Heterogeneous Catalysis In article number 2308934, Bong-Joong Kim and co-workers devise a method to exsolve metal dopants from amorphous perovskite oxides, followed by the crystallization of these oxides through vacuum-annealing at elevated temperatures. This process extracts all heavily doped Co atoms from SrTiO3, resulting in uniformly distributed, high-density CoO nanoparticles embedded in the oxide support, providing structural stability, and enhancing photoelectrochemical performance.