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The size of the band gap and the energy position of the band edges make several oxynitride semiconductors promising candidates for efficient hydrogen and oxygen production under solar light illumination. Intense research efforts dedicated to oxynitride materials have unveiled the majority of their most important properties. However, two crucial aspects have received much less attention: One is the critical issue of compositional/structural surface modifications that occur during operation and how these affect photoelectrochemical performance. The second concerns the relation between electrochemical response and the crystallographic surface orientation of the oxynitride semiconductor. These are indeed topics of fundamental importance, since it is exactly at the surface where the visible-light-driven electrochemical reaction takes place. In contrast to conventional powder samples, thin films represent the best model system for these investigations. This study reviews current state-of-the-art oxynitride thin film fabrication and characterization, before focusing on LaTiO2N, selected as a representative photocatalyst. An investigation of the initial physicochemical evolution of the surface is reported. Then, it is shown that after stabilization the absorbed photon-to-current conversion efficiency of epitaxial thin films can differ by about 50% for different crystallographic surface orientations, and be up to 5 times larger than for polycrystalline samples. [ABSTRACT FROM AUTHOR]

A novel approach for tailoring strained Pt model electrocatalysts using pulsed laser deposition is presented. The physical properties of Pt films grown on single-crystalline (100)- and (111)-oriented strontium titanate depend significantly on the various deposition parameters (e.g., fluence, temperature, background atmosphere, postannealing, and number of process steps), as revealed by scanning electron microscopy and X-ray studies. By properly selecting the deposition conditions, thin, epitaxial, and strained (100)- and (111)-oriented Pt films suitable as model electrodes can be prepared. Cyclic voltammetry measurements indicate that the strain in the Pt films changes significantly the Pt surface properties, such as the hydrogen underpotential deposition (Hupd) features. CO oxidation experiments demonstrate that the strain affects strongly also the position of the CO oxidation peak shifting it to more positive potentials. This might be attributed to a modification of the adsorption behavior of oxygenated species on the strained interface. This research clearly highlights the potential of using as-produced Pt film as model catalysts to study the effect of strain on electrocatalytic reactions while minimizing possible side effects connected to the common preparation methods for strained Pt catalysts, such as alloy formation, alloy leeching, or conductive support contributions. [ABSTRACT FROM AUTHOR]

Reducing the operating temperature in the 500-750 °C range is needed for widespread use of solid oxide fuel cells (SOFCs). Proton-conducting oxides are gaining wide interest as electrolyte materials for this aim. We report the fabrication of BaZr0.8Y0.2O3−δ (BZY) proton-conducting electrolyte thin films by pulsed laser deposition on different single-crystalline substrates. Highly textured, epitaxially oriented BZY films were obtained on (100)-oriented MgO substrates, showing the largest proton conductivity ever reported for BZY samples, being 0.11 S cm−1 at 500 °C. The excellent crystalline quality of BZY films allowed for the first time the experimental measurement of the large BZY bulk conductivity above 300 °C, expected in the absence of blocking grain boundaries. The measured proton conductivity is also significantly larger than the conductivity values of oxygen-ion conductors in the same temperature range, opening new potential for the development of miniaturized SOFCs for portable power supply. [ABSTRACT FROM AUTHOR]

Abstract: Anode-supported solid oxide fuel cells (SOFCs) based on thin BaZr0.8Y0.2O3− δ (BZY) electrolyte films were fabricated by pulsed laser deposition (PLD) on sintered NiO–BZY composite anodes. After in situ reduction of NiO to Ni, the anode substrates became porous, while retaining good adhesion with the electrolyte. A slurry-coated composite cathode made of La0.6Sr0.4Co0.2Fe0.8O3 − δ (LSCF) and BaCe0.9Yb0.1O3 − δ (BCYb), specifically developed for proton conducting electrolytes, was used to assemble fuel cell prototypes. Depositing by PLD 100nm thick LSCF porous films onto the BZY thin films was essential to improve the cathode/electrolyte adhesion. A power density output of 110mW/cm2 at 600°C, the largest reported value for an anode-supported fuel cell based on BZY at this temperature, was achieved. Electrochemical impedance spectroscopy (EIS) measurements were used to investigate the different contributions to the total polarization losses. [Copyright &y& Elsevier]

Highly textured thin films with small grain boundary regions can be used as model systems to directly measure the bulk conductivity of oxygen ion conducting oxides. Ionic conducting thin films and epitaxial heterostructures are also widely used to probe the effect of strain on the oxygen ion migration in oxide materials. For the purpose of these investigations a good lattice matching between the film and the substrate is required to promote the ordered film growth. Moreover, the substrate should be a good electrical insulator at high temperature to allow a reliable electrical characterization of the deposited film. Here we report the fabrication of an epitaxial heterostructure made with a double buffer layer of BaZrO3 and SrTiO3 grown on MgO substrates that fulfills both requirements. Based on such template platform, highly ordered (001) epitaxially oriented thin films of 15% Sm-doped CeO2 and 8 mol% Y2O3 stabilized ZrO2 are grown. Bulk conductivities as well as activation energies are measured for both materials, confirming the success of the approach. The reported insulating template platform promises potential application also for the electrical characterization of other novel electrolyte materials that still need a thorough understanding of their ionic conductivity. [ABSTRACT FROM AUTHOR]