Electrochemical study on Ce_0.85Sm_0.15O_1.925–BaCe_0.83Y_0.17O_3−δ composite electrolyte

Highlights: • We fabricated the composite electrolytes with SDC and BCY. • The grain boundary resistance could be significantly decreased. • Two grain boundary responses are identified, which is a new phenomenon. • The interfacial polarization resistances R_p can be decreased by adding BCY to SDC. • Single cell performance could be obviously enhanced. - Abstract: The composites of Ce_0.85Sm_0.15O_1.925 (SDC) and BaCe_0.83Y_0.17O_3−δ (BCY) are investigated as electrolytes for solid oxide fuel cells (SOFCs). The electrolyte materials SDC and BCY are synthesized by the glycine–nitrate route and the sol–gel process, respectively. Composite electrolytes are then prepared by mixing SDC and BCY in weight ratios of 9:1 (SB91), 8:2 (SB82), 7:3 (SB73) and 5:5 (SB55). Results from X-ray diffraction (XRD) demonstrate that Sm³⁺ can diffuse from SDC to BCY. The SEM results reveal that the average grain size decreases with increasing BCY content. Impedance spectroscopy measurements reveal that the grain boundary resistance can be significantly reduced by adding 10–20 wt.% BCY to SDC. Among all of the samples, SB91 exhibits the lowest total resistance. In the impedance spectra of SB73 and SB55, two grain boundary responses can be identified. Compared with SDC and BCY, the composite electrolytes exhibit lower electrode interfacial polarization resistances. Single cells based on the electrolytes are fabricated using Ni_0.9Cu_0.1O_x/SDC as anode and LaSr_0.25Ba_0.75Co₂O_5+δ as cathode. The cell based on SB91 electrolyte exhibits the lowest total resistance under open circuit conditions and the maximum power density of the cell based on SB91 electrolyte reaches 0.495 W cm⁻² at 800 °C