Activity and Stability of Perovskite Oxides at Neutral pH for Oxygen Evolution Catalysis

Recently, many perovskite oxides have been well studied as the electrocatalysts for the oxygen evolution reaction (OER) in alkaline electrolytes. However, the OER electrocatalysis of perovskite catalysts at near-neutral pH is still less investigated, which is critical in many electrochemical techniques for the storage and application of sustainable energy, such as photo-electrochemical devices and metal-air batteries. In this work, we systematically studied the activity and stability of a series of highly active and common perovskite catalysts for OER at pH 7. For activity, we found that many previous design principles for oxide catalysts to achieve high OER activity at pH 13, such as having an e_g filling close to unity or having an O p-band close to Fermi level, are still appropriate activity descriptors at pH 7. For stability, which was a greater challenge at pH 7 than at pH 13, we identified two different modes of catalyst degradation. Perovskites with O p-band close to Fermi level showed leaching of A-site atoms and surface amorphization at any condition in pH 7 electrolyte, while those with O p-band far from Fermi level were stable under low OER current/potential but unstable at high current/potential accompanied with the leaching of B-site atoms. These two degradation modes can be explained and supported by the respective formation energies of the modified surfaces from DFT calculation. These new findings provided new insights into the degradation mechanism of oxides OER catalysts, as well as new design principles for developing high-stability and high-activity perovskite OER catalysts for neutral-pH or low-pH applications.