Soonwook Hong

PEALD YSZ-based bilayer electrolyte for thin film-solid oxide fuel cells

Yttria-stabilized zirconia (YSZ) thin film electrolyte deposited by plasma enhanced atomic layer deposition (PEALD) was investigated. PEALD YSZ-based bi-layered thin film electrolyte was employed for thin film solid oxide fuel cells on nanoporous anodic aluminum oxide substrates, whose electrochemical performance was compared to the cell with sputtered YSZ-based electrolyte. The cell with PEALD YSZ electrolyte showed higher open circuit voltage (OCV) of 1.0 V and peak power density of 182 mW cm(-2) at 450 °C compared to the one with sputtered YSZ electrolyte(0.88 V(OCV), 70 mW cm(-2)(peak power density)). High OCV and high power density of the cell with PEALD YSZ-based electrolyte is due to the reduction in ohmic and activation losses as well as the gas and electrical current tightness.

Optimized antireflective silicon nanostructure arrays using nanosphere lithography

Broadband optical antireflective arrays of sub-wavelength structures were fabricated on silicon substrates using colloidal nanosphere lithography in conjunction with reactive ion etching. The morphology of the nanostructures, including the shape, base diameter and height, was precisely controlled by modifying the conventional process of nanosphere lithography. We investigated their effects on the optical characteristics based on experimentally measured reflectance performance. The Si nanostructure arrays demonstrated optical antireflection performance with an average reflectance of about 1% across the spectral range from 300 to 800 nm, i.e. near-ultraviolet to visible wavelengths. This fabrication method can be used to create a large surface area and offers a promising approach for antireflective applications.

Single-chamber fabrication of high-performance low-temperature solid oxide fuel cells with grain-controlled functional layers

A one-step process has been developed for the fabrication of thin film membrane–electrode assemblies with multi-layer electrolytes for use in high-performance, low-temperature solid oxide fuel cells (LT-SOFCs). By controlling the sputter processing conditions, a dense yttria-stabilized zirconia (YSZ) electrolyte film was fabricated onto a porous aluminum oxide (AAO) anodic substrate. Thin, grain-controlled layers (GCLs) were subsequently formed at the cathodic interface to provide a homogeneous functional layer, which significantly enhanced the kinetics of the oxygen reduction reaction (ORR). This is attributed to the fine grains and increased grain boundary density of this layer, which were achieved without thermal annealing. Using this new device architecture, the fuel cell was able to reach a peak power density of 343 mW cm−2 at 450 °C.