Challenging thermodynamics: combining immiscible elements in a single-phase nano-ceramic

The Hume-Rothery rules governing solid-state miscibility limit the compositional space for new inorganic material discovery. Here, we report a non-equilibrium, one-step, and scalable flame synthesis method to overcome thermodynamic limits and incorporate immiscible elements into single phase ceramic nanoshells. Starting from prototype examples including (NiMg)O, (NiAl)O_x, and (NiZr)O_x, we then extend this method to a broad range of Ni-containing ceramic solid solutions, and finally to general binary combinations of elements. Furthermore, we report an “encapsulated exsolution” phenomenon observed upon reducing the metastable porous (Ni_0.07Al_0.93)O_x to create ultra-stable Ni nanoparticles embedded within the walls of porous Al₂O₃ nanoshells. This nanoconfined structure demonstrated high sintering resistance during 640 h of catalysis of CO₂ reforming of methane, maintaining constant 96% CH₄ and CO₂ conversion at 800 °C and dramatically outperforming conventional catalysts. Our findings could greatly expand opportunities to develop novel inorganic energy, structural, and functional materials.