Dual-phase Yb-doped La2Ce2O7 materials for fuel flexible SOFCs

Abstract

La_2−xYb_xCe₂O₇ (where x = 0, 0.05, 0.10, 0.15, and 0.20) has been studied as a possible electrolyte material for solid oxide fuel cells (SOFCs), demonstrating a novel material. Nanosized La_2−xYb_xCe₂O₇ ceramics have been synthesized via the glycine nitrate combustion method. To elucidate the dual phase character (F-type and C-type phase) present in the Yb-doped La₂Ce₂O₇, extensive X-ray diffraction and Raman spectroscopy analyses have been performed to thoroughly investigate the crystal structure and phases. Furthermore, doping has been shown to affect the dual phases present in the system. The ionic conductivity and the space charge potential of the Yb-doped La₂Ce₂O₇ have been analyzed in details and the highest ionic conductivity of 3.3 × 10⁻³ S cm⁻¹ at 700 °C is achieved at x = 0.05. Therefore, the La_1.95Yb_0.05Ce₂O₇ composition has been chosen for the electrophoretic deposition (EPD) for SOFCs fabrication. The La_1.95Yb_0.05Ce₂O₇ film, coated using EPD in isopropanol, is found to be crack-free and dense with a thickness of approximately 14 μm. The maximum power density of the fabricated cell is observed to be 589 and 420 mW cm⁻² at 700 °C in wet hydrogen and methane fuel, respectively. Impedance spectrum analysis utilizing the distribution of relaxation time (DRT) analysis shows that the gas diffusion process in the electrodes plays a significant role in the overall polarization of the cell.