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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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Tracking Site-specific C-C Coupling of Formaldehyde Molecules on Rutile TiO2(110)
Direct imaging of site-specific reactions of individual mole-cules as a function of temperature is a long-sought goal in molecular science. Here, we report the direct visualization of molecular coupling of formaldehyde on reduced rutile TiO2(110) surfaces as we track the same set of molecules when the temperature is increased from 75 to 170 K using scanning tunneling microscope (STM). Our recent study showed that formaldehyde preferably adsorbs on bridging-bonded oxygen (Ob) vacancy (VO) defect site. Herein, images from the same area as the temperature is increased show that VO-bound formaldehyde couples with Ti-bound formaldehyde forming a diolate intermediate. Exposure of formaldehyde at room temperature leads to diolate as the majority species on the surface and no VO-bound formaldehyde is observed. The diolate species are the key reaction intermediates in the formation of ethylene reported in previous ensemble-averaged studies.
Suppressing Defect Formation Pathways in the Direct C-H Arylation Polymerization of Photovoltaic Copolymers
Direct CH arylation polymerization (DARP) holds great promise for the green, atom-efficient synthesis of p-conjugated copolymers for use in high-performance polymer solar cells (PSCs). However, CH arylation regioselectivity control for monomers containing multiple reactive aryl CH bonds is not well understood, and nonselective reactivity results in material defects with unknown effects on PSC performance. Here, the effects of reaction conditions on copolymer molecular mass, dispersity, and PSC performance as well as defect formation pathways occurring during the DARP synthesis of an archetypal benzodithiophene-alt-diketopyrrolopyrrole copolymer, PBDTTDPP, are scrutinized. Small molecule model studies analyzed by HPLC-HRMS elucidate the effects of DARP conditions on trace chemical defect (primarily hydrodehalogenation and beta-CH arylation) formation. Copolymer branching arising from nonselective beta-CH arylation of monomers at the polymer chain end is identified as the principal photovoltaically deleterious defect. Fine-tuning the DARP reaction conditions reduces branching densities to below 1%, with an exceptional CH regioselectivity of >110:1. The optimal copolymers achieve superior PSC performance versus defect-rich DARP-derived copolymers and rival those from Stille polycondensations.
Arene C–H Functionalization by p-Block Metal Tl(III) Occurs at the Borderline of C–H Activation and Electron Transfer
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Conductive Polymer Binder-Enabled SiO–Sn x Co y C z Anode for High-Energy Lithium-Ion Batteries
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Solventless C–C Coupling of Low Carbon Furanics to High Carbon Fuel Precursors Using an Improved Graphene Oxide Carbocatalyst
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Probing the C–O Bond-Formation Step in Metalloporphyrin-Catalyzed C–H Oxygenation Reactions
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