A new higher-order Ruddlesden-Popper phase composition LaPr3Ni3O9.76 was synthesised by a sol-gel route and studied for potential intermediate-temperature solid oxide fuel cell cathode properties by electrochemical impedance spectroscopy. The focus of the work was optimisation of the microstructure and interface structure to realise the best performance, and therefore symmetrical cells after impedance testing were subsequently studied by scanning electron microscopy for post-microstructural analysis. It was observed that the cathode ink prepared after ball milling the material and then triple roll milling the prepared ink gave the lowest area specific resistance (ASR) of 0.17 Ω cm2 at 700 °C when a La0.8Sr0.2Ga0.8Mn0.2O3-δ (LSGM) electrolyte that had been previously polished was used. The post-microstructural studies, as expected, showed an improved interface structure and relatively good particle interconnectivity and much less sintering when compared to the symmetrical half-cells constructed using the ink prepared from the as-synthesised material. The interface structure was further improved significantly by adding a ∼10 µm thick LSGM ink interlayer, which was reflected in the electrochemical performance, reducing the ASR of the material from 0.17 Ω cm2 to 0.08 Ω cm2 at 700 °C. This is to date the best performance reported for an n = 3 Ruddlesden-Popper phase material with LSGM as the electrolyte.

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Systematic studies of the air electrode and full solid oxide fuel cell performance of La3PrNi3O9.76, and La2Pr2Ni3O9.65 n = 3 Ruddlesden–Popper phases are reported. These phases were found to adopt orthorhombic symmetry with a decrease in lattice parameters on increasing Pr content, consistent with the solid solution series end members. From electrochemical impedance spectroscopy measurements of symmetrical cells, the electrodes were found to possess area specific resistances of 0.07 Ω cm2 for the La2Pr2Ni3O9.65 cathode and 0.10 Ω cm2 for the La3PrNi3O9.76 cathode at 750 °C, representing a significant improvement on previously reported compositions. This significant improvement in performance is attributed to the optimisation of the electrode microstructure, introduction of an electrolyte interlayer and the resulting improved adhesion of the electrode layer. Following this development, the new electrode materials were tested for their single-cell performance, with the maximum power densities obtained for La2Pr2Ni3O9.65 and La3PrNi3O9.76 being 390 mW cm−2 and 400 mW cm−2 at 800 °C, respectively. As these single-cell measurements were based on thick electrolytes, there is considerable scope to enhance over cell performance in future developments.