Enhancing the Electrochemical Performance of Perovskite-Like Ruddlesden–Popper Oxide Pr ₂ NiO ₄ through a Gd-Doping Strategy

This study investigates the synergistic optimization of structural stability and electrochemical performance in Gd³⁺-doped Pr_2-<i>x</i>Gd_<i>x</i>NiO₄ (<i>x</i> = 0-0.150) Ruddlesden-Popper (R-P) oxides. Phase analysis coupled to this confirmed that the materials retained the K₂NiF₄-type R-P structure. Thermal expansion analysis demonstrated that Pr_1.9Gd_0.1NiO₄ possesses an average linear thermal expansion coefficient (TEC) of 12.62 × 10^-6 K^-1, showing excellent interfacial compatibility with a gadolinium-doped ceria (GDC) electrolyte. Electrochemical characterization revealed that the symmetric cell Pr_1.9Gd_0.1NiO₄|GDC|Pr_1.9Gd_0.1NiO₄ achieved a low area-specific polarization resistance (<i>R</i>_p) of 1.40 × 10^-2 Ω cm² at 800 °C in air, with an oxygen reduction reaction (ORR) activation energy (<i>E</i>_a) of 0.8 eV. The single cell (NiO-GDC|GDC|Pr_1.9Gd_0.1NiO₄) delivered a maximum power density of 0.74 W cm^-2 at 800 °C and maintained stable operation for 100 h under 0.30 A cm^-2. These results highlight the effectiveness of A-site Gd³⁺ doping in enhancing the electrochemical performance and durability of Pr₂NiO₄-based cathodes, providing critical insights for developing solid oxide fuel cells.