Synergistic Doping in Proton-Conducting Oxides Unlocks High Conductivity and Low Proton Trapping

The development of proton-conducting oxides is pivotal for advancing solid oxide fuel cells (SOFCs), yet it is perpetually hampered by a critical trade-off between high proton conductivity and good sinterability. Conventional doping strategies, typically employing single elements, often improve one property at the expense of the other. Here, we break this long-standing compromise by introducing a multi-element doping strategy, creating a novel proton conductor, BaCe_0.7Zr_0.1Gd_0.04Nd_0.04Sm_0.04Y_0.04Yb_0.04O₃ (GNSYYb), which simultaneously exhibits superior sinterability, the highest proton defect concentration, and the largest grain size among all singly doped analogues. As a result, GNSYYb possesses the highest bulk conductivity. More profoundly, comparative H₂O/D₂O isotope studies indicate a significantly mitigated proton trapping effect in GNSYYb, as evidenced by its lower activation energy shift and a conductivity ratio (σ_H/σ_D) closer to the theoretical value. This reduction in trapping energy barriers is identified as a key factor for its enhanced proton mobility. Consequently, a proton-conducting SOFC (H-SOFC) with a thin GNSYYb electrolyte demonstrates an exceptional peak power density of 2399 mW cm⁻² at 700°C, outperforming most reported BaCeO_3–BaZrO₃-based cells. This work not only presents a superior electrolyte candidate for H-SOFCs but also establishes multi-element doping as a transformative paradigm for designing high-performance proton-conducting oxides.