We demonstrate a method for the synthesis of multicomponent nanostructures consisting of CdS and CdSe with rod and tetrapod morphologies. A seeded synthesis strategy is used in which spherical seeds of CdSe are prepared first using a hot-injection technique. By controlling the crystal structure of the seed to be either wurtzite or zinc-blende, the subsequent hot-injection growth of CdS off of the seed results in either a rod-shaped or tetrapod-shaped nanocrystal, respectively. The phase and morphology of the synthesized nanocrystals are confirmed using X-ray diffraction and transmission electron microscopy, demonstrating that the nanocrystals are phase-pure and have a consistent morphology. The extinction coefficient and quantum yield of the synthesized nanocrystals are calculated using UV-Vis absorption spectroscopy and photoluminescence spectroscopy. The rods and tetrapods exhibit extinction coefficients and quantum yields that are higher than that of the bare seeds. This synthesis demonstrates the precise arrangement of materials that can be achieved at the nanoscale by using a seeded synthetic approach.
The Haber Bosch process has served as the dominant method of synthesizing ammonia over the last century. Ammonia produced through this route leads to a stoichiometric carbon dioxide footprint and also involves harsh conditions which limit modularity of the process. We are developing a continuous lithium-mediated approach through which nitrogen can be fixed at ambient conditions while eliminating the carbon dioxide footprint. We have elucidated the reaction network through which ammonia synthesis occurs in competition with hydrogen evolution. The coupling of kinetics and transport has a significant influence on the rates of ammonia synthesis, providing a means to improve selectivity of nitrogen fixation. We have designed non-aqueous gas diffusion electrodes which overcome transport limitations and enable high-rate ammonia synthesis at ambient conditions. Understanding of the roles played by the solvent enable control over the solid-electrolyte interphase, which exerts a significant effect on reaction selectivity.
Lactones serve as key synthetic intermediates for the large-scale production of several important chemicals, such as polymers, pharmaceuticals, and scents. Current thermochemical methods for the formation of some lactones rely on molecular oxidants, which yield stoichiometric side products that result in a poor atom economy and impose safety hazards when in contact with organic substrates and solvents. Electrochemical synthesis can alleviate these concerns by exploiting an applied potential to enable the possibility of a clean and safe route for lactonization. In this study, we investigated the mechanism of electrochemical lactone formation from cyclic ketones. When using a platinum anode and cathode in acetonitrile with 10 M H2O and 400 mM cyclohexanone, we found that non-Baeyer–Villiger products, δ-hexanolactone and γ-caprolactone, are formed with a total Faradaic efficiency of ∼20%. Isotope labeling experiments support that water is the oxygen atom source for this reaction. In addition, electrochemical kinetic data suggest a first-order dependence on water at low water concentrations (<2 M H2O) and a zeroth order dependence on the substrate, cyclohexanone. A Tafel slope of 139 mV/decade was measured at 400 mM cyclohexanone and 10 M H2O, implying an initial electron transfer as the rate-determining step. Literature-proposed mechanisms for similar transformations suggest an outer-sphere pathway. However, on the basis of the collected electrochemical kinetic data, we propose the possibility that Pt reacts with water in an initial electron transfer that forms Pt–OH, which can subsequently react with the ketone substrate. A subsequent electron transfer forms a ring-opened carboxylic acid cation that can reclose to form either of the observed five- or six-membered ring lactone products.
This dataset contains 344 different digitized and tagged Tafel slope datasets from the CO2 reduction literature. We re-analyze this data with a Bayesian data analysis procedure that estimates a Tafel slope and yields distributional uncertainty information about its value. We are releasing this dataset along with our study to facilitate re-analyzing and refitting our data using different models and approaches.
We report a direct and efficient electrochemical carboxylation of benzylic C–N bonds with CO2 at room temperature. The reaction has been successfully applied to both primary and secondary benzylic C–N bonds with the compatibility of a variety of functional groups. This procedure does not require stoichiometric metals, external reducing agents, or sacrificial anodes, making column chromatography unnecessary for product purification. Differential electrochemical mass spectrometry (DEMS) was used to elucidate key intermediates of the electrocarboxylation reaction.
The transduction of electrical energy into chemical bonds represents one potential strategy for storing energy derived from intermittent sources such as solar and wind. Driving the electrochemical reduction of carbon dioxide using light requires (1) developing light absorbers which convert photons into electron-hole pairs and (2) catalysts which utilize these electrons and holes to reduce carbon dioxide and oxidize water, respectively. For both the light absorbers and catalysts, the use of nanoscale particles is advantageous, as charge transport length scales are minimized in the case of nanoscale light absorbers and catalytic surface-area-to-volume ratio is maximized for nanoscale catalysts. In many cases, although semiconductors and metals in the form of thin films and foils are increasingly well-characterized as photoabsorbers and electrocatalysts for carbon dioxide reduction, respectively, the properties of their nanoscale counterparts remain poorly understood.This dissertation explores the nature of the light absorption mode of non-stoichiometric semiconductors which are utilized as light absorbers and the development of catalysts with enhanced stability, activity, and selectivity for carbon dioxide reduction. Chapter 1 provides an overview of the state of development of methods of transducing the energy of photons into chemical bonds. Chapters 2 and 3 investigate the development of stable, active, and selective catalysts for the electrochemical reduction of carbon dioxide. Chapter 2 examines how copper nanoparticles have enhanced activities and selectivities for methanation compared to copper foils. Chapter 3 focuses on the development of strategies to stabilize high-surface-area catalysts to prevent surface area loss during electrochemical carbon dioxide reduction.Chapters 4 and 5 entail a fundamental understanding of the light absorption mode of nanoscale photoabsorbers used in both photoelectrochemical cells and in photovoltaics. Chapter 4 focuses on the nature of the light absorption mode of non-stoichiometric tungsten oxide, a material which has been explored as a photoanode for the photon driven oxidation of water. Chapter 5 examines the tunability of the light absorption mode of nanoscale copper sulfide, a material which has been explored as a photoabsorber for photovoltaics. An understanding of the light absorption mode of non-stoichiometric oxides and sulfides at the nanoscale is critical for the use of these materials in redox active environments.
This data set contains digitized and tagged polarization and partial current density data for 18 datasets of CO2 reduction to H2 and CO over Ag catalysts, as well as 8 datasets of CO2 reduction to HCOO-, CO, and H2 over Sn catalysts. We analyze this data using a coupled continuum modeling and covariance matrix adaptation approach for which the codebase is provided in DOI: 10.5281/zenodo.7866195.
