Electrocatalysis is indispensable to various emerging energy conversion and storage devices such as fuel cells and water electrolyzers. Owing to their unique physicochemical properties, perovskite oxide materials are one of the most promising water oxidation (OER) catalysts solely comprising earth-abundant elements. Nonetheless, many perovskite oxide catalysts suffer from a number of inherent problems such as the A-site cation segregation on the surface, coarse particles due to agglomeration/sintering, and surface decomposition during catalytic reactions. Besides, the catalytic activity is often incomparable with those of the state-of-the-art catalysts. In this work, we developed a proton-assisted approach to mitigate these common challenges. The protonation via the interaction of oxygen vacancies and water molecules induced the formation of protonic defects and the lattice expansion of the perovskite, leading to the fracture of big particles to yield small nanoparticles. This hydration in an acidic solution also selectively removed the A-site cation segregates and generated a spinel/perovskite heterostructure on the surface. We verified this approach using three typical perovskite OER catalysts including Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF), La0.6Sr0.4Co0.8Fe0.2O3 (LSCF), and La0.75Sr0.25MnO3 (LSM). The processed catalysts showed much improved activity while maintaining their excellent stability, surpassing most of today's OER catalysts based on complex oxides.
Keywords: cation segregation; grain refinement; hydration; spinel/perovskite heterostructure; surface reconstruction.