Magnetron sputtered gadolinia-doped ceria diffusion barriers for metal-supported solid oxide fuel cells

Abstract

Gadolinia-doped ceria (GDC) thin films are deposited by reactive magnetron sputtering in an industrial-scale setup and implemented as barrier layers between the cathode and electrolyte in metal-based solid oxide fuel cells consisting of a metal support, an electrolyte of ZrO 2 co-doped with Sc 2 O 3 and Y 2 O 3 (ScYSZ) and a Sr-doped lanthanum cobalt oxide cathode. In order to optimize the deposition of GDC to obtain high electrochemical performance of the cells, the influence of film thickness and adatom mobility is studied. The adatom mobility is varied by tuning the deposition temperature and substrate bias voltage.A GDC layer thickness of 0.6 µm is found to effectively block Sr diffusion when bias voltage and deposition temperature is tuned to promote dense coatings. The adatom mobility has a large influence on the film density. Low temperature and bias voltage result in underdense column boundaries which function as channels for Sr to diffuse to the GDC-ScYSZ interface. By tuning deposition temperature, bias voltage and film thickness area specific resistances down to 0.34 Ωcm 2 are achieved at cell tests performed at an operating temperature of 650 °C.

Annealing temperature induced improved crystallinity of YSZ thin film

“…The position of the XRD peaks were also altered with the change in annealing temperature. Careful refinment of four intense peaks (figure 1) revealed that the value of FHWM determined using Gaussion fit were slightly higher than the one referred in the database, indicating freely distributed stress in the film [37]. Moreover, the peaks position were occurred at higher angles (2θ=30.22°, 50.51, and 59.98) for sample annealed at 600°C compared to those synthesized at lower temperature 300 to 500°C.…”

Mobilty of Sr in Gadolinia Doped Ceria SOFC Chemical Barrier Layers Prepared Using Spray Pyrolysis, Pulsed Laser Deposition and Magnetron Sputtering Methods

“…Knibbe et al (3) reported that grain boundaries of the dense epitaxial GDC layer facilitate Sr diffusion. Decrease of electrochemical performance because of Sr mobility in metal-supported SOFC with magnetron sputtered protective layer, if layer was thinner than 0.6 µm and LSC cathode was sintered at 800°C, has been demonstrated (4). Positive influence of Sr on the GDC densification, having some effect already at 400°C, has been reported by Suresh et al (5).…”

Optimized magnetron sputtering process for the deposition of gadolinia doped ceria layers with controlled structural properties

“…Especially in devices made of yttria-stabilized zirconia (YSZ) electrolytes and La1-xSrxCo1-yFeyO3-δ (LSCF) electrodes, the diffusion of Sr can lead to the formation of insulating SrZrO3 [1,2]. Gadolinia doped ceria (GDC) thin films can be used in such devices as a Sr diffusion barrier in order to extend their lifetime [3,4].…”