A comprehensive investigation of the luminescent properties of carbon nitride polymers, based on tri-s-triazine units, has been conducted. Steady-state temperature-and excitation-power-dependent as well as time-resolved measurements with near-UV excitation (λ = 325 nm and 405 nm) yield strong photoluminescence, covering the visible spectrum. The spectral, thermal, and temporal features of the photoluminescence can be satisfactorily described by the excitation and radiative recombination of molecular excitons, localized at single tri-s-triazine units. The discussed model is in accordance with the recently reported absorption features of carbon nitride polymers. Thus, from the point of view of optical spectroscopy, the material effectively behaves as a monomer.

a Polymeric carbon nitride (g-C 3 N 4 ) films were synthesized on polycrystalline semiconductor CuInS 2 chalcopyrite thin film electrodes by thermal polycondensation and were investigated as photocathodes for the hydrogen evolution reaction (HER) under photoelectrochemical conditions. The composite photocathode materials were compared to g-C 3 N 4 powders and were characterized with grazing incidence X-ray diffraction and X-ray photoemission spectroscopy as well as Fourier transform infrared and Raman spectroscopies. Surface modification of polycrystalline CuInS 2 semiconducting thin films with photocatalytically active g-C 3 N 4 films revealed structural and chemical properties corresponding to the properties of g-C 3 N 4 powders. The g-C 3 N 4 /CuInS 2 composite photocathode material generates a cathodic photocurrent at potentials up to +0.36 V vs. RHE in 0.1 M H 2 SO 4 aqueous solution (pH 1), which corresponds to a +0.15 V higher onset potential of cathodic photocurrent than the unmodified CuInS 2 semiconducting thin film photocathodes. The cathodic photocurrent for the modified composite photocathode materials was reduced by almost 60% at the hydrogen redox potential. However, the photocurrent generated from the g-C 3 N 4 /CuInS 2 composite electrode was stable for 22 h. Therefore, the presence of the polymeric g-C 3 N 4 films composed of a network of nanoporous crystallites strongly protects the CuInS 2 semiconducting substrate from degradation and photocorrosion under acidic conditions. Conversion of visible light to hydrogen by photoelectrochemical water splitting can thus be successfully achieved by g-C 3 N 4 films synthesized on polycrystalline CuInS 2 chalcopyrite electrodes.

In regard to earth-abundant cobalt water oxidation catalysts, very recent findings show the reorganization of the materials to amorphous active phases under catalytic conditions. To further understand this concept, a unique cobalt-substituted crystalline zinc oxide (Co:ZnO) precatalyst has been synthesized by low-temperature solvolysis of molecular heterobimetallic Co(4-x)Zn(x) O4 (x = 1-3) precursors in benzylamine. Its electrophoretic deposition onto fluorinated tin oxide electrodes leads after oxidative conditioning to an amorphous self-supported water-oxidation electrocatalyst, which was observed by HR-TEM on FIB lamellas of the EPD layers. The Co-rich hydroxide-oxidic electrocatalyst performs at very low overpotentials (512 mV at pH 7; 330 mV at pH 12), while chronoamperometry shows a stable catalytic current over several hours.

Recently, it has been shown that an abundant material, polymeric carbon nitride, can produce hydrogen from water under visible-light irradiation in the presence of a sacrificial donor. We present herein the preparation and characterization of graphitic carbon nitride (g-C(3)N(4)) films on p-type semiconducting CuGaSe(2) chalcopyrite thin-film substrates by thermal condensation of a dicyandiamide precursor under inert-gas conditions. Structural and surface morphological studies of the carbon nitride films suggest a high porosity of g-C(3)N(4) thin films consisting of a network of nanocrystallites. Photoelectrochemical investigations show light-induced hydrogen evolution upon cathodic polarization for a wide range of proton concentrations in the aqueous electrolyte. Additionally, synchrotron radiation-based photoelectron spectroscopy has been applied to study the surface/near-surface chemical composition of the utilized g-C(3)N(4) film photocathodes. For the first time, it has been shown that g-C(3)N(4) films coated on p-type CuGaSe(2) thin films can be successfully applied as new photoelectrochemical composite photocathodes for light-induced hydrogen evolution.

Homoepitaxial p-InP(100) thin films prepared by MOVPE (metallorganic vapor phase epitaxy) were transformed into an InP/oxidephosphate/Rh heterostructure by photoelectrochemical conditioning. Surface sensitive synchrotron radiation photoelectron spectroscopy indicates the formation of a mixed oxide constituted by In(PO 3 ) 3 , InPO 4 and In 2 O 3 as nominal components during photo-electrochemical activation. The operation of these films as hydrogen evolving photocathode proved a light-to-chemical energy conversion efficiency of 14.5%. Surface activation arises from a shift of the semiconductor electron affinity by 0.44 eV by formation of In-Cl interfacial dipoles with a density of about 10 12 cm −2 . Predominant local In 2 O 3 -like structures in the oxide introduce resonance states near the semiconductor conduction band edge imparting electron conductivity to the phosphate matrix. Surface reflectance investigations indicate an enhanced light-coupling in the layered architecture. Solar hydrogen generation from water represents a viable route for establishing a carbon-neutral energy infrastructure based on renewable energy resources.1-4 To achieve this long-term objective, numerous approaches are currently being pursued comprising adapting systems derived from photosynthesis, 5-7 identification of appropriate catalysts, 8 development of transition metal oxide photoelectrodes 9,10,11 as well as devising efficient semiconductor tandem structures.12-14 Because biomimetic systems inspired by natural photosynthesis are characterized by rather low theoretical efficiencies, 6 the use of photoresponsive semiconductor materials for the splitting of water appears currently most promising. It can be shown that dual-bandgap systems reach theoretically efficiencies well above 40% at AM1.5. 15 The development horizon suggests therefore the use of technologically advanced semiconductor materials which would allow comparably fast technical realization. Further, the orthogonalization of charge carrier and photon pathways as well as an increased built-in potential by interfacial doping was recently exploited to achieve efficiencies near 10% using Si as substrate. 16 p-type InP is one of the most efficient photocathode materials for hydrogen evolution available. Heller and Vadimsky 17 have shown three decades ago that hydrogen evolution can occur with an efficiency of 12% if rhodium is deposited as catalytically active and optically transparent thin-film on top of an In 2 O 3 /InP structure. In this work, a new approach based on thin film photoelectrodes is presented. The photocathode is realized by homoepitaxial growth of thin films onto InP wafers which allows the use of liftoff procedures already known for photovoltaic systems. 18,19 The removal of the thin film photocathodes from the growth substrate is thereby possible after fabrication of the devices. This approach reduces production costs, which is a decisive factor for many III-V devices. In this report, we evaluate the applicability of homoepitaxial devices with emphasis in...

wileyonlinelibrary.comin the fi elds of heterogeneous catalysis, [1][2][3][4] electrocatalysis, [ 2,5,6 ] gas sensing, [ 7,8 ] battery development, [ 9,10 ] and drug delivery. [ 5,11 ] Yolk@shell materials are composed of single (or multiple) nanoscaled cores of a material A encapsulated inside a hollow nanosphere of a material B (A@void@B, in short A@B). Depending on the envisioned application, the surrounding hollow shell can be dense or porous (permeable) allowing control of the interactions between the core and the outer environment.For many applications, it has been shown that yolk@shell nanocomposites feature enhanced properties as a result of their unique structure on the nanometer scale. In the fi eld of heterogeneous catalysis for example, it has been demonstrated that supported metal nanoparticle (M NP ) catalysts with a yolk@shell structure are highly resistant against temperature and/or reaction induced M NP sintering, thus preserving the catalysts activity. As such, a variety of yolk@shell nanocatalysts have been designed, including M NP @carbon, [12][13][14] M NP @silica, [ 2,15 ] Au NP @TiO 2 , [ 16 ] and Au NP @ZrO 2 , [ 17,18 ] all superior in terms of catalytic activity and stability when compared to their non-yolk@shell counterparts.Despite their proven potential, the application of yolk@shell structures remains however limited due to challenging and Due to their unique morphology-related properties, yolk@shell materials are promising materials for catalysis, drug delivery, energy conversion, and storage. Despite their proven potential, large-scale applications are however limited due to demanding synthesis protocols. Overcoming these limitations, a simple softtemplated approach for the one-pot synthesis of yolk@shell nanocomposites and in particular of multicore metal nanoparticle@metal oxide nanostructures (M NP @MO x ) is introduced. The approach here, as demonstrated for Au NP @ ITO TR (ITO TR standing for tin-rich ITO), relies on polystyrene-block -poly(4vinylpyridine) (PS-b -P4VP) inverse micelles as two compartment nanoreactor templates. While the hydrophilic P4VP core incorporates the hydrophilic metal precursor, the hydrophobic PS corona takes up the hydrophobic metal oxide precursor. As a result, interfacial reactions between the precursors can take place, leading to the formation of yolk@shell structures in solution. Once calcined these micelles yield Au NP @ITO TR nanostructures, composed of multiple 6 nm sized Au NPs strongly anchored onto the inner surface of porous 35 nm sized ITO TR hollow spheres. Although of multicore nature, only limited sintering of the metal nanoparticles is observed at high temperatures (700 °C). In addition, the as-synthesized yolk@shell structures exhibit high and stable activity toward CO electrooxidation, thus demonstrating the applicability of our approach for the design of functional yolk@shell nanocatalysts.

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Chronoamperometric conditioning of float zone n-Si(111) in 2M NaOH solution in the potential range negative from open-circuit potential is performed in a combined electrochemistry/ultrahigh-vacuum surface analysis experiment. Synchrotron Radiation Photoelectron Spectroscopy measurements at the U49/2 beamline at Bessy II using the SoLiAs facility show formation of a ultrahigh-vacuum-stable permanent accumulation layer without junction formation. Comparison of the Thomas–Fermi screening potential and the mean inelastic scattering length λesc of photoelectrons at hν=150eV (λesc=4Å) and hν=585eV (λesc=15Å) indicates a surface electron concentration of 3×1018cm−3 for a bulk doping level of 1015cm−3. The observed shift of the Si2p3∕2 and 2p1∕2 core level with photon energy is in excellent agreement with the shifted onset of the x-ray photoelectron spectroscopy valence-band spectrum measured at hν=150eV.