Improved Reversibility of Thin-Film Solid Oxide Cells at 500 °C by Tailoring Sputtering Processes for Depositing Yttria-Stabilized Zirconia Electrolyte.

The present study investigates the impact of sputtering configurations on the microstructure and crystallinity of thin-film yttria-stabilized zirconia electrolytes for anodized aluminum oxide-supported all-sputtered thin-film reversible solid oxide cells. Employing various sputtering parameters, such as target-substrate distance and substrate rotation speed, the present study reveals distinct surface characteristics and crystalline structures of thin-film yttria-stabilized zirconia. The microstructure analysis includes scanning electron microscopy and atomic force microscopy examinations, uncovering the influence of the process parameters on the surface morphology, roughness, and grain size. X-ray diffraction data illustrate the texture preferences and crystallite characteristics. The electrochemical characterization of the reversible solid oxide cells demonstrates that the optimized sputtering configuration significantly outperforms the others in both SOFC and SOEC modes, showing exceptional current densities of 964 mA/cm2 at 1.3 V in electrolysis mode at 500 °C. Electrochemical impedance spectroscopy further reveals improved charge transfer reactions at the interface of the electrolyte. The enhanced electrochemical performance is attributed to the unique microstructure and crystallinity of the thin film of yttria-stabilized zirconia. The record-breaking electrolysis performance of this work at 500 °C underscores the potential of tailored sputtering parameters in optimizing the reversible solid oxide cell performance.

Nanocrystal Engineering of Thin-Film Yttria-Stabilized Zirconia Electrolytes for Low-Temperature Solid-Oxide Fuel Cells.

To overcome significantly sluggish oxygen-ion conduction in the electrolytes of low-temperature solid-oxide fuel cells (SOFCs), numerous researchers have devoted considerable effort to fabricating the electrolytes as thin as possible. However, thickness is not the only factor that affects the electrolyte performance; roughness, grain size, and internal film stress also play a role. In this study, yttria-stabilized zirconia (YSZ) was deposited via a reactive sputtering process to fabricate high-performance thin-film electrolytes. Various sputtering chamber pressures (5, 10, and 15 mTorr) were investigated to improve the electrolytes. As a result, high surface area, large grain size, and residual tensile stress were successfully obtained by increasing the sputtering pressure. To clarify the correlation between the microstructure and electrolyte performance, a YSZ thin-film electrolyte was applied to anodized aluminum oxide-supported SOFCs composed of conventional electrode materials which are Ni and Pt as the anode and the cathode, respectively. The thin-film SOFC with YSZ deposited at 15 mTorr exhibited the lowest ohmic resistance and, consequently, the highest maximum power density (493 mW/cm2) at 500 °C whose performance is more than five times higher than that of the cell with YSZ deposited at 5 mTorr (94.1 mW/cm2). Despite the basic electrode materials, exceptionally high performance at low operating temperature was achieved via controlling the single fabrication condition for the electrolyte.

A Self-Crystallized Nanofibrous Ni-GDC Anode by Magnetron Sputtering for Low-Temperature Solid Oxide Fuel Cells.

The optimum composition ratio of the anode cermet (Ni-GDC) for solid oxide fuel cells (SOFCs) varies because the electron-collecting mechanism is different depending on its applications. A Co-sputtering method facilitates ratio control with sputtering power adjustment. However, there is a practical issue with fabricating anode cermet with various ratios attributed to the large sputtering yield gap of the metal target, Ni, and the ceramic target, gadolinia-doped ceria (GDC). Therefore, in this study, a Gd-Ce metal alloy was applied instead of GDC to match the sputtering rate with that of Ni, which enables a wide ratio range achievement. A thin film of Gd-Ce oxidized after deposition and successfully transformed to crystallized GDC under a SOFC operation environment. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) confirmed its crystallinity, and the film deposited with various power ratios was sputtered on the ScSZ electrolyte pellet to clarify the optimum Ni-GDC ratio for thin-film SOFCs. Last, the Ni-GDC was applied to anodized aluminum oxide (AAO)-supported SOFCs to maximize the performance. The performance change according to the thickness of Ni-GDC was identified, and the best performance among them was 638 mW/cm2 at 500 °C.

Structure dependent luminescence, peroxidase mimetic and hydrogen peroxide sensing of samarium doped cerium phosphate nanorods.

Rare earth phosphates have been used extensively in luminescent phosphors, bio-imaging, catalysis, and sensors. However, there is a need to correlate the structural-chemical changes associated with stability and performance. In the present work, hydrothermally synthesized CePO4:Smx (x = 0, 5 and 10 mol%) nanorods were annealed at different temperatures to understand the modulations in structure as well as optical and enzyme mimetic properties. As prepared samarium doped cerium phosphate (SCP) nanorods crystallized in a hydrated hexagonal structure transformed into an anhydrous hexagonal and a monoclinic structure on annealing at 400 °C and 800 °C, respectively. Though temperature did not affect the rod-like morphology of the SCP, the lattice strain changed from compressive to tensile. Monoclinic SCP exhibited excellent emission until 5% Sm3+ doping while the quenching effect dominated at 10% Sm3+. Monoclinic SCP samples demonstrated higher peroxidase-like enzymatic activity in comparison to natural enzyme HRP and hexagonal SCP. A mechanism for the enhanced peroxidase-like activity of the monoclinic structure was proposed based on the fluorescence property of terephthalic acid and the surface peroxo complex using Raman spectroscopy. Fluorimetric detection based on the luminescent quenching effect of the monoclinic SCP nanorods treated with different concentrations of hydrogen peroxide showed a linear response from 0 to150 µM concentration with a detection limit (LOD) of 3.17 µM H2O2. Our results demonstrate the importance of structure for enzyme mimetic activity.