Infiltrated thin film structure with hydrogel-mediated precursor ink for durable SOFCs

Abstract

The hydrogel of biomolecule-assisted metal/organic complex has the superior ability to form a uniform, continuous, and densely integrated structure, which is necessary for fine thin film fabrication. As a representative of nature-originated polymers with abundant reactive side chains, we select the gelatin molecule as an element for weaving the metal cations. Here, we demonstrate the interaction between the metal cation and gelatin molecules, and associate it with coating quality. We investigate the rheological property of gelatin solutions interacting with metal cation from the view of cross-linking and denaturing of gelatin molecules. Also, we quantitatively compare the corresponding interactions by monitoring the absorbance spectrum of the cation. The coated porous structure is systematically investigated from the infiltration of gelatin-mediated Gd_0.2Ce_0.8O_2-δ (GDC) precursor into Sm_0.5Sr_0.5CoO_3-δ (SSC) porous scaffold. By applying the actively interacting gelatin-GDC system, we achieve a thin film of GDC on SSC with excellent uniformity. Compare to the discrete coating from the typical infiltration process, the optimized thin film coated structure shows enhanced performance and stability.

Figure 1

Overall process of surface coating onto the SSC cathode using infiltration process and the resultant SEM images of coated structure: (a) SSC particle scaffold on GDC pellet, (b) infusing GDC precursor solutions, (c) discrete GDC coating from GDC/glycine solution, and (d) continuous GDC coating from GDC/gelatin solution, after calcination at 800 °C.

Figure 2

Viscosity of (a) glycine solution, and (e) gelatin solution, according to GDC precursor mole concentration. SEM images of the coating morphology from glycine/GDC (top) and gelatin/GDC (bottom) infiltration with the concentration of (b) and (f) 0.025 M, (c) and (g) 0.05 M, and (d) and (h) 0.4 M.

Figure 3

UV–Vis absorbance spectra of 0.05 M GDC precursor solution in (a) 60/40 aqueous ethanol, (b) glycine solution, and (c) gelatin solution. The legend indicates the wt% concentration of each organic molecule. The inset images describe the interacting elements in each solution.

Figure 4

EIS results of Gly–GDC and Gel–GDC. (a) Rp of Gly–GDC and Gel–GDC as a function of the loading amount of GDC into the SSC cathode at 650 °C. (b) Representative impedance spectra of samples at optimized loading amount at 650 °C; Gly–GDC: 0.2 M, and Gel–GDC: 0.05 M.

Figure 5

Stability test for 100 h at 650 °C. (a) Nyquist plots of Pristine-SSC, Gly–GDC, and Gel–GDC for long-term operation, (b) Variation of R_ps for long-term operation, and (c) SEM images of the SSC with different coatings at 0 h and 100 h.