Engineering electrocatalytic activity in nanosized perovskite cobaltite through surface spin-state transition

The activity of electrocatalysts exhibits a strongly dependence on their electronic structures. Specifically, for perovskite oxides, Shao-Horn and co-workers have reported a correlation between the oxygen evolution reaction activity and the e(g) orbital occupation of transition-metal ions, which provides guidelines for the design of highly active catalysts. Here we demonstrate a facile method to engineer the e(g) filling of perovskite cobaltite LaCoO3 for improving the oxygen evolution reaction activity. By reducing the particle size to similar to 80 nm, the e(g) filling of cobalt ions is successfully increased from unity to near the optimal configuration of 1.2 expected by Shao-Horn's principle. Consequently, the activity is significantly enhanced, comparable to those of recently reported cobalt oxides with e(g) similar to 1.2 configurations. This enhancement is ascribed to the emergence of spin-state transition from low-spin to high-spin states for cobalt ions at the surface of the nanoparticles, leading to more active sites with increased reactivity.