Metal particles supported on oxide surfaces are used as catalysts for a wide variety of processes in the chemical and energy conversion industries. For catalytic applications, metal particles are generally formed on an oxide support by physical or chemical deposition, or less commonly by exsolution from it. Although fundamentally different, both methods might be assumed to produce morphologically and functionally similar particles. Here we show that unlike nickel particles deposited on perovskite oxides, exsolved analogues are socketed into the parent perovskite, leading to enhanced stability and a significant decrease in the propensity for hydrocarbon coking, indicative of a stronger metal–oxide interface. In addition, we reveal key surface effects and defect interactions critical for future design of exsolution-based perovskite materials for catalytic and other functionalities. This study provides a new dimension for tailoring particle–substrate interactions in the context of increasing interest for emergent interfacial phenomena.

B-site doped, A-site deficient perovskite oxide titanates with formula La_0.4Sr_0.4Mⁿ⁺ _xTi_1−xO_3−γ−δ (M = Fe³⁺ or Ni²⁺; x = 0.06; γ = (4 − n)x/2) were employed as solid oxide electrolysis cell (SOEC) cathodes for hydrogen production via high temperature steam electrolysis at 900 °C. A-site deficiency provided additional driving force for the exsolution of a proportion of B-site dopants at the surface in the form of metallic nanoparticles under reducing SOEC cathode operating conditions. In the case of La_0.4Sr_0.4Fe_0.06Ti_0.94O_2.97, this represents the first time that Fe⁰ has been exsolved from a perovskite in such a way. Exsolution was due in part to the inability of the host lattice to accommodate vacancies (introduced (δ) oxygen vacancies () and fixed A-site () and inherent (γ) oxygen vacancies) beyond a certain limit. The presence of electrocatalytically active Fe⁰ or Ni⁰ nanoparticles and higher concentrations dramatically lowered the activation barrier to steam electrolysis compared to the parent material (x = 0). The use of defect chemistry to drive the exsolution of less reducible dopant cations could conceivably be extended to produce new catalytically active perovskites with unique properties.