The perovskite type oxonitridotantalates LnTaON with Ln=La, Ce, Pr, Nd, Sm, and Gd were synthesized by the ammonothermal method employing custom-built autoclaves made of nickel-based superalloy. Metal powders were reacted with NaOH and NaN as mineralizers under supercritical conditions with purified ammonia at temperature range of 870-1070 K and pressure values of 150-300 MPa. Crystal structures and the space groups were determined by using powder X-ray diffraction and refined by the Rietveld method. The refined lattice parameters are for LaTaON (a=5.7156(1), b=8.0675(1), c=5.7465(1) Å, R =0.0471), CeTaON (a=5.6761(11), b=8.0386(16), c=5.7891(12) Å, R =0.183), PrTaON (a=5.6920(1), b=8.0197(1), c=5.6804(1) Å, R =0.0349), NdTaON (a=5.6884(1), b=8.0037(2), c=5.6554(1) Å, R =0.026), SmTaON (a=5.6827(1), b=7.9656(2), c=5.6103(1) Å, R =0.042), GdTaON (a=5.6160(10), b=7.9359(12), c=5.5962(10) Å, R =0.118). LaTaON crystallizes in space group Imma (no. 74) and the other compounds LnTaON with Ln=Pr, Nd, Sm, Gd in Pnma (no. 62). SEM measurements were performed to investigate the elemental composition and morphology of the oxonitride perovskites. The bandgap values of the oxonitrides (LaTaON 1.8 eV, CeTaON 1.7 eV; PrTaON 1.9 eV, NdTaON 2.0 eV, SmTaON 2.0 eV, GdTaON 1.8 eV) were estimated by using UV/Vis measurements and the Kubelka-Munk function.

A nanowire photoanode SrTaO 2 N, a semiconductor suitable for overall water-splitting with a band gap of 2.3 eV, was coated with functional overlayers to yield a core−shell structure while maintaining its one-dimensional morphology. The nanowires were grown hydrothermally on tantalum, and the perovskite-related oxynitride structure was obtained by nitridation. Three functional overlayers have been deposited on the nanowires to enhance the efficiency of photoelectrochemical (PEC) water oxidation. The deposition of TiO x protects the oxynitride from photocorrosion and suppresses charge-carrier recombination at the surface. Ni(OH) x acts a hole-storage layer and decreases the dark-current contribution. This leads to a significantly improved extraction of photogenerated holes to the electrode−electrolyte surface. The photocurrents can be increased by the deposition of a cobalt phosphate (CoP i ) layer as a cocatalyst. The heterojunction nanowire photoanode generates a current density of 0.27 mA cm −2 at 1.23 V vs the reversible hydrogen electrode (RHE) under simulated sunlight (AM 1.5G). Simultaneously, the dark-current contribution, a common problem for oxynitride photoanodes grown on metallic substrates, is almost completely minimized. This is the first report of a quaternary oxynitride nanowire photoanode in core− shell geometry containing functional overlayers for synergetic hole extraction and an electrocatalyst.

Alkaline earth oxonitride perovskites EAMO 2 N (EA = Sr, Ba; M = Nb, Ta) were synthesized by the ammonothermal method at temperatures of 900 K and maximum pressures of up to 300 MPa in custom-built autoclaves starting from Nb or Ta and Sr or Ba metals. The reactions were performed under ammonobasic conditions using NaN 3 and NaOH as mineralizers. Powder X-ray diffraction and Rietveld refinement were used to determine the crystal structures. The elemental composition and morphology of the obtained products were investigated [a] 5020 group "Chemistry and Technology of the Ammonothermal Synthesis of Nitrides" (FOR 1600), project SCHN377/16-2, as well as the Fonds der Chemischen Industrie (FCI). We would like to thank Christian Minke for EDX, SEM, and NMR spectroscopic measurements, as well as Lukas Bauer (both at the Department of Chemistry of LMU Munich) for synthetic assistance.

Differences in the solar cell performance of solid-state PbS quantum-dot-sensitized solar cells fabricated with ex situ and in situ grown PbS quantum dots were investigated. The PbS quantum dots were either anchored on mesoporous TiO2 via l-glutathione (GSH) linker exchange or prepared in situ by the successive ionic layer adsorption/reaction (SILAR) method to create quantum-dot-sensitized solar cells. Spiro-OMeTAD was used as the organic p-type hole transporting material (HTM). The performance of the cells was evaluated with current–voltage, external quantum efficiency, and impedance spectroscopy (IS) measurements, and electron lifetimes were measured with open-circuit voltage decay (OCVD), intensity-modulated photovoltage spectroscopy (IMVS) techniques as well as with IS measurements. Analysis of the experimental data indicates that the SILAR route provides more intimate contacts at both TiO2/PbS and PbS/HTM interfaces, which results in more efficient charge injection and separation and thus higher photocurrents. However, the results of the OCVD, IMVS, and IS measurements demonstrate that the cells sensitized with PbS quantum dots prepared ex situ have longer electron lifetimes, indicating that back-transfer of electrons to the HTM is slower, probably as a consequence of passivation of surface states by the GSH ligands.