NiO-SDC Mixed Ionic Electronic Conducting Anode for Low Temperature Thin Film SOFCs

Solid oxide fuel cells (SOFCs) are promising candidates for next generation energy conversion devices due to its fuel flexibility, high efficiency, high energy density, and no CO poisoning. However, high operation temperature which is required due to poor ionic conductivity of oxide electrolyte of typical SOFCs disturbs the commercialization.

Various thin film techniques for fabrication of electrodes and electrolyte are applied to lower the operation temperature of SOFCs. Pulsed laser deposition (PLD), sputter, chemical vapor deposition (CVD), and atomic layer deposition (ALD) are used to prepare thin film electrodes or electrolyte.

Typical low temperature SOFCs use platinum (Pt) as an electrode material due to high electrical conductivity and superior catalytic activity of Pt for both hydrogen oxidation reactions and oxygen reduction reactions. Despite of these strong points, high cost, thermal degradation due to agglomeration, mismatch of thermal expansion coefficient and limited triple phase boundaries (TPB) are still remained.   

Mixed ionic electronic conducting (MIEC) anode materials such as NiO-YSZ, NiO-GDC, and NiO-SDC are usually used at typcial SOFCs due to high density of triple phase boundaries. These MIEC materials can relieve the thermal degradation and thermal stress. Cost is also reduced compared with Pt. Therefore, we applied the MIEC anode for low temperature thin film SOFCs.

In this study, we prepared anodic alumina oxide (AAO) based low temperature thin film SOFCs. NiO-SDC anode was fabricated via radio frequency sputtering method using NiO-SDC oxide target. The reactive RF sputtering process is conducted to prepare yttria-stabilized zirconia (YSZ) electrolyte on a NiO-SDC anode by using Y-Zr alloy target and Ar-O2 mixing gas. After electrolyte deposition, porous Pt cathode was deposited on the electrolyte by direct current sputtering method. Open circuit voltage (OCV), performance, and electrochemical impedance spectroscopy (EIS) were measured at 500C.