67 research outputs found
Designing a New Class of Electrocatalysts for Polymer Electrolyte Membrane Fuel Cells: Probing Size, Composition, and Structure Dependent Electrocatalytic Performance in High-Quality, One-Dimensional Noble Metal Nanostructures
No full textA key challenge in the practical commercialization of PEMFCs is the extremely high cost and relatively poor durability of carbon supported Pt nanoparticle (Pt NP/C) electrocatalysts utilized in both the anode and cathode half-cells. Herein, we synthesize and characterize a new class of high-quality one-dimensional noble metal nanostructures as a potentially new and promising structural paradigm for the next generation of electrocatalyst materials. Specifically, we investigate the nature of the complex interplay amongst size, chemical composition, and electrocatalytic performance in high-quality elemental and bimetallic 1D noble metal nanowire systems with an emphasis on achieving efficient and sustainable methods for catalyst preparation. In terms of nanowire dimensions and composition, an interesting and measureable size-dependent enhancement in performance emerges in the case of elemental Pt, Pd, and Pd1-xAux nanowires possessing diameters ranging from the submicron (d = ~200 nm) to the ultrathin regime (d = ~1 nm). In a similar context, we have considered the role of chemical composition in 1D electrocatalysts and noted significant composition-dependent enhancements in activity and durability in high-quality, bimetallic Pd1-xAux and Pd1-xPtx NWs. A key finding that is apparent from these experimental results is that widely seen behavioral trends in the composition- and size-dependent performance for 0D nanoparticle-based catalysts do not hold in the case of 1D architectures, because of the patently unique structural and electronic effects, associated with their anisotropic structures. As a culmination of our efforts to take advantage of these intrinsic structure-activity correlations, our group has developed a morphology-, size-, and composition-optimized Pd9Au NW possessing a Pt monolayer shell (PtML∼ Pd9Au NWs) electrocatalyst with an ultrathin 2 nm diameter, which yielded outstanding Pt mass and platinum group metal activities of 2.56 A/mgPt and 0.64 A/mgPGM, respectively, thereby surpassing the activity of conventional state-of-the-art Pt NP/C by more than ten-fold. | 290 page
One-dimensional noble metal electrocatalysts: a promising structural paradigm for direct methanolfuelcells
No full textJ Toxicol Environ Health A
No full textDue to their unique size, surface area, and chemical characteristics, nanoparticles' use in consumer products has increased. However, the toxicity of nanoparticle (NP) exposure during the manufacturing process has not been fully assessed. Tungstate NP are used in numerous products, including but not limited to scintillator detectors and fluorescent lighting. As with many NP, no apparent toxicity studies have been completed with tungstate NP. The hypothesis that tungstate NP in vitro exposure results in reactive oxygen species (ROS) formation and cytotoxicity was examined. Differences in toxicity based on tungstate NP size, shape (sphere vs. wire), and chemical characteristics were determined. RAW 264.7 mouse monocyte macrophages were exposed to tungstate NP, and ROS formation was assessed via electron spin resonance (ESR), and several assays including hydrogen peroxide, intracellular ROS, and Comet. Results showed ROS production induced by tungstate nanowire exposure, but this exposure did not result in oxidative DNA damage. Nanospheres showed neither ROS nor DNA damage following cellular exposure. Cells were exposed over 72 h to assess cytotoxicity using an MTT (tetrazolium compound) assay. Results showed that differences in cell death between wires and spheres occurred at 24 h but were minimal at both 48 and 72 h. The present results indicate that tungstate nanowires are more reactive and produce cell death within 24 h of exposure, whereas nanospheres are less reactive and did not produce cell death. Results suggest that differences in shape may affect reactivity. However, regardless of the differences in reactivity, in general both shapes produced mild ROS and resulted in minimal cell death at 48 and 72 h in RAW 264.7 cells.CC999999/Intramural CDC HHSUnited States
Tailoring Chemical Composition To Achieve Enhanced Methanol Oxidation Reaction and Methanol-Tolerant Oxygen Reduction Reaction Performance in Palladium-Based Nanowire Systems
No full textIn this article, we address two key
challenges in the development
of electrocatalysts for direct methanol fuel cells by rationally tailoring
the morphology and chemical composition of Pd-based nanowires (NWs)
for enhanced performance. First, we have examined the morphology and
composition-dependent performance of Pt1–xPdx NWs toward the methanol oxidation
reaction (MOR). Elemental Pt NWs were found to possess a significant
morphology-dependent enhancement of nearly 3-fold in terms of peak
MOR-specific activity over that of commercial Pt NP/C. In addition,
tailoring the chemical composition in Pt1–xPdx NWs can lead to measurable
increases in MOR kinetics, which can be attributed to improved oxidation
of formic acid and, potentially, increased selectivity for a direct,
CO-free pathway. Second, we have explored the stability of ORR performance
in the presence of measurable concentrations of methanol as a function
of chemical composition in Pt1–xPdx NWs and Pt-free Pd9Au
NWs. In the context of the Pt1–xPdx NWs, a distinctive volcano-type dependence
has been noted with respect to chemical composition, and on the basis
of the MOR activities and methanol tolerant ORR behavior, Pt7Pd3 NWs have been highlighted as an optimal catalyst architecture.
We have also analyzed the methanol tolerance in Pd9Au NWs,
which represents a highly active, durable Pt-free alternative to traditional
Pt-based nanostructured catalysts. Herein, we have demonstrated that
Pd9Au NWs (0.42 mA/cm2) with no effective Pt
content can outperform Pt-based nanostructures, such as Pt NWs (0.32
mA/cm2) and nanoparticulate Pt NP/C (0.24 mA/cm2) in the presence of 4 mM methanol/0.1 M HClO4
One-dimensional Nanostructures for PEM Fuel Cell Applications
No full textOne-dimensional Nanostructures for PEM Fuel Cell Applications provides a review of the progress made in 1D catalysts for applications in polymer electrolyte fuel cells. It highlights the improved understanding of catalytic mechanisms on 1D nanostructures and the new approaches developed for practical applications, also including a critical perspective on current research limits. The book serves as a reference for the design and development of a new generation of catalysts to assist in the realization of successful commercial use that have the potential to decarbonize the domestic heat and transport sectors.In addition, a further commercialization of this technology requires advanced catalysts to address major obstacles faced by the commonly used Pt/C nanoparticles. The unique structure of one-dimensional nanostructures give them advantages to overcome some drawbacks of Pt/C nanoparticles as a new type of excellent catalysts for fuel cell reactions. In recent years, great efforts have been devoted in this area, and much progress has been achieved
Probing Ultrathin One-Dimensional Pd–Ni Nanostructures As Oxygen Reduction Reaction Catalysts
No full textFunctioning Photoelectrochemical Devices Studied with Time-Resolved Terahertz Spectroscopy
No full textAmbient Surfactantless Synthesis, Growth Mechanism, and Size-Dependent Electrocatalytic Behavior of High-Quality, Single Crystalline Palladium Nanowires
No full textSurfactant-Free Synthesis of Three-Dimensional Perovskite Titania-Based Micron-Scale Motifs Used as Catalytic Supports for the Methanol Oxidation Reaction
No full textWe synthesized and subsequently rationalized the formation of a series of 3D hierarchical metal oxide spherical motifs. Specifically, we varied the chemical composition within a family of ATiO3 (wherein “A” = Ca, Sr, and Ba) perovskites, using a two-step, surfactant-free synthesis procedure to generate structures with average diameters of ~3 microns. In terms of demonstrating the practicality of these perovskite materials, we have explored their use as supports for the methanol oxidation reaction (MOR) as a function of their size, morphology, and chemical composition. The MOR activity of our target systems was found to increase with decreasing ionic radius of the “A” site cation, in order of Pt/CaTiO3 (CTO) > Pt/SrTiO3 (STO) > Pt/BaTiO3 (BTO). With respect to morphology, we observed an MOR enhancement of our 3D spherical motifs, as compared with either ultra-small or cubic control samples. Moreover, the Pt/CTO sample yielded not only improved mass and specific activity values but also a greater stability and durability, as compared with both commercial TiO2 nanoparticle standards and precursor TiO2 templates
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