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Self-assembled monolayers (SAMs) formed from thiol compounds bound to Ag and Au electrodes have been used as an important strategy in improving the stability and efficiency of optoelectronic devices. Thiol compounds provide only one binding site with the metal electrode which limits their influence. Dithiolane/dithiol compounds can provide multiple binding sites and could be useful in enhancing the performance of the device. In this study, inverted organic semiconducting hole-only devices were fabricated by using Ag back electrodes in conjunction with SAMs formed from disulfide lipoic acid-based compounds and were compared to a long aliphatic chain thiol. The binding and the electronic properties as well as electrical characteristics of the SAMs on silver were studied to look at the influence of their structure on charge injection in the organic semiconductor devices. It was found that the SAMs formed with (±)-α-lipoic acid, isolipoic acid, and (±)-4-phenylbutyl 5-(1,2-dithiolan-3-yl) pentanoate significantly improved the charge injection by either changing the work function of the Ag or altering the physical interaction between the polymer and the metal surface. This study may lead to an understanding of how the nature of the functional groups of the SAM and the number of bonds formed between each SAM molecule and the metal electrode influence the contact resistance and the performance of organic semiconductor devices.

Temporally resolved spectroscopy is a powerful approach for gaining detailed mechanistic understanding of water oxidation at robust Earth-abundant metal oxide catalysts for guiding efficiency improvement of solar fuel conversion systems. Beyond detecting and structurally identifying surface intermediates by vibrational and accompanying optical spectroscopy, knowledge of how charges, sequentially delivered to the metal oxide surface, drive the four-electron water oxidation cycle is critical for enhancing catalytic efficiency. Key issues addressed in this Perspective are the experimental requirements for establishing the kinetic relevancy of observed surface species and the discovery of the rate-boosting role of encounters of two or more one-electron surface hole charges, often in the form of randomly hopping metal oxo or oxyl moieties, for accessing very low-barrier O-O bond-forming pathways. Recent spectroscopic breakthroughs of metal oxide photo- and electrocatalysts inspire future research poised to take advantage of new highly sensitive spectroscopic tools and of methods for fast catalysis triggering.

Enzymes feature the concerted operation of multiple components around an active site, leading to exquisite catalytic specificity. Realizing such configurations on synthetic catalyst surfaces remains elusive. Here, we report a nanoparticle/ordered-ligand interlayer that contains a multi-component catalytic pocket for high-specificity CO2 electrocatalysis. The nanoparticle/ordered-ligand interlayer comprises a metal nanoparticle surface and a detached layer of ligands in its vicinity. This interlayer possesses unique pseudocapacitive characteristics where desolvated cations are intercalated, creating an active-site configuration that enhances catalytic turnover by two orders and one order of magnitude against a pristine metal surface and nanoparticle with tethered ligands, respectively. The nanoparticle/ordered-ligand interlayer is demonstrated across several metals with up to 99% CO selectivity at marginal overpotentials and onset overpotentials of as low as 27 mV, in aqueous conditions. Furthermore, in a gas-diffusion environment with neutral media, the nanoparticle/ordered-ligand interlayer achieves nearly unit CO selectivity at high current densities (98.1% at 400 mA cm−2). The complex, multi-component environments found in enzymes induce high catalytic specificity, but are difficult to achieve in synthetic catalysts. Now, researchers report a catalyst comprising a dynamic, ordered layer of ligands above a nanoparticle surface that creates a pocket to facilitate CO2 electroreduction.

Natural photosynthesis relies on a sophisticated charge transfer pathway among multiple components with precise spatial, energetic, and temporal organizations in the aqueous environment. It continues to inspire and challenge the design and fabrication of artificial multicomponent colloidal nanostructures for solar-to-fuel conversion. Herein, we introduce a plasmonic photocatalyst synthesized with colloidal methods with five integrated components including cocatalysts installed in orthogonal locations. The precise deposition of individual inorganic components on an Au/TiO2 nanodumbell nanostructure is enabled by photoreduction and photo-oxidation, which selectively occurs at the TiO2 tip sites and Au lateral sites, respectively. Under visible-light irradiation, the photocatalyst exhibited activity of oxygen evolution from water without scavengers. We demonstrate that each component is essential for improving the photocatalytic performance. In addition, mechanistic studies suggest that the photocatalytic reaction requires combining the hot charge carriers derived from exciting both the d-sp interband transition and the localized surface plasmon resonance of Au.

Monitoring of water oxidation by the established Co cubane catalyst Co4O4(OAc)4(py)4 (abbrev. Co4O4, OAc = acetate, py = pyridine) by time-resolved rapid-scan ATR FT-IR spectroscopy revealed the O–...

Ultrathin amorphous silica membranes with embedded organic molecular wires (oligo(p-phenylenevinylene), three aryl units) provide chemical separation of incompatible catalytic environments of CO2 reduction and H2O oxidation while maintaining electronic and protonic coupling between them. For an efficient nanoscale artificial photosystem, important performance criteria are high rate and directionality of charge flow. Here, the visible-light-induced charge flow from an anchored Ru bipyridyl light absorber across the silica nanomembrane to Co3O4 water oxidation catalyst is quantitatively evaluated by photocurrent measurements. Charge transfer rates increase linearly with wire density, with 5 nm-2 identified as an optimal target. Accurate measurement of wire and light absorber densities is accomplished by the polarized FT-IRRAS method. Guided by density functional theory (DFT) calculations, four wire derivatives featuring electron-donating (methoxy) and -withdrawing groups (sulfonate, perfluorophenyl) with highest occupied molecular orbital (HOMO) potentials ranging from 1.48 to 0.64 V vs NHE were synthesized and photocurrents evaluated. Charge transfer rates increase sharply with increasing driving force for hole transfer from the excited light absorber to the embedded wire, followed by a decrease as the HOMO potential of the wire moves beyond the Co3O4 valence band level toward more negative values, pointing to an optimal wire HOMO potential around 1.3 V vs NHE. Comparison with photocurrents of samples without nanomembrane indicates that silica layers with optimized wires are able to approach undiminished electron flux at typical solar intensities. Combined with the established high proton conductivity and small-molecule blocking property, the charge transfer measurements demonstrate that oxidation and reduction catalysis can be efficiently integrated on the nanoscale under separation by an ultrathin silica membrane.

Although oxygen is a common ligand in supported metal catalysts, its coordination has been challenging to elucidate. We now characterize a diiridium complex that has been previously shown by X-ray diffraction crystallography to incorporate a μ-η1:η1-peroxo ligand. We observe markedly enhanced intensity at 788 cm-1 in the Raman spectrum of this complex, which is a consequence of bonding of the peroxo ligand but does not shift upon 18O labeling. Electronic structure calculations at the density functional theory level suggest that this increase in Raman intensity results from bands associated with rocking of CH2 substituents directly attached to P(Ph)2 groups coupling with the O-O band. These results provide part of the foundation for understanding oxygen ligands on a silica-supported tetrairidium carbonyl cluster stabilized with bulky electron-donating phosphine ligands [p-tert-butyl-calix[4]arene(OPr)3(OCH2PPh2) (Ph = phenyl; Pr = propyl)]. Reaction of the cluster with O2 also led to the growing in of a Raman band at 788 cm-1, similar to that in the diiridium complex and also assigned to the bonding of a bridging peroxo ligand. Infrared spectra recorded as the supported cluster reacted in sequential exposures to (i) H2, (ii) O2, (iii) H2, and (iv) CO indicate that two bridging peroxo ligands were bonded irreversibly per tetrairidium cluster, replacing bridging carbonyl ligands without altering either the cluster frame or the phosphine ligands. X-ray absorption near edge and infrared spectra include isosbestic points signifying a stoichiometrically simple reaction of the cluster with O2, and mass spectra of the effluent gas show that CO2 formed by oxidation of one terminal CO ligand per cluster as H2 (and not H2O) formed, evidence that hydride ligands had been present on the cluster following treatment (i). The understanding of how O2 reacts with the metal polyhedron provides a foundation for understanding of how oxidation catalysis may proceed on the surfaces of noble metals.

Cu nanocrystals as catalysts for CO2 reduction are a subject of considerable contemporary interest, but their stability has not been considered as extensively. Herein, we report on the reconstructi...

The efficiency of photocatalytic systems is strongly depending on the charge carrier transfer from the excited semiconductor to co-catalyst particles attached on its surface. In this study, we investigated the influence of photo-induced charge transfer in photoplatinized TiO 2 P25 photocatalysts by diffuse reflectance FTIR spectroscopy of CO molecules adsorbed on the Pt co-catalyst under well-defined gas phase conditions. In contrast to aqueous conditions, where shifts of the CO stretching vibration of up to 50 cm −1 have been reported, the observed shifts under gas phase conditions are very small (−1). This demonstrates that the difference in dielectric properties between aqueous electrolytes and vacuum are critical for the development of prominent shifts of adsorbed CO bands upon trapping of photogenerated charge carriers on co-catalyst particles. The experimental findings are discussed in terms of an electrostatic Stark effect, charge screening, co-adsorption, coverage-dependent shifts of the vibrational bands of adsorbed CO and photocatalytic surface reactions.

Author(s): Jo, WJ; Katsoukis, G; Frei, H | Abstract: A large jump of proton transfer rates across solid-to-solid interfaces by inserting an ultrathin amorphous silica layer into stacked metal oxide nanolayers is discovered using electrochemical impedance spectroscopy and Fourier-transform infrared reflection absorption spectroscopy (FT-IRRAS). The triple stacked nanolayers of Co3O4, SiO2, and TiO2 prepared by atomic layer deposition (ALD) enable a proton flux of 2400 ± 60 s−1 nm−2 (pH 4, room temperature), while a single TiO2 (5 nm) layer exhibits a threefold lower flux of 830 s−1 nm−2. Based on FT-IRRAS measurements, this remarkable enhancement is proposed to originate from the sandwiched silica layer forming interfacial SiOTi and SiOCo linkages to TiO2 and Co3O4 nanolayers, respectively, with the O bridges providing fast H+ hopping pathways across the solid-to-solid interfaces. Together with the complete O2 impermeability of a 2 nm ALD-grown SiO2 layer, the high flux for proton transport across multi-stack metal oxide layers opens up the integration of incompatible catalytic environments to form functional nanoscale assemblies such as artificial photosystems for CO2 reduction by H2O.

Monitoring of visible light sensitized reduction of CO2 at Cu nanoparticles in aqueous solution by rapid-scan ATR FT-IR spectroscopy on the time scale of seconds allowed structural identification of a one-electron intermediate and demonstrated its kinetic relevancy for the first time. Isotopic labeling (12C: 1632, 1358, 1346 cm–1; 13C: 1588, 1326, 1316 cm–1) revealed a species of carbon dioxide dimer radical anion structure, most likely bound to the catalyst surface through carbon. Intermediacy of Cu—C(═O)OCO2– surface species is in agreement with a recently proposed mechanism for electrocatalytic CO2 reduction at Cu metal nanoparticles based on Tafel slope analysis. Spontaneous decrease of the intermediate after termination of the photosensitization pulse (Sn porphyrin excited at 405 nm) was accompanied by the growth of HCO3–. CO was produced as well, but sensitive detection required photolysis for tens of minutes. A direct kinetic link between a C2O4– surface intermediate and the CO product was also dem...

© 2017 American Chemical Society. The mechanism of visible light-induced hole transfer from a molecular light absorber, in the form of a free-base porphyrin, coupled to a Co3O4nanoparticle catalyst for water oxidation by a molecular wire (p-oligo(phenylenevinylene) featuring three aryl units) is investigated by transient absorption spectroscopy. The wires are covalently anchored on the Co3O4surface and embedded in a dense, yet ultrathin (2 nm), silica layer that separates light absorber and catalyst. The porphyrin is electrostatically adsorbed on the silica surface, and aqueous colloidal solutions of the core-shell particles are used for transient optical measurements. Pulsed optical excitation of the porphyrin results in rapid injection of the photogenerated hole onto the molecular wire and concurrent formation of reduced light absorber in less than 1 picosecond (ps). Ultrafast charge separation was monitored by transient absorption of the wire radical cation, which is given by bands in the 500 to 600 nm region and at 1130 nm, while formation of reduced porphyrin was characterized by absorption at 700 nm. Forward transfer of the hole to Co3O4catalyst proceeds in 255 ± 23 ps. Ultrafast transfer of positive charge from the molecular assembly to a metal oxide nanoparticle catalyst for water oxidation is unprecedented. Holes on Co3O4recombined with electrons of the reduced sensitizer with biphasic kinetics on a much longer time scale of ten to several hundred nanoseconds. The unusually efficient hole transfer coupling of a molecular light absorber with an Earth-abundant metal oxide catalyst by silica-embedded p-oligo(phenylenevinylene) offers an approach for integrated artificial photosystems featuring product separation on the nanoscale.

The conversion of carbon dioxide and water to fuel in artificial systems requires efficient coupling of light absorbers and catalysts, and assembly of the components into hierarchical structures to close the photocatalytic cycle. Recent breakthroughs in the embodiment of molecular photoactive components in ultrathin oxide layers, and the introduction of new materials approaches for interfacial charge transfer have led to substantially improved coupling of chromophores and catalysts. These advances are accelerating the exploration of novel architectures for reducing CO2 by H2O in scalable, single integrated photosystems to reach the high power efficiencies recently demonstrated with photovoltaic-assisted approaches.

Water oxidation, as a mandatory reaction of solar fuels conversion systems, requires the use of light absorbers with electronic properties that are well matched with those of the multi-electron catalyst in order to achieve high efficiency. Molecular light absorbers offer flexibility in fine tuning of orbital energetics, and metal oxide nanoparticles have emerged as robust oxygen evolving catalysts. Hence, these material choices offer a promising approach for the development of photocatalytic systems for water oxidation. However, efficient charge transfer coupling of molecular light absorbers and metal oxide nanoparticle catalysts has proven a challenge. Recent new approaches toward the efficient coupling of these components based on synthetic design improvements combined with direct spectroscopic observation and kinetic evaluation of charge transfer processes are discussed.

Although oxygen is a common ligand in supported metal catalysts, its coordination has been challenging to elucidate. We now characterize a diiridium complex that has been previously shown by X-ray diffraction crystallography to incorporate a μ-η

Surface sensitive infrared spectroscopic methods are employed for elucidating the structure and orientation of charge conducting molecular wires of type oligo(p-phenylenevinylene) covalently anchored on an ultrathin planar Co oxide catalyst surface and embedded in a few nanometer thick amorphous silica membrane. Comparison of polarized FT-IRRAS with nonpolarized grazing angle ATR FT-IR spectra of nanolayer samples supported on a flat Pt surface and transmission spectra of powder samples showed distinct intensity differences for molecular in-plane and out-of-plane modes that reveal the spatial orientation with respect to the oxide surface. All observations support an upright orientation of the molecular wire axis, which is further confirmed by comparison with IRRAS measurements of physisorbed, horizontally positioned wire molecules. The structural integrity of the molecules is maintained after embedding in the silica membrane by plasma-enhanced atomic layer deposition at 40 °C. The results provide the first spectroscopic evidence of perpendicular orientation of the wire molecules. The complementary surface sensitive infrared measurements by FT-IRRAS and grazing angle ATR FT-IR constitute a powerful approach for elucidating the structure and orientation of surface-anchored molecules and the integrity upon casting into oxide layers such as silica for developing artificial photosystems. Use of the nanolayer construct in IRRAS spectroelectrochemical cell configuration will enable in situ monitoring of the structural and orientation integrity of the silica embedded molecular wires under the sustained electron and proton flux conditions of photocatalytic operation.

By electrochemically coupling microbial and abiotic catalysts, bioelectrochemical systems such as microbial electrolysis cells and microbial electrosynthesis systems synthesize energy-rich chemicals from energy-poor precursors with unmatched efficiency. However, to circumvent chemical incompatibilities between the microbial cells and inorganic materials that result in toxicity, corrosion, fouling, and efficiency-degrading cross-reactions between oxidation and reduction environments, bioelectrochemical systems physically separate the microbial and inorganic catalysts by macroscopic distances, thus introducing ohmic losses, rendering these systems impractical at scale. Here we electrochemically couple an inorganic catalyst, a SnO2 anode, with a microbial catalyst, Shewanella oneidensis, via a 2-nm-thick silica membrane containing -CN and -NO2 functionalized p-oligo(phenylene vinylene) molecular wires. This membrane enables electron flow at 0.51 μA cm−2 from microbial catalysts to the inorganic anode, while blocking small molecule transport. Thus the modular architecture avoids chemical incompatibilities without ohmic losses and introduces an immense design space for scale up of bioelectrochemical systems., Bioelectrochemical cells have huge potential, yet incompatibilities between the microbe and abiotic catalysts can affect efficiency. Here, the authors report the development of thin silica membranes with bridging molecular wires that chemically separate yet electrically connect the two components.

We propose a mechanism of water splitting on cobalt oxide surface with atomistic thermodynamic and kinetic details. The density-functional theory studies suggest that the oxidation process could proceed with several nonelectrochemical (spontaneous) intermediate steps, following the initial electrochemical hydroxyl-to-oxo conversion. More specifically, the single oxo sites CoIV═O can hop (via surface proton/electron hopping) to form oxo pair CoIV(═O)-O-CoIV═O, which will undergo nucleophilic attack by a water molecule and form the hydroperoxide CoIII–OOH. Encounter with another oxo would generate a superoxo CoIII–OO, followed by the O2 release. Finally the addition and deprotonation of a fresh water molecule will restart the catalytic cycle by forming the hydroxyl CoIII–OH at this active site. Our theoretical investigations indicate that all nonelectrochemical reactions are kinetically fast and thermodynamically downhill. This hypothesis is supported by recent in situ spectroscopic observations of surface ...

In the search for the two-electron-reduced intermediate of the tetraaza catalyst [Co(II)N4H(MeCN)](2+) (N4H = 2,12-dimethyl-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),2,11,13,15-pentaene) for CO2 reduction and elementary steps that result in the formation of CO product, rapid-scan FT-IR spectroscopy of the visible-light-sensitized catalysis, using Ir(ppy)3 in wet acetonitrile (CD3CN) solution, led to the observation of two sequential intermediates. The initially formed one-electron-reduced [Co(I)N4H](+)-CO2 adduct was converted by the second electron to a transient [Co(I)N4H](+)-CO2(-) complex that spontaneously converted CO2 to CO in a rate-limiting step on the second time scale in the dark under regeneration of the catalyst (room temperature). The macrocycle IR spectra of the [Co(I)N4H](+)-CO2(-) complex and the preceding one-electron [Co(I)N4H](+)-CO2 intermediate show close similarity but distinct differences in the carboxylate modes, indicating that the second electron resides mainly on the CO2 ligand. Vibrational assignments are corroborated by (13)C isotopic labeling. The structure and stability of the two-electron-reduced intermediate derived from the time-resolved IR study are in good agreement with recent predictions by DFT electronic structure calculations. This is the first observation of an intermediate of a molecular catalyst for CO2 reduction during the bond-breaking step producing CO. The reaction pathway for the Co tetraaza catalyst uncovered here suggests that the competition between CO2 reduction and proton reduction of a macrocyclic multi-electron catalyst is steered toward CO2 activation if the second electron is directly captured by an adduct of CO2 and the one-electron-reduced catalyst intermediate.

This journal is © The Royal Society of Chemistry. The ultra-bright femtosecond X-ray pulses provided by X-ray Free Electron Lasers (XFELs) open capabilities for studying the structure and dynamics of a wide variety of biological and inorganic systems beyond what is possible at synchrotron sources. Although the structure and chemistry at the catalytic sites have been studied intensively in both biological and inorganic systems, a full understanding of the atomic-scale chemistry requires new approaches beyond the steady state X-ray crystallography and X-ray spectroscopy at cryogenic temperatures. Following the dynamic changes in the geometric and electronic structure at ambient conditions, while overcoming X-ray damage to the redox active catalytic center, is key for deriving reaction mechanisms. Such studies become possible by using the intense and ultra-short femtosecond X-ray pulses from an XFEL, where sample is probed before it is damaged. We have developed methodology for simultaneously collecting X-ray diffraction data and X-ray emission spectra, using an energy dispersive spectrometer, at ambient conditions, and used this approach to study the room temperature structure and intermediate states of the photosynthetic water oxidizing metallo-protein, photosystem II. Moreover, we have also used this setup to simultaneously collect the X-ray emission spectra from multiple metals to follow the ultrafast dynamics of light-induced charge transfer between multiple metal sites. A Mn-Ti containing system was studied at an XFEL to demonstrate the efficacy and potential of this method.

Coupling of robust, all-inorganic heterobinuclear light absorbers to metal oxide catalysts for water oxidation across an ultrathin product-separating silica membrane requires charge transfer through organic molecular wires embedded in the silica. A synthetic approach for assembling the bimetallic units on the silica surface is introduced that is compatible with the presence of encapsulated organic molecules. Accurate selection and fine tuning of the concentration of embedded conducting wires are enabled by a two-step method consisting of surface attachment of a tripodal anchor, trimethoxysilyl aniline, followed by attachment of p-oligo(phenylene vinylene) through amide linkage. Each step of the assembly process was monitored and characterized by a combination of Fourier transform infrared, Fourier transform-Raman, and UV-vis spectroscopy techniques. Hole transfer was observed from transient CoIII, formed by TiIVOCoII → TiIIIOCoIII charge transfer excitation of the chromophore, to p-oligo(phenylene vinylene) molecule within the 8 ns width of the photolysis laser pulse by transient optical absorption spectroscopy of the wire radical cation. The rectifying property of the light absorber-wire assembly enabled by appropriate selection of redox potentials of metals and embedded wire obviates the need for a molecularly defined linkage between the components. Combined with the previously observed ultrafast hole injection from the embedded wires to Co oxide catalyst, the result implies visible-light-induced hole transfer from visible-light-excited binuclear light absorber to water oxidation catalyst across the silica separation membrane in a few nanoseconds or faster. Demonstration and understanding of this interfacial charge-transfer step is critical for developing nanoscale core-shell architectures for complete photosynthetic cycles.

All-inorganic heterobinculear units can be excited to a metal-to-metal charge transfer (MMCT) state by visible and ultraviolet light and form the core of multicomponent artificial photosystems that rely on conjugated molecular wires to transmit electrons and holes across ultrathin silica separation membranes to catalytic sites. To understand electron transfer from a heterobinuclear unit to an organic molecule, model systems consisting of pyridine interacting with ZrIVOCoII or TiIVOCoII sites on silica nanoparticles were assembled and spectroscopically characterized. Transient optical absorption spectroscopy combined with infrared analysis revealed that visible light excitation of assemblies in which pyridine interacts with the Zr center of the ZrOCo unit results in sub-10 ns separation by electron transfer to the organic moiety. Rapid-scan FT-IR spectroscopy supported by density functional theory confirmed the identity of the pyridine radical anion charge-separated state. This state shows a lifetime of 220 (±60) ms prior to complete recovery of the initial state, suggesting spin crossover along the electron transfer path. No hole transfer from excited ZrIVOCoII ZrIIIOCoIII to pyridine is observed. The rectifying charge transfer behavior is an important design aspect for developing efficient artificial photosystems.

Macroscale arrays of cobalt oxide-silica core-shell nanotubes with high aspect ratio and ultrathin walls of less than 20 nm have been fabricated. The silica shells feature embedded oligo-para(phenylenevinylene) molecules for charge transport across the insulating silica layer, which is tightly controlled by their electronic properties. The assembly is based on the use of a sacrificial Si nanorod array template combined with atomic layer deposition, covalent anchoring of organic wire molecules, and dry cryo-etching. High-resolution TEM imaging of samples prepared by microtome affords structural details of single core-shell nanotubes. The integrity of silica-embedded organic wire molecules exposed to atomic layer deposition, thermal treatment, and harsh etching procedures is demonstrated by grazing angle ATR FT-IR, FT-Raman, and XPS spectroscopy. The inorganic oxide-based core-shell nanotubes with ultrathin gas-impermeable, proton-conducting silica shells functionalized by molecular wires enable complete nanoscale photosynthetic units for CO2 reduction by H2O under membrane separation. Arrays of massive numbers of such core-shell nanotube units afford a design that extends the separation of the incompatible H2O oxidation and CO2 reduction catalysis environments across the continuum of length scales from nanometers to centimeters.

Hierarchical assembly of an oxo-bridged binuclear ZrOCoII light absorber unit coupled to a cuprous oxide nanocluster catalyst for CO2 reduction on mesoporous silica support is demonstrated. The proper positioning of the Cu oxide cluster was achieved by photodeposition of a [Cu(NCCH3)4]2+precursor by visible light excitation of the ZrOCo charge transfer chromophore, followed by mild calcination at 350 C. Illumination of the CuxOy-ZrOCo unit so formed in the presence of a diethylamine electron donor resulted in the reduction of surface Cu centers to Cu0 as demonstrated by the characteristic infrared band of adsorbed 13CO probe molecules at 2056 cm–1. For analogous CuxOy-TiOCoII units, the oxidation state makeup of the surface Cu centers was dominated by CuI, and the Cu0, CuI, and CuII composition was found to depend on the wavelength of MMCT excitation. The observed strong dependence of the CO2 photoreduction yield on the oxidation state of the surface Cu centers directly proves that CO2 is reduced on the C...

To examine the prevalence and determinants of handbike use in persons living with spinal cord injury in Switzerland.A population-based cross-sectional survey in Switzerland.The crude prevalence of handbike use among the 1549 participants was 22.6%, varying between 25.3% in men and 17.7% in women. Prevalence was higher in complete than in incomplete spinal cord injury (SCI) (41.5% versus 11.9% in paraplegia, 25.6% versus 11.1% in tetraplegia). Multivariable analysis of handbike use confirmed differences with lesion characteristics and gender and showed a decline with age, lowest rates in the low-income group, variation with language, but no association with level of education or cause of spinal cord injury. In total, 45.8% of users reported to engage in handcycling at least once a week. Frequent contextual reasons for refraining from handcycling were: no interest (26%); inability due to disability (20%); unfamiliarity with the handbike (19%) and financial constraints (14%).Conditional on the major determinants that include demographic factors and lesion characteristics, main barriers involve contextual factors that can principally be overcome. Our findings thus suggest scope for promoting handcycling as a means towards a healthy and more physically active lifestyle in persons living with SCI.Handcycling is an effective means of improving health and quality of life of persons with a spinal cord injury. Persons with the following traits are most likely to use the handbike: persons younger than 62 years, with a complete paraplegia, who are German-speaking (vs. French/Italian) and having a middle or high net income. Indicated reasons for not using a handbike varied by SCI characteristics and included disinterest, inability related to the level of impairment, unfamiliarity and financial costs. Barriers that involve the above mentioned contextual factors can principally be overcome by targeted policy or information campaigns.

©2017 by Annual Reviews. All rights reserved. Water oxidation is an essential reaction of an artificial photosystem for solar fuel generation because it provides electrons needed to reduce carbon dioxide or protons to a fuel. Earth-abundant metal oxides are among the most attractive catalytic materials for this reaction because of their robustness and scalability, but their efficiency poses a challenge. Knowledge of catalytic surface intermediates gained by vibrational spectroscopy under reaction conditions plays a key role in uncovering kinetic bottlenecks and provides a basis for catalyst design improvements. Recent dynamic infrared and Raman studies reveal the molecular identity of transient surface intermediates of water oxidation on metal oxides. Combined with ultrafast infrared observations of how charges are delivered to active sites of the metal oxide catalyst and drive the multielectron reaction, spectroscopic advances are poised to play a key role in accelerating progress toward improved catalysts for artificial photosynthesis.

The mechanism of visible light-induced hole transfer from a molecular light absorber, in the form of a free-base porphyrin, coupled to a Co

The oxo-bridged heterobinuclear chromophore TiOMn2+ has been covalently anchored onto a silica nanoparticle surface, allowing for the preparation of optically transparent solid state samples. Optical spectra of the material yield a broad metal-to-metal charge-transfer (MMCT) transition in the UV with a tail extending to 550 nm. Fitting the absorption band to a Gaussian curve gives a maximum at 44 610 (±230) cm–1 (587 (±20) M–1 cm–1) with a full width at half-maximum of 17 320 (±160) cm–1, and yields an electronic coupling constant, HABopt, of 4200 cm–1 by Hush analysis. Transient absorption measurements of transparent pressed pellets in vacuum yield a 2.43 (±0.20) μs lifetime at room temperature. The temperature dependence of the lifetime in the range of 10–40 °C gives an activation energy of 1.67 (±0.36) kcal/mol and pre-exponential factor A of 7.3 (±4.4) × 106 s–1. This temperature dependence results in an electronic coupling constant HABkin of less than 1 cm–1. The disparity between the large electroni...

Oxo-bridged heterobinuclear units of the type Zr(IV)OCo(II) covalently anchored on the pore surface of mesoporous silica SBA-15 have been synthesized with high selectivity. The unit exhibits a visible light absorbing metal-to-metal charge-transfer absorption (MMCT) extending to about 550 nm. The oxo-bridged structure of the binuclear moiety is manifested by spectral blue-shifts of the optical Co(II) spin–orbit bands due to reduced π-electron donating ability of the bridging oxygen caused by the electron-withdrawing Zr center. EXAFS measurements of the Zr and Co K-edges and curve fitting analysis revealed a Zr to Co distance of 3.4 A. The coordination geometry of the Zr and Co metal centers in monometallic Zr and Co-SBA-15 samples is closely preserved in the ZrOCo unit. Illumination of the MMCT absorption at 420 nm and shorter wavelengths resulted in the reduction of CO2 to gas phase CO and HCO2–, the latter adsorbed on the silica pore surface. The branching between carbon monoxide and formate was found to...

Artificial photosynthesis is an attractive approach for the generation of renewable fuels because such systems will be suitable for deployment on highly abundant, non-arable land. Recently emerged methods of nanoscience to create conformal, ultrathin oxide layers enable the hierarchical integration of light absorbers, catalysts, and membranes into systems with far simpler synthetic approaches than available till now. This holds in particular for the coupling of molecular light absorbers and catalysts for sunlight to fuel conversion, providing photoelectrodes with greatly improved stability. Moreover, the use of ultrathin inert oxides as proton conducting, molecule impermeable membranes has opened up the integration of reduction and oxidation half reactions into complete photosynthetic systems on the shortest possible length scale-the nanometer scale. This capability affords minimization of energy-degrading resistance losses caused by ion transport over macroscale distances while separating the incompatible water oxidation and carbon dioxide reduction catalysis environments on the nanoscale. Understanding of charge transport between molecular components embedded in the oxide layers is critical for guiding synthetic design improvements of the light absorber-catalyst units to optimize performance and integrate them into complete artificial photosystems. Recent results and insights from transient optical, vibrational, and photoelectrochemical studies are presented, and future challenges and opportunities for engaging dynamic spectroscopies to accelerate the development of nanoscale integrated artificial photosystems are discussed.