Single-crystalline, wormlike hematite photoanodes for efficient solar water splitting

A hematite photoanode showing a stable, record-breaking performance of 4.32 mA/cm(2) photoelectrochemical water oxidation current at 1.23 V vs. RHE under simulated 1-sun (100 mW/cm(2)) irradiation is reported. This photocurrent corresponds to ca. 34% of the maximum theoretical limit expected for hematite with a band gap of 2.1 V. The photoanode produced stoichiometric hydrogen and oxygen gases in amounts close to the expected values from the photocurrent. The hematitle has a unique single-crystalline "wormlike" morphology produced by in-situ two-step annealing at 550 degrees C and 800 degrees C of beta-FeOOH nanorods grown directly on a transparent conducting oxide glass via an all-solution method. In addition, it is modified by platinum doping to improve the charge transfer characteristics of hematite and an oxygen-evolving co-catalyst on the surface.open2

Formation of Molecular Monolayers on TiO₂ Surfaces: A Surface Analogue of the Williamson Ether Synthesis

Strategies to modify metal oxide surfaces are important because of the increasing applications of metal oxides in catalysis, sensing, electronics, and renewable energy. Here, we report the formation of molecular monolayers on anatase nanocrystalline TiO2 surfaces at near-ambient temperatures by a simple one-step immersion. This is achieved by an analogue of the Williamson ether synthesis, in which the hydroxyl groups of the TiO2 surface react with iodo-alkane molecules to release HI and form a Ti–O–C surface linkage. The grafted molecules were characterized by Fourier-transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) to confirm the formation of covalently bonded monolayers. Kinetic studies yielded an activation barrier of ∼59 kJ/mol for the grafting reaction. Measurements of hydrolytic stability of the grafted molecules in water show that approximately half the molecules are removed within minutes to hours at temperatures of 25–100 °C with an activation energy of ∼82 kJ/mol, while the remaining molecules are stable for much longer periods of time. These different stabilities are discussed in terms of the different types of Ti–O–C bonds that can form on TiO2 surfaces

Bridge-Dependent Interfacial Electron Transfer from Rhenium−Bipyridine Complexes to TiO₂ Nanocrystalline Thin Films

We have measured the electron injection kinetics of four rhenium−bipyridine complexes (Re1C, ReEC, Re1TC, and Re2TC) on TiO2 nanocrystalline films using transient infrared spectroscopy. The self-assembled monolayer formation of these complexes was characterized by UV−visible spectroscopy, infrared reflection absorption spectroscopy, and X-ray photoelectron spectroscopy. These complexes bind to the TiO2 surface through the formation of carboxylate groups, and these self-assembled layers are approximately a monolayer. The kinetics studies address the effect of insulating and conjugated spacers and the length of conjugation on the electron-transfer process. The insulating bridge leads to a slower injection rate and poorer injection yield compared with the conjugated spacers. The electron injection of Re2TC was found to be a fast, high-yielding, and multiple electron injector process. The ground and electronically excited states of the dye complexes were characterized using ground-state and time-dependent density functional theory. We present the role of electronic conjugation in modulating electron injection using a combination of computational and experimental work and find that these metal-based complexes adsorbed on a semiconductor surface can be used to read out the electron injection kinetics through tailored molecular bridges

Bridge-Dependent Interfacial Electron Transfer from Rhenium−Bipyridine Complexes to TiO₂ Nanocrystalline Thin Films

We have measured the electron injection kinetics of four rhenium−bipyridine complexes (Re1C, ReEC, Re1TC, and Re2TC) on TiO2 nanocrystalline films using transient infrared spectroscopy. The self-assembled monolayer formation of these complexes was characterized by UV−visible spectroscopy, infrared reflection absorption spectroscopy, and X-ray photoelectron spectroscopy. These complexes bind to the TiO2 surface through the formation of carboxylate groups, and these self-assembled layers are approximately a monolayer. The kinetics studies address the effect of insulating and conjugated spacers and the length of conjugation on the electron-transfer process. The insulating bridge leads to a slower injection rate and poorer injection yield compared with the conjugated spacers. The electron injection of Re2TC was found to be a fast, high-yielding, and multiple electron injector process. The ground and electronically excited states of the dye complexes were characterized using ground-state and time-dependent density functional theory. We present the role of electronic conjugation in modulating electron injection using a combination of computational and experimental work and find that these metal-based complexes adsorbed on a semiconductor surface can be used to read out the electron injection kinetics through tailored molecular bridges

Bridge-Dependent Interfacial Electron Transfer from Rhenium−Bipyridine Complexes to TiO₂ Nanocrystalline Thin Films

We have measured the electron injection kinetics of four rhenium−bipyridine complexes (Re1C, ReEC, Re1TC, and Re2TC) on TiO2 nanocrystalline films using transient infrared spectroscopy. The self-assembled monolayer formation of these complexes was characterized by UV−visible spectroscopy, infrared reflection absorption spectroscopy, and X-ray photoelectron spectroscopy. These complexes bind to the TiO2 surface through the formation of carboxylate groups, and these self-assembled layers are approximately a monolayer. The kinetics studies address the effect of insulating and conjugated spacers and the length of conjugation on the electron-transfer process. The insulating bridge leads to a slower injection rate and poorer injection yield compared with the conjugated spacers. The electron injection of Re2TC was found to be a fast, high-yielding, and multiple electron injector process. The ground and electronically excited states of the dye complexes were characterized using ground-state and time-dependent density functional theory. We present the role of electronic conjugation in modulating electron injection using a combination of computational and experimental work and find that these metal-based complexes adsorbed on a semiconductor surface can be used to read out the electron injection kinetics through tailored molecular bridges