In Situ X-ray Absorption Spectroscopy Study of the Deactivation Mechanism of a Ni-SrTiO Photocatalyst Slurry Active in Water Splitting.

We used in situ X-ray absorption spectroscopy (XAS) to investigate the composition-performance correlation of Ni-SrTiO photocatalysts active for water splitting. After preparation and exposure to ambient conditions, the Ni particles on SrTiO consist of Ni(0) and Ni(II) phases, with a 4:1 at % ratio, in a metal/oxide core/shell configuration, as confirmed by XPS and TEM-EDX. In situ XAS experiments using an aqueous slurry of the Ni-SrTiO photocatalyst and simultaneous continuous exposure to 365 nm light with a power density of 100 mW cm and the X-rays do not reveal significant changes in oxidation state of the Ni particles.

Limiting Molecular Twisting: Upgrading a Donor-Acceptor Dye to Drive H Evolution.

The donor-acceptor (D-A) dye 4-(bis-4-(5-(2,2-dicyano-vinyl)-thiophene-2-yl)-phenyl-amino)-benzoic acid (P1) has been frequently used to functionalize NiO photocathodes and induce photoelectrochemical reduction of protons when coupled to a suitable catalyst. Photoinduced twisting of the P1 dye is steered on NiO by co-adsorption of tetradecanoic acid (C, myristic acid (MA)). Density Functional Theory and time-resolved photoluminescence studies confirm that twisting lowers the energy levels of the photoexcited D-A dye.

Photophysical Study on the Effect of the External Potential on NiO-Based Photocathodes.

In the present study, we investigate the effects of the applied external potential on a dye-sensitized NiO photocathode by time-resolved photoluminescence and femtosecond transient absorption spectroscopy under operating conditions. Instead of the anticipated acceleration of photoinduced hole injection from dye into NiO at a more negative applied potential, we observe that both hole injection and charge recombination are slowed down. We cautiously assign this effect to a variation in OH ion concentration in the inner Helmholtz plane of the electrochemical double layer with applied potential, warranting further investigation for the realization of efficient solar fuel devices.

Nanometer-Resolved Operando Photo-Response of Faceted BiVO Semiconductor Nanoparticles.

Photo(electro)catalysis with semiconducting nanoparticles (NPs) is an attractive approach to convert abundant but intermittent renewable electricity into stable chemical fuels. However, our understanding of the microscopic processes governing the performance of the materials has been hampered by the lack of operando characterization techniques with sufficient lateral resolution. Here, we demonstrate that the local surface potentials of NPs of bismuth vanadate (BiVO) and their response to illumination differ between adjacent facets and depend strongly on the pH of the ambient electrolyte.

Disentangling Hot Carrier Decay and the Nature of Low- to High- Transfer Processes in Quasi-Two-Dimensional Layered Perovskites.

Quasi-two-dimensional (2D) metal halide perovskites (MHPs) are promising photovoltaic (PV) materials because of their impressive optical and optoelectronic properties and improved stability compared to their 3D counterparts. The presence of domains with varying numbers of inorganic layers between the organic spacers (-phases), each with different bandgaps, makes the photoinduced carrier dynamics in films of these materials complex and intriguing. Existing interpretations of the ultrafast femto- or picosecond spectroscopy data have been inconsistent, most of them focusing either on exciton/charge transfer from low- to high- phases or on hot carrier cooling, but not combined.

CuBO : A Potential Alternative for NiO as a Hole Acceptor Layer.

P-type metal oxides, and in particular NiO, are typically used as hole accepting layers in dye-sensitized photocathodes. Delafossites (CuMO ) with M=B, Al, Cr or Ga have recently been proposed as attractive substitutes for NiO, with theoretically a higher hole mobility than NiO, therefore allowing a higher efficiency when the photocathode is applied in solar to fuel devices. We have experimentally validated the photoelectrochemical performance of photocathodes consisting of nanoporous CuBO (CBO) on Fluorine-doped Tin Oxide substrates, photosensitized with a light absorbing P1 dye.

Photon Energy-Dependent Ultrafast Exciton Transfer in Chlorosomes of and the Role of Supramolecular Dynamics.

The antenna complex of green sulfur bacteria, the chlorosome, is one of the most efficient supramolecular systems for efficient long-range exciton transfer in nature. Femtosecond transient absorption experiments provide new insight into how vibrationally induced quantum overlap between exciton states supports highly efficient long-range exciton transfer in the chlorosome of . Our work shows that excitation energy is delocalized over the chlorosome in <1 ps at room temperature.

Photophysical Characterization of Ru Nanoclusters on Nanostructured TiO by Time-Resolved Photoluminescence Spectroscopy.

Despite the promising performance of Ru nanoparticles or nanoclusters on nanostructured TiO in photocatalytic and photothermal reactions, a mechanistic understanding of the photophysics is limited. The aim of this study is to uncover the nature of light-induced processes in Ru/TiO and the role of UV versus visible excitation by time-resolved photoluminescence (PL) spectroscopy. The PL at a 267 nm excitation is predominantly due to TiO, with a minor contribution of the Ru nanoclusters.

Electrochemical decarboxylation of acetic acid on boron-doped diamond and platinum-functionalised electrodes for pyrolysis-oil treatment.

Electrochemical decarboxylation of acetic acid on boron-doped-diamond (BDD) electrodes was studied as a possible means to decrease the acidity of pyrolysis oil. It is shown that decarboxylation occurs without the competitive oxygen evolution reaction (OER) on BDD electrodes to form methanol and methyl acetate by consecutive reaction of hydroxyl radicals with acetic acid. The performance is little affected by the applied current density (and associated potential), concentration, and the pH of the solution.

What It Takes for Imidazolium Cations to Promote Electrochemical Reduction of CO.

Imidazolium cations enhance the performance of several electrodes in converting CO to CO in non-aqueous media. In this publication, we elucidate the origin of the function of imidazolium cations when exposed to Au electrodes in anhydrous acetonitrile in CO atmosphere. We demonstrate that imidazolium cations lead to unprecedentedly low overpotentials for CO reduction to CO on Au, with ∼100% Faradaic efficiency.

Dual Role of Surface Hydroxyl Groups in the Photodynamics and Performance of NiO-Based Photocathodes.

Photoelectrochemical (PEC) cells containing photocathodes based on functionalized NiO show a promising solar-to-hydrogen conversion efficiency. Here, we present mechanistic understanding of the photoinduced charge transfer processes occurring at the photocathode/electrolyte interface. We demonstrate via advanced photophysical characterization that surface hydroxyl groups formed at the NiO/water interface not only promote photoinduced hole transfer from the dye into NiO, but also enhance the rate of charge recombination.

Facet-Dependent Surface Charge and Hydration of Semiconducting Nanoparticles at Variable pH.

Understanding structure and function of solid-liquid interfaces is essential for the development of nanomaterials for various applications including heterogeneous catalysis in liquid phase processes and water splitting for storage of renewable electricity. The characteristic anisotropy of crystalline nanoparticles is believed to be essential for their performance but remains poorly understood and difficult to characterize. Dual scale atomic force microscopy is used to measure electrostatic and hydration forces of faceted semiconducting SrTiO nanoparticles in aqueous electrolyte at variable pH.

CrO-Mediated Performance Enhancement of Ni/NiO-Mg:SrTiO in Photocatalytic Water Splitting.

By photodeposition of CrO on SrTiO-based semiconductors doped with aliovalent Mg(II) and functionalized with Ni/NiO catalytic nanoparticles (economically significantly more viable than commonly used Rh catalysts), an increase in apparent quantum yield (AQYs) from ∼10 to 26% in overall water splitting was obtained. More importantly, deposition of CrO also significantly enhances the stability of Ni/NiO nanoparticles in the production of hydrogen, allowing sustained operation, even in intermittent cycles of illumination. elemental analysis of the water constituents during or after photocatalysis by inductively coupled plasma mass spectrometry/optical emission spectrometry shows that after CrO deposition, dissolution of Ni ions from Ni/NiO-Mg:SrTiO is significantly suppressed, in agreement with the stabilizing effect observed, when both Mg dopant and CrO are present.

Unraveling the Mechanisms of Beneficial Cu-Doping of NiO-Based Photocathodes.

Dye-sensitized photoelectrochemical (DSPEC) water splitting is an attractive approach to convert and store solar energy into chemical bonds. However, the solar conversion efficiency of a DSPEC cell is typically low due to a poor performance of the photocathode. Here, we demonstrate that Cu-doping improves the performance of a functionalized NiO-based photocathode significantly.

Synergy of ferroelectric polarization and oxygen vacancy to promote CO photoreduction.

Solar-light driven CO reduction into value-added chemicals and fuels emerges as a significant approach for CO conversion. However, inefficient electron-hole separation and the complex multi-electrons transfer processes hamper the efficiency of CO photoreduction. Herein, we prepare ferroelectric BiTiNbO nanosheets and employ corona poling to strengthen their ferroelectric polarization to facilitate the bulk charge separation within BiTiNbO nanosheets.

Optimizing CO Coverage on Rough Copper Electrodes: Effect of the Partial Pressure of CO and Electrolyte Anions (pH) on Selectivity toward Ethylene.

The conversion of the initial intermediate CO in the electrochemical reduction reaction of CO on the surface of oxide-derived Cu electrodes has been investigated as a function of partial pressure and pH, manipulated by the composition of the electrolyte. We show that in inert gas, an increase in partial pressure of CO results in a continuous increase in Faradaic efficiency (FE) for ethylene, at various potentials ranging from -0.7 to -1.

Modular microreactor with integrated reflection element for online reaction monitoring using infrared spectroscopy.

We report on the fabrication of an internal reflection element (IRE) combined with a modular polymer microfluidic chip that can be used for attenuated total reflection (ATR) infrared spectroscopy. The IRE is fabricated from a silicon wafer. Two different polymers are used for the fabrication of the two types of modular microfluidic chips, namely polydimethylsiloxane (PDMS) and cyclic olefin copolymer (COC).

Preparation of Ti, Ti/TiC or Ti/TiN based hollow fibres with extremely low electrical resistivity.

Porous Ti based hollow fibres with extremely low electrical resistivity (4.1-9.6 μΩ m), orders of magnitude smaller than reported for Ti-fibres in the literature, were produced by dry-wet spinning of a mixture of Ti-particles, polyethersulfone (PES), and -methylpyrrolidone (NMP).

Electrochemically Induced pH Change: Time-Resolved Confocal Fluorescence Microscopy Measurements and Comparison with Numerical Model.

Confocal fluorescence microscopy is a proven technique, which can image near-electrode pH changes. For a complete understanding of electrode processes, time-resolved measurements are required, which have not been achieved previously. Here we present the first measurements of time-resolved pH profiles with confocal fluorescence microscopy.

Photocatalytic Oxidation of Propane Using Hydrothermally Prepared Anatase-Brookite-Rutile TiO Samples. An In Situ DRIFTS Study.

Photocatalytic oxidation of propane using hydrothermally synthesized TiO samples with similar primary crystal size containing different ratios of anatase, brookite and rutile phases has been studied by measuring light-induced propane conversion and in situ DRIFTS (diffuse reflectance Fourier transform infrared spectroscopy). Propane was found to adsorb on the photocatalysts, both in the absence and presence of light. The extent of adsorption depends on the phase composition of synthesized titania powders and, in general, it decreases with increasing rutile and brookite content.

Silver Nanocubes Coated in Ceria: Core/Shell Size Effects on Light-Induced Charge Transfer.

Plasmonic sensitization of semiconductors is an attractive approach to increase light-induced photocatalytic performance; one method is to use plasmonic nanostructures in core@shell geometry. The occurrence and mechanism of synergetic effects in photocatalysis of such geometries are under intense debate and proposed to occur either through light-induced charge transfer (CT) or through thermal effects. This study focuses on the relation between the dimensions of Ag@CeO nanocubes, the wavelength-dependent efficiency, and the mechanism of light-induced direct CT.

Comparative Analysis of Photocatalytic and Electrochemical Degradation of 4-Ethylphenol in Saline Conditions.

We evaluated electrochemical degradation (ECD) and photocatalytic degradation (PCD) technologies for saline water purification, with a focus on rate comparison and formation and degradation of chlorinated aromatic intermediates using the same non-chlorinated parent compound, 4-ethylphenol (4EP). At 15 mA·cm, and in the absence of chloride (0.6 mol·L NaNO was used as supporting electrolyte), ECD resulted in an apparent zero-order rate of 30 μmol L·h, whereas rates of ∼300 μmol L·h and ∼3750 μmol L·h were computed for low (0.

Integration of Molybdenum-Doped, Hydrogen-Annealed BiVO with Silicon Microwires for Photoelectrochemical Applications.

H-BiVO :Mo was successfully deposited on microwire-structured silicon substrates, using indium tin oxide (ITO) as an interlayer and BiOI prepared by electrodeposition as precursor. Electrodeposition of BiOI, induced by the electrochemical reduction of -benzoquinone, appeared to proceed through three stages, being nucleation of particles at the base and bottom of the microwire arrays, followed by rapid (homogeneous) growth, and termination by increasing interfacial resistances. Variations in charge density and morphology as a function of spacing of the microwires are explained by (a) variations in mass transfer limitations, most likely associated with the electrochemical reduction of -benzoquinone, and (b) inhomogeneity in ITO deposition.

Driving Surface Redox Reactions in Heterogeneous Photocatalysis: The Active State of Illuminated Semiconductor-Supported Nanoparticles during Overall Water-Splitting.

Materials used for photocatalytic overall water splitting (POWS) are typically composed of light-absorbing semiconductor crystals, functionalized with so-called cocatalytic nanoparticles to improve the kinetics of the hydrogen and/or oxygen evolution reactions. While function, quantity, and protection of such metal(oxide) nanoparticles have been addressed in the literature of photocatalysis, the stability and transients in the active oxidation-state upon illumination have received relatively little attention. In this Perspective, the latest insights in the active state of frequently applied cocatalysts systems, including Pt, Rh/CrO, or Ni/NiO , will be presented.