Exsolution of metal nanoparticles by control of point defects

Exsolution involves redox precipitation of metal nanoparticles from metal oxides, resulting in materials that exhibit excellent electrocatalytic properties and hold great promise for novel types of nanoscale heterostructures. However, a coherent understanding of the phenomenon is lacking. Here, exsolution is described by three point defect equations involving the reduction of the host oxide, reduction and exsolution of the transition metal, and annihilation of host unit cells. Guided by their predictions, significantly enhanced exsolution in terms of molar amount, rate, and nucleation density is shown by acceptor substitution to the system La0.2Ca0.7Ti0.95Cu0.05O3−δ through atomic scale imaging and in situ X-ray diffraction and spectroscopy. It is demonstrated that the oxygen stoichiometry of the parent oxide increases upon exsolution despite oxygen loss in the reducing environment. Furthermore, strain in both the host oxide and the exsolved metal can constitute an additional thermodynamic barrier for exsolution beyond the availability of the required point defects.