Because of the generally lower activation energy associated with proton conduction in oxides compared to oxygen ion conduction, protonic ceramic fuel cells (PCFCs) should be able to operate at lower temperatures than solid oxide fuel cells (250° to 550°C versus ≥600°C) on hydrogen and hydrocarbon fuels if fabrication challenges and suitable cathodes can be developed. We fabricated the complete sandwich structure of PCFCs directly from raw precursor oxides with only one moderate-temperature processing step through the use of sintering agents such as copper oxide. We also developed a proton-, oxygen-ion-, and electron-hole-conducting PCFC-compatible cathode material, BaCo(0.4)Fe(0.4)Zr(0.1)Y(0.1)O(3-δ) (BCFZY0.1), that greatly improved oxygen reduction reaction kinetics at intermediate to low temperatures. We demonstrated high performance from five different types of PCFC button cells without degradation after 1400 hours. Power densities as high as 455 milliwatts per square centimeter at 500°C on H2 and 142 milliwatts per square centimeter on CH4 were achieved, and operation was possible even at 350°C.

Photoluminescence (PL) spectroscopy was used to characterize nanoscale ZnO impurities, amine-donor charge-transfer exciplexes, and framework decomposition in samples of MOF-5 prepared by various methods. The combined results cast doubt on previous reports describing MOF-5 as a semiconductor and demonstrate that PL as a tool for characterizing MOF purity possesses advantages such as simplicity, speed, and sensitivity over currently employed powder XRD MOF characterization methods.

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Proton conducting BaCe0.6Zr0.3Y0.1O3-δ (BCZY63) pellets were fabricated by the solid-state reactive sintering method whereby a small extra amount of a metal oxide additive (5 mol%) was included in the precursor mixture before sintering. The effect of the addition of six different metal oxide additives (CuO, ZnO, Fe2O3, MnO2, PdO, and Cr2O3) on the transport properties of BCZY63 was investigated. Although most additives (e.g. ZnO, Fe2O3, MnO2, Cr2O3) led to a decrease (sometimes minor) in conductivity, CuO and PdO dopants yielded an increase in total conductivity compared to the BCZY63 control. The enhancement in the total conductivity is found to be related to two factors: 1) the additive can act as a sintering aid to produce larger grain size; 2) substitutional doping of the BCZY structure by metal ions from additives can lead to increased bulk proton concentration. Due to its excellent sinterability and moderately improved proton conductivity, CuO-doped BCZY63 was subsequently applied as the dense electrolyte layer in protonic ceramic fuel cells utilizing a recently developed single firing step fabrication technique to produce high quality single cells that showed exceptional performance and long-term stability.

Transparent conducting oxide (TCO) coatings with decreased cost and greater process or performance versatility are needed for a variety of optoelectronic applications. Among potential new TCO candidates, doped titanium dioxide is receiving particular interest. In this study, niobium-doped titania bilayer structures consisting of a nanoscale seed layer (deposited by atomic layer deposition or RF magnetron sputtering) followed by a thick bulk-like layer were grown directly on glass in order to examine the effects of the seed layer processing on the subsequent crystallization and electrical properties of these heterostructures. Observations from Raman spectroscopy suggest that higher oxygen content in the seed layer suppresses the formation of detrimental titania polymorph phases, found in films produced by annealing directly after synthesis without any exposure to oxygen. Furthermore, our results indicate that the generation of excellent Nb:TiO2 conductors on glass (without breaking vacuum) only occurs within a narrow processing range and that the sequential deposition of oxygen-poor layers on oxygen-rich layers is a critical step towards achieving films with low resistivity.