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RECENT AMPED EFRC NEWS

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  New Paper – A Semiconductor-Mediator-Catalyst Artificial Photosynthetic System for Photoelectrochemical Water Oxidation

  In fabricating an artificial photosynthesis (AP) electrode for water oxidation, we have devised a semiconductor-mediator-catalyst structure that mimics photosystem II (PSII). It is based on a surface layer of vertically grown nanorods of Fe2O3 on fluorine doped tin oxide (FTO) electrodes … Continued

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  New Paper – Design and characterization of surface molecular assemblies for the preparation of solar fuels

  A key issue in solar energy conversion is the utilization of solar energy for the preparation of solar fuels. In this area, artificial photosynthesis offers promising approaches for the conversion of H2O and CO2 into usable solar fuels. This review … Continued

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  New Paper – An Iron Bis(carbene) Catalyst for Low Overpotential CO2 Electroreduction to CO: Mechanistic Insights from Kinetic Zone Diagrams, Spectroscopy, and Theory

  A common challenge in molecular electrocatalysis is the relationship between maximum activity and the overpotential required to reach that rate, with faster catalysts incurring higher overpotentials. This work follows a strategy based on independent tuning of ligands in the primary … Continued

• New Paper – Mixed Tin-Titanium Oxides by Atomic Layer Deposition on Planar Substrates: Physical and Electronic Structure

  Ternary atomic layer deposition of Sn-doped TiOx (Sn:TiOx) and Ti-doped SnOx (Ti:SnOx) was performed using tetrakisdimethylamidotitanium (IV) and tin(IV) with water at 150 °C on (1 0 0) Si and quartz substrates. The physical structure of the films was investigated using scanning electron, atomic force, … Continued

• New Paper – Influence of Surface and Structural Variations in Donor−Acceptor−Donor Sensitizers on Photoelectrocatalytic Water Splitting

  Conjugated organic chromophores composed of linked donor (D) and acceptor (A) moieties have attracted considerable attention for photoelectrochemical applications. In this work, we compare the optoelectronic properties and photoelectrochemical performance of two D–A–D structural isomers with thiophene-X-carboxylic acid (X denotes 3 … Continued

• New Paper – Polymer Chromophore-Catalyst Assembly for Photocatalytic CO2 Reduction

  A polystyrene-based chromophore–catalyst assembly (PS-RuC/RuCat) was synthesized and applied for photocatalytic CO2 reduction in an organic solution in the presence of a sacrificial donor. The polymer assembly contains Ru(bpy)32+ (RuC, bpy = 2,2′-bipyridine) as the chromophore and a derivative of … Continued

• New Paper – Interfacial Electron Transfer through Ultrathin ALD TiOX Layers: A Comparative Study of TiO2/TiOX and SnO2/TiOX Core/Shell Nanocrystals

  Mesoporous anatase TiO2, mixed anatase/brookite TiO2, and rutile-type SnO2 nanocrystalline films were coated with ultrathin (<5 nm) TiOx by the atomic layer deposition (ALD) of tetrakisdimethylamidotitanium(IV) and water at 150 °C to fabricate SnO2/TiOx and TiO2/TiOx core/shell materials. The core/shell … Continued

• New Paper – It Is Good to Be Flexible: Energy Transport Facilitated by Conformational Fluctuations in Light-Harvesting Polymers

  We investigate the mechanism of energy transfer between ruthenium(II) (Ru) and osmium(II) (Os) polypyridyl complexes affixed to a polyfluorene backbone (PF-RuOs) using a combination of time-resolved emission spectroscopy and coarse-grained molecular dynamics (CG MD). Photoexcitation of a Ru chromophore initiates … Continued

• New Paper – Dye-Sensitized Nonstoichiometric Strontium Titanate Core-Shell Photocathodes for Photoelectrosynthesis Applications

  A core/shell approach that utilizes a high-surface area conducting core and an outer semiconductor shell is exploited to prepare p-type dye-sensitized solar energy cells that operate with a minimal applied bias. Photocathodes were prepared by coating thin films of nanocrystalline … Continued

• New Paper – An Iron Pyridyl-Carbene Electrocatalyst for Low Overpotential CO2 Reduction to CO

  Electrocatalysts for CO2 reduction based on first-row transition metal ions have attracted attention as abundant and affordable candidates for energy conversion applications. Yet very few molecular iron electrocatalysts exhibit high selectivity for CO. Iron complexes supported by a redox-active 2,2′:6′,2″-terpyridine … Continued

• New Paper – Tunneling and Thermally Activated Electron Transfer in Dye-Sensitized SnO2|TiO2 Core|Shell Nanostructures

  The mechanism for interfacial electron transfer (ET) from a metal oxide core|shell nanostructure to a [RuIII(2,2′-bipyridine)2(4,4′-(PO3H2)2-2,2′-bipyridine)]3+ sensitizer was probed through spectroscopic quantification of the ET kinetics over a 70 °C temperature range in an aqueous 0.1 M HClO4 solution. Mesoporous thin films … Continued

• New Paper – Enabling Aqueous NiO Photocathodes by Passivating Surface Sites That Facilitate Proton-Coupled Charge Transfer

  Photoelectrodes consisting of wide-band gap metal oxides functionalized with chromophores and catalysts are a potential low-cost solution to generate solar fuels from aqueous solution. NiO is a common photocathode material used in these systems, yet it generally exhibits poor performance … Continued

• New Paper – Organic Chromophores Designed for Hole Injection into Wide-Band-Gap Metal Oxides for Solar Fuel Applications

  The power conversion efficiency of tandem dye-sensitized photoelectrosynthesis cells is limited by the number of p-type metal oxide semiconductors and chromophores available for the photocathode. Here, a new class of donor–acceptor–donor organic chromophores is introduced with deep highest occupied molecular … Continued

• New Paper – Solvent influence on non-adiabatic interfacial electron transfer at conductive oxide electrolyte interfaces

  The kinetics for interfacial electron transfer (ET) from a transparent conductive oxide (tin-doped indium oxide, ITO, Sn:In2O3) to molecular acceptors 4-[N,N-di(p-tolyl)amino]benzylphosphonic acid, TPA, and [RuII(bpy)2(4,4′-(PO3H2)2-bpy)]2+, RuP, positioned at variable distances within and beyond the electric double layer (EDL), were quantified … Continued

• New Paper – Perspectives on Dye Sensitization of Nanocrystalline Mesoporous Thin Films

  Recent advances in our mechanistic understanding of dye-sensitized electron transfer reactions occurring at metal oxide interfaces are described. These advances were enabled by the advent of mesoporous thin films, comprised of anatase TiO2 nanocrystallites, that are amenable to spectroscopic and … Continued

• New Paper – Ultrafast Energy Transfer in Fully Conjugated Thiophene-Benzothiadiazole Capped Poly(Phenylene Ethynylene) Molecular Wires

  Energy transfer was explored in a series of poly(phenylene ethynylene) (PPE) polymers with increasing lengths that were end-capped with thiophene-benzothiadiazole (TBT) groups to form fully conjugated donor–acceptor polymers. For the polymers in solution, ultrafast transient absorption and time-resolved fluorescence spectroscopy … Continued

• New Paper – Photophysical characterization of new osmium (II) photocatalysts for hydrohalic acid splitting

  Two osmium(II) photocatalysts bearing a dicationic 4,4′-bis-(trimethylaminomethyl)-2,2′-bipyridine (tmam) ligand and 2,2′-bipyridine {[Os(bpy)2(tmam)]4+} or 4,4′-(CF3)2-2,2′-bipyridine {[Os((CF3)2bpy)2(tmam)]4+} ancillary ligands were synthesized and characterized for application in HX splitting. Iodide titration studies in acetone solutions provided evidence for an in situ formed terionic complex with two iodide … Continued

• New Paper – Kinetic Evidence that the Solvent Barrier for Electron Transfer is Absent in the Electric Double Layer

  Classical capacitance studies have revealed that the first layer of water present at an aqueous metal-electrolyte interface has a die-lectric constant less than 1/10th that of bulk water. Modern theory indicates that under such solvent conditions the barrier for elec-tron … Continued

• New Paper – Abrupt degenerately-doped silicon nanowire tunnel junctions

  The presence of narrow, degenerately-doped axial silicon nanowire (SiNW) p–n junctions via off-axis electron holography (EH) has been confirmed. SiNWs were grown via the vapor-solid-liquid (VLS) mechanism using gold (Au) as the catalyst, silane (SiH4 ), diborane (B2H6 ) and phosphine (PH3 ) as the … Continued

• New Paper – Ultrafast Relaxations in Ruthenium Polypyridyl Chromophores Determined by Stochastic Kinetics Simulations

  Maximizing the efficiency of solar energy conversion using dye assemblies rests on understanding where the energy goes following absorption. Transient spectroscopies in solution are useful for this purpose, and the time-resolved data are usually analyzed with a sum of exponentials. … Continued

• New Paper – Kinetics of the Trans Effect in Ruthenium Complexes Provide Insight into the Factors that Control Activity and Stability in CO2 Electroreduction

  Comparative kinetic studies of a series of new ruthenium complexes provide a platform for understanding how strong trans effect ligands and redox-active ligands work together to enable rapid electrochemical CO2 reduction at moderate overpotential. After synthesizing isomeric pairs of ruthenium … Continued

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  New Paper ‒ Cation Effects in p-Type Dye Sensitized Solar Cells

  The performance of dye sensitized solar cells (DSSCs) depends on the properties and interactions of three fundamental components: the semiconductor, chromophore, and electrolyte. For the electrolyte, the dependence of DSSC performance on the identity and valence state of the spectator … Continued

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  New Paper ‒ BODIPY Dyes as Visible Light Absorber/Sensitizers on Semiconductor Oxide Surfaces

  The synthesis, characterization, electrochemical and photophysical properties of the phosphonate-derivatized Carbazole (CBZ) and boron dipyrromethene (BODIPY) chromophores in the dyes, BODIPY(CBZ)2PO3H2 [8] and BODIPY(Tol)2PO3H2 [7], are described. The oxide-bound dyes have been explored as light absorbers in dye-sensitized photoelectrosynthesis cell … Continued

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  New Paper ‒ Electron Transfer Reorganization Energies in the Electrode–Electrolyte Double Layer

  The total reorganization energy, λ, for interfacial electron transfer, ET, from a conductive electrode to redox-active molecules at fixed positions within the electric double layer, EDL, has been determined experimentally. Conductive indium–tin-oxide (ITO, In2O3:Sn) mesoporous films were functionalized with 4-[N,N-di(p-tolyl)-amino]benzylphosphonic … Continued

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  New Paper ‒ Self-Assembled Chromophore/Catalyst Bilayer for Water Oxidation in a Dye-Sensitized Photoelectrosynthesis Cell

  A new approach is described for the preparation of water oxidation photoanodes in a Dye-Sensitized Photoelectrosynthesis Cell (DSPEC) for water splitting. It is based on a chromophore (C) – catalyst (Cat) assembly prepared by a self-assembled bilayer (SAB) on a … Continued

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  DOE Newsletter Editorial Board: Congratulations Eric Assaf

  Congratulations to Eric Assaf, 3rd year graduate student in the Miller group and member of the AMPED EFRC Catalysis Team, who has been accepted to the editorial board of the DOE EFRC quarterly newsletter Frontiers in Energy Research. This newsletter … Continued

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  New Paper ‒ Factors that Control the Direction of Excited State Electron Transfer at Dye-Sensitized Oxide Interfaces

  Molecular excited states at conductive and semiconductive interfaces were found to transfer an electron to the oxide (injection) or accept an electron from the oxide (hole transfer). The direction of this electron transfer was determined by the metal oxide electronic … Continued

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  New Paper ‒ A stable dye-sensitized photoelectrosynthesis cell mediated by a NiO overlayer for water oxidation

  In the development of photoelectrochemical cells for water splitting or CO2 reduction, a major challenge is O2 evolution at photoelectrodes that, in behavior, mimic photosystem II. At an appropriate semiconductor electrode, a water oxidation catalyst must be integrated with a visible … Continued

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  New Paper ‒ Electron Localization & Transport in SnO2/TiO2 Mesoporous Thin Films

  A study of SnO2/TiO2 core/shell films was undertaken to investigate the influence of shell thickness and post deposition sintering on electron localization and transport properties. Electrochemical reduction of the materials resulted in the appearance of a broad visible –near IR … Continued

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  New Paper ‒ Atomic Layer Deposition of SnOx onto Mesoporous, Nanocrsytalline TiO2 and SnO2 Thin Films

  The atomic layer deposition of tetrakisdimethylamidotin(IV) and water on mesoporous thin films of nanocrystalline anatase TiO2, rutile SnO2, and rutile TiO2 was investigated. For all deposition conditions tested, highly oxygen deficient coatings were created, and purge time and temperature were … Continued