopic Characterization of Non-Precious Metal Fe-N-C ORR Catalysts Synthesized By Direct Flame Spray Pyrolysis

The electrocatalyst is one of the major components of low temperature Proton Exchange Membrane (PEM) fuel cells, and despite being the focus of research and development for several decades, platinum nanoparticles supported on high surface area carbon remain the state-of-the-art for both acid and alkali based fuel cells. A major obstacle to the commercialization of PEM fuel cells is the cost associated with the use of expensive Pt group electrocatalysts on both the anode and cathode. DOE projections estimate that in high volume production, the cost of platinum alone could account for about 50% of the total cost of fuel cell power systems [1, 2]. There have been many attempts to alleviate this problem by reducing platinum loading on both electrodes. However, progress in reducing stack cost by reducing the platinum content has been offset by the increasing global price and limited availability of platinum. In addition, due to the sluggish oxygen reduction kinetics, the platinum loading on the cathode side when using pure hydrogen as a fuel source, is at least 3-5 times more than the loading on the anode side. Consequently, there is considerable interest in developing Pt-free Oxygen Reduction Reaction (ORR) catalysts that are cheaper to manufacture and more readily available than their Pt-based counterparts [3]. Nitrogen doped graphitic carbon is a promising candidate for Pt-free electrocatalysts. The incorporation of transition metals such as Fe or Co results in the formation of a metal-nitrogen coordination (M-Nx, where x is usually 2 or 4) which has been found to greatly enhance activity of non-precious metal catalysts towards oxygen reduction. M-N-C catalysts are typically synthesized through the pyrolysis of metal, nitrogen and carbon containing precursors in an inert or ammonia atmosphere between 800-1000°C followed by additional acid leaching and heat treatment steps [4-6]. The performance and durability of the catalyst under fuel cell operation conditions is dependent on the pore size distribution and active site density, both of which are significantly influenced by the synthesis process. Fe-N-C catalysts were synthesized for this study by a modified flame based deposition technique called Reactive Spray Deposition Technology (RSDT). The catalyst material was produced through the incomplete combustion of an atomized spray composed of anhydrous FeCl3 and cyanamide dissolved in a xylene-methanol-propane precursor mix. A nitrogen-gas sheath was also employed around the flame to reduce the entrainment of air into the flame. The oxygen lean conditions in the flame resulted in the formation of carbonaceous material due to the incomplete combustion of the organic precursors. XRD and Raman results indicated the presence of partially graphitic carbon with a disordered structure. The RSDT synthesis technique resulted in a morphology with mesoporous and macroporous features, as evidenced by SEM imaging and BET measurements (figures 1a and 1b). TGA analysis of the catalyst revealed the presence of amorphous carbon and soot mixed in with the graphitic material, suggesting further optimization of the synthesis process may be required. XPS analysis was performed to analyze the nature of the N-C bonding and detect the presence of the catalytically active Fe-Nx moieties (figure 1c). Electrochemical analysis of the catalyst will be conducted using Rotating Disk Electrode to measure the ORR activity and stability in acid medium. MEAs prepared from the Fe-N-C catalyst will be used to study the performance and durability under actual fuel cell operation conditions. Figure 1: (a) Secondary electron SEM image, and (b) BET analysis results of Fe-N-C catalyst synthesized by RSDT. (c) High resolution XPS scan of RSDT synthesized catalyst showing N1s peak along with table listing fraction of area under fitted peaks.

Morphology-Controlled One-Step Synthesis of Nanostructured LiNi1/3Mn1/3Co1/3O2 Electrodes for Li-Ion Batteries.

Nanostructured electrodes effectively enhance the kinetics of the charge/discharge process in lithium-ion (Li-ion) batteries. However, the fabrication of these electrodes often involves complex processing steps. This study demonstrates a one-step improved flame spray pyrolysis synthesis approach to directly deposit the most common Li-ion battery cathode material LiNi1/3Mn1/3Co1/3O2 onto current collectors, which is identified as reactive spray deposition technology (RSDT). Because of the economical and continuous nature of RSDT, the industrial scale of manufacturing nanostructured electrodes for Li-ion batteries can be potentially developed. Morphologies of the electrodes are well controlled so that their electrochemical properties can be tailored to accommodate intended applications. In detail, by adjusting the precursor concentration in the solution feed during the operation of RSDT, the specific surface area of synthesized material can be fine-tuned accordingly. Although the electrodes prepared with low precursor concentration exhibit the highest surface area and deliver the highest initial discharge capacity of 192.1 mAh g–1, the most stable cycling performance is demonstrated by the electrodes fabricated with high precursor concentration, retaining 93.6% of the initial capacity after 100 cycles in half-cell testing. This innovative direct deposition method considerably simplifies the manufacture process of high-performance nanostructured electrodes and enables effortless modification of their properties. Moreover, no hazardous waste is generated from this synthesis route.

Novel flame synthesis of nanostructured α-Fe2O3 electrode as high-performance anode for lithium ion batteries

Nanostructured electrodes have significant potential for enhancing the kinetics of lithium storage in secondary batteries. A simple and economical manufacturing approach of these electrodes is crucial to the development and application of the next generation lithium ion (Li-ion) batteries. In this study, nanostructured α-Fe2O3 electrode is fabricated by a novel one-step flame combustion synthesis method, namely Reactive Spray Deposition Technology (RSDT). This process possesses the merits of simplicity and low cost. The structure and morphology of the electrode are investigated with X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Electrochemical performance of the nanostructured α-Fe2O3 electrodes as the anodes for Li-ion batteries is evaluated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy in coin-type half-cells. The as-prepared electrodes demonstrate superior cyclic performance at high current rate, which delivers a high reversible capacity of 1239.2 mAh g−1 at 1 C after 500 cycles. In addition, a discharge capacity of 513.3 mAh g−1 can be achieved at 10 C.

One-Step Synthesis of Co3O4 Thin Film by Reactive Spray Deposition Technology for Efficient Electrochemical Water Splitting

ABSTRACTEfficient catalysts for the oxygen evolution reaction (OER) are widely applied in fuel cells and rechargeable lithium air batteries. It is desirable but challenging to achieve comparable activity to that of the noble-metal catalyst with non-precious metal catalyst. Highly active Co3O4 thin film electrodes have been successfully synthesized by a rapid one-step flame combustion synthesis method called Reactive Spray Deposition Technology. X-ray diffraction confirms the absence of any impurity phase with this synthesis process. The detailed morphology of the Co3O4 thin film is investigated with scanning electron microscopy and transmission electron microscopy. Cyclic voltammetry is used to investigate the redox activity of Co3+ to Co4+ which is crucial for the OER performance. The as-prepared Co3O4 catalyst demonstrates promising activity for OER, with an overpotential of 399 mV (at 10 mA cm-2) for OER.

Analysis of H2/Air Polarization Curves: The Influence of Low Pt Loading and Fabrication Process

Significant effort has been devoted to reduce the cathode platinum loading for proton exchange membrane fuel cells (PEMFCs). To achieve this, it is imperative to have a comprehensive understanding of the polarization behavior for the low-Pt-loading electrodes, and to reduce the polarization loss due to oxygen transport limitation. Herein, a systematic breakdown of six types of polarization sources is presented to elaborate the effect of cathode Pt loading and the catalyst layer fabrication process. Four modifications are applied to accommodate low cathode Pt loading. GORE PRIMEA catalyst-coated membranes (CCMs) were used as a baseline and tested with 0.4 and 0.1 mg cm−2 cathode Pt loading. A novel electrode fabrication method, reactive spray deposition technology (RSDT), was employed to fabricate 0.1 mg cm−2 Pt loading cathode using Ketjen black carbon as catalyst supports. Non-electrode concentration overpotential is determined by the cathode Pt loading and the type of diffusion medium, while cathode electrode concentration overpotential is determined by the ionomer thin film and ionomer/Pt interface which are dependent on the fabrication process. It is shown that the RSDT process can improve fuel cell performance at 0.1 mg cm−2 cathode Pt loading by reducing the cathode electrode concentration overpotential.

Analysis of H2/Air Polarization Losses of Low-Platinum-Loading Cathodes with Various I/C Ratios and Carbon Supports

Reduction of platinum loading is one of the major challenges for the commercialization of proton exchange membrane fuel cells. The role of catalyst layer microstructure and ionomer content is critically important at ultra-low platinum loading due to enhanced oxygen transport resistance compared to high platinum loading. In the present work, catalyst-coated membranes with two types of carbon supports and various I/C ratios are fabricated using reactive spray deposition technology (RSDT) where low Pt loading (cathode 0.1 mg cm−2, anode 0.05 mg cm−2) catalyst layers are directly deposited on Nafion membranes. Similar performance is obtained at optimal I/C ratios for Pt/Ketjen Black (KB) CCMs and Pt /multi-wall carbon nanotube (MWNT) CCMs, with optimal I/C ratio being 1.0 and 0.5, respectively. Six types of polarization overpotentials are analyzed using a six-step method established in our previous work to elucidate the influence of catalyst layer microstructure and ionomer content on fuel cell performance. Since MWNT requires 50% less ionomer and are chemically more stable than KB, MWNT is a preferred support for ultra-low platinum loading electrodes. The six-step method connects catalyst layer properties with specifically targeted overpotentials and is thus a powerful tool in catalyst layer optimization.

One-Step Synthesis of Nanostructured Co3O4 Film on Nickel Foam As Electrode for Supercapacitor Application

In recent years, supercapacitors have drawn considerable interest from researchers as an alternative energy storage device to secondary batteries. They offer advantages such as high power density, high columbic efficiency and long cycling life [1, 2]. Among the transition metal oxides investigated for redox reaction based supercapacitors (pseudocapacitors), Co3O4 is of special interest due to its high theoretical specific capacitance (up to 3560 F g-1) and relatively low cost [3, 4]. However, low rate capability and poor cycling performance as a result of relatively low electrical conductivity limits its practical application in supercapacitors. Development of nanostructured Co3O4 materials offers a promising solution to this challenge as the transport pathways of electrons and ions are inherently short. Nanostructured Co3O4 film deposited on nickel foam has been prepared by an economical and scalable flame combustion method in one step, namely reactive spray deposition technology (RSDT). The microstructure of the electrode is investigated by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The nanostructured electrode provides high specific surface area and improves the kinetics of redox reaction [5]. The porous structure facilities the penetration of electrolyte and shortens the diffusion path of ions [6]. Electrochemical performance of the as-prepared Co3O4/Ni electrodes is evaluated by cyclic voltammetry, galvanostatic charge-discharge cycling and electrochemical impedance spectroscopy in coin-type (CR2032) half-cells.

Strategies to mitigate Pt dissolution in low Pt loading proton exchange membrane fuel cell: I. A gradient Pt particle size design

The catalyst durability at low Pt loading remains a barrier for industrial commercialization of the proton exchange membrane fuel cell. Degradation of low loaded Pt catalyst not only reduced the electrochemical surface area but also revealed a Pt depletion zone adjacent to the cathode/membrane interface where about 80% of the Pt was lost due to dissolution and migration into the membrane. We hypothesized that the Pt degradation can be mitigated using a gradient cathode design without sacrificing the initial fuel cell performance. With a focus on the mitigation, the first of two companion papers focuses on the Type I cathode with larger Pt particles (5nm average size) near the cathode/membrane interface. In the second of these two papers, the Type II cathode with higher Pt loading (60wt.% Pt on carbon) near the cathode membrane interface will be investigated. The catalyst coated membranes with gradient cathode were fabricated by reactive spray deposition technology with low Pt loading of 0.05mgcm−2 on the anode and 0.1mgcm−2 on the cathode. The DOE defined accelerated stress test was performed by imposing a triangular wave potential cycling from 0.6V to 1.0V for 30,000 cycles at 50mVs−1 scan rate. Results of accelerated stress test showed that the loss of electrochemical surface area and PEMFC performance were reduced for the Type I cathode compared to the control cathodes that consisted of 2nm averaged Pt particle size only. Microscopy analysis suggested two possible mechanisms for this durability improvement: 1) the reduction of the amount of Pt lost due to Pt dissolution, and 2) the preservation of Pt particles at the cathode/membrane interface. Comparison with the control cathode showed that the loss of Pt near the cathode/membrane interfaced were reduced from 80% to 40% and the overall Pt loss of the cathode were reduced from 30% to 15%.