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At least 433 records · Page 24

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DOE OSTI2022

The Signature C=C=O Stretch of Propenylketenes and Ketene Clusters [Book Chapter]

A combined experimental and theoretical approach has been used to examine the signature antisymmetric C=C=O stretch of prop-1-enylketene and prop-2-enylketene, as well as a series of ketene multimers and hydrates. Optimization and frequency calculations executed at the B3LYP/6-311G++(d,p) level of theory reveal four conformers of prop-1-enylketene and three conformers of prop-2-enylketene. These ketenes were generated via the pyrolysis of 3-pentenoic anhydride and 4-pentenoic anhydride, respectively, and isolated in low-temperature argon matrices prior to FTIR analysis. The resultant spectra display several bands consistent with B3LYP predictions. A similar computational and experimental survey of ketene multimers and hydrates, generated by the pyrolysis of acetic anhydride, has generated a list of frequencies for the antisymmetric C=C=O stretching mode. Furthermore, the results provide useful benchmarks for identification of propenylketenes in future experiments as well as insight for assigning other substituted ketenes in infrared spectra.

02 PETROLEUM↗

DOE OSTI2020

The Structural Origins of Intense Circular Dichroism in a Waggling Helicene Nanoribbon

We report the synthesis of a new perylene-diimide-based helical nanoribbon, which exhibits the largest molar electronic circular dichroism in the visible range of any molecule. Here, this nanoribbon also displays a substantial increase in molar circular dichroism relative to a smaller helical analogue, even though they share a similar structure: both nanoribbons incorporate two conformationally dynamic double-[4]helicene termini and a rigid [6]helicene-based core within their helical superstructures. Using DFT and TDDFT calculations, we find that the double-[4]helicenes within both nanoribbons orient similarly in solution; as such, conformational differences do not account for the disparities in circular dichroism. Instead, our results implicate the configuration of the double-[6]helicene within the larger nanoribbon as the source of the observed chiroptical amplification.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Ammonia Synthesis under Ambient Conditions: Insights into Water–Nitrogen–Magnetite Interfaces

New routes for transforming nitrogen into ammonia at ambient conditions would be a milestone toward an energy efficient and economically attractive production route in comparison to the traditional Haber-Bosch process. Recently, the synthesis of ammonia from water and nitrogen at room temperature and atmospheric pressure has been reported to be catalyzed by Fe 3 O 4 at the air-water interface. By integrating ambient pressure X-ray photoelectron spectroscopy and ab initio molecular dynamics and free energy calculations, we investigate the underlying thermodynamic mechanisms governing ammonia and hydrazine formation at the water-Fe 3 O 4 -nanoparticle interface. Here, we find that, unlike pure Fe 3 O 4 where N 2 can only interact with a limited number of Fe sites, hydroxylated species introduce large and diverse adsorption geometries where N 2 can bind through either Fe sites or Fe-OH groups, each of which are capable of independently facilitating proton-coupled electron transfer.

Chandy, Sruthy K. [University of California, Berke↗

DOE OSTI2024

Alkali cation-induced cathodic corrosion in Cu electrocatalysts

The reconstruction of Cu catalysts during electrochemical reduction of CO 2 is a widely known but poorly understood phenomenon. Herein, we examine the structural evolution of Cu nanocubes under CO 2 reduction reaction and its relevant reaction conditions using identical location transmission electron microscopy, cyclic voltammetry, in situ X-ray absorption fine structure spectroscopy and ab initio molecular dynamics simulation. Our results suggest that Cu catalysts reconstruct via a hitherto unexplored yet critical pathway - alkali cation-induced cathodic corrosion, when the electrode potential is more negative than an onset value (e.g., –0.4 V RHE when using 0.1 M KHCO 3 ). Having alkali cations in the electrolyte is critical for such a process. Consequently, Cu catalysts will inevitably undergo surface reconstructions during a typical process of CO 2 reduction reaction, resulting in dynamic catalyst morphologies. While having these reconstructions does not necessarily preclude stable electrocatalytic reactions, they will indeed prohibit long-term selectivity and activity enhancement by controlling the morphology of Cu pre-catalysts. Alternatively, by operating Cu catalysts at less negative potentials in the CO electrochemical reduction, we show that Cu nanocubes can provide a much more stable selectivity advantage over spherical Cu nanoparticles.