Super-high dual-ion conductivity of BaO-doped GDC electrolytes for solid oxide fuel cells

Abstract

Our recently developed method for measuring H⁺, O²⁻, and dual-ion conductivities has been employed to investigate BaZr_0.7Ce_0.2Y_0.1O_3−δ (BZCY)/Ce_0.9Gd_0.1O_2−δ (GDC) composite membranes. For the first time, we have identified the reason for the exceptionally high ionic conductivity of the 10 wt% BZCY/GDC composite. XRD results revealed that BaO doped into GDC during high-temperature sintering, with the 10 wt% BZCY/GDC composite achieving the highest BaO doping level. We propose that BaO-doped GDC, predominantly located at GDC grain boundaries, facilitates H⁺ conduction, leading to a high H⁺ conductivity of 15 mS cm⁻¹ at 650 °C. To verify the role of BaO doping, we prepared composite membranes using BaO instead of BZCY and observed the same enhancement in H⁺ conductivity. Compared to BaCe_0.7Zr_0.1Y_0.1Yb_0.1O_3−δ, the 10 wt% BZCY/GDC composite exhibited higher ionic conductivities, particularly in dual-ion conduction, due to the distinct pathways for H⁺ and O²⁻ transport. As a result, solid oxide fuel cells (SOFCs) with this electrolyte demonstrated the higher maximum power densities than those reported for dual-phase electrolytes in the literature. These findings highlight BaO-doped GDC as a promising dual-ion conducting electrolyte for SOFCs.