Julianne M. Thomsen
Yale University
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Julianne M. Thomsen.
Nature Communications | 2015
Stafford W. Sheehan; Julianne M. Thomsen; Ulrich Hintermair; Robert H. Crabtree; Gary W. Brudvig; Charles A. Schmuttenmaer
Molecular catalysts are known for their high activity and tunability, but their solubility and limited stability often restrict their use in practical applications. Here we describe how a molecular iridium catalyst for water oxidation directly and robustly binds to oxide surfaces without the need for any external stimulus or additional linking groups. On conductive electrode surfaces, this heterogenized molecular catalyst oxidizes water with low overpotential, high turnover frequency and minimal degradation. Spectroscopic and electrochemical studies show that it does not decompose into iridium oxide, thus preserving its molecular identity, and that it is capable of sustaining high activity towards water oxidation with stability comparable to state-of-the-art bulk metal oxide catalysts.
Journal of the American Chemical Society | 2014
Julianne M. Thomsen; Stafford W. Sheehan; Sara M. Hashmi; Jesús Campos; Ulrich Hintermair; Robert H. Crabtree; Gary W. Brudvig
Organometallic iridium complexes bearing oxidatively stable chelate ligands are precursors for efficient homogeneous water-oxidation catalysts (WOCs), but their activity in oxygen evolution has so far been studied almost exclusively with sacrificial chemical oxidants. In this report, we study the electrochemical activation of Cp*Ir complexes and demonstrate true electrode-driven water oxidation catalyzed by a homogeneous iridium species in solution. Whereas the Cp* precursors exhibit no measurable O2-evolution activity, the molecular species formed after their oxidative activation are highly active homogeneous WOCs, capable of electrode-driven O2 evolution with high Faradaic efficiency. We have ruled out the formation of heterogeneous iridium oxides, either as colloids in solution or as deposits on the surface of the electrode, and found indication that the conversion of the precursor to the active molecular species occurs by a similar process whether carried out by chemical or electrochemical methods. This work makes these WOCs more practical for application in photoelectrochemical dyads for light-driven water splitting.
Dalton Transactions | 2015
Julianne M. Thomsen; Daria L. Huang; Robert H. Crabtree; Gary W. Brudvig
Organometallic Ir precatalysts have been found to yield homogeneous Ir-based water-oxidation catalysts (WOCs) with very high activity. The Cp*Ir catalyst series can operate under a variety of regimes: it can either act as a homogeneous or a heterogeneous catalyst; it can be driven by chemical, photochemical, or electrochemical methods; and the molecular catalyst can either act in solution or supported as a molecular unit on a variety of solid oxides. In addition to optimizing the various reaction conditions, work has continued to elucidate the catalyst activation mechanism and identify water-oxidation intermediates. This Perspective will describe the development of the Cp*Ir series, their many forms as WOCs, and their ongoing characterization.
Nature Communications | 2016
Won-Hee Ryu; Forrest S. Gittleson; Julianne M. Thomsen; Jinyang Li; Mark Schwab; Gary W. Brudvig; André D. Taylor
One of the greatest challenges with lithium-oxygen batteries involves identifying catalysts that facilitate the growth and evolution of cathode species on an oxygen electrode. Heterogeneous solid catalysts cannot adequately address the problematic overpotentials when the surfaces become passivated. However, there exists a class of biomolecules which have been designed by nature to guide complex solution-based oxygen chemistries. Here, we show that the heme molecule, a common porphyrin cofactor in blood, can function as a soluble redox catalyst and oxygen shuttle for efficient oxygen evolution in non-aqueous Li-O2 batteries. The hemes oxygen binding capability facilitates battery recharge by accepting and releasing dissociated oxygen species while benefiting charge transfer with the cathode. We reveal the chemical change of heme redox molecules where synergy exists with the electrolyte species. This study brings focus to the rational design of solution-based catalysts and suggests a sustainable cross-link between biomolecules and advanced energy storage.
Journal of the American Chemical Society | 2016
Ke R. Yang; Adam J. Matula; Gihan Kwon; Jiyun Hong; Stafford W. Sheehan; Julianne M. Thomsen; Gary W. Brudvig; Robert H. Crabtree; David M. Tiede; Lin X. Chen; Victor S. Batista
The solution structures of highly active Ir water-oxidation catalysts are elucidated by combining density functional theory, high-energy X-ray scattering (HEXS), and extended X-ray absorption fine structure (EXAFS) spectroscopy. We find that the catalysts are Ir dimers with mono-μ-O cores and terminal anionic ligands, generated in situ through partial oxidation of a common catalyst precursor. The proposed structures are supported by (1)H and (17)O NMR, EPR, resonance Raman and UV-vis spectra, electrophoresis, etc. Our findings are particularly valuable to understand the mechanism of water oxidation by highly reactive Ir catalysts. Importantly, our DFT-EXAFS-HEXS methodology provides a new in situ technique for characterization of active species in catalytic systems.
Journal of Materials Chemistry | 2015
Prashanth K. Poddutoori; Julianne M. Thomsen; Rebecca L. Milot; Stafford W. Sheehan; Christian F. A. Negre; Venkata Krishna Garapati; Charles A. Schmuttenmaer; Victor S. Batista; Gary W. Brudvig; Art van der Est
We introduce phosphorus(V) porphyrins (PPors) as sensitizers of high-potential photoanodes with potentials in the 1.62–1.65 V (vs. NHE) range when codeposited with Ir(III)Cp* on SnO2. The ability of PPors to advance the oxidation state of the Ir(III)Cp* to Ir(IV)Cp*, as required for catalytic water oxidation, is demonstrated by combining electron paramagnetic resonance (EPR), steady-state fluorescence and time-resolved terahertz spectroscopy (TRTS) measurements, in conjunction with quantum dynamics simulations based on DFT structural models. Contrary to most other types of porphyrins previously analyzed in solar cells, our PPors bind to metal-oxide surfaces through axial coordination, a binding mode that makes them less prone to aggregation. The comparison of covalent binding via anchoring groups, such as m-hydroxidebenzoate (−OPh–COO−) and 3-(3-phenoxy)-acetylacetonate (−OPh–AcAc) as well as by direct deposition upon exchange of a chloride (Cl−) ligand provides insight on the effect of the anchoring group on forward and reverse light-induced interfacial electron transfer (IET). TRTS and quantum dynamics simulations reveal efficient photoinduced electron injection, from the PPor to the conduction band of SnO2, with faster and more efficient IET from directly bound PPor than from anchor-bound PPors. The photocurrents of solar cells, however, are higher for PPor–OPh–COO− and PPor–OPh–AcAc than for the directly bound PPor–O− for which charge recombination is faster. The high-potentials and the ability to induce redox state transitions of Ir(III)Cp* suggest that PPor/SnO2 assemblies are promising photoanode components for direct solar water-oxidation devices.
Inorganic Chemistry | 2016
Daria L. Huang; Rodrigo Beltrán-Suito; Julianne M. Thomsen; Sara M. Hashmi; Kelly L. Materna; Stafford W. Sheehan; Brandon Q. Mercado; Gary W. Brudvig; Robert H. Crabtree
This paper introduces Ir(I)(CO)2(pyalc) (pyalc = (2-pyridyl)-2-propanoate) as an atom-efficient precursor for Ir-based homogeneous oxidation catalysis. This compound was chosen to simplify analysis of the water oxidation catalyst species formed by the previously reported Cp*Ir(III)(pyalc)OH water oxidation precatalyst. Here, we present a comparative study on the chemical and catalytic properties of these two precursors. Previous studies show that oxidative activation of Cp*Ir-based precursors with NaIO4 results in formation of a blue Ir(IV) species. This activation is concomitant with the loss of the placeholder Cp* ligand which oxidatively degrades to form acetic acid, iodate, and other obligatory byproducts. The activation process requires substantial amounts of primary oxidant, and the degradation products complicate analysis of the resulting Ir(IV) species. The species formed from oxidation of the Ir(CO)2(pyalc) precursor, on the other hand, lacks these degradation products (the CO ligands are easily lost upon oxidation) which allows for more detailed examination of the resulting Ir(pyalc) active species both catalytically and spectroscopically, although complete structural analysis is still elusive. Once Ir(CO)2(pyalc) is activated, the system requires acetic acid or acetate to prevent the formation of nanoparticles. Investigation of the activated bis-carbonyl complex also suggests several Ir(pyalc) isomers may exist in solution. By (1)H NMR, activated Ir(CO)2(pyalc) has fewer isomers than activated Cp*Ir complexes, allowing for advanced characterization. Future research in this direction is expected to contribute to a better structural understanding of the active species. A diol crystallization agent was needed for the structure determination of 3.
Organometallics | 2013
Jonathan Graeupner; Ulrich Hintermair; Daria L. Huang; Julianne M. Thomsen; Mike Takase; Jesús Campos; Sara M. Hashmi; Menachem Elimelech; Gary W. Brudvig; Robert H. Crabtree
Organometallics | 2012
Jonathan Graeupner; Timothy P. Brewster; James D. Blakemore; Nathan D. Schley; Julianne M. Thomsen; Gary W. Brudvig; Nilay Hazari; Robert H. Crabtree
Journal of Physical Chemistry C | 2017
Rebecca J. Kamire; Kelly L. Materna; William L. Hoffeditz; Brian T. Phelan; Julianne M. Thomsen; Omar K. Farha; Joseph T. Hupp; Gary W. Brudvig; Michael R. Wasielewski