Methods Thin-film characterization Chemical composition of thin films was analyzed by X-ray photoelectron spectroscopy (XPS) (AXIS Hsi, Kratos Analytical, Ltd., Manchester, UK). Possible surface contamination was eliminated by 150 eV of Ar-ion

etching for 30 s prior to XPS analysis. The microstructure of thin films was investigated using focused ion beam and field emission scanning electron microscopy (FE-SEM) (Quanta 3D FEG, FEI Company, Hillsboro, OR, USA), and a few nanometer-thick Pt layer was coated on samples to prevent thin films from being etched by FE-SEM AP26113 ic50 imaging. Electrochemical evaluation A test cell was attached to a custom-made hydrogen feeding chamber using a ceramic adhesive (CP4010, Aremco Products, Inc., Briarcliff Manor, NY, USA) and heated to 450°C using a halogen heating system. Dry H2 gas with a mass flow of 25 selleck chemicals llc sccm was supplied to the anode side, and cathode was exposed to atmospheric environment. Anode was connected to a silver wire, and cathode was contacted by a hardened steel probe. Polarization of thin-film fuel cells was analyzed using an electrochemical testing system (1287/1260, Solartron Analytical, Hampshire, UK). Results and discussion

Thin-film electrolyte fabrication GDC thin-film was fabricated by a C646 commercial sputter (A-Tech System Ltd., Incheon, South Korea). Gd-Ce alloy (with 10 at.% Gd) was used as the GDC target. Target-to-substrate (T-S) distance was 80 mm. GDC thin films were deposited at a mixed Ar/O2 gas pressure of 5 mTorr. Volume fraction of O2 to Ar was 0.2. RF power was set at 150 W. The growth rates of GDC thin films deposited at 100°C and 500°C were approximately 42 and 20 nm/h, respectively. Considering that the packing density of GDC thin-film increases as the substrate

temperature increases [21], the substrate was heated to a high temperature of 500°C [1] in order to accommodate more volume for bulk ionic conduction. To determine the chemical composition of GDC thin films, XPS analysis was carried out. A GDC thin-film deposited at 500°C (GDC-H) was compared to a film prepared at room temperature (GDC-R). Figure 1a,b respectively Rutecarpine shows the XPS spectra of Ce 3d and Gd 4d core levels of GDC-R and GDC-H. As shown in Figure 1a, the Ce 3d core level of GDC-R did not show spin orbital doublets (V ′, U ′) unlike GDC-H, which is a characteristic of the Ce3+ binding state [22]. This result reveals that GDC-H contains reduced cerium oxide (e.g., Ce2O3) as well as cerium dioxide. The Gd 4d core level in Figure 1b illustrated characteristic peaks that are very similar to those of gadolinium oxide, and there was no distinct difference between the two samples. As for atomic concentrations, GDC-H had a higher Gd doping concentration (Gd 4d ≈ 13%) than the GDC target (approximately 10%).