Two negatives make a positive: Benefits of co-doping on electrical property of new protonic ceramic fuel cell electrolyte SrSn0.8Sc0.2O3−δ at low temperatures

Proton ceramic fuel cells (PCFCs) face significant challenges in developing electrolytes that simultaneously exhibit high proton conductivity and good sinterability at reduced temperatures. While SrSn_0.8Sc_0.2O_3−δ (SSS) has emerged as a promising alternative to traditional BaZrO₃- and BaCeO₃-based systems due to its superior thermochemical stability, its conductivity remains insufficient for practical low-temperature (<500 °C) applications. In this study, where single doping fails, we develop a rational co-doping strategy through the incorporation of both Ba and Yb to simultaneously enhance bulk conductivity and reduce grain boundary resistance in SSS electrolytes. The optimized composition, Sr_0.95Ba_0.05Sn_0.8Sc_0.15Yb_0.05O_3−δ, shows a 26.3 % increase in conductivity and a 71.7 % reduction in grain boundary resistance at 400 °C, due to synergistic phase modification and defect optimization. Single-cell tests demonstrate practical benefits, as the co-doped electrolyte delivering a 38.7 % increase in power density at 500 °C compared to its undoped counterpart. These findings contribute valuable insights into the development of improved proton-conducting electrolytes through controlled co-doping, and suggest a promising avenue for optimizing SSS-based materials in low-temperature PCFCs.