Dual-modulated ruddlesden-popper air electrode via Gd/Nb co-doping: Achieving high performance and durability in protonic ceramic cells

Proton-conducting solid oxide cells (PCCs) are regarded as a highly promising technology for achieving efficient power generation and hydrogen production. However, the slow dynamics and limited durability hinder the performance of air electrodes. In this study, we present a series of cobalt-free Ruddlesden-Popper perovskites co-doped with Gd and Nb, with the nominal formula Pr 2-x Gd x Ni 1-y Nb y O 4+δ . Structural characterization confirms the Pr 1.9 Gd 0.1 Ni 0.9 Nb 0.1 O 4+δ (PGNNb) materials formed composite architecture comprising a Pr 1.9-x Gd 0.1 Ni 0.9 Nb 0.1 O 4+δ matrix covered with PrO 1.83 particles, which synergistically enhances triple-conductivity. The optimized PGNNb electrode exhibits outstanding dual-mode functionality: at 700 °C, it provides a peak power density of 1.41 W cm -2 and a low polarization resistance of 0.067 Ω cm 2 in fuel cell mode, while delivering an impressive current density of 3.34 A cm -2 at 1.3 V in electrolysis mode. Importantly, the composite structure exhibits excellent long-term stability, maintaining consistent performance over 120 h at -0.35 A cm -2 in fuel cell mode and 80 h at 0.6 A cm -2 in electrolysis mode, with no observable degradation. These advancements are attributed to the dual-doping-induced lattice stabilization, suppressed Ni segregation, and optimized proton/oxygen-ion transport pathways.