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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Synthesis of Porous Carbon Supported Palladium Nanoparticle Catalysts by Atomic Layer Deposition: Application for Rechargeable Lithium–O2 Battery
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Atomic Layer Deposition of a Submonolayer Catalyst for the Enhanced Photoelectrochemical Performance of Water Oxidation with Hematite
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Mesoporous Graphene-Like Carbon Sheet: High-Power Supercapacitor and Outstanding Catalyst Support
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Chemical Vapor Deposition for Atomically Dispersed and Nitrogen Coordinated Single Metal Site Catalysts
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Microstructure of Bimetallic Pt-Pd Catalysts under Oxidizing Conditions
Diesel oxidation catalysts (DOCs), which decrease the amount of harmful carbon monoxide (CO), nitrogen oxide (NO), and hydrocarbon (HC) emissions in engine exhaust, typically utilize Pt and Pd in the active phase. There is universal agreement that the addition of Pd improves both the catalytic performance and the durability of Pt catalysts. However, the mechanisms by which Pd improves the performance of Pt are less clear. Because these catalysts operate under oxidizing conditions, it is important to understand these catalysts in their working state. Herein, we report the microstructure of Pt[BOND]Pd catalysts that are aged in air at 750 °C. After 10 h of aging, EXAFS and XANES analysis show that the Pt is fully reduced but that almost 30 % of the Pd species are present as an oxide. HRTEM images show no evidence of surface oxides on the metallic Pt[BOND]Pd particles. Instead, the PdO is present as a separate phase that is dispersed over the alumina support. Within the metallic particles, Pt and Pd are uniformly distributed and there is no evidence of core–shell structures. Therefore, the improved catalytic performance is likely associated with the co-existence of metallic Pt and Pd on the catalyst surface.
Investigation of Oxygen Reduction Activity of Catalysts Derived from Co and Co/Zn Methyl-Imidazolate Frameworks in Proton Exchange Membrane Fuel Cells
We demonstrated that the oxygen reduction reaction (ORR) activity over the catalysts derived from pyrolyzed cobalt zeolitic imidazolate frameworks depends strongly on the imidazole ligand structure and cobalt content. The activity and durability of these catalysts were tested in the proton exchange membrane fuel cell for the first time. The membrane electrode assembly containing a catalyst derived from Co/Zn bimetallic ZIF at cathode achieved an open circuit voltage of 0.93 V, a current density of 28 mA cm-2 at 0.8 ViR-free and a peak power density of 374 mW cm-2.
High-Temperature-Stable and Regenerable Catalysts: Platinum Nanoparticles in Aligned Mesoporous Silica Wells
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Enhanced Dry Reforming of Methane on Ni and Ni-Pt Catalysts Synthesized by Atomic Layer Deposition
Atomic layer deposition (ALD) was used to deposit Ni and Pt on alumina supports to form monometallic and bimetallic catalysts with initial particle sizes of 1–2.4 nm. The ALD catalysts were more active (per mass of metal) than catalysts prepared by incipient wetness (IW) for dry reforming of methane (DRM), and they did not form carbon whiskers during reaction due to their sufficiently small size. Catalysts modified by Pt ALD had higher rates of reaction per mass of metal and inhibited coking, whereas NiPt catalysts synthesized by IW still formed carbon whiskers. Temperature-programmed reduction of Ni catalysts modified by Pt ALD indicated the presence of bimetallic interaction. Density functional theory calculations suggested that under reaction conditions, the NiPt surfaces form Ni-terminated surfaces that are associated with higher DRM rates (due to their C and O adsorption energies, as well as the CO formation and CH4 dissociation energies).
Phosphonic acid modifiers for enhancing selective hydrodeoxygenation over Pt catalysts: The role of the catalyst support
Bifunctional catalysts comprised of both noble metal and Bronsted acid sites are of growing interest for many reactions, such as the hydrodeoxygenation (HDO) of oxygenates produced by the deconstruction of lignocellulosic biomass. One method of preparing a bifunctional metal-acid catalyst is to modify the supporting material of a metal catalyst with acid-containing ligands, such as phosphonic acids (PAs), which provide tunable Bronsted acid sites at the metal-support interface. Here, we explore the potential for PA modification to improve HDO rates on Al 2 O 3 , TiO 2 , CeO 2 , and SiO 2 -Al 2 O 3 supports. PAs containing either alkyl or carboxylic acid (CA) tails were used to modify Pt catalysts on each support. PA modification improved HDO rates for the model compound benzyl alcohol when applied to Pt supported by Al 2 O 3 , TiO 2 , and CeO 2 , but had a negative effect on the HDO rate of Pt/SiO 2 -Al 2 O 3 . Measurements of the relative strength of Bronsted acid sites present on the modified and unmodified catalysts suggested that PAs improved HDO when they provided new or stronger Bronsted acid sites. Additionally, the strength of the Bronsted acid sites provided by PA modifiers were tunable by altering the tail functionality, which affected the rates of HDO. These results suggest that PAs can be used to modify a variety of supports to prepare bifunctional acid-metal catalysts.
Impact of IrRu oxygen evolution reaction catalysts on Pt nanostructured thin films under start-up/shutdown cycling
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Dual atom catalysts for rapid electrochemical reduction of CO to ethylene
Strong CO adsorption and facile CO dimerization are the key challenges in electrochemical CO2 reduction towards multi-carbon (C2+) products. We recently showed that CoPc immobilized on a single-walled carbon nanotube can selectively reduce CO2 to methanol. This is enabled through molecular strain, which dramatically improves the CO adsorption energy to CoPc, which in turn facilitates methanol formation. We now examine the extended Phthalocyanine (PcEx) dual atom catalyst (DAC), which is intrinsically strained and contains two catalyst centers, making it a candidate for reducing CO to C2+ products. Using Quantum Mechanics (QM), we screened 20 elements embedded in the PcEx, seeking catalysts with weak hydrogen binding, strong CO binding, and facile CO dimerization. We identi>ied Fe, Ru, Co, and Ir as the best performers and subsequently evaluated the entire CO to C2H4 mechanism (9 steps) using each of these elements as catalysts. In terms of limiting potential and overall exergonicity, we identi>ied CoPcEx as the best catalyst, followed by IrPcEx. We then examined the full CO to C2H4 mechanism on the bimetallic IrCoPcEx catalyst using grand canonical QM to obtain the reaction energetics as a function of applied potential. We conclude that the bimetallic IrCoPcEx is most promising for ef>iciently converting CO to ethylene.
ElectroCat: DOE's approach to PGM-free catalyst and electrode R&D
The successful development of high-performance, durable platinum group metal-free (PGM-free) electrocatalysts and electrodes for polymer electrolyte membrane fuel cells (PEMFCs) will ultimately improve the cost-competiveness of fuel cells in a wide range of applications. This is considered to be a critical development especially for automotive fuel cell applications in order to bring the system cost of an automotive fuel cell system down to the $30/kW cost target set by the U.S. Department of Energy (DOE). The platinum group metal (PGM) electrocatalysts are a major contributor to the system cost. Addressing the technical challenges to PGM-free electrocatalyst and electrode development, therefore, represents one of DOE's most pressing research and development (R&D) priorities. ElectroCat was formed by the DOE as part of the Energy Materials Network (EMN) in early 2016, and shares with other EMN consortia the goal of decreasing the time to market for advanced materials related to clean energy technologies, in the context of increasing U.S. fuel cell electric vehicle (FCEV) manufacturing competitiveness. To accomplish this, the consortium performs core research and development and provides universities and companies streamlined access to the unique, world-class set of tools and expertise relevant to early-stage applied PGM-free catalyst R&D of the member national laboratories. Moreover, ElectroCat fosters a systematic methodology by which prospective catalysts and electrodes are prepared and analyzed rapidly and comprehensively using high-throughput, combinatorial methods. Catalyst discovery is augmented by theory as well as foundational electrocatalysis and materials knowledge at the participating national laboratories. Furthermore, ElectroCat has developed a data sharing framework, requisite of all EMN consortia, for disseminating its findings to the public via a searchable database, to further expedite incorporation of PGM-free electrocatalysts into next-generation fuel cells by advancing the general understanding of the PGM-free electrocatalyst field.
Investigation of Silica-Supported Vanadium Oxide Catalysts by High-Field 51 V Magic-Angle Spinning NMR
Supported V2O5/SiO2 catalysts were studied using solid state 51V MAS NMR at a sample spinning rate of 36 kHz and at a magnetic field of 19.975 T for a better understanding of the coordination of the vanadium oxide as a function of environmental conditions . Structural transformations of the supported vanadium oxide species between the catalyst in the dehydrated state and hydrated state under an ambient environment were revisited to examine the degree of oligomerization and the effect of water. The experimental results indicate the existence of a single dehydrated surface vanadium oxide species that resonates at -675 ppm and two vanadium oxide species under ambient conditions that resonate at -566 and -610 ppm, respectively. No detectable structural difference was found as a function of vanadium oxide loading on SiO2 (3% V2O5/SiO2 and 8% V2O5/SiO2). Quantum chemistry simulations of the 51V NMR chemical shifts on predicted surface structures were used as an aide in understanding potential surface vanadium oxide species on the silica support. The results suggest the formation of isolated surface VO4 units for the dehydrated catalysts with the possibility of dimer and cyclic trimer presence. The absence of bridging V-O-V vibrations (~200-300 cm-1) in the Raman spectra [Gao et al. J. Phys. Chem. B 1998, 102, 10842-10852], however, indicates that the isolated surface VO4 sites are the dominant dehydrated surface vanadia species on silica. Upon exposure to water, hydrolysis of the bridging V-O-Si bonds is most likely responsible for the decreased electron shielding experienced by vanadium. No indicators for the presence of hydrated decavanadate clusters or hydrated vanadia gels previously proposed in the literature were detected in this study.