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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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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Asymmetrical C–C Coupling for Electroreduction of CO on Bimetallic Cu–Pd Catalysts

Electroreduction of carbon monoxide (CO) possesses great potential for achieving the renewable synthesis of hydrocarbon chemicals from CO 2 . We report here selective reduction of CO to acetate using Cu–Pd bimetallic electrocatalysts. High activity and selectivity are demonstrated for CO-to-acetate conversion with >200 mA/cm 2 in geometric current density and >65% in Faradaic efficiency (FE). An asymmetrical C–C coupling mechanism is proposed to explain the composition-dependent catalytic performance and high selectivity toward acetate. This mechanism is supported by the computationally predicted shift of the *CO adsorption from the top-site configuration on Cu (or Cu-rich) surfaces to the bridge sites of Cu–Pd bimetallic surfaces, which is also associated with the reduction of the CO hydrogenation barrier. Further kinetic analysis of the reaction order with respect to CO and Tafel slope supports a reaction pathway with *CO–*CHO recombination following a CO hydrogenation step, which could account for the electroreduction of CO to acetate on the Cu–Pd bimetallic catalysts. Furthermore, our work highlights how heteroatomic alloy surfaces can be tailored to enable distinct reaction pathways and achieve advanced catalytic performance beyond monometallic catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Synergistic double-atom catalysts of metal-boron anchored on g-C 2 N for electrochemical nitrogen reduction: Mechanistic insight and catalyst screening

The rational design of a novel catalytic center with a sound basis remains both challenging and rewarding for the electrochemical reduction of N 2 (eNRR), which has provided a feasible route for achieving clean and sustainable NH 3 production under ambient conditions. Herein, using density functional theory calculations, we demonstrate that hybrid metal (M)-boron (B) double-atom catalysts (DACs) embedded in g-C 2 N substrate (M-B@C 2 N, M = 3d, 4d and 5d transition metals) can achieve both high catalytic activity and high selectivity in eNRR. The proposed M-B@C 2 N DACs have exhibited impressive feasibility and stability thanks to the resilient and robust C 2 N substrate with abundant pyridinic N atoms distributed among right-sized pore structures. Our results reveal that like the metal center, the embedded B atom can actively involve in Ntriple bondN bond activation via π*-backdonation mechanism concomitant with the substantial charge transfer to adsorbed *N 2 , leading to sizable Nsingle bondN bond elongation. Accordingly, both adsorption energy and Nsingle bondN bond length of *N 2 can be employed as catalytic descriptors for predicting eNRR activity in terms of the limiting potentials (UL). Using high-throughput screening method, we found that six M-B@C 2 N candidates have stood out as the outstanding electrocatalysts for driving eNRR, namely, M = Ti (U L = 0 V), Mo (U L = 0 V), Nb (U L = -0.04 V), W (U L = -0.23 V), Zr (U L = -0.26 V), V (U L = -0.28 V). The underlying origin is attributed to the balanced and constrained N-affinity of M-B dual site working in synergy, which can thus be used as one important guide of catalyst design.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Modulating Chemical Environments of Metal–Organic Framework-Supported Molybdenum(VI) Catalysts for Insights into the Structure–Activity Relationship in Cyclohexene Epoxidation

Solid supports are crucial in heterogeneous catalysis due to their profound effects on catalytic activity and selectivity. However, elucidating the specific effects arising from such supports remains challenging. We selected a series of metal–organic frameworks (MOFs) with 8-connected Zr 6 nodes as supports to deposit molybdenum(VI) onto to study the effects of pore environment and topology on the resulting Mo-supported catalysts. As characterized by X-ray absorption spectroscopy (XAS) and single-crystal X-ray diffraction (SCXRD), we modulated the chemical environments of the deposited Mo species. For Mo-NU-1000, the Mo species monodentately bound to the Zr 6 nodes were anchored in the microporous c-pore, but for Mo-NU-1008 they were bound in the mesopore of Mo-NU-1008. Both monodentate and bidentate modes were found in the mesopore of Mo-NU-1200. Cyclohexene epoxidation with H 2 O 2 was probed to evaluate the support effect on catalytic activity and to unveil the resulting structure–activity relationships. SCXRD and XAS studies demonstrated the atomically precise structural differences of the Mo binding motifs over the course of cyclohexene epoxidation. No apparent structural change was observed for Mo-NU-1000, whereas the monodentate mode of Mo species in Mo-NU-1008 and the monodentate and bidentate Mo species in Mo-NU-1200 evolved to a new bidentate mode bound between two adjacent oxygen atoms from the Zr 6 node. This work demonstrates the great advantage of using MOF supports for constructing heterogeneous catalysts with modulated chemical environments of an active species and elucidating structure–activity relationships in the resulting reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Reorganization Energies for Interfacial Proton-Coupled Electron Transfer to a Water Oxidation Catalyst

The reorganization energy (λ) for interfacial electron transfer (ET) and proton-coupled electron transfer (PCET) from a conductive metal oxide (In 2 O 3 :Sn, ITO) to a surface-bound water oxidation catalyst were extracted from kinetic data measured as a function of the thermodynamic driving force. Visible light excitation resulted in rapid excited-state injection (k inj > 10 8 s -1 ) to the ITO, which photo-initiated the two interfacial reactions of interest. The rate constants for both reactions increased with the driving force, −ΔG°, to a saturating limit, k max , with rate constants consistently larger for ET than for PCET. Marcus-Gerischer analysis of the kinetic data provided the reorganization energy for interfacial PCET (0.90 ± 0.02 eV) and ET (0.40 ± 0.02 eV), respectively. The magnitude of k max for PCET was found to decrease with pH, behavior that was absent for ET. Both the decrease in k max and the larger reorganization energy for an unwanted competing PCET reaction from the ITO to the oxidized catalyst showcases a significant kinetic advantage for driving solar water oxidation at high pH. Computational analysis revealed a larger inner-sphere reorganization energy contribution for PCET than for ET arising from a more significant change in the Ru–O bond length for PCET. Extending Marcus-Gerischer theory to PCET by including the excited electron-proton vibronic states and the proton donor-acceptor motion provided an apparent reorganization energy of 1.01 eV. Furthermore, this study demonstrates that the Marcus-Gerischer theory initially developed for ET can be reliably extended to PCET for quantifying and interpreting reorganization energies observed experimentally.

Catalysts Kinetic parameters↗
DOE OSTI2024

Effect of Engineered Cracks in Catalyst Layers on PEMFC Catalyst Layer Durability

Proton exchange membrane fuel cells (PEMFCs) are expected to play a pivotal role in decarbonizing the transportation sector, and particularly heavy-duty vehicles (HDVs). However, improvements in durability are needed for PEMFCs to compete with state-of-the-art power sources for HDVs. Here, we examine how catalyst layer (CL) cracks that are engineered affect the CL durability by using patterned silicon templates to control the CL crack density at the micrometer scale. Electrochemical analyses show that the initial PEMFC performance is relatively unaffected by crack density, but the performance after durability testing was strongly affected. Specifically, CLs with high crack density showed higher performance relative to CLs without cracks after application of a carbon corrosion accelerated stress test. Electrochemical analyses coupled with X-ray computed tomography and scanning transmission electron microscopy with energy dispersive X-ray spectroscopy showed that the cracks provide shorter oxygen diffusion pathways to reaction sites, leading to decreased oxygen transport resistance. Additionally, we observed that the catalyst durability is unaffected by cracks. Our results provide a mechanistic explanation of the role of cracks in CL durability.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2021

Catalyst Revised: Rethinking the ParaView in Situ Analysis and Visualization API

As in situ analysis goes mainstream, ease of development, deployment, and maintenance becomes essential, perhaps more so than raw capabilities. In this paper, we present the design and implementation of Catalyst, an API for in situ analysis using ParaView, which we refactored with these objectives in mind. Furthermore, our implementation combines design ideas from in situ frameworks and HPC tools like Ascent and MPICH.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2020

The Role of Co-ZSM-5 Catalysts in Aerobic Oxidation of Ethylbenzene

Various forms of cobalt catalysts have been studied extensively for selective aerobic oxidation of hydrocarbons. However, it remains unclear whether cobalt can directly activate molecular oxygen under mild reaction conditions. Here we investigated the catalytic roles of cobalt in ethylbenzene oxidation with and without a hydroperoxide initiator. The contribution of different cobalt species was studied by varying the metal loading on Co-impregnated ZSM-5 samples. Quantitative EPR was used to determine the impact of cobalt catalysts on the free radical concentrations. Furthermore, this work provided strong evidence that cobalt, in several different forms, catalyzes hydrocarbon oxidation by facilitating peroxy bond cleavage, instead of direct oxygen activation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Recent Advances in the Understanding of Boron-Containing Catalysts for the Selective Oxidation of Alkanes to Olefins

The production of ethylene and propylene through aerobic alkane oxidation without significant coproduction of CO and CO 2 (CO x ) presents a challenge to academic and industrial researchers alike. Recently, boron-containing materials such as hexagonal boron nitride (hBN) have been identified as active and selective catalysts for the oxidative dehydrogenation (ODH) of propane to propylene with minimal CO x selectivity. Additionally, high olefin selectivity is also obtained in the oxidation of other alkanes and other materials such as metal borides and supported B/SiO 2 have been successfully applied to this transformation. Here, recent advances in the understanding of these catalysts in the oxidation of light alkanes are presented here providing a framework for further study of this exciting field.

03 NATURAL GAS↗
DOE OSTI2020

Mesoscopic analyses of the impact of morphology and operating conditions on the transport resistances in a proton-exchange-membrane fuel-cell catalyst layer

Exploring the origins of local transport resistance and characterizing the oxygen transport resistances in the catalyst layer (RCL) are critical for cost reduction. In this paper, a comprehensive mesoscopic model for simulating coupled transport processes of oxygen and water vapor for different structural parameters under different operating conditions in reconstructed microstructures is proposed. The local transport resistance is calculated after achieving the limiting current density and the effective diffusivity of oxygen. The results demonstrate that RCL increases greatly with decreasing platinum loading (LPt) and the transport resistances in other components of the cell dominate for high-loadings. Both the reduced oxygen permeation coefficient in the ionomer thin-film and the adsorption resistance account for the origins of local transport resistance. The local transport resistance increases with the bare carbon ratio for a constant LPt and Pt/C ratio due to the decreased effective ionomer surface, and increases with the I/C ratio due to the increased ionomer thickness and decreased Knudsen diffusivity. Due to the presence of liquid water, a slight decrease followed by an increase of the local transport resistance versus relative humidity is obtained. The contribution of ionomer thin-films to RCL is more sensitive to liquid saturation compared with that of pores. This journal is

Mu, YT↗
DOE OSTI2022

Free Energy Dependencies for Interfacial Electron Transfer from Tin-Doped Indium Oxide (ITO) to Molecular Photoredox Catalysts

John B. Goodenough proposed that interfacial electron transfer kinetics from main group metal oxides should be fundamentally different from that of transition metal oxides, an expectation that has not been widely tested. Herein, the kinetics for interfacial electron transfer from mesoporous transparent conductive oxide Tin-doped Indium Oxide (ITO) to four photoredox catalysts (PCs) were characterized in acetonitrile electrolytes. The photocatalysts had the form: [Ru(4,4ʹ-R 2 -2,2′-bipyridine) 2 (4,4ʹ-(PO 3 H 2 ) 2 -2,2′-bipyridine)] 2+ , where R was H, methoxy, tert -butyl, and Br. The impact of the surface binding group was characterized with [Ru(2,2′-bipyridine) 2 (4,4ʹ-(CO 2 H) 2 -bpy)] 2+ . The interfacial electron transfer reaction ITO(e − )∣PC + → ITO∣PC was quantified by nanosecond absorption spectroscopy as a function of the applied potential (and hence ‒Δ G °). Specific conditions of applied potential were identified where the kinetics were sensitive to the incident irradiance. A layer-by-layer method was used to insert ionic methylene bridge(s) between the PC and the oxide surface. Marcus-Gerischer analysis of the kinetic data indicates non-adiabatic interfacial electron transfer with total reorganization energies that increase when bridges were placed between the photocatalyst and the ITO surface.

Bangle, Rachel E.↗