Intrinsic Effects of Ruddlesden‐Popper‐Based Bifunctional Catalysts for High‐Temperature Oxygen Reduction and Evolution

Abstract Unveiling the intrinsic effects of Ruddlesden‐Popper (RP) series A_n+1B_nO_3n+1 (A = La, B = Ni, Co, Mn, Cu, n = 1, 2 and 3) catalysts is essential in order to optimize the activity of oxygen reduction reaction (ORR) and evolution reaction (OER). Here, it is demonstrated that the oxygen vacancy is not the key point for RP to realize high ORR and OER activity at high temperature. Instead, interstitial O²⁻ with high concentration and fast migration, and lattice oxygen with high activity are favorable for the high‐temperature catalytic activity. Aliovalent cation doping is an effective strategy to modify the catalytic activity. For the RP catalysts, low‐valence ion doping does not introduce oxygen vacancies, which suppresses the activity of lattice oxygen and decreases the interstitial O²⁻ concentration; whereas high‐valence ion doping enhances the interstitial O^2– concentration and the lattice oxygen activity. The evaluations of six RP series (La₂NiO₄, La₂CoO₄, La₃Co₂O₇, La₄Ni₃O₁₀, La₂MnO₄, and La₂CuO₄ based) and twenty samples as oxygen electrodes for solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs) demonstrate that this finding is applicable to all the selected RP series.