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Abstract

Polymer-assisted deposition (PAD) technique was developed to fabricate ferroelectric BaTiO3(BTO) thin films directly on polycrystalline nickel foils. The growth dynamics was systematically studied to optimize the single-phase BTO films with good dielectric properties. It is critical to pretreat nickel foils with hydrogen peroxide (H2O2) solution to form thin nickel oxide layers on the surfaces for the growth of BTO films. Both the concentration of H2O2solution and the pretreated time were found to strongly affect the dielectric constant of BTO films, which may be associated with the oxygen diffusion from nickel oxide buffer layers to BTO layers during annealing. The BTO thin films with optimized growth conditions have good crystal structure and electrical properties, suggesting that the as-grown BTO films by PAD technique can be utilized for new devices development and energy storage applications.

Self-assembled epitaxial nanocomposite CoFe2O4:SrTiO3and CoFe2O4:MgO thin films were grown on LaAlO3substrates by a chemical solution approach of polymer-assisted deposition. X-ray diffraction and transmission electron microscopy analyses indicated that both phases in the composites were epitaxial with respect to the major axes of the substrate. Compared to the single-phase ferrimagnetic spinel CoFe2O4films and the bilayer CoFe2O4/SrTiO3and CoFe2O4/MgO films, the composite films exhibited reduced coercivity and enhanced magnetic anisotropy.

Tunable and enhanced low‐field magnetoresistance (LFMR) is observed in epitaxial (La0.7Sr0.3MnO3)0.5:(ZnO)0.5(LSMO:ZnO) self‐assembled vertically aligned nanocomposite (VAN) thin films, which have been grown on SrTiO3(001) substrates by pulsed laser deposition (PLD). The enhanced LFMR properties of the VAN films reach values as high as 17.5% at 40 K and 30% at 154 K. They can be attributed to the spin‐polarized tunneling across the artificial vertical grain boundaries (GBs) introduced by the secondary ZnO nanocolumns and the enhancement of spin fluctuation depression at the spin‐disordered phase boundary regions. More interestingly, the vertical residual strain and the LFMR peak position of the VAN films can be systematically tuned by changing the deposition frequency. The tunability of the physical properties is associated with the vertical phase boundaries that change as a function of the deposition frequency. The results suggest that the tunable artificial vertical GB and spin‐disordered phase boundary in the unique VAN system with vertical ferromagnetic‐insulating‐ferromagnetic (FM‐I‐FM) structure provides a viable route to manipulate the low‐field magnetotransport properties in VAN films with favorable epitaxial quality.

Abstract

A thin layer of a vertically aligned nanocomposite (VAN) structure is deposited between the electrolyte, Ce0.9Gd0.1O1.95(CGO), and the thin‐film cathode layer, La0.5Sr0.5CoO3(LSCO), of a thin‐film solid‐oxide fuel cell (TFSOFC). The self‐assembled VAN nanostructure contains highly ordered alternating vertical columns of CGO and LSCO formed through a one‐step thin‐film deposition process that uses pulsed laser deposition. The VAN structure significantly improves the overall performance of the TFSOFC by increasing the interfacial area between the electrolyte and cathode. Low cathode polarization resistances of 9 × 10−4and 2.39 Ω were measured for the cells with the VAN interlayer at 600 and 400 °C, respectively. Furthermore, anode‐supported single cells with LSCO/CGO VAN interlayer demonstrate maximum power densities of 329, 546, 718, and 812 mW cm−2at 550, 600, 650, and 700 °C, respectively, with an open‐circuit voltage (OCV) of 1.13 V at 550 °C. The cells with the interlayer triple the overall power output at 650 °C compared to that achieved with the cells without an interlayer. The binary VAN interlayer could also act as a transition layer that improves adhesion and relieves both thermal stress and lattice strain between the cathode and the electrolyte.

While dimethyl ether (DME) has been long viewed as a promising alternative fuel for direct fuel cells, DME electrooxidation in general and at PtRu catalysts in particular has remained kinetically handicapped relative to methanol oxidation at PtRu alloys. In this work, a ternary carbon-supported PtRuPd catalyst was developed for DME electrooxidation using the polyol method. The as-synthesized PtRuPd/C catalyst shows higher activity for DME oxidation than the state-of-the-art Pt50Ru50/C catalyst (HiSPEC® 12100) in both the electrochemical cell and fuel cell testing. The effect is likely due to the activation of the C-O bond cleavage by Pd. An extensive physical characterization, including XRF, TGA, SEM, TEM and XRD, was conducted to provide insights into the composition, morphology, and structure of the PtRuPd/C catalyst.